The comparison of the effects of two different dose calculation algorithms on cardiac dose- volume parameters in Hodgkin lymphoma patients receiving mediastinal radiotherapy

Aim: In this study it was aimed to compare PB (?pencil beam?) and CS (?convolution superposition?) dose calculation algorithms with respect to cardiac dose-volume parameters V5, V25, V30 and MCD (median cardiac dose) in the radiotherapy treatment plans of Hodgkin lymphoma (HL) patients.Material and Method: The treatment plans of all HL patients who have completed mediastinal radiotherapy before 01.01.2011 in Dokuz Eylul University Department of Radiation Oncology were reviewed retrospectively from the archive of computerized treatment planning system (TPS). Ten of them were found eligible according to inclusion criteria. Dose calculation was performed using PB and CS algorithms in Nucletron Oncentra MasterPlan Version 3.3 SP3 program for both 6 and 18 MV-X photon energies. Two algorithms were compared with respect to cardiac dose-volume parameters (V5, V25, V30 and MCD). The analysis of the data was performed using Wilcoxon signed rank test in SPSS 15.0 statistical analysis program.Results: For 6 MV-X photon energy, mean relative difference was found statistically significantly higher in the PB algorithm being % 1.75 (p=0.012) and % 6.76 (p=0.028) for V25 and V30, respectively. For 18 MV-X photon energy, mean relative difference was found statistically significantly higher in the PB algorithm being % 3.25 (p=0.021) and % 13.95 (p=0.007) for V25 and V30, respectively. In terms of MCD, mean relative difference was found higher without statistical significance in the PB algorithm being % 2.32 (p=0.169) and % 0.01 (p=0.241) for 6 MV-X and 18 MV-X photon energies, respectively. As for V5, mean relative difference was found higher without statistical significance in the CS algorithm being % 0.01 (p=0.173) and % 0.01 (p=0.213) for 6 MV-X and 18 MV-X photon energies, respectively.Conclusion: In our study, higher cardiac V25 and V30 values were obtained using PB algorithm compared to CS algorithm in HL patients? radiotherapy plans of mediastinal region where tissue inhomogeneity is apparent. It has been known that CS algorithm is close to the ?gold standard? ?Monte Carlo? algorithm in terms of sensitivity in radiotherapy planning. However ?Monte Carlo? algorithm is seldom used in daily practice in commercial TPSs for photon dose calculations. As a result, it is appropriate to prefer CS algorithm instead of PB algorithm due to the incresed accuracy in dose calculation.Key words: Convolution / superposition, pencil beam, Hodgkin lymphoma, cardiac dose-volume parameters