The dose calculation algorithm significantly impacts the accuracy of dose calculations in heterogeneous media. This study aimed to evaluate the dosimetric differences between analytical anisotropic algorithm (AAA) and Acuros (AXB) algorithms in lung stereotactic body radiation therapy (SBRT).

Ten lung cancer patients were selected for SBRT planning. Patients were divided into two groups based on respiratory motion management: free-breathing and deep inspiration breath-hold (DIBH). The 6 MV volumetric modulated arc therapy (VMAT) plans were created with a prescription dose of 50 Gy in 5 fractions using the Eclipse planning. The plans were initially created using AAA and normalized the prescribed dose to cover 95% of the planning target volume (PTV). The plans were recalculated with the AXB with fixed monitor units (MUs) to observe the effect of different dose calculation algorithms.

The results showed that plan quality degraded in the AXB algorithm when using fixed MUs. Mean CT number of iGTV and PTV in free breath was lower than DIBH. The larger difference in inhomogeneous media was observed in the free-breathing group, where the mean CT number of iGTV and PTV in free-breath was lower than DIBH. For PTV, the minimum dose (D98%) was higher in AAA (48.8 Gy) for both free-breath and DIBH, whereas AXB was presented as 46.2 Gy in free-breath and 46.3 Gy for DIBH, respectively. The maximum dose (D2%), mean dose (D50%) for PTV, mean lung dose, V20Gy for normal lung, Dmax and D5cc for the heart showed no significant differences between the two algorithms for both respiratory motion managements. AAA demonstrated better conformity, homogeneity, and a steeper dose gradient compared to AXB, but AAA required a longer computation time.

With this presented data, the demonstrated PTV and lung dose are comparable for AAA and AXB. The significant differences are found for both PTV and OARs in free-breath respiratory motion management, with lower PTV dose coverage and the higher dose to normal lungs (V5Gy) with AXB. The computation time of AXB is approximately 7 times faster than AAA. However, clinical implementation should involve optimizing plans using AXB in addition to calculations.