Dosimetric comparison of automated noncoplanar volumetric-modulated arc therapy and intensity-modulated proton therapy for total scalp irradiation in angiosarcoma of the scalp

OBJECTIVES: To compare the dosimetric performance of HyperArc (HA) and intensity-modulated proton therapy (IMPT) for total scalp irradiation (TSI) in patients with angiosarcoma of the scalp (AS). METHODS: HA and IMPT treatment plans were retrospectively generated for 27 patients with AS. Prescription doses of 70 and 56 Gy (relative biological effectiveness [RBE]) in 35 fractions were delivered to targets 1 and 2, respectively, using a simultaneous integrated boost technique. HA was optimised to planning target volumes, whereas IMPT employed clinical target volume-based robust optimisation. Dose-volume parameters for targets and organs at risk were compared. Beam-on time was evaluated. RESULTS: Both techniques achieved adequate target coverage within dose constraints; HA demonstrated superior dose homogeneity and conformity for target 1, whereas IMPT exhibited greater dose heterogeneity. IMPT significantly reduced low-dose brain exposure [V5 Gy (RBE)] and high-dose exposure to the optic pathway, eyes, lenses, and hippocampus. HA significantly reduced intermediate-to-high brain exposure [V10-V60 Gy (RBE)], mean brain dose, and parotid dose. Moreover, HA achieved a shorter beam-on time. CONCLUSIONS: HA and IMPT offer complementary advantages for TSI in AS. HA improves dose homogeneity, reduces intermediate-to-high brain dose, and enhances treatment efficiency; conversely, IMPT better limits low-dose brain exposure and spares critical neural and ocular structures. Modality selection should be individualized according to patient-specific clinical needs. ADVANCES IN KNOWLEDGE: This study presents a direct dosimetric comparison of HyperArc and intensity-modulated proton therapy for total scalp irradiation in angiosarcoma of the scalp, demonstrating complementary strengths that may guide individualized modality selection.