Monte Carlo modeling of the response of NRC's Sr90∕Y90 primary beta standard.
Med Phys
; 32(10): 3084-3094, 2005 Oct.
Article
em En
| MEDLINE
| ID: mdl-28523831
ABSTRACT
The BEAMnrc/EGSnrc Monte Carlo code system is employed to develop a model of the National Research Council of Canada primary standard of absorbed dose to tissue in a beta radiation field, comprising an extrapolation chamber and Sr90∕Y90 beta source. We benchmark the model against the measured response of the chamber in terms of absorbed dose to air, for three different experimental setups when irradiated by the Sr90∕Y90 source. For the first setup, the chamber cavity depth is fixed at 0.2cm and the source-to-chamber distance varied between 11 and 60cm. In the other two cases, the source-to-chamber distance is fixed at 30cm. In one case the response for different chamber depths is studied, while in the other case the chamber depth is fixed at 0.2cm as different thicknesses of Mylar™ are added to the front surface of the extrapolation chamber. The agreement as a function of distance between the calculated and measured responses is within 0.37% for a variation in response of a factor of 29. In the case of dose versus chamber depth, the agreement is within 0.4% for the ISO-recommended nominal depths of 0.025-0.25cm. Agreement between calculated and measured responses is very good (between 0.02% and 0.2%) for added Mylar foils of thicknesses up to 10.8mgcm-2. For larger Mylar thicknesses, deviations of 0.6%-1.2% are observed, which are possibly due to the systematic uncertainties associated with the restricted collisional stopping powers of air or Mylar used in the calculations. We conclude that our simulation model represents the extrapolation chamber and Sr90∕Y90 source with adequate accuracy to calculate correction factors for accurate realization of dose rate to tissue at a depth of 7mgcm-2 in an ICRU tissue phantom, despite the fact that the uncertainties in the physical characteristics of the source leave some uncertainty in certain calculated quantities.
Cavitation; Collisional energy loss; Dosimetry; Effects of ionizing radiation on biological systems; Electric measurements; Electrodes; Error analysis; Graphite; Monte Carlo methods; Radioactive sources; Silver; Simulation; beta-ray effects; biological effects of ionising particles; biological tissues; biomedical equipment; dosimetry; phantoms; radiation therapy; strontium; yttrium
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1
Coleções:
01-internacional
Base de dados:
MEDLINE
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
Med Phys
Ano de publicação:
2005
Tipo de documento:
Article
País de afiliação:
Canadá