MEASUREMENT OF OFF-AXIS AND PERIPHERAL SKIN DOSE USING RADIOCHROMIC FILM

A radiotheraphy skin dose profile can be obtained with radiochromic fi lm. The central axis skin dose relative to D-max for a 10 x 10 cm(2) f ield 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. A t 10 MV the skin dose 2 cm outside the geometric held edge was measure d as 6%, 10% and 17% for 10 x 10 cm(2), 20 x 20 cm(2) and 30 x 30 cm(2 ) field sizes respectively. Off-axis skin dose decreased as distance i ncreased from central axis for fields with Perspex block trays. For a 20 x 20 cm(2) field, an approximately 5-8% drop in percentage skin dos e was observed from central axis to the beam edge.