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Accurate calibration of a polymer gel dosimeter with a plastic scintillation detector.
- Source :
-
Medical Physics . May2011, Vol. 38 Issue 5, p2754-2761. 8p. - Publication Year :
- 2011
-
Abstract
- Purpose: Three dimensional dose polymer gel dosimetry measurements provide unique information on sophisticated dose distributions. In this study, the authors propose a novel method to improve the accuracy of polymer gel dosimeters by inserting a plastic scintillation detector (PSD) to provide a dose reference. Methods: PSD dosimeters were calibrated using chromatic deconvolution and then inserted into polyacrylanide gel (PAG) dosimeters. The gel and the PSDs were immersed into water and irradiated with 6 MV wedge filtered beams to obtain a wide range of dose variation. Calibration vials containing the same gel were also irradiated to generate a standard calibration curve. The distribution of magnetic nuclear transverse relaxation rate (R2) values of the gel was determined with a multislice multiecho MRI sequence at 1.5 T. Another calibration curve was obtained by assigning the R2 values in the gel surrounding the scintillators to the dose determined by the PSDs. A reference calibration point from a PSD located in a low dose gradient area served to correct the standard calibration method yielding three novel calibration methods. The results were compared with EBT2 GAFCHROMICâ„¢ film measurements acquired in the same condition and with the Pinnacle3 treatment planning dose calculations. Results: The mean absolute error of the standard calibration method ranged from 6.1 to 12.4%. The corresponding gamma index (3%/3 mm distance to agreement) criterion was satisfied for only 56% of the pixels in the middle slice of the gel compared to Pinnacle3 dose calculations and to EBT2 film measurements in the center part of the field. Calibration methods using a PSD reduced the mean absolute error to less than 4%; this value was under 2.6% for one of the three methods. In that case, 98% of the pixels satisfied the gamma index criterion. Conclusions: The accuracy of PAG dosimeters may be highly improved using one reference dose point measurement using a plastic scintillation detector. The best calibration procedure corrected the slope of the calibration curve derived from the calibration vials to match the R2 value around a PSD calibration, while keeping the R2 value at 0 Gy constant. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00942405
- Volume :
- 38
- Issue :
- 5
- Database :
- Academic Search Index
- Journal :
- Medical Physics
- Publication Type :
- Academic Journal
- Accession number :
- 60594676
- Full Text :
- https://doi.org/10.1118/1.3578601