Reducing the skin dose from secondary electrons in kilovoltage radiotherapy: a pliable coating for custom lead cut-outs

Abstract

AbstractLead cut-outs used to shape fields in kilovoltage radiotherapy can increase the surface dose on the patient. The physical processes leading to increased surface doses are summarised, and an empirical investigation of the efficacy of various coatings in reducing the skin dose generated by secondary electrons released in the lead during irradiation is presented, based on measurements using a thin window parallel plate ionisation chamber in 135 kVp and 225 kVp beams from a Pantak DXT-300 kilovoltage therapy unit. A new flexible coating for lead cut-outs has been formulated and tested. This coating, which is a combination of Copydex and emulsion paint, has been shown to be effective in reducing the skin dose generated by secondary electrons released in the lead during irradiation. The coating is easy to clean, and its inherent elasticity prevents cracking of the coating in clinical use. Its only disadvantage is that rough handling, or contact with sharp objects, can peel the coating at the point of contact.