Radiation dosimetry of a conformal heat-brachytherapy applicator.

Abstract

The purpose of this paper is to report the radiation dosimetric characteristics of a new combination applicator for delivering heat and radiation simultaneously to large area superficial disease 98%, homogeneity index > 0.95 and the percentage of normal tissue irradiated is < 20%. The dose gradient at the skin surface varies from 3 to 5 cGy/mm depending on bolus thickness and lesion depth. Attenuation of the photon beam by the printed circuit antenna array is of the order 0.25% and secondary electron emissions are absorbed completely within 5 mm of water bolus and plastic layers. Both phenomena can then be neglected in dose calculations allowing commercial software to be used for treatment planning. This novel applicator should prove useful for the treatment of diffuse chestwall disease located over contoured anatomy that may be difficult to treat with single field external beam therapy. By delivering heat and radiation simultaneously, increased synergism is expected with a TER in the range of 2–5. Lowering radiation dose by an equivalent factor may produce lower radiation toxicity with similar efficacy, while preserving the option of subsequent retreatment(s) with thermoradiotherapy in order to further extend patient survival.