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Calculation of beta-ray dose distributions from ophthalmic applicators and comparison with measurements in a model eye

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Cross, WG Hokkanen, J Jarvinen, H Mourtada, F Sipila, P Vynckier, Stefaan [UCL]

Dose distributions throughout the eye, from three types of beta-ray ophthalmic applicators, were calculated using the EGS4, ACCEPT 3.0, and other Monte Carlo codes. The applicators were those for which doses were measured in a recent international intercomparison [Med. Phys. 28, 1373 (2001)], planar applicators of Ru-106-Rh-106 and Sr-90-Y-90 and a concave Ru-106-Rh-106 applicator. The main purpose was to compare the results of the various codes with average experimental values. For the planar applicators, calculated and measured doses on the source axis agreed within the experimental errors (<10%) to a depth of 7 mm for Ru-106-Rh-106 and 5 mm for Sr-90-Y-90. At greater distances the measured values are larger than those calculated. For the concave Ru-106-Rh-106 applicator, there was poor agreement among available calculations and only those calculated by ACCEPT 3.0 agreed with measured values. In the past, attempts have been made to derive such dose distributions simply, by integrating the appropriate point-source dose function over the source, Here, we investigated the accuracy of this procedure for encapsulated sources, by comparing such results with values calculated by Monte Carlo, An attempt was made to allow for the effects of the silver source window but no corrections were made for scattering from the source backing. In these circumstances, at 6 mm depth, the difference in the results of the two calculations was 14%-18% for a planar Ru-106-Rh-106 applicator and up to 30% for the concave applicator. It becomes worse at greater depths. These errors are probably caused mainly by differences between the spectrum of beta particles transmitted by the silver window and those transmitted by a thickness of water having the same attenuation properties. (C) 2001 American Association of Physicists in Medicine.

Document type Article de périodique (Journal article) – Article de recherche
Access type Accès restreint
Publication date 2001
Language Anglais
Journal information "Medical Physics" - Vol. 28, no. 7, p. 1385-1396 (2001)
Peer reviewed yes
Publisher Amer Inst Physics (Melville)
issn 0094-2405
Publication status Publié
Affiliations UCL - MD/MINT - Département de médecine interne
UCL - (SLuc) Service de radiothérapie oncologique
Keywords beta dosimetry ; beta particles ; dosimetry ; eye doses ; ophthalmic applicators
Links
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Bibliographic reference Cross, WG ; Hokkanen, J ; Jarvinen, H ; Mourtada, F ; Sipila, P ; et. al. Calculation of beta-ray dose distributions from ophthalmic applicators and comparison with measurements in a model eye. In: Medical Physics, Vol. 28, no. 7, p. 1385-1396 (2001)
Permanent URL http://hdl.handle.net/2078.1/42616