Incident contamination lepton doses measured using radiochromic film in radiotherapy

Measurement of lepton contamination is achieved across a radiotherapy photon beam and peripheral doses using radiochromic film. An extrapolation technique is used where several layers are suspended in air to measure incident contamination without the-effects of phantom scatter. Surface dose was measured as 11% of D-max for 6 MV beams at central axis and 9% for 10 MV photons for a 10 x 10 cm field size. Peripheral lepton doses were found to decrease compared to central, however, were still measurable. Peripheral lepton dose was found to increase with field size and was 12% and 15%, 2 cm outside the geometric held edge of a 30 x 30 cm field size at 6 and 10 MV respectively. Radiochromic film is a suitable dosimeter for measurement of lepton contamination absorbed dose to surface layers of skin. (C) 1998 Elsevier Science Ltd. All rights reserved.