Aim: Purpose of this study is to dosimetrically compare head and neck (H and N) cancer patients planned with multivendor volumetric modulated arc therapy (VMAT) technology. VMAT treatment planning can be done using biological (treatment planning system [TPSB]: Monaco) or physical (TPSP: Eclipse)-based cost function optimization techniques. Planning and dosimetric comparisons were done in both techniques for H and N cases.
Materials and methods: Twenty H and N patients were retrospectively selected for this study. VMAT plans were generated using TPSP (V11.0) and TPSB (V3.0) TPS. A total dose of 66 Gy (planning target volume 1 [PTV1]) and 60 Gy (PTV2) were prescribed to primary and nodal target volumes. Clinical planning objectives were achieved by both the optimization techniques. Dosimetric parameters were calculated for PTVs, and quantitative analyses were performed for critical organs. Monitor units were compared between two TPSs, and gamma analysis was performed between I'matriXX measured and TPS calculated.
Results: Clinically, acceptable VMAT plans showed comparable dose distributions between TPSB and TPSP optimization techniques. Comparison of mean dose, homogeneity index, and conformity index for PTV1 showed no statistical difference (P - 0.922, 0.096, and 0.097); however, in PTV2 statistically significant difference was observed (P - 0.024, 0.008, and 0.002) between TPSB and TPSP. TPSB optimization showed statistically significant superiority for spinal cord and brainstem (D1% P - 0.0078, 0.00002) whereas improved parotid sparing was observed in TPSP optimization (mean dose P - 0.00205). Gamma analysis illustrated that both systems could produce clinically deliverable plans.
Conclusion: VMAT plans by TPSP and TPSB offered clinically acceptable dose distributions. TPSB-based optimization showed enhanced sparing of serial organs whereas TPSP-based optimization showed superior sparing of parallel organs.