Comparison of the effects of two different dose algorithms in cardiac dose parameters for hodgkin lymphoma patients receiving mediastinal radiotheraphy

Objective:   This study aimed to compare pencil beam (PB) and convolution superposition (CS) dose calculation algorithms with respect to cardiac dose-volume parameters V5, V25, V30 and MHD (median heart dose) in Hodgkin lymphoma (HL) patients who received mediastinal radiotherapy (RT). Material and Methods:   Ten eligible cases with the diagnosis of HL who completed mediastinal RT at Dokuz Eylul University Department of Radiation Oncology before 01.01.2011 formed the study population.  Related 3D conformal RT treatment plans were obtained from the Treatment Planning System (TPS) (Nucletron Oncentra Master Plan Version 3.3 SP3 program). Calculations were done for 6 and 18 MV-X beam energy, respectively by using PB and CS algorithms in the TPS. Two algorithms were compared in terms of cardiac dose-volume parameters (V5, V25, V30 and MHD). Results:  Mean relative difference for both V25 and V30 was found to be significantly higher in favor of PB algorithm in both 6 MV-X and 18 MV-X photon energy.  Mean relative differences were 1.75% (p=0.012) and 6.76% (p=0.028) for the V25 and V30 parameters, respectively in 6 MV-X and 3.25% (p=0.021) and 13.95% (p=0.007) for the V25 and V30 parameters, respectively in 18 MV-X energy. Conclusion:   When PB algorithm is used in RT treatment planning of HL patients for the mediastinal region where tissue inhomogeneity is relatively high, heart V25 and V30 parameters were shown to result in higher values compared to CS algorithm in our study.  It is more appropriate to prefer CS algorithm instead of  PB algorithm since it increases accuracy of calculations in the treatment planning of mediastinal RT.