Impact of dose calculation algorithms on the dosimetric and radiobiological indices for lung stereotactic body radiotherapy (SBRT) plans calculated using LQ–L model

Purpose: To investigate discrepancies in dose calculation algorithms used for lung stereotactic body radiotherapy (SBRT) plans. Methods and materials: In total, 30 patients lung SBRT treatment plans, initially generated using BrainLab Pencil Beam (BL_PB) algorithm for 10 Gy x 5 Fractions to the planning target volume (PTV) were included in the study. These plans were recalculated using BrainLab Monte Carlo (BL_MC), Eclipse AAA (EC_AAA), Eclipse Acuros XB (EC_AXB) and ADAC Pinnacle CCC (AP_CCC) algorithms. Dose volume histograms of PTV were used to calculate dosimetric and radiobiological quality indices, and equivalent dose to 2 Gy per fraction using linear-quadratic-linear model. The BL_MC algorithm is considered gold standard tool to compare PTV parameters and quality indices to investigate dose calculation discrepancies of abovementioned plans. Results: BL_PB overestimates doses that may be due to inability of the algorithm to properly account for electron scattering and transport in inhomogeneous medium. Compared with BL_MCNO plans, the EC_AAA and EC_AXB yield lower homogeneity indices and overestimate the dose in the penumbra region, whereas AP_CCC plans were comparable for small PTV (approximate to 8 cc) and had significant difference for large PTV. Conclusion: BL_PB algorithm overestimates PTV doses than BL_MC calculated doses. The EC_AAA, EC_AXB and AP_CCC algorithms calculate doses within acceptable limits of radiotherapy dose delivery recommendations.