KEY POINTS
- This first clinical series included 36 patients with 46 superficial skin or soft-tissue malignancies treated from December 2023 to 2025. The population was heavily treatment-refractory: 90% had received at least two previous systemic regimens, 43% of lesions had been previously irradiated, and 61% had ulcerated, bleeding, eroded or fungating skin.
- X-ray minibeam RT was delivered with a clinical orthovoltage unit through tungsten collimators creating 0.5-mm-wide beams spaced 1.1 mm center-to-center. Median surface peak and valley doses were 25.9 Gy and 3.4 Gy per fraction, respectively, with a median two fractions; subsequent fractions used rotated collimators to create a crossfire dose pattern.
- Most lesions—39 of 46 (85%)—received minibeam RT alone, while seven received additional conventional RT within two weeks. Beam energy was 180 kV in 89% and 100 kV in 11%, and median irradiation time was approximately 9.5 minutes per fraction.
- Clinically meaningful symptom improvement—including pain relief, tumor shrinkage or hemostasis—was documented in 86% of patients. Among 40 RECIST-evaluable lesions, 22.5% achieved complete response, 25.0% partial response and 45.0% stable disease.
- With median follow-up of 15.1 months, the 12-month cumulative incidence of local progression was only 7.7% (95% CI 2.6–22.8%) among lesions treated with minibeams alone, corresponding to approximately 92.3% local control. Across all 46 lesions, including those receiving planned conventional RT, progression was 11.1% (95% CI 4.9–22.5%).
- Four of 36 patients (11.1%) had documented regression outside the irradiated field without a change in systemic therapy, described as abscopal responses. These cases occurred during ongoing systemic treatments including checkpoint inhibitors, targeted therapy or endocrine/HER2-directed therapy, so they cannot establish a minibeam-specific systemic effect.
- Acute skin toxicity was usually mild: 58% had grade 1 dermatitis, one patient grade 2, and no grade ≥3 dermatitis occurred. Two patients (6%) experienced other grade 3 events—persistent ulceration and necrosis—both in areas with substantial pretreatment tissue compromise; there were no grade 4–5 toxicities. Median overall survival was 14 months.
CLINICAL TAKEAWAY
Submillimeter minibeam RT has moved from preclinical physics into actual patients, and the early local-control and symptom-relief results are striking given how heavily pretreated this cohort was. But this is 36 patients without a comparator, with heterogeneous histologies and treatments; conventional efficacy claims or claims of an abscopal mechanism would be premature.
SOURCE
International Journal of Radiation Oncology, Biology, Physics