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Title: Fluence perturbation in photon beams under nonequilibrium conditions

Abstract

The perturbation effect in parallel-plate ionization chambers used for buildup measurements has been investigated. The fluence perturbation due to electrons emitted through the side walls are thoroughly investigated by measurements using film and extrapolation chambers and by calculations. The electron fluence varies both with side wall material and chamber geometry. In order to obtain a small perturbation effect, the chamber should have a large guard width compared to the electrode separation and the side walls should have as large an angle as possible with the central axis. The side wall should be of the same material as the rest of the chamber. The perturbation effect is also dependent on the electron contamination of the beam and angular distribution of the electron fluence. It is thus not possible to correct the perturbation effect in one parallel-plate chamber with fixed plate separation with correction factors obtained with extrapolation chambers of other dimensions. In order to make accurate surface dose measurements extrapolation chambers are therefore strongly recommended in favor of fixed parallel-plate chambers.

Authors:
;
Publication Date:
Research Org.:
Karolinska Institute, Stockholm, Sweden
OSTI Identifier:
5580686
Resource Type:
Journal Article
Journal Name:
Med. Phys.; (United States)
Additional Journal Information:
Journal Volume: 2
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 62 RADIOLOGY AND NUCLEAR MEDICINE; IONIZATION CHAMBERS; PERTURBATION THEORY; ELECTRONS; EXTRAPOLATION CHAMBERS; PHOTON BEAMS; RADIATION DOSES; RADIOTHERAPY; BEAMS; DOSEMETERS; DOSES; ELEMENTARY PARTICLES; FERMIONS; LEPTONS; MEASURING INSTRUMENTS; MEDICINE; NUCLEAR MEDICINE; RADIATION DETECTORS; RADIOLOGY; THERAPY; 440102* - Radiation Instrumentation- Radiation Dosemeters; 550603 - Medicine- External Radiation in Therapy- (1980-)

Citation Formats

Nilsson, B, and Montelius, A. Fluence perturbation in photon beams under nonequilibrium conditions. United States: N. p., 1986. Web. doi:10.1118/1.595895.
Nilsson, B, & Montelius, A. Fluence perturbation in photon beams under nonequilibrium conditions. United States. doi:10.1118/1.595895.
Nilsson, B, and Montelius, A. Sat . "Fluence perturbation in photon beams under nonequilibrium conditions". United States. doi:10.1118/1.595895.
@article{osti_5580686,
title = {Fluence perturbation in photon beams under nonequilibrium conditions},
author = {Nilsson, B and Montelius, A},
abstractNote = {The perturbation effect in parallel-plate ionization chambers used for buildup measurements has been investigated. The fluence perturbation due to electrons emitted through the side walls are thoroughly investigated by measurements using film and extrapolation chambers and by calculations. The electron fluence varies both with side wall material and chamber geometry. In order to obtain a small perturbation effect, the chamber should have a large guard width compared to the electrode separation and the side walls should have as large an angle as possible with the central axis. The side wall should be of the same material as the rest of the chamber. The perturbation effect is also dependent on the electron contamination of the beam and angular distribution of the electron fluence. It is thus not possible to correct the perturbation effect in one parallel-plate chamber with fixed plate separation with correction factors obtained with extrapolation chambers of other dimensions. In order to make accurate surface dose measurements extrapolation chambers are therefore strongly recommended in favor of fixed parallel-plate chambers.},
doi = {10.1118/1.595895},
journal = {Med. Phys.; (United States)},
number = ,
volume = 2,
place = {United States},
year = {1986},
month = {3}
}