Spatially Fractionated Radiation Therapy for Palliation in Patients With Large Cancers: A Retrospective Study

Purpose Spatially fractionated radiation therapy (SFRT) is an irradiation technique developed to improve large cancer response. Although preliminary studies report highly positive results, data are still limited. The aim of this retrospective monocentric study was to investigate SFRT safety and activity. Methods and Materials We analyzed all patients who underwent SFRT as a palliative treatment for large solid extracranial cancer (>4.5 cm) at our institution. The primary endpoint was objective response rate assessment at 3 months. Additionally, patients' antalgic response, target volume reduction, and performance status modification were measured. Toxicity data were recorded. Results From November 2021 to August 2023, 20 consecutive patients (20 lesions) underwent SFRT. We prescribed a minimum dose of 20 Gy in 5 fractions to 95% of the Planning Target Volume (PTV_20) and a minimum dose of 50 Gy to 50% of the sphere volume. The median beam-on time was 5 minutes (IQR 1-3 , 4-7 minutes; range, 3-16 minutes). Patients' median age was 70 years (range, 18-85 years). The median lesion volume was 560.4 cm3 (IQR 1-3 , 297.4-931.5 cc; range, 168.3-3838.3 cm3). Of the 20 patients, 14 and 10 were alive at 3 and 6 months, respectively. The 3-month objective response rate was 79% (95% CI, 49%-95%), with a median target volume reduction of 54% (IQR 1-3 , 32%-69%; range, 6%-80%). At 6 months, all patients were free from local disease progression. All patients reported an antalgic response with a rapid onset. All treatment-related toxicities occurred within 1 month after SFRT and quickly recovered. No acute toxicity ≥ grade 3 and late toxicity was reported. No patient experienced a worsening in performance status. Conclusions Our results provide further evidence supporting SFRT as a safe and promising option for palliative patients affected by large neoplastic lesions.