Verification of lung dose in an anthropomorphic phantom calculated by the collapsed cone convolution method.

Verification of calculated lung dose in an anthropomorphic phantom is performed using two dosimetry media. Dosimetry is complicated by factors such as variations in density at slice interfaces and appropriate position on CT scanning slice to accommodate these factors. Dose in lung for a 6 MV and 10 MV anterior-posterior field was calculated with a collapsed cone convolution method using an ADAC Pinnacle, 3D planning system. Up to 5% variations between doses calculated at the centre and near the edge of the 2 cm phantom slice positioned at the beam central axis were seen, due to the composition of each phantom slice. Validation of dose was performed with LiF thermoluminescent dosimeters (TLDs) and X-Omat V radiographic film. Both dosimetry media produced dose results which agreed closely with calculated results nearest their physical positioning in the phantom. The collapsed cone convolution method accurately calculates dose within inhomogeneous lung regions at 6 MV and 10 MV x-ray energy.