Partial and full arc with DynamicARC technique in pencil beam scanning proton therapy for bilateral head and neck cancer: A feasibility and dosimetric study.

Purpose: A novel proton beam delivery method known as DynamicARC spot scanning has been introduced. The current study aims to determine whether the partial proton arc technique, in conjunction with DynamicARC pencil beam scanning (PBS), can meet clinical acceptance criteria for bilateral head and neck cancer (HNC) and provide an alternative to full proton arc and traditional intensity-modulated proton therapy (IMPT).

Method: The study retrospectively included anonymized CT datasets from ten patients with bilateral HNC, all of whom had previously received photon treatment. The clinical target volumes (CTV) were categorized into three levels: CTV_7000, CTV_5950, and CTV_5600. IMPT plans included three beams, whereas DynamicARC plans included dual-partial-arcs (DPA), single-partial-arc (SPA), and single-full-arc (SFA). All plans underwent robust optimization considering setup (± 3 mm) and range (± 3%) uncertainties applied to the CTVs. DynamicARC plans were evaluated against the NRG-HN009 criteria and IMPT plans using various metrics.

Results: All four techniques-IMPT, DPA, SPA, and SFA-demonstrated substantial compliance with NRG-HN009 dosimetric criteria. DynamicARC produced superior dose conformity, lower hotspot, and improved homogeneity for high-risk CTV compared to IMPT, with comparable performance for intermediate- and low-risk CTVs. DynamicARC reduced the D_mean to the parotid glands by average differences of 14.5%-22.1% and to the oral cavity by an average difference of 15.75% compared to IMPT. DPA and SPA techniques achieved reductions in total integral dose of 3.7%-5.7% relative to IMPT. Overall, DPA yielded dosimetric results comparable to those of SFA while offering more conformal dose distributions and slightly better organ at risk sparing than SPA.

Conclusion: On the ProteusOne with a partial gantry system, DPA and SPA, in conjunction with DynamicARC PBS protons, provided clear dosimetric advantages over three-field IMPT. Future clinical implementation and further research into optimizing DynamicARC protocols are warranted to fully realize the benefits of these techniques in clinical settings.