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.