Purpose: The Halcyon radiotherapy platform at Groote Schuur Hospital was delivered with a factory-configured analytical anisotropic algorithm (AAA) beam model for dose calculation. In a recent system upgrade, the Acuros XB (AXB) algorithm was installed. Both algorithms adopt fundamentally different approaches to dose calculation. This study aimed to compare the dose distributions of cervical carcinoma RapidArc plans calculated using both algorithms.Methods: A total of 15 plans previously calculated using the AAA were retrieved and recalculated using the AXB algorithm. Comparisons were performed using the planning target volume (PTV) maximum (max) and minimum (min) doses, D95%, D98%, D50%, D2%, homogeneity index (HI), and conformity index (CI). The mean and max doses and D2% were compared for the bladder, bowel, and femoral heads.Results: The AAA calculated slightly higher targets, D98%, D95%, D50%, and CI, than the AXB algorithm (44.49 Gy vs. 44.32 Gy, P=0.129; 44.87 Gy vs. 44.70 Gy, P=0.089; 46.00 Gy vs. 45.98 Gy, P=0.154; and 0.51 vs. 0.50, P=0.200, respectively). For target min dose, D2%, max dose, and HI, the AAA scored lower than the AXB algorithm (41.24 Gy vs. 41.30 Gy, P=0.902; 47.34 Gy vs. 47.75 Gy, P<0.001; 48.62 Gy vs. 50.14 Gy, P<0.001; and 0.06 vs. 0.07, P=0.002, respectively). For bladder, bowel, and left and right femurs, the AAA calculated higher mean and max doses.Conclusions: Statistically significant differences were observed for PTV D2%, max dose, HI, and bowel max dose (P>0.05).
The Halcyon O-ring gantry linear accelerator from Varian Medical Systems is delivered with a hardcoded beam-source model and Analytical Anisotropic Algorithm dose calculation algorithm as standard, while the Acuros XB algorithm is a purchasable option. The models in both algorithms are factory-configured and do not permit fine-tuning by the user. In this study, we compared the two algorithms for sequential boost RapidArc treatment planning of Head & Neck cancers using D98%, D95%, D50%, D2% and maximum dose to assess dose coverage of nodal and tumor planning target volumes (PTV_N and PTV_T, respectively), and cochlear D5%, parotid D20%, D50%, mean dose, and cord maximum dose to evaluate doses to organsat-risk. The conformity index (CI), homogeneity index (HI) and total number of monitor units (MU) quantified plan quality. We found statistically significant differences in PTV_N D2%, maximum dose, HI, PTV_T D98%, D95%, D2%, Max, HI, and total MU. Statistically significant differences in Cochlear D5% and Parotid mean doses were also encountered. These differences may not necessarily be clinically significant, however. Therefore, we believe that both calculation algorithms are adequate for RapidArc planning of Head & Neck cancers.
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