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An absorbed dose to water standard for HDR I 192 r brachytherapy sources based on water calorimetry: Numerical and experimental proof‐of‐principle
Author(s) -
Sarfehnia Arman,
Stewart Kristin,
Seuntjens Jan
Publication year - 2007
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 - 10.1118/1.2815941
Subject(s) - kerma , calorimeter (particle physics) , absorbed dose , multiphysics , calorimetry , brachytherapy , dosimetry , materials science , percentage depth dose curve , thermoluminescent dosimeter , thermoluminescent dosimetry , nuclear engineering , nuclear medicine , detector , optics , computational physics , ionization chamber , dosimeter , physics , radiation therapy , medicine , finite element method , ion , engineering , quantum mechanics , thermodynamics , ionization
Water calorimetry is an established technique for absorbed dose to water measurements in external beams. In this paper, the feasibility of direct absorbed dose measurements for high dose rate (HDR) iridium‐192( I192 r )sources using water calorimetry is established. Feasibility is determined primarily by a balance between the need to obtain sufficient signal to perform a reproducible measurement, the effect of heat loss on the measured signal, and the positioning uncertainty affecting the source‐detector distance. The heat conduction pattern generated in water by the Nucletron microSelectron‐HDRI192 r brachytherapy source was simulated using COMSOL MULTIPHYSICS TM software. Source heating due to radiation self‐absorption was calculated using EGSnrcMP. A heat‐loss correctionk cwas calculated as the ratio of the temperature rise under ideal conditions to temperature rise under realistic conditions. The calorimeter setup used a parallel‐plate calorimeter vessel of 79 mm diameter and 1.12 mm thick front and rear glass windows located 24 mm apart. Absorbed dose was measured with two sources with nominal air kerma strengths of 38 000 and 21 000 U, at source‐detector separations ranging from 24.7 to 27.6 mm and irradiation times of 36.0 to 80.0 s. The preliminary measured dose rate per unit air kerma strength of( 0.502 ± 0.007 ) μ Gy / ( s U )compares well with the TG‐43 derived 0.505 μ Gy / ( s U ) . This work shows that combined dose uncertainties of significantly less than 5 % can be achieved with only modest modifications of current water calorimetry techniques and instruments. This work forms the basis of a potential future absolute dose to water standard for HDRI192 r brachytherapy.