Premium
Sci‐Sat AM: Radiation Dosimetry and Practical Therapy Solutions ‐ 03: Energy dependence of a clinical probe‐format calorimeter and its pertinence to absolute photon and electron beam dosimetry
Author(s) -
Renaud James,
Seuntjens Jan,
Sarfehnia Arman
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4961857
Subject(s) - dosimetry , dosimeter , absorbed dose , ionization chamber , calorimeter (particle physics) , linear particle accelerator , photon , dose profile , imaging phantom , bremsstrahlung , beam (structure) , electron , radiation , calibration , materials science , physics , atomic physics , nuclear medicine , optics , nuclear physics , ion , ionization , medicine , detector , quantum mechanics
Purpose: To evaluate the intrinsic and absorbed‐dose energy dependence of a small‐scale graphite calorimeter probe (GPC) developed for use as a routine clinical dosimeter. The influence of charge deposition on the response of the GPC was also assessed by performing absolute dosimetry in clinical linac‐based electron beams. Methods: Intrinsic energy dependence was determined by performing constant‐temperature calorimetry dose measurements in a water‐equivalent solid phantom, under otherwise reference conditions, in five high‐energy photon (63.5 < % dd (10) X < 76.3), and five electron (2.3 cm < R 50 < 8.3 cm) beams. Reference dosimetry was performed for all beams in question using an Exradin A19 ion chamber with a calibration traceable to national standards. The absorbed‐dose component of the overall energy dependence was calculated using the EGSnrc egs_chamber user code. Results: A total of 72 measurements were performed with the GPC, resulting in a standard error on the mean absorbed dose of better than 0.3 % for all ten beams. For both the photon and electron beams, no statistically‐significant energy dependence was observed experimentally. Peak‐to‐peak, variations in the relative response of the GPC across all beam qualities of a given radiation type were on the order of 1 %. No effects, either transient or permanent, were attributable to the charge deposited by the electron beams. Conclusions: The GPC's apparent energy‐independence, combined with its well‐established linearity and dose rate independence, make it a potentially useful dosimetry system capable measuring photon and electron doses in absolute terms at the clinical level.