Measurement of the Percentage Surface Dose Using in Nuclear Medicine and the Factors Acting on it

Abstract

All radiotherapy photon beams are accompanied to some extent by secondary electrons, which originate by interactions with lead collimators, shadow trays and the air through which the beam passes.Surface dose, the shape of the dose build-up curve and the depths of the maximum dose are all influenced by this electron contamination.The aim of this study is to measure the radiation dose in electron build-up region, the skin surface and to qualify the electron contamination and the factors acting on it such as source – surface distance (SSD) and field size (FS). The present study of a Co-60 teletherapy source employs a LiF / Teflon thermoluminescent detectors to measure the surface dose in perspex phantom. Percentage surface dose was measured at source-surface distances of (60 cm) to (90 cm), with an open beam using (5x5 cm2, 10x10 cm2, 15x15 cm2, 20x20 cm2, 25x25 cm2) beam size as defined at the surface.