KEY POINTS
- This single-institution retrospective study included 42 patients with 47 spine metastases treated using pencil-beam scanning stereotactic proton ablative radiotherapy between 2015 and 2019. Sixty-six percent of lesions had received prior radiotherapy.
- Treatment was delivered in 1–5 fractions, most commonly 3 fractions (81%). Median prescribed doses were 39 Gy to the high-dose CTV and 24 Gy to the low-dose CTV, with a simultaneous integrated boost used for 91% of lesions.
- With median imaging follow-up of 13 months, local control was 74% at both 1 and 2 years (95% CI 58–91%). Ten lesions progressed locally: 8 in-field and 2 marginal, most often within the vertebral body.
- Higher low-dose CTV D95% was associated with a lower risk of local progression (HR 0.94, 95% CI 0.90–0.995; p=0.048), while larger low-dose CTV volume was associated with greater progression risk (HR 1.01; p=0.02). Reirradiation was not significantly associated with worse local control.
- Acute events included 9 pain flares and 1 grade 3 dermatitis. Late events included 3 vertebral compression fractures and 1 grade 3 peripheral neuropathy attributed to cement extravasation after kyphoplasty. No radiation myelopathy occurred.
CLINICAL TAKEAWAY
Spine proton ablative radiotherapy appears technically feasible for carefully selected patients, particularly when reirradiation or sparing of anterior organs makes photon planning difficult. However, the 74% local-control rate is not clearly superior to contemporary photon SABR benchmarks, and the absence of comparative plans, small heterogeneous cohort, and short follow-up prevent conclusions about a proton-specific clinical advantage.