SU-E-T-398: Verification of Gamma Knife EXtend System Based Fractionated Treatment Planning Using EBT2 Film (original) (raw)
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Verification of Gamma Knife extend system based fractionated treatment planning using EBT2 film
Medical physics, 2013
This paper presents EBT2 film verification of fractionated treatment planning with the Gamma Knife (GK) extend system, a relocatable frame system for multiple-fraction or serial multiple-session radiosurgery. A human head shaped phantom simulated the verification process for fractionated Gamma Knife treatment. Phantom preparation for Extend Frame based treatment planning involved creating a dental impression, fitting the phantom to the frame system, and acquiring a stereotactic computed tomography (CT) scan. A CT scan (Siemens, Emotion 6) of the phantom was obtained with following parameters: Tube voltage--110 kV, tube current--280 mA, pixel size--0.5 × 0.5 and 1 mm slice thickness. A treatment plan with two 8 mm collimator shots and three sectors blocking in each shot was made. Dose prescription of 4 Gy at 100% was delivered for the first fraction out of the two fractions planned. Gafchromic EBT2 film (ISP Wayne, NJ) was used as 2D verification dosimeter in this process. Films were...
Journal of Medical Physics, 2006
The quantitative dose validation of intensity modulated radiotherapy (IMRT) requires the three-dimensional highresolution dosimetry systems with uniform sensitivity over its entire sensitive region. Silver halide radiographic films offer good resolution for two-dimensional dosimetry. Threedimensional verification can be accomplished by measuring at different planes using films. The spectral sensitivity and response to the developing conditions are the important limiting factors of the silver halide films. [1] Self-developing radiochromic films offer high-resolution dose measurements with relatively insensitive spectral response. [2] Since these films are self-developing, the uncertainties associated with the developing conditions are ruled out. The present study deals with the evaluation of new type of radiochromic films-Gafchromic external beam therapy (EBT) film-for its use of IMRT plan validation. The results obtained with EBT films are compared with the results of commonly used Kodak extended dose range 2 (EDR2) films. Materials and Methods Film calibration The calibration data set for both EDR2 and EBT films were obtained by exposing the films with doses ranging from 19.6 cGy to 700 cGy using 6MV photon beams. The film was kept at a dmax in solid water phantom in a plane perpendicular to the beam axis. The processed EDR2 films were scanned using VIDAR 16 (VXR-16) digitizer and RIT 113 film dosimetry software. The irradiated EBT films were scanned 3 h after irradiation along portrait direction to allow the saturation of color growth, as recommended by the film manufacturer. The EBT films are scanned with the yellow filter supplied by the film manufacturer to enhance the sensitivity of the film with VXR 16 scanner as the EBT film strongly absorbs the higher wavelength region of the visible spectrum. The measured optical density (OD) was plotted
Medical Dosimetry, 2006
The quantitative dose validation of intensity-modulated radiation therapy (IMRT) plans require 2-dimensional (2D) high-resolution dosimetry systems with uniform response over its sensitive region. The present work deals with clinical use of commercially available self-developing Radio Chromic Film, Gafchromic EBT film, for IMRT dose verification. Dose response curves were generated for the films using a VXR-16 film scanner. The results obtained with EBT films were compared with the results of Kodak extended dose range 2 (EDR2) films. The EBT film had a linear response between the dose range of 0 to 600 cGy. The dose-related characteristics of the EBT film, such as post irradiation color growth with time, film uniformity, and effect of scanning orientation, were studied. There was up to 8.6% increase in the color density between 2 to 40 hours after irradiation. There was a considerable variation, up to 8.5%, in the film uniformity over its sensitive region. The quantitative differences between calculated and measured dose distributions were analyzed using DTA and Gamma index with the tolerance of 3% dose difference and 3-mm distance agreement. The EDR2 films showed consistent results with the calculated dose distributions, whereas the results obtained using EBT were inconsistent. The variation in the film uniformity limits the use of EBT film for conventional large-field IMRT verification. For IMRT of smaller field sizes (4.5 ؋ 4.5 cm), the results obtained with EBT were comparable with results of EDR2 films.
Surface dose measurement with Gafchromic EBT3 film for intensity modulated radiotherapy technique
EPJ Web of Conferences
Accurate dose measurement in the buildup region is extremely difficult. Studies have reported that treatment planning systems (TPS) cannot calculate surface dose accurately. The aim of the study was to compare the film measurements and TPS calculations for surface dose in head and neck cancer treatment using intensity modulated radiation therapy (IMRT). IMRT plans were generated for 5 head and neck cancer patients by using Varian Eclipse TPS. Quality assurance (QA) plans of these IMRT plans were created on rando phantoms for surface dose measurements. EBT3 films were cut in size of 2.5 x 2.5 cm 2 and placed on the left side, right side and the center of larynx and then the films were irradiated with 6 MV photon beams. The measured doses were compared with TPS. The results of TPS calculations were found to be lower compared to the EBT3 film measurements at all selected points. The lack of surface dose calculation in TPS should be considered while evaluating the radiotherapy plans.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2015
EBT2 film is a convenient dosimetry quality-assurance (QA) tool with high 2D dosimetry resolution and a self-development property for use in verifications of radiation therapy treatment planning and special projects; however, the user will suffer from a relatively higher degree of uncertainty (more than 7 6% by Hartmann et al. ), and the trouble of cutting one piece of film into small pieces and then reintegrating them each time. To prevent this tedious cutting work, and save calibration time and budget, a dose range analysis is presented in this study for EBT2 film calibration using the Percentage-Depth-Dose (PDD) method. Different combinations of the three dose ranges, 9-26 cGy, 33-97 cGy and 109-320 cGy, with two types of curve fitting algorithms, film pixel values and net optical densities converting into doses, were tested and compared. With the lowest error and acceptable inaccuracy of less than 3 cGy for the clinical dose range (9-320 cGy), a single film calibrated by the net optical density algorithm with the dose range 109-320 cGy was suggested for routine calibration.
Accuracy of GafChromic EBT Film as Dose Meter in Radiotherapy QA
IFMBE Proceedings, 2009
Contemporary radiation therapy dose delivery methods like e.g. IMRT and RapidArc needs high-accurate quality assurance dose detection methods. For this purpose GafChromic EBT film is available. No developing process is required like for radiographic film, while the read out of the EBT films can be performed with cheap flatbed scanners. However, before clinical use the film -flatbed scanner (Epson 1680 Expression Pro as well as Epson 10000XL) combination should be tested on their characteristics and achievable overall dosimetric accuracy. Hereto comparison measurements in water with ionization chamber, diode (array) and EBT film were performed for standard and IMRT radiation fields. We observed that absolute dose measurement with EBT film can be performed with an uncertainty up to 1.8% (1 SD) for a single film and 1.4% (1 SD) applying per measurement 2 films simultaneously, and when precautions are taken. Precautions which should be considered are: 1) inhomogeneity effects in film thickness; 2) strictness in film orientation during calibration and film scanning; 3) variation in optical density read out over the scan window of the scanner which depends furthermore on the dose delivered to the EBT film. The first aspect is related to film production processes. The second aspect is related to the orientation of the polymer molecules in the film. The third aspect is related to light polarization capacity of the EBT film polymer molecules in combination with an inherent creation of polarized light in the scanner itself during transport of the light ray from each point in the light tube to the CCD chip.
This work illustrates a procedure to assess the overall accuracy associated with Gamma Knife treatment planning using plugging. The main role of source plugging or blocking is to create dose falloff in the junction between a target and a critical structure. We report the use of MAGAT gel dosimeter for verification of an experimental treatment plan based on plugging. The polymer gel contained in a head-sized glass container simulated all major aspects of the treatment process of Gamma Knife radiosurgery. The 3D dose distribution recorded in the gel dosimeter was read using a 1.5T MRI scanner. Scanning protocol was: CPMG pulse sequence with 8 equidistant echoes, TR = 7 s, echo step = 14 ms, pixel size = 0.5 mm × 0.5 mm, and slice thickness of 2 mm. Using a calibration relationship between absorbed dose and spin-spin relaxation rate (R2), we converted R2 images to dose images. Volumetric dose comparison between treatment planning system (TPS) and gel measurement was accomplished using an in-house MATLAB-based program. The isodose overlay of the measured and computed dose distribution on axial planes was in close agreement. Gamma index analysis of 3D data showed more than 94% voxel pass rate for different tolerance criteria of 3%/2 mm, 3%/1 mm and 2%/2 mm. Film dosimetry with GAFCHROMIC EBT 2 film was also performed to compare the results with the calculated TPS dose. Gamma index analysis of film measurement for the same tolerance criteria used for gel measurement evaluation showed more than 95% voxel pass rate. Verification of gamma plan calculated dose on account of shield is not part of acceptance testing of Leksell Gamma Knife (LGK). Through this study we accomplished a volumetric comparison of dose distributions measured with a polymer gel dosimeter and Leksell GammaPlan (LGP) calculations for plans using plugging. We propose gel dosimeter as a quality assurance (QA) tool for verification of plug-based planning.
Treatment planning systems (TPSs) still face challenges in determining the peripheral and surface doses specially when using thermoplastic mask and bolus. This study aims to assess the peripheral and surface dose using diode and Gafchromic EBT3 films dosimeters. In addition to investigate the impact of thermoplastic mask with different thickness of bolus on these doses. Methods: The measurements were performed for an Alderson Rando phantom. The maxilla and prostate were delineated as the target, because the maxilla is close to the surface, to determine the impact of thermoplastic mask and bolus on the skin dose. Results: The measured surface dose for IMRT was higher compared to TPS with an average difference of 21.5%, 20.2%, 18.7%, and 13.4% in the absence of thermoplastic mask and bolus, with mask, with bolus 5 mm and with bolus 10 mm respectively. For 3D-CRT, the measured surface dose was also higher compared to TPS with an average difference of 20.7%, 19.6%, 16.1%, and 13.3% in the absence of thermoplastic mask and bolus, with mask, with bolus 5 mm and with bolus 10 mm respectively. For the prostate, the PD that is close to the target was in good agreement between peripheral dose measured with diode and acquired from TPS. Whereas TPS underestimated the PD for both 3D-CRT and IMRT at locations that are away from the target. Moreover, when comparing 3D-CRT to IMRT for PD, 3D-CRT resulted in higher for distances close to the target, whereas the IMRT indeed delivered higher than 3D-CRT to locations that are away from the target. Conclusions: This study showed that diode dosimeter is recommended to estimate both peripheral and surface doses whereas EBT3 films dosimeter is recommended to estimate surface dose and not for PD.
ABSTRACT: The performance of treatment planning system (TPS) nowadays is a key component in order to deliver an accurate treatment towards target volume in any radiation therapy process. Thus, the purpose of this study is to verify the point doses calculated by Oncentra Brachytherapy Treatment Planning Software 4.1 (Nucletron, Netherlands). Three different simple geometric catheter configurations were planned in TPS, and point doses of TPS calculation were compared with manual calculation and measured point doses using Gafchromic EBT2 films. For manual calculation of three simple geometric catheter configurations planned, 68% of calculated dose agreed with TPS calculation within 10%. This is because the TPS and manual calculations are based on the similar AAPM TG-43 formalism. Meanwhile, 11% of the measured point doses agreed with the TPS calculation within 10%. The films had high spatial resolution, which was highly sensitive for measuring doses in high dose gradient but it also led to overestimation of the dose. It was also inaccurate in detecting the lower dose region due to energy dependence. In conclusion, manually calculated point doses gave the most reliable point dose results compared to the measured point doses in this study. The method used in this study can be used as a procedure for evaluating the accuracy of calculated point doses prior installing and commissioning a new TPS. Keywords: AAPM TG-43 formalism, brachytherapy treatment planning system, point doses measurements
Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density
Journal of Applied Clinical Medical Physics, 2016
Radiochromic film has become an important tool to verify dose distributions for intensity-modulated radiotherapy (IMRT) and quality assurance (QA) procedures. A new radiochromic film model, EBT3, has recently become available, whose composition and thickness of the sensitive layer are the same as those of previous EBT2 films. However, a matte polyester layer was added to EBT3 to prevent the formation of Newton's rings. Furthermore, the symmetrical design of EBT3 allows the user to eliminate side-orientation dependence. This film and the flatbed scanner, Epson Perfection V750, form a dosimetry system whose intrinsic characteristics were studied in this work. In addition, uncertainties associated with these intrinsic characteristics and the total uncertainty of the dosimetry system were determined. The analysis of the response of the radiochromic film (net optical density) and the fitting of the experimental data to a potential function yielded an uncertainty of 2.6%, 4.3%, and 4.1% for the red, green, and blue channels, respectively. In this work, the dosimetry system presents an uncertainty in resolving the dose of 1.8% for doses greater than 0.8 Gy and less than 6 Gy for red channel. The films irradiated between 0 and 120 Gy show differences in the response when scanned in portrait or landscape mode; less uncertainty was found when using the portrait mode. The response of the film depended on the position on the bed of the scanner, contributing an uncertainty of 2% for the red, 3% for the green, and 4.5% for the blue when placing the film around the center of the bed of scanner. Furthermore, the uniformity and reproducibility radiochromic film and reproducibility of the response of the scanner contribute less than 1% to the overall uncertainty in dose. Finally, the total dose uncertainty was 3.2%, 4.9%, and 5.2% for red, green, and blue channels, respectively. The above uncertainty values were obtained by minimizing the contribution to the total dose uncertainty of the film orientation and film homogeneity.