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Calorimetric and ionimetric dosimetry intercomparisons I: U.S. neutron radiotherapy centers
Author(s) -
McDonald Joseph C.,
Ma IChang,
Liang John,
Eenmaa Juri,
Awschalom Miguel,
Smathers James B.,
Graves Robert,
August Leon S.,
Shapiro Philip
Publication year - 1981
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 - 10.1118/1.594905
Subject(s) - ionization chamber , dosimetry , absorbed dose , imaging phantom , ionization , calorimeter (particle physics) , neutron , materials science , nuclear medicine , percentage depth dose curve , nuclear physics , physics , ion , optics , medicine , quantum mechanics , detector
In the U.S. neutron radiotherapy trial centers, absorbed dose is routinely measured using commercially available A‐150 tissue equivalent (TE) plastic ionization chambers. The collecting volumes of these chambers are filled with either methane‐based tissue equivalent gas or air. Absorbed dose in A‐150 plastic, determined with these ionization chambers, was compared to that measured by an A‐150 plastic calorimeter in an A‐150 plastic phantom. These comparisons have yielded the following information: (1) Agreement of the total absorbed dose measured using the ionization chambers was within 2.5% of the calorimeter at all the centers visited to date. (2) For all the neutron fields measured, the product of the stopping power ratio( s w,g ) N′between the A‐150 plastic chamber wall and TE gas, and the average energy expended in the gas per ion pair formed, W̄ N /e , was computed assuming Bragg–Gray theory and found to be 31.0±0.7 J/C. (3) The displacement correction factor employed to normalize measurements at a depth in a phantom using the type IC‐17 ionization chamber was verified to be approximately 0.97±0.01.