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. 2025 Apr 20:16:100749.
doi: 10.1016/j.ijpt.2025.100749. eCollection 2025 Jun.

First Clinical Implementation of Step-and-Shoot Proton Arc Therapy for Head and Neck Cancer Treatment

Peilin Liu  1 , Xiaoda Cong  1 , Jian Liang  1 , Xiangkun Xu  1 , Weili Zheng  1 , Craig Stevens  1 , Rohan Deraniyagala  1 , Xiaoqiang Li  1 , Xuanfeng Ding  1
Affiliations

First Clinical Implementation of Step-and-Shoot Proton Arc Therapy for Head and Neck Cancer Treatment

Peilin Liu et al. Int J Part Ther. .

Abstract

Purpose: Dynamic Spot-scanning Proton Arc (SPArc-Dynamic) therapy has gained attention for enhancing dosimetric plan quality. However, its full clinical implementation remains under development. As an interim milestone, we developed step-and-shoot arc therapy (SPArc-step&shoot) for head-neck cancer treatment.

Patients and methods: An in-house spot and energy-layer sparsity optimization algorithm was integrated into a clinical treatment planning system. The algorithm prioritized higher MU-weighted energy layers and spots to ensure delivery efficiency and superior plan quality while meeting machine requirements (≥0.02MU/spot). A Dynamic SPArc simulator calculated delivery times, and a machine-learning-based synthetic CT(synCT) platform monitored dose robustness. In June 2024, a head-neck cancer patient with parotid gland malignancy was treated using SPArc-step&shoot (6600 cGy[relative biological effectiveness] in 33 fx) with 9 static fields at 20-degree intervals. Comparative plans (SFO-IMPT, SPArc-Dynamic) were evaluated for dose metrics, delivery times, and adaptive planning.

Results: SPArc-step&shoot and SPArc-Dynamic showed similar target coverage and organ-at-risks sparing, and the plan quality is superior to the 3-field SFO-IMPT in the brainstem, oral cavity, and spinal cord sparing. The simulated continuous arc delivery time is 15.9, 6.32, and 4.31 minutes for SPArc-step&shoot, SFO-IMPT, and SPArc-Dynamic, respectively. The actual recorded average treatment delivery time for SPArc-step&shoot in 33 fx is 16.7 ± 1.56 minutes. QA-CT and synCT showed a similar target coverage degradation and perturbation, and a replan was initiated.

Conclusion: The SPArc-step&shoot therapy was successfully implemented in the clinical settings, and first patient was successfully treated between June and August 2024. The synCT platform serves a critical role in the daily monitoring process as SPArc-Dynamic might be more sensitive to the patient geometry changes in HNC treatment.

Keywords: Adaptive planning; Neck-neck cancer; Step-and-shoot proton arc therapy.

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Conflict of interest statement

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Xuanfeng Ding reports financial support was provided by IBA. Xuanfeng Ding reports a relationship with Ion Beam Applications SA that includes funding grants, speaking and lecture fees, and travel reimbursement. Xuanfeng Ding has patent Particle Arc Therapy licensed to IBA. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Angular distribution of gantry angle versus selected beam energy and number of protons per control point for SPArc-step&shoot and SPArc-dynamic.
Figure 2
Figure 2
A representative slice of dose distribution comparison from the head-neck cancer patient. (A) SFO-IMPT plan; (B) SPArc-Dynamic plan; (C) SPArc-step&shoot; (D) dose-volume histograms (solid line: SFO-IMPT plan; dotted line: SPArc-Dynamic plan; and short dashed line: SPArc-step&shoot plan). Abbreviation: IMPT, intensity modulated proton therapy.
Figure 3
Figure 3
A representative slice of dose distribution comparison from the head-neck cancer patient and among nominal SPArc-step&shoot plan calculation on the initial CT, QA-CT on 11th fx and synCT from CBCT on 11th fx (A) nominal plan on initial CT; (B) nominal plan on QA-CT; (C) nominal plan on synCT; (D) dose-volume histograms (solid line: initial CT; dotted line: QA-CT; and short dashed line: synCT). Abbreviation: CBCT, cone beam computed tomography; QA, quality assurance.
Figure 4
Figure 4
D98 of 33-fraction delivery, the offline adaptive plan has been applied to ensure the target dose coverage from the 13th fraction.
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