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SU‐EE‐A2‐03: Evaluating AAPM TG‐43 In‐Water HDR 192Ir Brachytherapy Reference Dosimetry: A Comparison Study
Author(s) -
Sarfehnia A,
Kawrakow I,
Seuntjens J
Publication year - 2010
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 - 10.1118/1.3468014
Subject(s) - dosimetry , ionization chamber , calibration , monte carlo method , materials science , brachytherapy , primary standard , dosimeter , nuclear medicine , physics , ionization , medicine , radiation therapy , mathematics , ion , statistics , quantum mechanics
Purpose : To investigate the accuracy of AAPM TG‐43 in HDR 192 Ir brachytherapy in water reference dosimetry by comparing the protocol against ionometric and Gafchromic film calibration procedures introduced as well as a water calorimetry‐based primary standard. Methods and Materials : Dose to water D water was measured directly in water using an Exradin A1SL farmer‐type chamber and EBT‐1 Gafchromic films. The chamber had a NIST‐traceable 60 Co calibration factor while the films were calibrated under 6 MV photons. Accurate Monte Carlo modeling and simulation of the chamber (egs++) and EBT Gafchromic films (DOSRZnrc) were performed to convert calibration factors of the two detectors from their respective conditions into 192 Ir brachytherapy. The D water results were compared to measurements made using a Standard Imaging well‐type chamber following AAPM TG‐43 protocol and water calorimetry primary standard measurements. Results : By calculating the ratio of dose‐to‐water to dose‐to‐gas for the A1SL chamber under reference 60 Co conditions and 192 Ir setup conditions, the ionization measurements in 192 Ir were converted to dose to water. The Monte Carlo calculations in film dosimetry revealed that if the intrinsic energy dependence of the film is negligible, a sensitometric curve obtained with 6 MV can be used in 192 Ir measurements, with the energy dependence correction being 0.9971 (1σ=0.1%). The overall one‐sigma uncertainty on ionization chamber, Gafchromic film, and water calorimetry dose rate measurement amounts to 1.44%, 1.78%, and 1.96%, respectively. The indirect D water measurements from TG‐43 agreed to within 1.4% with ionometric measurements, 0.3% with Gafchromic measurements, and 0.6% with Calorimetric absolute dose measurements. Conclusions : Accurate ionometric and Gafchromic film based calibration protocols are introduced. For 192 Ir brachytherapy, the 1‐sigma uncertainty of TG‐43 reference dosimetry was found to be better than 1.4%.