Measurement of 6-MV X-ray surface dose when topical agents are applied prior to external beam irradiation.

Abstract

Radiation therapy patients are typically warned not to apply lotions, deodorants, or powders to the skin within the treatment area because of the possible increase in surface dose due primarily to a bolus effect. This study investigates the effect of 15 products, with and without high atomic number components, on surface dose. A Markus-type parallel plate ionization chamber in a polystyrene phantom was used to measure surface doses for normal applications of the products for a small (5 x 5-cm2) and a large (25 x 25-cm2) field size. The greatest surface dose increase for any product was 5.4% (21.8-27.2%) of the d(max) dose for the small field and 1.0% (43.6-44.6%) for the large field. Products with high-atomic-number components did not increase the surface dose relative to radiation therapy specialty products. No large increase in surface dose was detected with a normal application of the products. However, the possibility exists that an increase in skin reaction may occur owing to chemical irritants in the applied product.