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Direct measurement of absorbed dose to water in HDR I 192 r brachytherapy: Water calorimetry, ionization chamber, Gafchromic film, and TG‐43
Author(s) -
Sarfehnia Arman,
Kawrakow Iwan,
Seuntjens Jan
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 - 10.1118/1.3352685
Subject(s) - ionization chamber , absorbed dose , brachytherapy , dosimetry , materials science , nuclear medicine , dosimeter , ionization , medical physics , optics , environmental science , radiochemistry , physics , medicine , radiology , radiation therapy , chemistry , ion , quantum mechanics
Purpose: Gafchromic film and ionometric calibration procedures for HDR I192 r brachytherapy sources in terms of dose rate to water are presented and the experimental results are compared to the TG‐43 protocol as well as with the absolute dose measurement results from a water calorimetry‐based primary standard. Methods: EBT‐1 Gafchromic films, an A1SL Exradin miniature Shonka thimble type chamber, and an SI HDR 1000 Plus well‐type chamber (Standard Imaging, Inc., Middleton, WI) with an ADCL traceableS kcalibration coefficient (following the AAPM TG‐43 protocol) were used. The Farmer chamber and Gafchromic film measurements were performed directly in water. All results were compared to direct and absolute absorbed dose to water measurements from a 4 ° C stagnant water calorimeter. Results: Based on water calorimetry, the authors measured the dose rate to water to be 361 ± 7 μ Gy / ( h U )at a 55 mm source‐to‐detector separation. The dose rate normalized to air‐kerma strength for all the techniques agree with the water calorimetry results to within 0.83%. The overall 1‐sigma uncertainty on water calorimetry, ionization chamber, Gafchromic film, and TG‐43 dose rate measurement amounts to 1.90%, 1.44%, 1.78%, and 2.50%, respectively. Conclusions: This work allows us to build a more realistic uncertainty estimate for absorbed dose to water determination using the TG‐43 protocol. Furthermore, it provides the framework necessary for a shift from indirect HDR I192 r brachytherapy dosimetry to a more accurate, direct, and absolute measurement of absorbed dose to water.