Verification of lung dose in an anthropomorphic phantom calculated bythe collapsed cone convolution method

Abstract

Verification of calculated lung dose in an anthropomorphic phantom isperformed using two dosimetry media. Dosimetry is complicated by factorssuch as variations in density at slice interfaces and appropriate position on CTscanning slice to accommodate these factors. Dose in lung for a 6 MV and10 MV anterior-posterior field was calculated with a collapsed coneconvolution method using an ADAC Pinnacle, 3D planning system. Up to 5%variations between doses calculated at the centre and near the edge of the2 cm phantom slice positioned at the beam central axis were seen, due tothe composition of each phantom slice. Validation of dose was performedwith LiF thermoluminescent dosimeters (TLDs) and X-Omat V radiographicfilm. Both dosimetry media produced dose results which agreed closely withcalculated results nearest their physical positioning in the phantom. Thecollapsed cone convolution method accurately calculates dose withininhomogeneous lung regions at 6 MV and 10 MV x-ray energy.