gopishankar natanasabapathi | All India Institute of Medical Sciences, New Delhi (original) (raw)

Papers by gopishankar natanasabapathi

Research paper thumbnail of PO98

Research paper thumbnail of The conformity index for the therapeutic option of glomus jugulare gamma knife stereotactic radio surgical treatment planning

Journal of Medical Physics, 2007

Research paper thumbnail of MRI-based polymer gel dosimetry for validating plans with multiple matrices in Gamma Knife stereotactic radiosurgery

Journal of Applied Clinical Medical Physics, Jan 31, 2011

One of treatment planning techniques with Leksell GammaPlan (LGP) for Gamma Knife stereotactic ra... more One of treatment planning techniques with Leksell GammaPlan (LGP) for Gamma Knife stereotactic radiosurgery (GKSRS) uses multiple matrices with multiple dose prescriptions. Computational complexity increases when shots are placed in multiple matrices with different grid sizes. Hence, the experimental validation of LGP calculated dose distributions is needed for those cases. For the current study, we used BANG3 polymer gel contained in a head-sized glass bottle to simulate the entire treatment process of GKSRS. A treatment plan with three 18 mm shots and one 8 mm shot in separate matrices was created with LGP. The prescribed maximum dose was 8 Gy to three shots and 16 Gy to one of the 18 mm shots. The 3D dose distribution recorded in the gel dosimeter was read using a Siemens 3T MRI scanner. The scanning parameters of a CPMG pulse sequence with 32 equidistant echoes were as follows: TR = 7 s, echo step = 13.6 ms, field-of-view = 256 mm × 256 mm, and pixel size = 1 mm × 1 mm. Interleaved acquisition mode was used to obtain 15 to 45 2-mm-thick slices. Using a calibration relationship between absorbed dose and the spin-spin relaxation rate (R2), we converted R2 images to dose images. MATLAB-based in-house programs were used for R2 estimation and dose comparison. Gamma-index analysis for the 3D data showed gamma values less than unity for 86% of the voxels. Through this study we accomplished the first application of polymer gel dosimetry for a true comparison between measured 3D dose distributions and LGP calculations for plans using multiple matrices for multiple targets.

Research paper thumbnail of Polymer gel dosimetry for measuring the dose near thin high-Z materials irradiated with high energy photon beams

Medical Physics, Nov 15, 2016

To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z mater... more To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z materials placed in a water-like medium by using a polymer gel dosimeter (PGD) when the medium was irradiated with high energy photon beams. Methods: PGD is potentially a useful tool for this application because it can record the dose around a small object made of a high-Z material in a continuous 3D medium. In this study, the authors manufactured a methacrylic acid-based normoxic PGD, nMAG. Two 0.5 mm thick lead foils (1 × 1 cm) were placed in foil supports with 0.7 cm separation in a 1000 ml polystyrene container filled with nMAG. The authors used two foil configurations, i.e., orthogonal and parallel. In the orthogonal configuration, two foils were placed in the direction orthogonal to the beam axis. The parallel configuration had two foils arranged in parallel to the beam axis. The phantom was irradiated with an 18 MV photon beam of 5 × 5 cm field size. It was imaged with a three-Tesla (3 T) magnetic resonance imaging (MRI) scanned using the Car-Purcell-Meiboom-Gill pulse sequence. The spin-spin relaxation time (R2) to-dose calibration data were obtained by using small vials filled with nMAG and exposing to known doses. The DOSXYZnrc Monte Carlo (MC) code was used to get the expected dose distributions. More than 35 × 10 6 of histories were simulated so that the average error was less than 1%. An in-house -based software was used to obtain the dose distributions from the measured R2 data as well as to compare the measurements and the MC predictions. The dose change due to the presence of the foils was studied by comparing the dose distributions with and without foils (or the reference). Results: For the orthogonal configuration, the measured dose along the beam axis showed an increase in the upstream side of the first foil, between the foils, and on the downstream side of the second foil. The range of increased dose area was 1.1 cm in the upstream of the first foil. However, in the downstream of the second foil, it was 0.2 cm, beyond which the dose fell below the reference dose by 10%. The dose profile between the foils showed a well-like shape with the minimum dose still larger than the reference dose by 1.8%. The minimum dose point was closer to the first foil than to the second foil. For the parallel configuration, the dose between foils was the largest at the center. The increased dose area opposite to the gap between foils extended outward to 1 cm. The spatial dose distributions of PGD and MC showed the same geometrical patterns except for the points inside the foils for both orthogonal and parallel foil arrangements. Conclusions: The authors demonstrated that the nMAG PGD with MRI could be used to measure the 3D dosimetric structures at the mm-scale in the vicinity of the foil. The current study provided more accurate 3D spatial dose distribution than the previous studies. Furthermore, the measurements were validated by the MC simulation.

Research paper thumbnail of A practical strategy for incorporating the convolution algorithm in Leksell GammaPlan for routine treatment planning†

PubMed, 2022

Purpose: This study aims to establish criteria for convolution dose calculations and an efficient... more Purpose: This study aims to establish criteria for convolution dose calculations and an efficient procedure to include the heterogeneity effects in GammaKnife radiosurgery (GKRS) treatment plans. Methods and materials: We analyzed 114 GKRS cases of various disease types, tumor locations, sizes, the number of fractions, and prescription doses. There was a total of 205 tumors. CT scans were performed in addition to routine MRI scans for all treatments. All treatment plans were created using the TMR10 algorithm (TMR10). We repeated the dose calculations for this study with the convolution algorithm (Conv). We calculated the ratios between Conv and TMR10 of the treatment volume (TxtVol), the volume covered by half of the prescription dose (TxtVol2), the minimum, maximum, and mean doses in the tumor (minDose, maxDose, and meanDose), and the volume of tumor covered by the prescription isodose (covVol). We then categorized those quantities for locations of tumors represented by the shortest distance of the skull surface from the tumor center (distC) and the tumor edge (distE). [Table: see text]. Results: All six ratios increased with increasing distC and distE. For example, the median minDose ratio increased from 0.885 to 0.933 as distE increased. There was a statistically significant difference in the minDose ratio between tumors of distE < 2 cm and distE ≥ 2 cm. On the other hand, the median maxDose ratio was about 0.933 [0.928-0.939], being almost independent of distE. This suggested a 6.1% overestimation of the delivered dose with TMR10. Conclusion: The heterogeneity effects must be considered for the volume dose calculations by applying the convolution algorithm when the distance of the skull surface from the closest point of the tumor is less than 2 cm to achieve less than 3% accuracy.

Research paper thumbnail of SU-E-T-398: Verification of Gamma Knife EXtend System Based Fractionated Treatment Planning Using EBT2 Film

Medical Physics, Jun 1, 2012

Research paper thumbnail of Three-dimensional radiation dosimetry using polymer gel and solid radiochromic polymer: From basics to clinical applications

World Journal of Radiology, 2017

Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients b... more Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly measure the dose distributions in threedimensional (3D) space are not commonly available. One such 3D dose measurement device is the polymerbased dosimeter, which changes the material property in response to radiation. These are available in the gel form as polymer gel dosimeter (PGD) and ferrous gel dosimeter (FGD) and in the solid form as solid plastic dosimeter (SPD). Those are made of a continuous uniform medium which polymerizes upon irradiation. Hence, the intrinsic spatial resolution of those dosimeters is very high, and it is only limited by the method by which one converts the dose information recorded by the medium to the absorbed dose. The current standard methods of the dose quantification are magnetic resonance imaging, optical computed tomography, and X-ray computed tomography. In particular, magnetic resonance imaging is well established as a method for obtaining clinically relevant dosimetric data by PGD and FGD. Despite the likely possibility of doing 3D dosimetry by PGD, FGD or SPD, the tools are still lacking wider usages for clinical applications. In this review article, we summarize the current status of PGD, FGD, and SPD and discuss the issue faced by these for wider acceptance in radiation oncology clinic and propose some directions for future development.

Research paper thumbnail of Development and characterization of urethane substituted diacetylene based radiochromic films for medical radiation dosimetry

Radiation Physics and Chemistry, Dec 1, 2020

In this work urethane substituted diacetylene compound was synthesized to prepare its radiochromi... more In this work urethane substituted diacetylene compound was synthesized to prepare its radiochromic films which can be sensitive to therapeutic radiation doses. The developed radiochromic films showed significant color change from white to blue in 0-16 Gy dose range. The colorimetric spectral response of the developed films was studied and a maximum absorption at 624 nm was observed which increased with the radiation doses. The change in the morphology of the films pre and post irradiation was analyzed by acquiring their SEM images. The radiation induced color changes were studied quantitatively in terms of optical density by using high resolution Epson scanner along with MATLAB software. The dose response of the developed films was compared with the commercially available Gafchromic EBT3 films. Both the films showed similar dose response with an uncertainty of less than 2%. The post irradiation stability and environmental stability of the films were also analyzed. The films were found to be highly stable under normal environmental conditions with only 1.67% and 1.19% variation in optical density due to the change in temperature and light intensity, respectively. The developed radiochromic films were tissue equivalent and possessed promising characteristics for a potential film dosimeter for medical applications.

Research paper thumbnail of LGP skull vs manual skull contouring in gamma knife stereotactic radio surgery

Research paper thumbnail of Multi Session Gamma-Knife Stereotactic Radiosurgery: Technology Development, Advancement and Use

Gamma knife stereotactic Radiosurgery (GKSRS) is a highly conformal radiation dose delivery syste... more Gamma knife stereotactic Radiosurgery (GKSRS) is a highly conformal radiation dose delivery system to well defined targets within the brain without much damaging normal healthy neighboring tissue. This precise radiation dose delivery method requires rigid frame fixation followed by the MR/CT and/or angiography imaging with commanding treatment planning system for perfect calculations. Experiencing the radiobiological benefits of hypo-fractionation, the evidences shows, multiple session radiosurgery or fractionated gamma knife stereotactic radiosurgery (fGKSRS) for single or multiple lesions may be beneficial for the treatment of brain tumor. A newly developed extend system (ES) is used to treat brain tumors with modified gamma knife stereotactic radiosurgery technique. The ES comprises of a carbon fiber frame system (extend frame), a vacuum pump (vacuum surveillance system connected to the vacuum compressor), mouth piece with dental impression connected to the front piece of frame and a customized vacuum head rest to maintains reproducibility of fractionation. As there is no pin through skin, ES gives absolute comfort to the patient. The extend frame assembly of Leksell Gamma Knife Perfexion (GKPFX) enables fractionated treatments in addition to volume staging. It also facilitates to treat larger lesions or the tumors near vital regions. GKPFX Radiation dose of 14 – 25 Gy in 5 pituitary region tumors and 2 can now also allow treating tumors of paranasal sinuses, orbit and upper meningiomas near optic nerve and brain stem with 31 fractions were cervical spine in a single fraction or with fractionation. Optimization and delivered through ES successfully. Average tumor size treated was 8.87 justification of fGKSRS regime could be considered as an option for cc (max 16.04 cc) with 92.6 % coverage. 3.5 - 5.0 Gy/fraction in 4 -5 radiosurgery with GKPFX. ES can safely deliver doses to the volumes fGKSRS fractions are delivered in consecutive days. Maximum and unable to treat previously. Fractionation could be preferred for large minimum radii error was measured as 1.2 mm and 0.1 mm. An average tumors to spare normal vicinity tissue because while treating large error of 0.66 mm was recorded with 0.9 mm maximum specific patient volume in a single high radiation dose, significant amount of normal positioning error. Average maximum point dose to optic nerve and healthy tissue may receives high radiation dose. Up to 7 - 8 Gy of brain stem was found 11.84 Gy (integral dose 2.78 mJ) and 13.16 Gy radiation dose per fraction over a course of maximum five session (integral dose 62.51 mJ) respectively. (maintaining the SRS recommendations) to achieve the predetermined output of delivered radiation dose could be applied with ES. The fGKSRS may attain good results for the tumor near critical organs like brain All patients have tolerated the treatment well with specific dental bite stem, optic nerve or motor/ speech function sites. block. The setup is accurate and reliable with efficient conformity. The ES has extended the clinical advantage as the extended range of Treatment process involves preparation of dental impression, fitting the indications for gamma knife SRS/SRT with fractionation or multi fraction patient head on vacuum cushion with dental impression front piece, techniques. Further more patients to be treated with the technique to vacuum adjustable for comfort and/or saliva suction, multiple radii conclude its accuracy, reproducibility and efficiency with steep dose fall measurement and record on each position round the head. The patient outside the target. More patient treatment and experiencing positive then taken to CT imaging with dental impression and extend frame results /follow ups will make the full use of its advantage. fixation base with vacuum support. Skull radii at various points and position are measured before imaging using repositioning check tool (RCT) to satisfying positional accuracy and reproducibility while compared these radii measurements before each fraction of radiation treatment. CT of the head taken with CT adapter. Acquired stereotactic Swapnil Chougule S/O Prof. Arun Chougule, Jaipur has launched a CT images are co-registered with volumetric MR image for treatment campaign against smoking among college-goers with the name I SMOK planning. Radii measurements are taken with high precision electronic (I Support the MOvement to Kill cancer) in association with his 23 fellow probes which locates the patient head within the extend frame. Vacuum students of IIT Mumbai and in co-ordination with UNISEF, UNESCO and surveillance interlocks pause the treatment if the patient moves within Indian Cancer Society. Congrats!!! the extend frame.

Research paper thumbnail of Interstitial brachytherapy guided intensity modulated radiation therapy (IBGIMRT) in cervical cancer: a dosimetric study

PubMed, Jun 1, 2009

Purpose: Interstitial brachytherapy (IBT) is used as an alternative to intracavitary radiotherapy... more Purpose: Interstitial brachytherapy (IBT) is used as an alternative to intracavitary radiotherapy in the management of cervical carcinoma. We have devised a new technique called interstitial brachytherapy guided intensity modulated radiotherapy (IBGIMRT) which can potentially reduce doses to organs at risk (OaRs). It utilizes IMRT planning on the target volume (TV) defined by implantation of IBT needles. This study compares the dosimetry of IBT and IBGIMRT. Material and methods: CT scan images of 18 patients with cervical cancer, who have been already treated by HDR-BT, were used to generate two rival plans, IBT and IBGIMRT, for a prescription dose of 10 Gy. Following dosimetric factors were used for comparison: volume receiving 95% of prescription dose (V95), conformity index (COIN) and external volume index (EI) for target and for OaR, dose received by volume of 1 cm3 (D1cc), 2 cm3 (D2cc), 5 cm3 (D5cc) and also volume receiving 50% and 75% of prescription dose (V50 and V75). Results: The two plans resulted in COIN difference of 49.8% (p < 0.0001) and EI difference of 36.4% (p < 0.0028) in favor of IBGIMRT. Mean D1cc, D2cc and D5cc values for bladder were 8.3 Gy, 7.6 Gy and 6.4 Gy; and 7.8 Gy, 7.3 Gy and 5.8 Gy with IBT and IBGIMRT, respectively (p > 0.05). Similar figures for rectum with IBT vs. IBGIMRT were 11.2 Gy vs. 7.02 Gy, 10.5 Gy vs. 6.4 Gy and 9.1 Gy vs. 4.8 Gy respectively (p < 0.01). Conclusions: Our novel technique, IBGIMRT, has shown its dosimetric superiority and therefore needs to be studied in clinical set up.

Research paper thumbnail of Quantification of narrow band UVB radiation doses in phototherapy using diacetylene based film dosimeters

Scientific Reports, 2021

Narrow band ultraviolet B (NB UVB) radiation doses are administered during phototherapy for vario... more Narrow band ultraviolet B (NB UVB) radiation doses are administered during phototherapy for various dermatological ailments. Precise quantification of these doses is vital because the absorbed irradiation can cause adverse photochemical reactions which can lead to potential phototherapeutic side effects. The paper presents development of diacetylene based dosimeter for the determination of therapeutic NB UVB doses during phototherapy. The amide terminated diacetylene analogues have been synthesized by tailoring them with different functional groups. The synthesized diacetylene monomers have been introduced in a polyvinyl alcohol binder solution to obtain a film dosimeter. The influence of different headgroups on the colorimetric response to UV radiation has been studied. Among all the synthesized diacetylene analogues, the naphthylamine substituted diacetylene exhibited excellent color transition from white to blue color at 100 mJ cm−2 NB UVB radiation dose. The developed amide film...

Research paper thumbnail of SU-E-T-563: Multi-Fraction Stereotactic Radiosurgery with Extend System of Gamma Knife: Treatment Verification Using Indigenously Designed Patient Simulating Multipurpose Phantom

Medical Physics, 2015

ABSTRACT Aim of the study is to evaluate mechanical and radiological accuracy of multi-fraction r... more ABSTRACT Aim of the study is to evaluate mechanical and radiological accuracy of multi-fraction regimen and validate Gamma knife based fractionation using newly developed patient simulating multipurpose phantom. A patient simulating phantom was designed to verify fractionated treatments with extend system (ES) of Gamma Knife however it could be used to validate other radiotherapy procedures as well. The phantom has options to insert various density material plugs and mini CT/MR distortion phantoms to analyze the quality of stereotactic imaging. An additional thorax part designed to predict surface doses at various organ sites. The phantom was positioned using vacuum head cushion and patient control unit for imaging and treatment. The repositioning check tool (RCT) was used to predict phantom positioning under ES assembly. The phantom with special inserts for film in axial, coronal and sagittal plane were scanned with X-Ray CT and the acquired images were transferred to treatment planning system (LGP 10.1). The focal precession test was performed with 4mm collimator and an experimental plan of four 16mm collimator shots was prepared for treatment verification of multi-fraction regimen. The prescription dose of 5Gy per fraction was delivered in four fractions. Each fraction was analyzed using EBT3 films scanned with EPSON 10000XL Scanner. The measurement of 38 RCT points showed an overall positional accuracy of 0.28mm. The mean deviation of 0.28% and 0.31 % were calculated as CT and MR image distortion respectively. The radiological focus accuracy test showed its deviation from mechanical center point of 0.22mm. The profile measurement showed close agreement between TPS planned and film measured dose. At tolerance criteria of 1%/1mm gamma index analysis showed a pass rate of &gt; 95%. Our results show that the newly developed multipurpose patient simulating phantom is highly suitable for the verification of fractionated stereotactic radiosurgery using ES of Gamma knife. The study is a part of intramural research project of Research Section, All India Institute of Medical Sciences New Delhi India (A 247).

Research paper thumbnail of SU-E-T-564: Statistical Variation and Acceptance of Non Invasive Immobilization Systems for Multi-Fraction Gamma Knife EXtend Stereotactic Radiosurgery

Medical Physics, 2014

ABSTRACT Purpose: Gamma Knife perfexion (GKPFX) with extend system is being used for multi-fracti... more ABSTRACT Purpose: Gamma Knife perfexion (GKPFX) with extend system is being used for multi-fraction or fractionated stereotactic radiosurgery (fGKSRS). Patient surveillance Unit (PSU) is used to attain a non invasive immobilization for fractionation. Calibrated digital probe is used to measure encoded mechanical positions on repositioning check tool (RCT). The objective of this study is to check consistency and statistical position variation during multi-fraction stereotactic radiosurgery using GKPFX extend system.

Research paper thumbnail of SU-E-T-607: An Experimental Validation of Gamma Knife Based Convolution Algorithm On Solid Acrylic Anthropomorphic Phantom

Medical Physics, 2014

ABSTRACT Purpose: To perform dosimetric evaluation of convolution algorithm in Gamma Knife (Perfe... more ABSTRACT Purpose: To perform dosimetric evaluation of convolution algorithm in Gamma Knife (Perfexion Model) using solid acrylic anthropomorphic phantom.

Research paper thumbnail of SU-E-T-678: Response Calibration Using Electron Depth-Dose Data for MRI-Based 3D Polymer Gel Dosimetry

Medical Physics, 2015

ABSTRACT To evaluate a calibration method using the depth-dose data of an electron beam for MRI-b... more ABSTRACT To evaluate a calibration method using the depth-dose data of an electron beam for MRI-based polymer gel dosimetry. MAGAT was manufactured in-house to fill two 400mL-cylindrical phantoms and nine 22mL-glass vials. Phantom-A was irradiated along the cylinder axis with a 9MeV electron beam of 6 cm x 6 cm field size (FS). Phantom-B was irradiated with a 6MV photon beam of 3 cm x 3 cm FS by a 360-degree arc technique. Eight vials were irradiated in a water-bath to various doses with a 20 cm x 20 cm FS 6MV photon beam. All irradiated phantoms and one un-irradiated vial were scanned with a 3T MRI scanner to obtain the spin-spin relaxation rate (R2) distributions. By comparing the measured R2-to-depth data with the known depth-dose data for Phantom-A, R2-to-dose calibration data were obtained (e-beam method). Another calibration data were obtained from the 9 vials data (9-vial method). We tested two regression equations, i.e., third-order polynomial and tangent functions, and two dose normalization methods, i.e., one-point and two-point methods. Then, these two calibration methods were used to obtain the 3D dose distribution of Phantom-B and evaluated by comparing the measured data with the dose distribution from a treatment planning system. The comparison was made with gamma passing rate (2%/2mm criteria). We did not observe a clear advantage of the e-beam method over the 9-vial method for the 3D dose comparison with the test case. Nevertheless, we found that the e-beam method required a smaller dose scaling for the dose comparison. Furthermore, the tangent function showed better data fitting than the polynomial function with smaller uncertainty of the estimated coefficients. Considering the overall superior performance, we recommend the e-beam method with the tangent function as the regression equation and one-point dose normalization for the MRI-based polymer gel dosimetry.

Research paper thumbnail of Three-dimensional dosimetry of TomoTherapy by MRI-based polymer gel technique

Journal of Applied Clinical Medical Physics, 2010

Verification of the dose calculation model and the software used for treatment planning is an imp... more Verification of the dose calculation model and the software used for treatment planning is an important step for accurate radiation delivery in radiation therapy. Using BANG3 polymer gel dosimeter with a 3 Tesla magnetic resonance imaging (MRI) scanner, we examined the accuracy of TomoTherapy treatment planning and radiation delivery. We evaluated one prostate treatment case and found the calculated three-dimensional (3D) dose distributions agree with the measured 3D dose distributions with an exception in the regions where the dose was much smaller (25% or less) than the maximum dose (2.5 Gy). The analysis using the gamma-index (3% dose difference and 3 mm distance-to-agreement) for a volume of 12 cm × 11 cm × 9 cm containing the planning target volume showed that the gamma values were smaller than unity for 53% of the voxels. Our measurement protocol and analysis tools can be easily applied to the evaluation of other newer complex radiation delivery techniques, such as intensity-modulated arc therapy, with a reasonably low financial investment.

Research paper thumbnail of Imrt and Vmat Commissioning for Versa HD Linear Accelerator Using Aapm TG-119

International Journal of Advanced Research, 2017

Purpose of study is to evaluate the end to end commissioning accuracy of intensity modulated radi... more Purpose of study is to evaluate the end to end commissioning accuracy of intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for Versa HD linear accelerator using AAPM TG-119 protocol. Materials & methods: IMRT and VMAT plans were created for TG119 test cases. All the plans were generated using Monaco 5.1 treatment planning system (TPS) for Elekta Versa HD linear accelerator. Prescription and planning goals were as kept as per TG119. For point dose measurement CC01 (0.01cc) ion chamber was used and measurements were carried out as per TG119 specified points in high and low dose gradient regions. Planar dose measurement I'matriXX along with multicube-lite phantom was used. Planned and measured dose planes were compared using gamma index criteria. Results: All planning goals have been achieved as per TG119 report. At high dose point measurement mean dose differences averaged over different techniques planned with different energies for all test cases was 0.002±0.020, and corresponding confidence limit was 0.041. At low dose point measurement mean dose averaged over different techniques planned with different energies for all test cases was-0.004±0.021, and corresponding confidence limit was 0.045. For planar dose measurement gamma passing rate averaged over all test cases was 99.40%±0.40 for 3%/3mm criteria and 97.82%±0.13 for 2%/2mm criteria respectively. Present work overall confidence limit for composite planar dose measurement was 1.38(i.e., 98.62% passing) for 3%/3mm and 2.45(i.e., 97.55% passing) for 2%/2mm criteria. Conclusion: Planning and delivery of IMRT/VMAT has been validated using published TG119 report results.

Research paper thumbnail of SU-E-T-14: A Comparative Study Between Forward and Inverse Planning in Gamma Knife Radiosurgery for Acoustic Neuroma Tumours

Medical Physics, 2015

ABSTRACT To evaluate forward and inverse planning methods for acoustic neuroma cases treated in G... more ABSTRACT To evaluate forward and inverse planning methods for acoustic neuroma cases treated in Gamma Knife Perfexion. Five patients with acoustic neuroma tumour abutting brainstem were planned twice in LGP TPS (Version 10.1) using TMR10 algorithm. First plan was entirely based on forward planning (FP) in which each shot was chosen manually. Second plan was generated using inverse planning (IP) for which planning parameters like coverage, selectivity, gradient index (GI) and beam-on time threshold were set. Number of shots in IP was automatically selected by objective function using iterative process. In both planning methods MRI MPRAGE sequence images were used for tumour localization and planning. A planning dose of 12Gy at 50% isodose level was chosen. Number of shots used in FP was greater than IP and beam-on time in FP was in average 1.4 times more than IP. One advantage of FP was that the brainstem volume subjected to 6Gy dose (25% isodose) was less in FP than IP. Our results showed use of more number of shots as in FP results in GI less than or equal to 2.55 which is close to its lower limit. Dose homogeneity index (DHI) analysis of FP and IP showed average values of 0.59 and 0.67 respectively. General trend in GK for planning in acoustic neuroma cases is to use small collimator shots to avoid dose to adjacent critical structures. More number of shots and prolonged treatment time causes inconvenience to the patients. Similarly overuse of automatic shot shaping as in IP results in increased scatter dose. A compromise is required in shot selection for these cases. IP method could be used in acoustic neuroma cases to decrease treatment time provided the source sector openings near brainstem are shielded or adjusted appropriately to reduce brainstem dose.

Research paper thumbnail of Digital Filtering Techniques to Reduce Image Noise and Improve Dose Resolution in X-Ray CT Based Normoxic Gel Dosimetry

Modern Practices in Radiation Therapy, 2012

Research paper thumbnail of PO98

Research paper thumbnail of The conformity index for the therapeutic option of glomus jugulare gamma knife stereotactic radio surgical treatment planning

Journal of Medical Physics, 2007

Research paper thumbnail of MRI-based polymer gel dosimetry for validating plans with multiple matrices in Gamma Knife stereotactic radiosurgery

Journal of Applied Clinical Medical Physics, Jan 31, 2011

One of treatment planning techniques with Leksell GammaPlan (LGP) for Gamma Knife stereotactic ra... more One of treatment planning techniques with Leksell GammaPlan (LGP) for Gamma Knife stereotactic radiosurgery (GKSRS) uses multiple matrices with multiple dose prescriptions. Computational complexity increases when shots are placed in multiple matrices with different grid sizes. Hence, the experimental validation of LGP calculated dose distributions is needed for those cases. For the current study, we used BANG3 polymer gel contained in a head-sized glass bottle to simulate the entire treatment process of GKSRS. A treatment plan with three 18 mm shots and one 8 mm shot in separate matrices was created with LGP. The prescribed maximum dose was 8 Gy to three shots and 16 Gy to one of the 18 mm shots. The 3D dose distribution recorded in the gel dosimeter was read using a Siemens 3T MRI scanner. The scanning parameters of a CPMG pulse sequence with 32 equidistant echoes were as follows: TR = 7 s, echo step = 13.6 ms, field-of-view = 256 mm × 256 mm, and pixel size = 1 mm × 1 mm. Interleaved acquisition mode was used to obtain 15 to 45 2-mm-thick slices. Using a calibration relationship between absorbed dose and the spin-spin relaxation rate (R2), we converted R2 images to dose images. MATLAB-based in-house programs were used for R2 estimation and dose comparison. Gamma-index analysis for the 3D data showed gamma values less than unity for 86% of the voxels. Through this study we accomplished the first application of polymer gel dosimetry for a true comparison between measured 3D dose distributions and LGP calculations for plans using multiple matrices for multiple targets.

Research paper thumbnail of Polymer gel dosimetry for measuring the dose near thin high-Z materials irradiated with high energy photon beams

Medical Physics, Nov 15, 2016

To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z mater... more To investigate the feasibility of three-dimensional (3D) dose measurements near thin high-Z materials placed in a water-like medium by using a polymer gel dosimeter (PGD) when the medium was irradiated with high energy photon beams. Methods: PGD is potentially a useful tool for this application because it can record the dose around a small object made of a high-Z material in a continuous 3D medium. In this study, the authors manufactured a methacrylic acid-based normoxic PGD, nMAG. Two 0.5 mm thick lead foils (1 × 1 cm) were placed in foil supports with 0.7 cm separation in a 1000 ml polystyrene container filled with nMAG. The authors used two foil configurations, i.e., orthogonal and parallel. In the orthogonal configuration, two foils were placed in the direction orthogonal to the beam axis. The parallel configuration had two foils arranged in parallel to the beam axis. The phantom was irradiated with an 18 MV photon beam of 5 × 5 cm field size. It was imaged with a three-Tesla (3 T) magnetic resonance imaging (MRI) scanned using the Car-Purcell-Meiboom-Gill pulse sequence. The spin-spin relaxation time (R2) to-dose calibration data were obtained by using small vials filled with nMAG and exposing to known doses. The DOSXYZnrc Monte Carlo (MC) code was used to get the expected dose distributions. More than 35 × 10 6 of histories were simulated so that the average error was less than 1%. An in-house -based software was used to obtain the dose distributions from the measured R2 data as well as to compare the measurements and the MC predictions. The dose change due to the presence of the foils was studied by comparing the dose distributions with and without foils (or the reference). Results: For the orthogonal configuration, the measured dose along the beam axis showed an increase in the upstream side of the first foil, between the foils, and on the downstream side of the second foil. The range of increased dose area was 1.1 cm in the upstream of the first foil. However, in the downstream of the second foil, it was 0.2 cm, beyond which the dose fell below the reference dose by 10%. The dose profile between the foils showed a well-like shape with the minimum dose still larger than the reference dose by 1.8%. The minimum dose point was closer to the first foil than to the second foil. For the parallel configuration, the dose between foils was the largest at the center. The increased dose area opposite to the gap between foils extended outward to 1 cm. The spatial dose distributions of PGD and MC showed the same geometrical patterns except for the points inside the foils for both orthogonal and parallel foil arrangements. Conclusions: The authors demonstrated that the nMAG PGD with MRI could be used to measure the 3D dosimetric structures at the mm-scale in the vicinity of the foil. The current study provided more accurate 3D spatial dose distribution than the previous studies. Furthermore, the measurements were validated by the MC simulation.

Research paper thumbnail of A practical strategy for incorporating the convolution algorithm in Leksell GammaPlan for routine treatment planning†

PubMed, 2022

Purpose: This study aims to establish criteria for convolution dose calculations and an efficient... more Purpose: This study aims to establish criteria for convolution dose calculations and an efficient procedure to include the heterogeneity effects in GammaKnife radiosurgery (GKRS) treatment plans. Methods and materials: We analyzed 114 GKRS cases of various disease types, tumor locations, sizes, the number of fractions, and prescription doses. There was a total of 205 tumors. CT scans were performed in addition to routine MRI scans for all treatments. All treatment plans were created using the TMR10 algorithm (TMR10). We repeated the dose calculations for this study with the convolution algorithm (Conv). We calculated the ratios between Conv and TMR10 of the treatment volume (TxtVol), the volume covered by half of the prescription dose (TxtVol2), the minimum, maximum, and mean doses in the tumor (minDose, maxDose, and meanDose), and the volume of tumor covered by the prescription isodose (covVol). We then categorized those quantities for locations of tumors represented by the shortest distance of the skull surface from the tumor center (distC) and the tumor edge (distE). [Table: see text]. Results: All six ratios increased with increasing distC and distE. For example, the median minDose ratio increased from 0.885 to 0.933 as distE increased. There was a statistically significant difference in the minDose ratio between tumors of distE < 2 cm and distE ≥ 2 cm. On the other hand, the median maxDose ratio was about 0.933 [0.928-0.939], being almost independent of distE. This suggested a 6.1% overestimation of the delivered dose with TMR10. Conclusion: The heterogeneity effects must be considered for the volume dose calculations by applying the convolution algorithm when the distance of the skull surface from the closest point of the tumor is less than 2 cm to achieve less than 3% accuracy.

Research paper thumbnail of SU-E-T-398: Verification of Gamma Knife EXtend System Based Fractionated Treatment Planning Using EBT2 Film

Medical Physics, Jun 1, 2012

Research paper thumbnail of Three-dimensional radiation dosimetry using polymer gel and solid radiochromic polymer: From basics to clinical applications

World Journal of Radiology, 2017

Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients b... more Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly measure the dose distributions in threedimensional (3D) space are not commonly available. One such 3D dose measurement device is the polymerbased dosimeter, which changes the material property in response to radiation. These are available in the gel form as polymer gel dosimeter (PGD) and ferrous gel dosimeter (FGD) and in the solid form as solid plastic dosimeter (SPD). Those are made of a continuous uniform medium which polymerizes upon irradiation. Hence, the intrinsic spatial resolution of those dosimeters is very high, and it is only limited by the method by which one converts the dose information recorded by the medium to the absorbed dose. The current standard methods of the dose quantification are magnetic resonance imaging, optical computed tomography, and X-ray computed tomography. In particular, magnetic resonance imaging is well established as a method for obtaining clinically relevant dosimetric data by PGD and FGD. Despite the likely possibility of doing 3D dosimetry by PGD, FGD or SPD, the tools are still lacking wider usages for clinical applications. In this review article, we summarize the current status of PGD, FGD, and SPD and discuss the issue faced by these for wider acceptance in radiation oncology clinic and propose some directions for future development.

Research paper thumbnail of Development and characterization of urethane substituted diacetylene based radiochromic films for medical radiation dosimetry

Radiation Physics and Chemistry, Dec 1, 2020

In this work urethane substituted diacetylene compound was synthesized to prepare its radiochromi... more In this work urethane substituted diacetylene compound was synthesized to prepare its radiochromic films which can be sensitive to therapeutic radiation doses. The developed radiochromic films showed significant color change from white to blue in 0-16 Gy dose range. The colorimetric spectral response of the developed films was studied and a maximum absorption at 624 nm was observed which increased with the radiation doses. The change in the morphology of the films pre and post irradiation was analyzed by acquiring their SEM images. The radiation induced color changes were studied quantitatively in terms of optical density by using high resolution Epson scanner along with MATLAB software. The dose response of the developed films was compared with the commercially available Gafchromic EBT3 films. Both the films showed similar dose response with an uncertainty of less than 2%. The post irradiation stability and environmental stability of the films were also analyzed. The films were found to be highly stable under normal environmental conditions with only 1.67% and 1.19% variation in optical density due to the change in temperature and light intensity, respectively. The developed radiochromic films were tissue equivalent and possessed promising characteristics for a potential film dosimeter for medical applications.

Research paper thumbnail of LGP skull vs manual skull contouring in gamma knife stereotactic radio surgery

Research paper thumbnail of Multi Session Gamma-Knife Stereotactic Radiosurgery: Technology Development, Advancement and Use

Gamma knife stereotactic Radiosurgery (GKSRS) is a highly conformal radiation dose delivery syste... more Gamma knife stereotactic Radiosurgery (GKSRS) is a highly conformal radiation dose delivery system to well defined targets within the brain without much damaging normal healthy neighboring tissue. This precise radiation dose delivery method requires rigid frame fixation followed by the MR/CT and/or angiography imaging with commanding treatment planning system for perfect calculations. Experiencing the radiobiological benefits of hypo-fractionation, the evidences shows, multiple session radiosurgery or fractionated gamma knife stereotactic radiosurgery (fGKSRS) for single or multiple lesions may be beneficial for the treatment of brain tumor. A newly developed extend system (ES) is used to treat brain tumors with modified gamma knife stereotactic radiosurgery technique. The ES comprises of a carbon fiber frame system (extend frame), a vacuum pump (vacuum surveillance system connected to the vacuum compressor), mouth piece with dental impression connected to the front piece of frame and a customized vacuum head rest to maintains reproducibility of fractionation. As there is no pin through skin, ES gives absolute comfort to the patient. The extend frame assembly of Leksell Gamma Knife Perfexion (GKPFX) enables fractionated treatments in addition to volume staging. It also facilitates to treat larger lesions or the tumors near vital regions. GKPFX Radiation dose of 14 – 25 Gy in 5 pituitary region tumors and 2 can now also allow treating tumors of paranasal sinuses, orbit and upper meningiomas near optic nerve and brain stem with 31 fractions were cervical spine in a single fraction or with fractionation. Optimization and delivered through ES successfully. Average tumor size treated was 8.87 justification of fGKSRS regime could be considered as an option for cc (max 16.04 cc) with 92.6 % coverage. 3.5 - 5.0 Gy/fraction in 4 -5 radiosurgery with GKPFX. ES can safely deliver doses to the volumes fGKSRS fractions are delivered in consecutive days. Maximum and unable to treat previously. Fractionation could be preferred for large minimum radii error was measured as 1.2 mm and 0.1 mm. An average tumors to spare normal vicinity tissue because while treating large error of 0.66 mm was recorded with 0.9 mm maximum specific patient volume in a single high radiation dose, significant amount of normal positioning error. Average maximum point dose to optic nerve and healthy tissue may receives high radiation dose. Up to 7 - 8 Gy of brain stem was found 11.84 Gy (integral dose 2.78 mJ) and 13.16 Gy radiation dose per fraction over a course of maximum five session (integral dose 62.51 mJ) respectively. (maintaining the SRS recommendations) to achieve the predetermined output of delivered radiation dose could be applied with ES. The fGKSRS may attain good results for the tumor near critical organs like brain All patients have tolerated the treatment well with specific dental bite stem, optic nerve or motor/ speech function sites. block. The setup is accurate and reliable with efficient conformity. The ES has extended the clinical advantage as the extended range of Treatment process involves preparation of dental impression, fitting the indications for gamma knife SRS/SRT with fractionation or multi fraction patient head on vacuum cushion with dental impression front piece, techniques. Further more patients to be treated with the technique to vacuum adjustable for comfort and/or saliva suction, multiple radii conclude its accuracy, reproducibility and efficiency with steep dose fall measurement and record on each position round the head. The patient outside the target. More patient treatment and experiencing positive then taken to CT imaging with dental impression and extend frame results /follow ups will make the full use of its advantage. fixation base with vacuum support. Skull radii at various points and position are measured before imaging using repositioning check tool (RCT) to satisfying positional accuracy and reproducibility while compared these radii measurements before each fraction of radiation treatment. CT of the head taken with CT adapter. Acquired stereotactic Swapnil Chougule S/O Prof. Arun Chougule, Jaipur has launched a CT images are co-registered with volumetric MR image for treatment campaign against smoking among college-goers with the name I SMOK planning. Radii measurements are taken with high precision electronic (I Support the MOvement to Kill cancer) in association with his 23 fellow probes which locates the patient head within the extend frame. Vacuum students of IIT Mumbai and in co-ordination with UNISEF, UNESCO and surveillance interlocks pause the treatment if the patient moves within Indian Cancer Society. Congrats!!! the extend frame.

Research paper thumbnail of Interstitial brachytherapy guided intensity modulated radiation therapy (IBGIMRT) in cervical cancer: a dosimetric study

PubMed, Jun 1, 2009

Purpose: Interstitial brachytherapy (IBT) is used as an alternative to intracavitary radiotherapy... more Purpose: Interstitial brachytherapy (IBT) is used as an alternative to intracavitary radiotherapy in the management of cervical carcinoma. We have devised a new technique called interstitial brachytherapy guided intensity modulated radiotherapy (IBGIMRT) which can potentially reduce doses to organs at risk (OaRs). It utilizes IMRT planning on the target volume (TV) defined by implantation of IBT needles. This study compares the dosimetry of IBT and IBGIMRT. Material and methods: CT scan images of 18 patients with cervical cancer, who have been already treated by HDR-BT, were used to generate two rival plans, IBT and IBGIMRT, for a prescription dose of 10 Gy. Following dosimetric factors were used for comparison: volume receiving 95% of prescription dose (V95), conformity index (COIN) and external volume index (EI) for target and for OaR, dose received by volume of 1 cm3 (D1cc), 2 cm3 (D2cc), 5 cm3 (D5cc) and also volume receiving 50% and 75% of prescription dose (V50 and V75). Results: The two plans resulted in COIN difference of 49.8% (p < 0.0001) and EI difference of 36.4% (p < 0.0028) in favor of IBGIMRT. Mean D1cc, D2cc and D5cc values for bladder were 8.3 Gy, 7.6 Gy and 6.4 Gy; and 7.8 Gy, 7.3 Gy and 5.8 Gy with IBT and IBGIMRT, respectively (p > 0.05). Similar figures for rectum with IBT vs. IBGIMRT were 11.2 Gy vs. 7.02 Gy, 10.5 Gy vs. 6.4 Gy and 9.1 Gy vs. 4.8 Gy respectively (p < 0.01). Conclusions: Our novel technique, IBGIMRT, has shown its dosimetric superiority and therefore needs to be studied in clinical set up.

Research paper thumbnail of Quantification of narrow band UVB radiation doses in phototherapy using diacetylene based film dosimeters

Scientific Reports, 2021

Narrow band ultraviolet B (NB UVB) radiation doses are administered during phototherapy for vario... more Narrow band ultraviolet B (NB UVB) radiation doses are administered during phototherapy for various dermatological ailments. Precise quantification of these doses is vital because the absorbed irradiation can cause adverse photochemical reactions which can lead to potential phototherapeutic side effects. The paper presents development of diacetylene based dosimeter for the determination of therapeutic NB UVB doses during phototherapy. The amide terminated diacetylene analogues have been synthesized by tailoring them with different functional groups. The synthesized diacetylene monomers have been introduced in a polyvinyl alcohol binder solution to obtain a film dosimeter. The influence of different headgroups on the colorimetric response to UV radiation has been studied. Among all the synthesized diacetylene analogues, the naphthylamine substituted diacetylene exhibited excellent color transition from white to blue color at 100 mJ cm−2 NB UVB radiation dose. The developed amide film...

Research paper thumbnail of SU-E-T-563: Multi-Fraction Stereotactic Radiosurgery with Extend System of Gamma Knife: Treatment Verification Using Indigenously Designed Patient Simulating Multipurpose Phantom

Medical Physics, 2015

ABSTRACT Aim of the study is to evaluate mechanical and radiological accuracy of multi-fraction r... more ABSTRACT Aim of the study is to evaluate mechanical and radiological accuracy of multi-fraction regimen and validate Gamma knife based fractionation using newly developed patient simulating multipurpose phantom. A patient simulating phantom was designed to verify fractionated treatments with extend system (ES) of Gamma Knife however it could be used to validate other radiotherapy procedures as well. The phantom has options to insert various density material plugs and mini CT/MR distortion phantoms to analyze the quality of stereotactic imaging. An additional thorax part designed to predict surface doses at various organ sites. The phantom was positioned using vacuum head cushion and patient control unit for imaging and treatment. The repositioning check tool (RCT) was used to predict phantom positioning under ES assembly. The phantom with special inserts for film in axial, coronal and sagittal plane were scanned with X-Ray CT and the acquired images were transferred to treatment planning system (LGP 10.1). The focal precession test was performed with 4mm collimator and an experimental plan of four 16mm collimator shots was prepared for treatment verification of multi-fraction regimen. The prescription dose of 5Gy per fraction was delivered in four fractions. Each fraction was analyzed using EBT3 films scanned with EPSON 10000XL Scanner. The measurement of 38 RCT points showed an overall positional accuracy of 0.28mm. The mean deviation of 0.28% and 0.31 % were calculated as CT and MR image distortion respectively. The radiological focus accuracy test showed its deviation from mechanical center point of 0.22mm. The profile measurement showed close agreement between TPS planned and film measured dose. At tolerance criteria of 1%/1mm gamma index analysis showed a pass rate of &gt; 95%. Our results show that the newly developed multipurpose patient simulating phantom is highly suitable for the verification of fractionated stereotactic radiosurgery using ES of Gamma knife. The study is a part of intramural research project of Research Section, All India Institute of Medical Sciences New Delhi India (A 247).

Research paper thumbnail of SU-E-T-564: Statistical Variation and Acceptance of Non Invasive Immobilization Systems for Multi-Fraction Gamma Knife EXtend Stereotactic Radiosurgery

Medical Physics, 2014

ABSTRACT Purpose: Gamma Knife perfexion (GKPFX) with extend system is being used for multi-fracti... more ABSTRACT Purpose: Gamma Knife perfexion (GKPFX) with extend system is being used for multi-fraction or fractionated stereotactic radiosurgery (fGKSRS). Patient surveillance Unit (PSU) is used to attain a non invasive immobilization for fractionation. Calibrated digital probe is used to measure encoded mechanical positions on repositioning check tool (RCT). The objective of this study is to check consistency and statistical position variation during multi-fraction stereotactic radiosurgery using GKPFX extend system.

Research paper thumbnail of SU-E-T-607: An Experimental Validation of Gamma Knife Based Convolution Algorithm On Solid Acrylic Anthropomorphic Phantom

Medical Physics, 2014

ABSTRACT Purpose: To perform dosimetric evaluation of convolution algorithm in Gamma Knife (Perfe... more ABSTRACT Purpose: To perform dosimetric evaluation of convolution algorithm in Gamma Knife (Perfexion Model) using solid acrylic anthropomorphic phantom.

Research paper thumbnail of SU-E-T-678: Response Calibration Using Electron Depth-Dose Data for MRI-Based 3D Polymer Gel Dosimetry

Medical Physics, 2015

ABSTRACT To evaluate a calibration method using the depth-dose data of an electron beam for MRI-b... more ABSTRACT To evaluate a calibration method using the depth-dose data of an electron beam for MRI-based polymer gel dosimetry. MAGAT was manufactured in-house to fill two 400mL-cylindrical phantoms and nine 22mL-glass vials. Phantom-A was irradiated along the cylinder axis with a 9MeV electron beam of 6 cm x 6 cm field size (FS). Phantom-B was irradiated with a 6MV photon beam of 3 cm x 3 cm FS by a 360-degree arc technique. Eight vials were irradiated in a water-bath to various doses with a 20 cm x 20 cm FS 6MV photon beam. All irradiated phantoms and one un-irradiated vial were scanned with a 3T MRI scanner to obtain the spin-spin relaxation rate (R2) distributions. By comparing the measured R2-to-depth data with the known depth-dose data for Phantom-A, R2-to-dose calibration data were obtained (e-beam method). Another calibration data were obtained from the 9 vials data (9-vial method). We tested two regression equations, i.e., third-order polynomial and tangent functions, and two dose normalization methods, i.e., one-point and two-point methods. Then, these two calibration methods were used to obtain the 3D dose distribution of Phantom-B and evaluated by comparing the measured data with the dose distribution from a treatment planning system. The comparison was made with gamma passing rate (2%/2mm criteria). We did not observe a clear advantage of the e-beam method over the 9-vial method for the 3D dose comparison with the test case. Nevertheless, we found that the e-beam method required a smaller dose scaling for the dose comparison. Furthermore, the tangent function showed better data fitting than the polynomial function with smaller uncertainty of the estimated coefficients. Considering the overall superior performance, we recommend the e-beam method with the tangent function as the regression equation and one-point dose normalization for the MRI-based polymer gel dosimetry.

Research paper thumbnail of Three-dimensional dosimetry of TomoTherapy by MRI-based polymer gel technique

Journal of Applied Clinical Medical Physics, 2010

Verification of the dose calculation model and the software used for treatment planning is an imp... more Verification of the dose calculation model and the software used for treatment planning is an important step for accurate radiation delivery in radiation therapy. Using BANG3 polymer gel dosimeter with a 3 Tesla magnetic resonance imaging (MRI) scanner, we examined the accuracy of TomoTherapy treatment planning and radiation delivery. We evaluated one prostate treatment case and found the calculated three-dimensional (3D) dose distributions agree with the measured 3D dose distributions with an exception in the regions where the dose was much smaller (25% or less) than the maximum dose (2.5 Gy). The analysis using the gamma-index (3% dose difference and 3 mm distance-to-agreement) for a volume of 12 cm × 11 cm × 9 cm containing the planning target volume showed that the gamma values were smaller than unity for 53% of the voxels. Our measurement protocol and analysis tools can be easily applied to the evaluation of other newer complex radiation delivery techniques, such as intensity-modulated arc therapy, with a reasonably low financial investment.

Research paper thumbnail of Imrt and Vmat Commissioning for Versa HD Linear Accelerator Using Aapm TG-119

International Journal of Advanced Research, 2017

Purpose of study is to evaluate the end to end commissioning accuracy of intensity modulated radi... more Purpose of study is to evaluate the end to end commissioning accuracy of intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for Versa HD linear accelerator using AAPM TG-119 protocol. Materials & methods: IMRT and VMAT plans were created for TG119 test cases. All the plans were generated using Monaco 5.1 treatment planning system (TPS) for Elekta Versa HD linear accelerator. Prescription and planning goals were as kept as per TG119. For point dose measurement CC01 (0.01cc) ion chamber was used and measurements were carried out as per TG119 specified points in high and low dose gradient regions. Planar dose measurement I'matriXX along with multicube-lite phantom was used. Planned and measured dose planes were compared using gamma index criteria. Results: All planning goals have been achieved as per TG119 report. At high dose point measurement mean dose differences averaged over different techniques planned with different energies for all test cases was 0.002±0.020, and corresponding confidence limit was 0.041. At low dose point measurement mean dose averaged over different techniques planned with different energies for all test cases was-0.004±0.021, and corresponding confidence limit was 0.045. For planar dose measurement gamma passing rate averaged over all test cases was 99.40%±0.40 for 3%/3mm criteria and 97.82%±0.13 for 2%/2mm criteria respectively. Present work overall confidence limit for composite planar dose measurement was 1.38(i.e., 98.62% passing) for 3%/3mm and 2.45(i.e., 97.55% passing) for 2%/2mm criteria. Conclusion: Planning and delivery of IMRT/VMAT has been validated using published TG119 report results.

Research paper thumbnail of SU-E-T-14: A Comparative Study Between Forward and Inverse Planning in Gamma Knife Radiosurgery for Acoustic Neuroma Tumours

Medical Physics, 2015

ABSTRACT To evaluate forward and inverse planning methods for acoustic neuroma cases treated in G... more ABSTRACT To evaluate forward and inverse planning methods for acoustic neuroma cases treated in Gamma Knife Perfexion. Five patients with acoustic neuroma tumour abutting brainstem were planned twice in LGP TPS (Version 10.1) using TMR10 algorithm. First plan was entirely based on forward planning (FP) in which each shot was chosen manually. Second plan was generated using inverse planning (IP) for which planning parameters like coverage, selectivity, gradient index (GI) and beam-on time threshold were set. Number of shots in IP was automatically selected by objective function using iterative process. In both planning methods MRI MPRAGE sequence images were used for tumour localization and planning. A planning dose of 12Gy at 50% isodose level was chosen. Number of shots used in FP was greater than IP and beam-on time in FP was in average 1.4 times more than IP. One advantage of FP was that the brainstem volume subjected to 6Gy dose (25% isodose) was less in FP than IP. Our results showed use of more number of shots as in FP results in GI less than or equal to 2.55 which is close to its lower limit. Dose homogeneity index (DHI) analysis of FP and IP showed average values of 0.59 and 0.67 respectively. General trend in GK for planning in acoustic neuroma cases is to use small collimator shots to avoid dose to adjacent critical structures. More number of shots and prolonged treatment time causes inconvenience to the patients. Similarly overuse of automatic shot shaping as in IP results in increased scatter dose. A compromise is required in shot selection for these cases. IP method could be used in acoustic neuroma cases to decrease treatment time provided the source sector openings near brainstem are shielded or adjusted appropriately to reduce brainstem dose.

Research paper thumbnail of Digital Filtering Techniques to Reduce Image Noise and Improve Dose Resolution in X-Ray CT Based Normoxic Gel Dosimetry

Modern Practices in Radiation Therapy, 2012