Dayananda R Sharma | Rashtriya Sanskrit Sansthan (original) (raw)

Papers by Dayananda R Sharma

Research paper thumbnail of Peripheral dose from uniform dynamic multileaf collimation fields: implications for sliding window intensity-modulated radiotherapy

British Journal of Radiology, 2006

The increase in the number of monitor units in sliding window intensitymodulated radiotherapy, co... more The increase in the number of monitor units in sliding window intensitymodulated radiotherapy, compared with conventional techniques for the same target dose, may lead to an increase in peripheral dose (PD). PD from a linear accelerator was measured for 6 MV X-ray using 0.6 cm 3 ionization chamber inserted at 5 cm depth into a 35 cm 6 35 cm 6 105 cm plastic water phantom. Measurements were made for field sizes of 6 cm 6 6 cm, 10 cm 6 10 cm and 14 cm 6 14 cm, shaped in both static and dynamic multileaf collimation (DMLC) mode, employing strip fields of fixed width 0.5 cm, 1.0 cm, 1.5 cm, and 2.0 cm, respectively. The effect of collimator rotation and depth of measurement on peripheral dose was investigated for 10 cm 6 10 cm field. Dynamic fields require 2 to 14 times the number of monitor units than does a static open field for the same dose at the isocentre, depending on strip field width and field size. Peripheral dose resulting from dynamic fields manifests two distinct regions showing a crest and trough within 30 cm from the field edge and a steady exponential fall beyond 30 cm. All dynamic fields were found to deliver a higher PD compared with the corresponding static open fields, being highest for smallest strip field width and largest field size; also, the percentage increase observed was highest at the largest outof-field distance. For 6 cm 6 6 cm field, dynamic fields with 0.5 cm and 2 cm strip field width deliver PDs 8 and 2 times higher than that of the static open field. The corresponding factors for 14 cm 6 14 cm field were 15 and 6, respectively. The factors by which PD for DMLC fields increase, relative to jaws-shaped static fields for out-offield distance beyond 30 cm, are almost the same as the corresponding increases in the number of monitor units. Reductions of 20% and 40% in PD were observed when the measurements were done at a depth of 10 cm and 15 cm, respectively. When the multileaf collimator executes in-plane (collimator 90˚) motion, peripheral dose decreases by as much as a factor of 3 compared with cross-plane data. The knowledge of PD from DMLC field is necessary to estimate the increase in whole-body dose and the likelihood of radiation induced secondary malignancy.

Research paper thumbnail of Stereotactic Radiotherapy Of Intracranial Lesions With Micro Multileaf Collimator Mounted On Linear Accelerator

Journal of Medical …, 2002

... Acta Radiology. 14,209 - 227 (1975). 5. Eric E. Klein, William, B. Harms, Daniel A. Low, Virg... more ... Acta Radiology. 14,209 - 227 (1975). 5. Eric E. Klein, William, B. Harms, Daniel A. Low, Virgil Willcut, and James, A. Purdy.,Clinical implementation of a commercial multileaf collimator : Dosimetry, networking, simulation, and quality assurance. ...

Research paper thumbnail of Performance characterization of siemens primus linear accelerator under small monitor unit and small segments for the implementation of step-and-shoot intensitymodulated radiotherapy

Journal of Medical Physics, 2006

Implementation of step-and-shoot intensity-modulated radiotherapy (IMRT) needs careful understand... more Implementation of step-and-shoot intensity-modulated radiotherapy (IMRT) needs careful understanding of the accelerator start-up characteristic to ensure accurate and precise delivery of radiation dose to patient. The dosimetric characteristic of a Siemens Primus linear accelerator (LA) which delivers 6 and 18 MV x-rays at the dose rate of 300 and 500 monitor unit (MU) per minutes (min) respectively was studied under the condition of small MU ranging from 1 to 100. Dose monitor linearity was studied at different dose calibration parameter (D1_C0) by measuring ionization at 10 cm depth in a solid water phantom using a 0.6 cc ionization chamber. Monitor unit stability was studied from different intensity modulated (IM) groups comprising various combinations of MU per field and number of fields. Stability of beam flatness and symmetry was investigated under normal and IMRT mode for 20×20 cm(2) field under small MU using a 2D Profiler kept isocentrically at 5 cm depth. Inter segment response was investigated form 1 to 10 MU by measuring the dose per MU from various IM groups, each consisting of four segments with inter-segment separation of 2 cm.In the range 1-4 MU, the dose linearity error was more than 5% (max -32% at 1 MU) for 6 MV x-rays at factory calibrated D1_C0 value of 6000. The dose linearity error was reduced to -10.95% at 1 MU, within -3% for 2 and 3 MU and ±1% for MU ≥4 when the D1_C0 was subsequently tuned at 4500. For 18 MV x-rays, the dose linearity error at factory calibrated D1_C0 value of 4400 was within ±1% for MU ≥3 with maximum of -13.5 observed at 1 MU. For both the beam energies and MU/field ≥4, the stability of monitor unit tested for different IM groups was within ±1% of the dose from the normal treatment field. This variation increases to -2.6% for 6 MV and -2.7% for 18 MV x-rays for 2 MU/field. No significant variation was observed in the stability of beam profile measured from normal and IMRT mode. The beam flatness was within 3% for 6 MV x-rays and more than 3% (Max 3.5%) for 18 MV x-rays at lesser irradiation time ≤3 MU. The beam stability improves with the increase in irradiation time. Both the beam energies show very good symmetry (≤2%) at all irradiation time.For all the three segment sizes studied, the nonlinearity was observed at smaller MU/segment in both the energies. When the MU/segment is ≥4, all segment size shows fairly linear relation with dose/MU. The smaller segment size shows larger nonlinearity at smaller MU/segment and become more linear at larger MU/segment. Based on our study, we conclude that the Primus LA from Siemens installed at our hospital is ideally suited for step-and-shoot IMRT preferably for radiation ON time ≥4MU per segment.

Research paper thumbnail of SU-FF-T-111: Commissioning and Comprehensive Quality Assurance of Commercial 3D Treatment Planning System Using IAEA Technical Report Series — 430

Research paper thumbnail of SU‐GG‐T‐213: Portal Dosimetry for Pre‐Treatment Verification of IMRT Plan: A Comparison with 2D Ion Chamber Array

Medical Physics, 2010

ABSTRACT Purpose: To compare portal dosimetry (PD) and 2D pixel ion chamber (MatriXX) for pre‐tre... more ABSTRACT Purpose: To compare portal dosimetry (PD) and 2D pixel ion chamber (MatriXX) for pre‐treatment verification of photon fluence. Method and Materials: PD was performed for 181 fields from 14 IMRT plans of various clinical sites using aSi1000 electronic portal imaging device (EPID) and portal dose prediction (PDP) algorithm implemented in Eclipse Treatment planning system (TPS). Agreement of PDP predicted and EPID measured photon fluence were evaluated using gamma (γ) index set at 3% at 3 mm. Three γ scaling parameters, maximum γ (γmax), average γ (γavg) and percentage of points with γ≤1 (γ%≤1) were estimated for each field. An independent measurement was carried out using MatriXX with detector plane at 100 cm and γmax, γavg and γ%≤1 were estimated using Omnipro IMRT analyzing software. Effect of extended source to detector distance (SDD) and gantry rotation on PD outcome was also investigated for another 45 IMRT fields. Results: PDP predicted and EPID measured photon fluence agrees well with overall mean values of γmax, γavg and γ%≤1 at 2.02, 0.24 and 99.43% respectively. γmax value was lower in 15 MV compared to 6 MV IMRT plan. Independent verification using MatriXX showed comparable overall mean values of γavg and γ%≤1 at 0.25 and 99.80%. However, in all plans, MatriXX showed significantly lower γmax (p<0.05) with an overall mean value of 1.35. In PD, compare to γ values at 100 cm SDD, γmax, γavg and γ%≤1 values improve from a mean of 0.16, 0.03 and 0.25 at 110 cm SDD to 0.34, 0.05 and 0.29 at 140 cm SDD. PD outcome was independent of gantry rotation. Conclusion: Both PD and MatriXX showed comparable result and can be use as an alternative to each other for relative photon fluence verification. While portal dosimetry reduces measurement time, absolute dose measurement needs further investigation.

Research paper thumbnail of Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using in-house fabricated CT phantoms

Journal of Medical Physics, 2006

Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms... more Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms/test tools following AAPM recommended methods to independently validate the auto-performance test (APT) results. Test results of all the elec tromechanical parameters were found within the specified limits. Radiation and sensitivity profile widths were within ± 0.05 cm of the set slice thickness. Effective energy corresponding to nominal kVp of 80, 110 and 130 were 49.99, 55.08 and 59.48 keV, respectively. Percentage noise obtained by APT was 1.32% while the independently measured value was 0.38%. Ob served contrast resolutions by independent method at 0.78% and 12% contrast difference were 4 mm and 1.25 mm (= 4 lp/ cm) respectively. However, high contrast resolution (limiting spatial resolution) by APT at 50, 10 and 2% MTF levels were 9, 12.5 and 14.1 lp/cm respectively. Difference in calculated and measured CT numbers of water, air, teflon, acrylic, polystyrene and polypropylene were in the range of 0 to 24 HU, while this difference was 46 and 94 HU in case of nylon and bakelite respectively. The contrast scale determined using CT linearity phantom was 1.998×10 -4 cm -1 /CT number. CT dose index (CTDI) and weighted CTDI (CTDI w ) measured at different kVp for standard head and body phantoms were smaller than manufacturer-specified and system-calculated values and were found within the manufacturer-specified limit of ± 20%. Mea sured CTDIs on surface (head: 3.6 cGy and body: 2.6 cGy) and at the center (3.3 cGy, head; and 1.2 cGy, body) were comparable to reported values of other similar CT scanners and were also within the industry-quoted CTDI range. Compre hensive QA and independent validation of APT results are necessary to obtain baseline data for CT virtual simulation.

Research paper thumbnail of Dosimetric comparison of linear accelerator-based stereotactic radiosurgery systems

Journal of Medical Physics, 2007

Stereotactic radiosurgery (SRS) is a special radiotherapy technique used to irradiate intracrania... more Stereotactic radiosurgery (SRS) is a special radiotherapy technique used to irradiate intracranial lesions by 3-D arrangements of narrow photon beams eliminating the needs of invasive surgery. Three different tertiary collimators, namely BrainLab and Radionics circular cones and BrainLab micro multileaf collimator (mMLC), are used for linear accelerator-based SRS systems (X-Knife). Output factor (S t ), tissue maximum ratio (TMR) and off axis ratio (OAR) of these three SRS systems were measured using CC01 (Scanditronix/ Welhofer) and Pinpoint (PTW) cylindrical and Markus plane parallel ionization chambers as well as TLD and radiochromic film. Measurement results of CC01 and Pinpoint chambers were very close to each other which indicate that further reduction in volume and physical dimensions of cylindrical ionization chamber is not necessary for SRS/SRT dosimetry. Output factors of BrainLab and Radionics SRS cones were very close to each other while output factors of equivalent diameter mMLC field were different from SRS circular cones. TMR of the three SRS systems compared were very close to one another. OAR of Radionics cone and BrainLab mMLC were very close to each other, within 2%. However, OARs of BrainLab cone were found comparable to OARs of Radionics cone and BrainLab mMLC within maximum variation of 4%. In addition, user-measured similar data of other three mMLC X-Knives were compared with the mMLC X-Knife data measured in this work and found comparable. The concept of switching over to mMLC-based SRS/SRT is thus validated from dosimetric characteristics

Research paper thumbnail of Dose optimization of intra-operative high dose rate interstitial brachytherapy implants for soft tissue sarcoma

Journal of Cancer Research and Therapeutics, 2009

Objective: A three dimensional (3D) image-based dosimetric study to quantitatively compare geomet... more Objective: A three dimensional (3D) image-based dosimetric study to quantitatively compare geometric vs. dose-point optimization in combination with graphical optimization for interstitial brachytherapy of soft tissue sarcoma (STS).

Research paper thumbnail of Comparison of geometric uncertainties using electronic portal imaging device in focal three-dimensional conformal radiation therapy using different head supports

Journal of Cancer Research and Therapeutics, 2008

Aims and Objectives: To study the geometric uncertainties in the treatment and evaluate the adequ... more Aims and Objectives: To study the geometric uncertainties in the treatment and evaluate the adequacy of the margins employed for planning target volume (PTV) generation in the treatment of focal conformal radiotherapy (CRT) for patients with brain tumors treated with different head support systems.

Research paper thumbnail of Feasibility Study of 3D CT Based Brachytherapy Planning for Accelerated Partial Breast Irradiation With Intraoperative Interstitial Implants

International Journal of Radiation Oncology*Biology*Physics, 2007

Purpose/Objective(s): To study the feasibility of 3D CT based brachytherapy planning for accelera... more Purpose/Objective(s): To study the feasibility of 3D CT based brachytherapy planning for accelerated partial breast irradiation using intraoperative interstitial implants. Materials/Methods: During October 2005 to March 2007, 26 women participated in the ongoing prospective study of APBI using interstitial brachytherapy as the sole modality of radiation for early breast cancer. Tumor bed demarcation was done intraoperatively during the breast conserving surgery with radiopaque clips and 2-4 plane implant was done with free hand placement of needles which were then replaced with plastic tube catheters. Axial CT scan with 3 mm spacing were obtained for all the patients on postoperative 2-3 day. Catheter reconstruction and delineation of lumpectomy cavity, planning target volume (PTV) and ipsilateral breast was carried out. Cavity with 1 cm margin was considered as PTV and was edited for chest wall and skin. Loading of the catheters was done based on the 3DCT image. Final plan was obtained by interactively optimizing using graphical optimization tool over the geometrically optimized plan and was evaluated on each axial slices and also based on the dosimetric outcomes such as coverage index (CI), and dose homogeneity index (DHI). In first 18 patients this plan was compared with plan extrapolated from Xray based planning. Immediate clinical outcome with respect to healing and early cosmetic outcome were studied. The dose of 34 Gy in 10 fractions over 1 week was delivered with twice daily fractionation using high dose rate iridium source. Results: Mean age of the patients was 54 years. Mean number of needles was 15 and the average number of planes were 3. The Median CI of lumpectomy cavity for the final plan was 0.87 (Range: 0.74-0.99). The corresponding value for PTV was 0.76 (Range: 0.66-0.86). Underdosage of the cavity and PTV if observed at the site of air below the staples was accepted by us so as to avoid the skin toxicity. The median DHI was 0.79 (0.62-0.85). In the X-ray based plan the CI cavity, CI PTV and DHI were 0.80, 0.70 and 0.81 respectively. There was statistically significant improvement in the CI of cavity and PTV with 3DCT based planning with graphical optimization. The treatment was tolerated well in all the patients. Two patients developed wound infection immediately after RT which led to delayed wound healing. In all other patients the skin healed without any complications. The immediate cosmetic outcome was good to excellent in 85% patients. Conclusions: 3D CT based brachytherapy along with graphical optimization allows better visualization of the target which leads to significant improvement in the CI when compared with X ray based plan and appears feasible in patients undergoing APBI using intraoperative implants.

Research paper thumbnail of Dosimetric Comparison of Conventional Radiograph- and Three-dimensional Computed Tomography-based Planning using Dose Volume Indices for Partial Breast Intraoperative Implants

Clinical Oncology, 2008

The dosimetric outcomes of radiograph-and computed tomography-based plans generated with various ... more The dosimetric outcomes of radiograph-and computed tomography-based plans generated with various optimisation strategies were compared using dose volume indices for partial breast intraoperative implants. Materials and methods: Eighteen patients with early stage breast cancer underwent conventional orthogonal radiograph and computed tomography to generate dosimetric data. Catheter reconstruction and delineation of the lumpectomy cavity, the planning target volume (PTV) and the ipsilateral breast were carried out on computed tomography images. For each patient, geometrically optimised plans (P xray and P CT ) were generated using the active loading length based on the PTV defined from radiographs (PTV xray ) and computed tomography (PTV CT ). The plan P CT was further optimised graphically and yielded P graphical . Plans were compared using the coverage index (CI), the external volume index (EI), the dose homogeneity index (DHI), the overdose volume index (OI) and the conformal index (COIN). Results: The mean CI of the lumpectomy cavity estimated from P xray , P CT and P graphical was 0.80, 0.82 and 0.92, respectively. The corresponding values for PTV CT were 0.69, 0.71 and 0.85. P graphical showed an increase in CI by 23 and 19% with respect to P xray and P CT (P ! 0.001 in all) with a decrease in DHI from 0.81 to 0.71 (P ! 0.001) and increase in OI from 0.041 to 0.087 (P ! 0.001). The EI was highest in P xray (mean 44 cm 3 ) as compared with 25 cm 3 in P CT and 30 cm 3 in P graphical . A significant improvement in COIN was observed in P graphical (mean 0.68) compared with P xray (0.48) and P CT (0.58) (P ! 0.001). Conclusions: Objective dosimetric evaluation on three-dimensional computed tomography confirms its superiority over conventional two-dimensional radiograph-based planning in terms of a reduction in normal breast irradiated with the prescription dose and improvement in conformity. Interactive graphical optimisation based on the target volume in computed tomography further improves conformity with a reduction in dose homogeneity. The use of dose volume indices allows the comparison of different plans and can be used as a tool to correlate dosimetric with clinical outcome.

Research paper thumbnail of Dosimetric Analysis and Comparison of Interstitial HDR Brachytherapy, IMRT, 3DCRT and Electron Beam Therapy as Boost Modalities After Whole Breast Radiation in Breast Conservation Therapy

Brachytherapy, 2011

Brachytherapy, Volume 10, Issue null, Pages S47, May 2011, Authors:Suman Mallik, MD, DNB; Kaustav... more Brachytherapy, Volume 10, Issue null, Pages S47, May 2011, Authors:Suman Mallik, MD, DNB; Kaustav Talapatra, MD; Dayananda Sharma, MSc; Vaibhab Mahtre, MSc; Malhotra Singh, MSc.

Research paper thumbnail of A modified technique for high-dose-rate intracavitary brachytherapy in advanced cancer of the cervix

Brachytherapy, 2003

To develop a modified technique for high-dose-rate intracavitary brachytherapy in cervical cancer... more To develop a modified technique for high-dose-rate intracavitary brachytherapy in cervical cancer stage IIIb. METHODS AND MATERIALS: Cervical carcinoma FIGO Stage III accounts for Ͼ60% of all cervical cancers with radiation being the mainstay of treatment for most patients. After external beam radiation therapy (EBRT), the cervix is often flush with the vagina and the shape of the vagina may be conical with its apex at the external os level. All patients receive 2 applications with HDR brachytherapy. At the first application after the placement of the central tandem, only one ovoid is inserted and the other ovoid is replaced by a rubber tube, and the applicator assembly is fixed as usual. The contralateral ovoid is inserted at the subsequent application. RESULTS: To date, 21 locally advanced cervical cancer patients have been treated using this technique. In these patients, the mean dose to right and left Point A was 93% (range, 86-100%; median, 93%) and 95% (range, 90-100%; median, 95%), respectively. The variation of doses to the contralateral Point A was 1-14%. The mean dose to the rectal and bladder mucosa was 62% (range, 43-80%; median, 64%) and 80% (range, 50-110%; median, 71%), respectively. CONCLUSION: This modified HDR intracavitary technique may prove an alternative for centers where interstitial brachytherapy for cancer of the cervix is not available. Ć

Research paper thumbnail of Radiation therapy planning of a breast cancer patient with in situ pacemaker–challenges and lessons

Acta Oncologica, 2008

A postmenopausal lady with an in situ pacemaker developed a lump in the left breast and was diagn... more A postmenopausal lady with an in situ pacemaker developed a lump in the left breast and was diagnosed to have breast cancer. The patient underwent breast conservative surgery and was planned for post operative radiotherapy. The location of the tumor relative to the pacemaker provided a unique challenge in planning radiotherapy and the patient had an uneventful post radiotherapy course. A literature review revealed that modern generation pacemakers are very sensitive to radiation compared to their older counterparts. The present article makes suggestions towards reducing dose in radiotherapy planning in pacemaker patients.

Research paper thumbnail of Peripheral dose from uniform dynamic multileaf collimation fields: implications for sliding window intensity-modulated radiotherapy

British Journal of Radiology, 2006

The increase in the number of monitor units in sliding window intensitymodulated radiotherapy, co... more The increase in the number of monitor units in sliding window intensitymodulated radiotherapy, compared with conventional techniques for the same target dose, may lead to an increase in peripheral dose (PD). PD from a linear accelerator was measured for 6 MV X-ray using 0.6 cm 3 ionization chamber inserted at 5 cm depth into a 35 cm 6 35 cm 6 105 cm plastic water phantom. Measurements were made for field sizes of 6 cm 6 6 cm, 10 cm 6 10 cm and 14 cm 6 14 cm, shaped in both static and dynamic multileaf collimation (DMLC) mode, employing strip fields of fixed width 0.5 cm, 1.0 cm, 1.5 cm, and 2.0 cm, respectively. The effect of collimator rotation and depth of measurement on peripheral dose was investigated for 10 cm 6 10 cm field. Dynamic fields require 2 to 14 times the number of monitor units than does a static open field for the same dose at the isocentre, depending on strip field width and field size. Peripheral dose resulting from dynamic fields manifests two distinct regions showing a crest and trough within 30 cm from the field edge and a steady exponential fall beyond 30 cm. All dynamic fields were found to deliver a higher PD compared with the corresponding static open fields, being highest for smallest strip field width and largest field size; also, the percentage increase observed was highest at the largest outof-field distance. For 6 cm 6 6 cm field, dynamic fields with 0.5 cm and 2 cm strip field width deliver PDs 8 and 2 times higher than that of the static open field. The corresponding factors for 14 cm 6 14 cm field were 15 and 6, respectively. The factors by which PD for DMLC fields increase, relative to jaws-shaped static fields for out-offield distance beyond 30 cm, are almost the same as the corresponding increases in the number of monitor units. Reductions of 20% and 40% in PD were observed when the measurements were done at a depth of 10 cm and 15 cm, respectively. When the multileaf collimator executes in-plane (collimator 90˚) motion, peripheral dose decreases by as much as a factor of 3 compared with cross-plane data. The knowledge of PD from DMLC field is necessary to estimate the increase in whole-body dose and the likelihood of radiation induced secondary malignancy.

Research paper thumbnail of Stereotactic Radiotherapy Of Intracranial Lesions With Micro Multileaf Collimator Mounted On Linear Accelerator

Journal of Medical …, 2002

... Acta Radiology. 14,209 - 227 (1975). 5. Eric E. Klein, William, B. Harms, Daniel A. Low, Virg... more ... Acta Radiology. 14,209 - 227 (1975). 5. Eric E. Klein, William, B. Harms, Daniel A. Low, Virgil Willcut, and James, A. Purdy.,Clinical implementation of a commercial multileaf collimator : Dosimetry, networking, simulation, and quality assurance. ...

Research paper thumbnail of Performance characterization of siemens primus linear accelerator under small monitor unit and small segments for the implementation of step-and-shoot intensitymodulated radiotherapy

Journal of Medical Physics, 2006

Implementation of step-and-shoot intensity-modulated radiotherapy (IMRT) needs careful understand... more Implementation of step-and-shoot intensity-modulated radiotherapy (IMRT) needs careful understanding of the accelerator start-up characteristic to ensure accurate and precise delivery of radiation dose to patient. The dosimetric characteristic of a Siemens Primus linear accelerator (LA) which delivers 6 and 18 MV x-rays at the dose rate of 300 and 500 monitor unit (MU) per minutes (min) respectively was studied under the condition of small MU ranging from 1 to 100. Dose monitor linearity was studied at different dose calibration parameter (D1_C0) by measuring ionization at 10 cm depth in a solid water phantom using a 0.6 cc ionization chamber. Monitor unit stability was studied from different intensity modulated (IM) groups comprising various combinations of MU per field and number of fields. Stability of beam flatness and symmetry was investigated under normal and IMRT mode for 20×20 cm(2) field under small MU using a 2D Profiler kept isocentrically at 5 cm depth. Inter segment response was investigated form 1 to 10 MU by measuring the dose per MU from various IM groups, each consisting of four segments with inter-segment separation of 2 cm.In the range 1-4 MU, the dose linearity error was more than 5% (max -32% at 1 MU) for 6 MV x-rays at factory calibrated D1_C0 value of 6000. The dose linearity error was reduced to -10.95% at 1 MU, within -3% for 2 and 3 MU and ±1% for MU ≥4 when the D1_C0 was subsequently tuned at 4500. For 18 MV x-rays, the dose linearity error at factory calibrated D1_C0 value of 4400 was within ±1% for MU ≥3 with maximum of -13.5 observed at 1 MU. For both the beam energies and MU/field ≥4, the stability of monitor unit tested for different IM groups was within ±1% of the dose from the normal treatment field. This variation increases to -2.6% for 6 MV and -2.7% for 18 MV x-rays for 2 MU/field. No significant variation was observed in the stability of beam profile measured from normal and IMRT mode. The beam flatness was within 3% for 6 MV x-rays and more than 3% (Max 3.5%) for 18 MV x-rays at lesser irradiation time ≤3 MU. The beam stability improves with the increase in irradiation time. Both the beam energies show very good symmetry (≤2%) at all irradiation time.For all the three segment sizes studied, the nonlinearity was observed at smaller MU/segment in both the energies. When the MU/segment is ≥4, all segment size shows fairly linear relation with dose/MU. The smaller segment size shows larger nonlinearity at smaller MU/segment and become more linear at larger MU/segment. Based on our study, we conclude that the Primus LA from Siemens installed at our hospital is ideally suited for step-and-shoot IMRT preferably for radiation ON time ≥4MU per segment.

Research paper thumbnail of SU-FF-T-111: Commissioning and Comprehensive Quality Assurance of Commercial 3D Treatment Planning System Using IAEA Technical Report Series — 430

Research paper thumbnail of SU‐GG‐T‐213: Portal Dosimetry for Pre‐Treatment Verification of IMRT Plan: A Comparison with 2D Ion Chamber Array

Medical Physics, 2010

ABSTRACT Purpose: To compare portal dosimetry (PD) and 2D pixel ion chamber (MatriXX) for pre‐tre... more ABSTRACT Purpose: To compare portal dosimetry (PD) and 2D pixel ion chamber (MatriXX) for pre‐treatment verification of photon fluence. Method and Materials: PD was performed for 181 fields from 14 IMRT plans of various clinical sites using aSi1000 electronic portal imaging device (EPID) and portal dose prediction (PDP) algorithm implemented in Eclipse Treatment planning system (TPS). Agreement of PDP predicted and EPID measured photon fluence were evaluated using gamma (γ) index set at 3% at 3 mm. Three γ scaling parameters, maximum γ (γmax), average γ (γavg) and percentage of points with γ≤1 (γ%≤1) were estimated for each field. An independent measurement was carried out using MatriXX with detector plane at 100 cm and γmax, γavg and γ%≤1 were estimated using Omnipro IMRT analyzing software. Effect of extended source to detector distance (SDD) and gantry rotation on PD outcome was also investigated for another 45 IMRT fields. Results: PDP predicted and EPID measured photon fluence agrees well with overall mean values of γmax, γavg and γ%≤1 at 2.02, 0.24 and 99.43% respectively. γmax value was lower in 15 MV compared to 6 MV IMRT plan. Independent verification using MatriXX showed comparable overall mean values of γavg and γ%≤1 at 0.25 and 99.80%. However, in all plans, MatriXX showed significantly lower γmax (p<0.05) with an overall mean value of 1.35. In PD, compare to γ values at 100 cm SDD, γmax, γavg and γ%≤1 values improve from a mean of 0.16, 0.03 and 0.25 at 110 cm SDD to 0.34, 0.05 and 0.29 at 140 cm SDD. PD outcome was independent of gantry rotation. Conclusion: Both PD and MatriXX showed comparable result and can be use as an alternative to each other for relative photon fluence verification. While portal dosimetry reduces measurement time, absolute dose measurement needs further investigation.

Research paper thumbnail of Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using in-house fabricated CT phantoms

Journal of Medical Physics, 2006

Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms... more Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms/test tools following AAPM recommended methods to independently validate the auto-performance test (APT) results. Test results of all the elec tromechanical parameters were found within the specified limits. Radiation and sensitivity profile widths were within ± 0.05 cm of the set slice thickness. Effective energy corresponding to nominal kVp of 80, 110 and 130 were 49.99, 55.08 and 59.48 keV, respectively. Percentage noise obtained by APT was 1.32% while the independently measured value was 0.38%. Ob served contrast resolutions by independent method at 0.78% and 12% contrast difference were 4 mm and 1.25 mm (= 4 lp/ cm) respectively. However, high contrast resolution (limiting spatial resolution) by APT at 50, 10 and 2% MTF levels were 9, 12.5 and 14.1 lp/cm respectively. Difference in calculated and measured CT numbers of water, air, teflon, acrylic, polystyrene and polypropylene were in the range of 0 to 24 HU, while this difference was 46 and 94 HU in case of nylon and bakelite respectively. The contrast scale determined using CT linearity phantom was 1.998×10 -4 cm -1 /CT number. CT dose index (CTDI) and weighted CTDI (CTDI w ) measured at different kVp for standard head and body phantoms were smaller than manufacturer-specified and system-calculated values and were found within the manufacturer-specified limit of ± 20%. Mea sured CTDIs on surface (head: 3.6 cGy and body: 2.6 cGy) and at the center (3.3 cGy, head; and 1.2 cGy, body) were comparable to reported values of other similar CT scanners and were also within the industry-quoted CTDI range. Compre hensive QA and independent validation of APT results are necessary to obtain baseline data for CT virtual simulation.

Research paper thumbnail of Dosimetric comparison of linear accelerator-based stereotactic radiosurgery systems

Journal of Medical Physics, 2007

Stereotactic radiosurgery (SRS) is a special radiotherapy technique used to irradiate intracrania... more Stereotactic radiosurgery (SRS) is a special radiotherapy technique used to irradiate intracranial lesions by 3-D arrangements of narrow photon beams eliminating the needs of invasive surgery. Three different tertiary collimators, namely BrainLab and Radionics circular cones and BrainLab micro multileaf collimator (mMLC), are used for linear accelerator-based SRS systems (X-Knife). Output factor (S t ), tissue maximum ratio (TMR) and off axis ratio (OAR) of these three SRS systems were measured using CC01 (Scanditronix/ Welhofer) and Pinpoint (PTW) cylindrical and Markus plane parallel ionization chambers as well as TLD and radiochromic film. Measurement results of CC01 and Pinpoint chambers were very close to each other which indicate that further reduction in volume and physical dimensions of cylindrical ionization chamber is not necessary for SRS/SRT dosimetry. Output factors of BrainLab and Radionics SRS cones were very close to each other while output factors of equivalent diameter mMLC field were different from SRS circular cones. TMR of the three SRS systems compared were very close to one another. OAR of Radionics cone and BrainLab mMLC were very close to each other, within 2%. However, OARs of BrainLab cone were found comparable to OARs of Radionics cone and BrainLab mMLC within maximum variation of 4%. In addition, user-measured similar data of other three mMLC X-Knives were compared with the mMLC X-Knife data measured in this work and found comparable. The concept of switching over to mMLC-based SRS/SRT is thus validated from dosimetric characteristics

Research paper thumbnail of Dose optimization of intra-operative high dose rate interstitial brachytherapy implants for soft tissue sarcoma

Journal of Cancer Research and Therapeutics, 2009

Objective: A three dimensional (3D) image-based dosimetric study to quantitatively compare geomet... more Objective: A three dimensional (3D) image-based dosimetric study to quantitatively compare geometric vs. dose-point optimization in combination with graphical optimization for interstitial brachytherapy of soft tissue sarcoma (STS).

Research paper thumbnail of Comparison of geometric uncertainties using electronic portal imaging device in focal three-dimensional conformal radiation therapy using different head supports

Journal of Cancer Research and Therapeutics, 2008

Aims and Objectives: To study the geometric uncertainties in the treatment and evaluate the adequ... more Aims and Objectives: To study the geometric uncertainties in the treatment and evaluate the adequacy of the margins employed for planning target volume (PTV) generation in the treatment of focal conformal radiotherapy (CRT) for patients with brain tumors treated with different head support systems.

Research paper thumbnail of Feasibility Study of 3D CT Based Brachytherapy Planning for Accelerated Partial Breast Irradiation With Intraoperative Interstitial Implants

International Journal of Radiation Oncology*Biology*Physics, 2007

Purpose/Objective(s): To study the feasibility of 3D CT based brachytherapy planning for accelera... more Purpose/Objective(s): To study the feasibility of 3D CT based brachytherapy planning for accelerated partial breast irradiation using intraoperative interstitial implants. Materials/Methods: During October 2005 to March 2007, 26 women participated in the ongoing prospective study of APBI using interstitial brachytherapy as the sole modality of radiation for early breast cancer. Tumor bed demarcation was done intraoperatively during the breast conserving surgery with radiopaque clips and 2-4 plane implant was done with free hand placement of needles which were then replaced with plastic tube catheters. Axial CT scan with 3 mm spacing were obtained for all the patients on postoperative 2-3 day. Catheter reconstruction and delineation of lumpectomy cavity, planning target volume (PTV) and ipsilateral breast was carried out. Cavity with 1 cm margin was considered as PTV and was edited for chest wall and skin. Loading of the catheters was done based on the 3DCT image. Final plan was obtained by interactively optimizing using graphical optimization tool over the geometrically optimized plan and was evaluated on each axial slices and also based on the dosimetric outcomes such as coverage index (CI), and dose homogeneity index (DHI). In first 18 patients this plan was compared with plan extrapolated from Xray based planning. Immediate clinical outcome with respect to healing and early cosmetic outcome were studied. The dose of 34 Gy in 10 fractions over 1 week was delivered with twice daily fractionation using high dose rate iridium source. Results: Mean age of the patients was 54 years. Mean number of needles was 15 and the average number of planes were 3. The Median CI of lumpectomy cavity for the final plan was 0.87 (Range: 0.74-0.99). The corresponding value for PTV was 0.76 (Range: 0.66-0.86). Underdosage of the cavity and PTV if observed at the site of air below the staples was accepted by us so as to avoid the skin toxicity. The median DHI was 0.79 (0.62-0.85). In the X-ray based plan the CI cavity, CI PTV and DHI were 0.80, 0.70 and 0.81 respectively. There was statistically significant improvement in the CI of cavity and PTV with 3DCT based planning with graphical optimization. The treatment was tolerated well in all the patients. Two patients developed wound infection immediately after RT which led to delayed wound healing. In all other patients the skin healed without any complications. The immediate cosmetic outcome was good to excellent in 85% patients. Conclusions: 3D CT based brachytherapy along with graphical optimization allows better visualization of the target which leads to significant improvement in the CI when compared with X ray based plan and appears feasible in patients undergoing APBI using intraoperative implants.

Research paper thumbnail of Dosimetric Comparison of Conventional Radiograph- and Three-dimensional Computed Tomography-based Planning using Dose Volume Indices for Partial Breast Intraoperative Implants

Clinical Oncology, 2008

The dosimetric outcomes of radiograph-and computed tomography-based plans generated with various ... more The dosimetric outcomes of radiograph-and computed tomography-based plans generated with various optimisation strategies were compared using dose volume indices for partial breast intraoperative implants. Materials and methods: Eighteen patients with early stage breast cancer underwent conventional orthogonal radiograph and computed tomography to generate dosimetric data. Catheter reconstruction and delineation of the lumpectomy cavity, the planning target volume (PTV) and the ipsilateral breast were carried out on computed tomography images. For each patient, geometrically optimised plans (P xray and P CT ) were generated using the active loading length based on the PTV defined from radiographs (PTV xray ) and computed tomography (PTV CT ). The plan P CT was further optimised graphically and yielded P graphical . Plans were compared using the coverage index (CI), the external volume index (EI), the dose homogeneity index (DHI), the overdose volume index (OI) and the conformal index (COIN). Results: The mean CI of the lumpectomy cavity estimated from P xray , P CT and P graphical was 0.80, 0.82 and 0.92, respectively. The corresponding values for PTV CT were 0.69, 0.71 and 0.85. P graphical showed an increase in CI by 23 and 19% with respect to P xray and P CT (P ! 0.001 in all) with a decrease in DHI from 0.81 to 0.71 (P ! 0.001) and increase in OI from 0.041 to 0.087 (P ! 0.001). The EI was highest in P xray (mean 44 cm 3 ) as compared with 25 cm 3 in P CT and 30 cm 3 in P graphical . A significant improvement in COIN was observed in P graphical (mean 0.68) compared with P xray (0.48) and P CT (0.58) (P ! 0.001). Conclusions: Objective dosimetric evaluation on three-dimensional computed tomography confirms its superiority over conventional two-dimensional radiograph-based planning in terms of a reduction in normal breast irradiated with the prescription dose and improvement in conformity. Interactive graphical optimisation based on the target volume in computed tomography further improves conformity with a reduction in dose homogeneity. The use of dose volume indices allows the comparison of different plans and can be used as a tool to correlate dosimetric with clinical outcome.

Research paper thumbnail of Dosimetric Analysis and Comparison of Interstitial HDR Brachytherapy, IMRT, 3DCRT and Electron Beam Therapy as Boost Modalities After Whole Breast Radiation in Breast Conservation Therapy

Brachytherapy, 2011

Brachytherapy, Volume 10, Issue null, Pages S47, May 2011, Authors:Suman Mallik, MD, DNB; Kaustav... more Brachytherapy, Volume 10, Issue null, Pages S47, May 2011, Authors:Suman Mallik, MD, DNB; Kaustav Talapatra, MD; Dayananda Sharma, MSc; Vaibhab Mahtre, MSc; Malhotra Singh, MSc.

Research paper thumbnail of A modified technique for high-dose-rate intracavitary brachytherapy in advanced cancer of the cervix

Brachytherapy, 2003

To develop a modified technique for high-dose-rate intracavitary brachytherapy in cervical cancer... more To develop a modified technique for high-dose-rate intracavitary brachytherapy in cervical cancer stage IIIb. METHODS AND MATERIALS: Cervical carcinoma FIGO Stage III accounts for Ͼ60% of all cervical cancers with radiation being the mainstay of treatment for most patients. After external beam radiation therapy (EBRT), the cervix is often flush with the vagina and the shape of the vagina may be conical with its apex at the external os level. All patients receive 2 applications with HDR brachytherapy. At the first application after the placement of the central tandem, only one ovoid is inserted and the other ovoid is replaced by a rubber tube, and the applicator assembly is fixed as usual. The contralateral ovoid is inserted at the subsequent application. RESULTS: To date, 21 locally advanced cervical cancer patients have been treated using this technique. In these patients, the mean dose to right and left Point A was 93% (range, 86-100%; median, 93%) and 95% (range, 90-100%; median, 95%), respectively. The variation of doses to the contralateral Point A was 1-14%. The mean dose to the rectal and bladder mucosa was 62% (range, 43-80%; median, 64%) and 80% (range, 50-110%; median, 71%), respectively. CONCLUSION: This modified HDR intracavitary technique may prove an alternative for centers where interstitial brachytherapy for cancer of the cervix is not available. Ć

Research paper thumbnail of Radiation therapy planning of a breast cancer patient with in situ pacemaker–challenges and lessons

Acta Oncologica, 2008

A postmenopausal lady with an in situ pacemaker developed a lump in the left breast and was diagn... more A postmenopausal lady with an in situ pacemaker developed a lump in the left breast and was diagnosed to have breast cancer. The patient underwent breast conservative surgery and was planned for post operative radiotherapy. The location of the tumor relative to the pacemaker provided a unique challenge in planning radiotherapy and the patient had an uneventful post radiotherapy course. A literature review revealed that modern generation pacemakers are very sensitive to radiation compared to their older counterparts. The present article makes suggestions towards reducing dose in radiotherapy planning in pacemaker patients.