A COMPARATIVE STUDY OF PENCIL BEAM AND COLLAPSED CONE CONVOLUTION DOSE CALCULATION ALGORITHMS IN PELVIC AND THORACIC TREATMENT PLANS

Abstract

Different algorithms used to calculate doses in radiotherapy planning adopt different techniques in simulating doses received by the target (tumor) volume. Such differences can come about in terms of dose distribution in the target volume and doses received by surrounding organs. Due to such differences, it is necessary to take into consideration the best algorithm suitable for a range of mediums i.e homogeneous and heterogeneous mediums. The differences in the way different algorithms simulate doses in different media may bring about dosimetric variations which can relatively affect treatment outcomes in 3D-conformal radiotherapy. The primary focus of this research was to compare dose variations for two dose calculations algorithms namely, Pencil Beam (PB) algorithm and the Collapsed Cone Convolution (CCC) in highly and less heterogeneous mediums. The study was an analytical retrospective study consisting of 8 pelvic and 7 thoracic treatment plans approved and scheduled to undergo 3D- CRT. The treatment plans were generated using PB and the same treatment plans recalculated using the CCC calculation algorithm. Dosimetric variations between the two dose calculation algorithms were observed and evaluated based on variations in plan parameters such as dose received by the tumor volume and the dose received by critical organs (OAR’s). Minimum and Maximum mean dose values were obtained from PTV and OAR’s from the two dose calculation algorithms. Differences in dose values between the two algorithms were analyzed using standard errors (SE) to determine if in fact the differences were significant. At a CI of 95% (P=0.05), it was found out that the two calculation algorithms demonstrated insignificant dose differences to a treatment plan. PB algorithm demonstrated high dose received to the tumor volume compared to the CCC algorithm. A visual analysis of the results using box plots demonstrated that the two algorithms showed no major differences in doses received by the PTV and OAR’s. It made no significant difference to a treatment plan if the planner (Medical Physicist) would adopt either of the algorithms in calculating doses for cervix or esophagus treatment plans using ONCENTRA Treatment Planning System.