out-of-field photon dosimetry study between 3-d conformal and intensity modulated radiation therapy in the management of prostate cancer

Background: the present work aims to study the out-of-field photon calculation accuracy of a commercial treatment planning system (tps), oncentra, for three-dimensional conformal radiotherapy (3d-crt) and intensity modulated radiation therapy (imrt) treatment techniques from elekta synergy medical linear accelerator. materials and methods: accuracy of individual out-of-field dose components was studied by defining a square field of 10 x 10 cm^2 in our tps and it is verified by using ionization chamber and tlds (thermoluminescent dosimeter) at 5 cm depth. using 3d-crt and imrt techniques ca (carcinoma) prostate treatment plans were created using 6 mv photon beam and calculated in oncentra masterplan v4.3 planning systems for out-of-field and further compared the same with tld measurements. results: individual components study shows the poor out-of-field calculations in tps, with respect to that obtained from tld measurements. underestimation increases from 10 % to 80 % as a contribution from various components while moving far from field edge. complex imrt plans resemble this underestimation of tps calculations in greater extend. conclusion: this study quantifies the poor accuracy for outoffield dose calculations in tps. no significant difference in 3d-crt and imrt plans is found at near field edge. while, as distance from field edge increases, underestimation of tps in imrt plan is higher. 10 % - 60 % difference in out-of-field dose was found as distance move from 2 cm to 7.5 cm far from field edge between tps estimations and the measurements.