KEY POINTS
- This prospective phase I dose-escalation study treated 69 persistent lesions in 57 patients within four months of a previous radiotherapy course. The cohort included primary, nodal and metastatic lesions across multiple tumor types.
- Patients were divided according to prior dose. Lesions previously receiving ≤50 Gy EQD2₃ received escalating stereotactic boosts of 25-35 Gy in 5 fractions, while lesions previously exposed to >50 Gy EQD2₃ received 20-30 Gy in 5 fractions.
- The highest planned levels of 35 Gy and 30 Gy were reached in the two respective arms, and the maximum tolerated dose was not exceeded.
- Among 65 evaluable lesions, complete response occurred in 80.0%, partial response in 13.8%, and stable disease in 4.6%, producing an overall response rate of 93.8% and disease control rate of 98.4%.
- One-year local control was 86.5%, remaining 84.0% at two years. Local control was similar between the lower- and higher-prior-dose arms, at 85.6% and 87.1% at one year (p = 0.943).
- One-year distant metastasis-free survival, disease-free survival and overall survival were 70.8%, 63.8% and 91.9%, respectively.
- Toxicity was generally limited. There was one grade 3 acute gastrointestinal event after 25 Gy in 5 fractions to a pelvic lesion previously treated with 55 Gy, and one grade 3 late duodenal bleeding event after 35 Gy in 5 fractions following 30 Gy in 10 fractions.
CLINICAL TAKEAWAY
A delayed stereotactic boost within four months of prior radiotherapy appears technically feasible in carefully selected patients with persistent disease, even after relatively high previous doses. The evidence is not sufficient to define a standard boost regimen because anatomy, histology and prior treatment were highly heterogeneous and cumulative dose assessment was limited.