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Title: Monte Carlo aided design of an improved well-type ionization chamber for low energy brachytherapy sources

Abstract

The determination of the air kerma strength of a brachytherapy seed is necessary for effective treatment planning. Well-type ionization chambers are used on site at therapy clinics to determine the air kerma strength of seeds. In this work, an improved well-type ionization chamber for low energy, low dose rate brachytherapy sources is designed using Monte Carlo transport calculations to aid in the design process. The design improvements are the elimination of the air density induced over-response effect seen in other air-communicating chambers for low energy photon sources, and a larger signal strength (response or current) for {sup 103}Pd and {sup 125}I based seeds. A prototype well chamber based on the Monte Carlo aided design but using graphite coated acrylic walls rather than the design basis air equivalent plastic (C-552) walls was constructed and experimentally evaluated. The prototype chamber produced an 85% stronger signal when measuring a commonly used {sup 103}Pd seed and a 26% stronger signal when measuring a commonly used {sup 125}I seed when compared to another commonly used well chamber. The normalized P{sub TP} corrected chamber response is, at most, 1.3% and 2.4% over unity for air densities/pressures corresponding to an elevation of 3048 m (10 000 feet)more » above sea level for the commonly used {sup 103}Pd and {sup 125}I based seeds respectively. Comparing calculated and measured chamber responses for common {sup 103}Pd and {sup 125}I based brachytherapy seeds show agreement within 0.6% and 0.2%, respectively. We conclude that Monte Carlo transport calculations accurately model the response of this new well chamber and in general can be used to predict the response of well chambers. The prototype chamber built in this work responds as predicted by the Monte Carlo calculations.« less

Authors:
; ;  [1]
  1. Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
Publication Date:
OSTI Identifier:
20951148
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 4; Other Information: DOI: 10.1118/1.2712416; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BRACHYTHERAPY; DESIGN; DOSIMETRY; GRAPHITE; IODINE 125; IONIZATION CHAMBERS; KERMA; MONTE CARLO METHOD; PALLADIUM 103

Citation Formats

Bohm, Tim D., Micka, John A., and De Werd, Larry A. Monte Carlo aided design of an improved well-type ionization chamber for low energy brachytherapy sources. United States: N. p., 2007. Web. doi:10.1118/1.2712416.
Bohm, Tim D., Micka, John A., & De Werd, Larry A. Monte Carlo aided design of an improved well-type ionization chamber for low energy brachytherapy sources. United States. doi:10.1118/1.2712416.
Bohm, Tim D., Micka, John A., and De Werd, Larry A. Sun . "Monte Carlo aided design of an improved well-type ionization chamber for low energy brachytherapy sources". United States. doi:10.1118/1.2712416.
@article{osti_20951148,
title = {Monte Carlo aided design of an improved well-type ionization chamber for low energy brachytherapy sources},
author = {Bohm, Tim D. and Micka, John A. and De Werd, Larry A.},
abstractNote = {The determination of the air kerma strength of a brachytherapy seed is necessary for effective treatment planning. Well-type ionization chambers are used on site at therapy clinics to determine the air kerma strength of seeds. In this work, an improved well-type ionization chamber for low energy, low dose rate brachytherapy sources is designed using Monte Carlo transport calculations to aid in the design process. The design improvements are the elimination of the air density induced over-response effect seen in other air-communicating chambers for low energy photon sources, and a larger signal strength (response or current) for {sup 103}Pd and {sup 125}I based seeds. A prototype well chamber based on the Monte Carlo aided design but using graphite coated acrylic walls rather than the design basis air equivalent plastic (C-552) walls was constructed and experimentally evaluated. The prototype chamber produced an 85% stronger signal when measuring a commonly used {sup 103}Pd seed and a 26% stronger signal when measuring a commonly used {sup 125}I seed when compared to another commonly used well chamber. The normalized P{sub TP} corrected chamber response is, at most, 1.3% and 2.4% over unity for air densities/pressures corresponding to an elevation of 3048 m (10 000 feet) above sea level for the commonly used {sup 103}Pd and {sup 125}I based seeds respectively. Comparing calculated and measured chamber responses for common {sup 103}Pd and {sup 125}I based brachytherapy seeds show agreement within 0.6% and 0.2%, respectively. We conclude that Monte Carlo transport calculations accurately model the response of this new well chamber and in general can be used to predict the response of well chambers. The prototype chamber built in this work responds as predicted by the Monte Carlo calculations.},
doi = {10.1118/1.2712416},
journal = {Medical Physics},
number = 4,
volume = 34,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}