Author: John T Barrett, Chulhaeng Huh, Farshad Mostafaei, Michelle Rocque, Austin Sanders 👨🔬
Affiliation: Department of Radiation Oncology, Medical College of Georgia, Augusta University, Department of Radiation Oncology, Augusta University, Georgia Radiation Therapy Center, Wellstar-MCG Health 🌍
Purpose: This study involved the use of Accuray’s TPS (Precision) and RayStation TPS for planning TBI treatments. TBI was delivered using Accuray’s Radixact machine, and dose calculation algorithm, dose conformality, and dose-volume histogram (DVH) were investigated.
Methods: Helical TomoTherapy delivers radiation with simultaneous movement of the gantry, couch, and MLC leaves, which improves dose conformality compared to linac methods per AAPM’s TG-29. TomoTherapy TPSs rely on advanced dose calculation algorithms like convolution-superposition (C-S) in Precision and collapsed cone convolution (CCC) in RayStation. Both methods calculate absorbed dose by convolving the TERMA and the kernel. C-S improves accuracy by scaling the kernel based on radiologic distance while CCC decreases calculation time by simplifying the kernel to a point with rays. To compare these methods, TBI plans delivering 200 cGy in 1 fraction were created in Precision and RayStation while achieving a minimum D95%≥100%. Head-first supine (HFS) and feet-first supine (FFS) plans with pitch factors of 0.267 and 0.295, respectively, were summed, and comparisons of dose distributions, DVHs, and modulation factors were made.
Results: Precision and RayStation show nearly identical mean and maximum dose to PTV and OARs with 4 cGy difference, except the brain has 11 cGy higher maximum dose with RayStation, while RayStation shows lower PTV and OAR minimum doses for PTV and OARs with maximum deviation of 9 cGy for the brain. However, RayStation has higher V105% across all structures, peaking at 10.9% for the brain. Modulation factors are 3.4, except RayStation’s HFS at 3.6. Both TPSs produce closely matched isodose levels, including the 105% isodose spanning the TBI match line.
Conclusion: Precision and RayStation produce similar TomoTherapy TBI plans with comparable beam shaping complexity, as shown by similar modulation factors. This study suggests Precision’s C-S may offer better plans with higher PTV minimum dose and lower V105%.