Measurement of off-axis and peripheral skin dose using radiochromic film

A radiotherapy skin dose profile can be obtained with radiochromic film. The central axis skin dose relative to Dmax for a 10x10cm2 field size was found to be 22%, 17% and 15.5% for 6 MV, 10 MV and 18 MV photon beams. Peripheral dose increased with increasing field size. At 10 MV the skin dose 2 cm outside the geometric field edge was measured as 6%, 10% and 17% for 10x10cm2, 20x20cm2 and 30x30cm2 field sizes respectively. Off-axis skin dose decreased as distance increased from central axis for fields with Perspex block trays. For a 20x20cm2 field, an approximately 5-8% drop in percentage skin dose was observed from central axis to the beam edge. (author)