KEY POINTS
- Between December 2023 and June 2025, 13 patients with mediastinal lymphoma were treated using intensity-modulated proton therapy during voluntary breath hold. Patients with nodal disease immediately adjacent to the diaphragm were excluded during this initial implementation phase.
- Treatment combined optical surface scanning with nasal high-flow therapy delivering humidified air at 40 L/min with 21% oxygen. Beam delivery was gated to a 3-mm respiratory window, while robust proton optimization incorporated 5-mm setup and 3% range uncertainty; intrathoracic CTVs received an additional 3-mm margin.
- In total, 187 proton fractions were analyzed. Patients required a median of one breath hold per CBCT and five per treatment delivery, while 8 of 13 patients could sustain median CBCT breath holds longer than 45 seconds.
- Surface reproducibility was high: mean intra-breath-hold stability was approximately 0.5 mm during CBCT and 0.4 mm during beam delivery, while median intrafraction stability remained below 1 mm for every patient and inter-breath-hold variation remained below 2 mm.
- Average surface-derived isocenter deviation was 2.9 ± 0.9 mm during beam-on, compared with 4.9 ± 2.2 mm during CBCT acquisition. Residual target shifts derived from image guidance remained below approximately 8 mm, comparable with the center's free-breathing experience.
- Treatment sessions averaged 44 ± 13 minutes. Simpler single-isocenter treatments with ≤4 beams took about 40 minutes versus 49 minutes for more complex plans, and fraction duration shortened by roughly 10–15 minutes over the course of treatment as patients became more accustomed to the technique.
- Weekly repeat CT showed acceptable coverage and organ doses in all but one patient; that patient required the cohort's only plan adaptation after mean heart dose increased by 1.8 Gy(RBE). Margin analysis indicated that an 8-mm uniform margin remained adequate, with interfraction motion slightly greater than intrafraction motion.
CLINICAL TAKEAWAY
Surface-gated IMPT with nasal high-flow support can make repeated breath holds sufficiently stable for clinical mediastinal lymphoma treatment, including relatively long proton fractions. The workflow appears robust in selected patients, but external surface stability is not equivalent to direct internal target tracking, and broader implementation will require careful selection, imaging and staffing.