Pii: S1350-4487(98)00072-9

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