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Sci—Sat AM: Brachy — 03: Feasibility study of the determination of absorbed dose to water using a fricke based system
Author(s) -
Gamal I El,
Cojocaru C,
Ross C,
Marchington D,
McEwen M
Publication year - 2012
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 - 10.1118/1.4740210
Subject(s) - dosimeter , dosimetry , absorbed dose , imaging phantom , kerma , brachytherapy , dose profile , materials science , thermoluminescent dosimetry , absorption (acoustics) , radiation , metrology , nuclear medicine , radiochemistry , nuclear engineering , thermoluminescent dosimeter , optics , physics , chemistry , radiation therapy , medicine , engineering
By measuring the dose to water directly a metrology standard, independent of air kerma, can be developed to make the basis of HDR brachytherapy dosimetry consistent with current dosimetry methods for external radiation beams. The Fricke dosimeter system, a liquid chemical dosimeter, provides a means of measuring the absorbed dose rate to water directly by measuring the radiation‐induced change in absorption of the Fricke solution. In an attempt to measure the absorbed dose to water directly for a 192 Ir HDR brachytherapy source a ring shaped Fricke holder was constructed from PMMA, essentially following the work of Austerlitz et al. (Med. Phys. 2008). Benchmark measurements conducted in a 60 Co beam yielded a standard uncertainty in the absorption reading of 0.16 %, comparable with previous results in the literature. Measurements of the standard uncertainty of the control (unirradiated) solution using the holder yielded 0.2 %, indicating good process control and minimal contamination from the holder itself. However, it was found that the holder sealing method (to allow measurements in a water phantom) significantly contaminated the Fricke solution, resulting in an excessive background reading. Irradiations were therefore conducted in air to determine the feasibility of the procedure. Irradiations with a 17 GBq source gave a standard uncertainty of approximately 0.5 %, indicating that the target uncertainty of 1.5% for the measurement of absorbed dose to water using a Fricke‐based primary standard is achievable. This would be comparable with calorimeter‐based systems currently being developed.