Experimental determination of the effective point of measurement for cylindrical ionization chambers in 60Co gamma radiation.
Phys Med Biol
; 57(11): 3463-75, 2012 Jun 07.
Article
em En
| MEDLINE
| ID: mdl-22581186
ABSTRACT
The displacement effect of cylindrical ionization chambers is taken into account either by an effective point of measurement (EPOM) or, alternatively, by using a displacement perturbation factor. The dependence of these effects in water was examined as a function of the cavity radius using cylindrical chambers with different radii and a plane-parallel chamber, whose EPOM is well known. Depth-dose curves were measured in terms of absolute absorbed dose in water and evaluated according to the international protocol IAEA TRS-398 as well as the German protocol DIN 6800-2. As expected, evaluation of absorbed dose under reference conditions following both protocols agreed well within a standard uncertainty of 0.1%. However, values of absorbed dose at depths beyond the dose maximum showed deviations up to 0.3% and 0.5% for IAEA TRS-398 and DIN 6800-2, respectively. Values in the build-up and maximum region did not agree very well. Deviations of more than 1% were found for both protocols. It was concluded that the corrections recommended in both protocols are not fully appropriate. A procedure is suggested to measure the absorbed depth-dose distribution including the build-up region with an improved accuracy by means of cylindrical chambers.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Radiometria
/
Raios gama
Idioma:
En
Revista:
Phys Med Biol
Ano de publicação:
2012
Tipo de documento:
Article