Abstract
Plaques containing beta-emitting isotopes have several medical applications. In particular, due to the short range of beta particles and the rapid fall off of dose rates they are suitable to be used in small and superficial skin cancer therapy, killing the tumor cells and preserving the underlying healthy structures. The analytical/numerical beta-point dose function formalism is used to a simple estimate of the relative dose rates around square and rectangular beta applicator containing the Yttrium-90 isotope. Maximum differences in relative dose rates along central axis of 13% at 6.6 mm depth and 20% at 5 mm depth were found, respectively, for the square and rectangular plaques as compared with the literature measurements data. Results have also indicated that for both plaques dose rates fall off to 50% of the reference value at about 2 mm depth; drop to just 10% at 4.5 mm depth, and become zero from 8 mm on. This fact confirms that these sources are suitable to be used in superficial skin cancer therapy. The method presented here may be used to estimate the relative dose rates around square and rectangular Y-90 beta applicators in a simple and fast way.
Highlights
Beta radiation may be used in various medical applications [1]
In this work we present a simple analytical/numerical method to estimate the relative dose rates along central and lateral axes of square and rectangular plaques containing the beta-emitting Yttrium90 isotope intended to be used in superficial skin cancer treatment and a comparison is made with available experimental data obtained using radiograph film and Fricke xylenol gel dosimeter (FXG) [5]
In the above equations the density of the medium is 1 g/cm3; the parameters ν, c and f are, respectively, 5.05 cm2/g, 0.95 and 4.48; the mean kinetic energy of the beta particles is 0.933 MeV. These parameters depend on the type of beta emitting radioisotope and were obtained by fitting the beta point-dose function (Eq 1) to beta-ray point-source dose distributions data in water obtained from Monte Carlo (MC) calculations as described in ref
Summary
Beta radiation may be used in various medical applications [1]. Planar as well concave sources containing the beta emitting nuclides 90Sr/90Y can be used for the post-operative treatment of pterygia, and for the treatment of keloid and glioblastoma; small seeds of 90Sr/90Y can be used in intravascular brachytherapy to prevent the re-closing of arteries after balloon angioplasty. Concave applicators containing 106Ru/106Rh can be used in ophthalmic brachytherapy for the treatment of choroid melanomas and retinoblastomas; beta emitting wire sources of 32P can be used in intravascular brachytherapy to prevent restenosis; recently, a feasibility study of the use of a circular patch containing microspheres of Y-90 to treat small skin lesions and estimates of relative dose rates to this applicator were published [2,3]. Beta particles have a short range within the tissue and a high-dose gradient. These properties play an important role in the treatment of small and superficial skin lesions, provided that the beta sources deliver a high dose in a few millimeters preserving the neighboring healthy tissues and personnel, making the radiation protection a simple task. Skin cancer is the most common kind of malignancy all over the world and the use of beta radiation to treat small skin lesions is interesting in that cases where surgery is not possible or recommended [4]
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