An investigation of dosedistribution calculation accuracy in match photon-electron radiation therapy for malignant pleural mesothelioma by Monte Carlo simulation

Background and To treatment of malignant pleural mesoteloma, in the absence of IMRT, photon beam and lung shield was used for treatment and then electron beam was used to treat shielding area. Photon dose distribution is influenced by inhomogeneity media, lateral electronic disequilibrium at interfaces, the block in middle of the field and narrow field. This study compares Monte Carlo (MC) with conventional treatment planning system (TPS) calculations for photon beam radiation therapy of malignant pleural mesoteloma (MPM) using lung island shield. Methods and Materials: Photon dose distribution using lung island shield calculated by three 1) MC 2) TPS 3) Film dosimetry in anthropomorphic phantom. MC commissioned by film dosimetry and TPS dose calculation accuracy investigated by MC simulation. Accuracy of treatment head simulation and tomographic phantom dose distribution was verified by matching percent depth dose (PDD) and dose profile in water phantom and film dosimetry in anthropomorphic phantom in two fields of with and without lung shield respectively. Compare to MC, TPS: 1) overestimates pleura dose coverage (90% prescribed dose) 3-12 mm and the dose in under the lung shield region 10-50% and 2) underestimated the dose profile width 1-16 mm in low dose region (< 50% prescribed dose) and the dose in out of field region 6-100%.