2739 - Palliative Spatially Fractionated Radiotherapy (SFRT): Institutional Experience Evaluating Subjective Treatment Response and Metabolic Safety
Presenter(s)
M. Gawkowska1, S. Blamek1, M. Gajek1, B. Bekman2, and J. Wydmanski1; 1Department of Radiotherapy, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch., Gliwice, Poland, 2Treatment Planning Department, Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch., Gliwice, Poland
Purpose/Objective(s):
SFRT is increasingly used for bulky tumors in the palliative setting. Concerns remain regarding efficacy and metabolic toxicity, including tumor lysis syndrome (TLS). We report institutional outcomes focusing on tolerance, subjective response, and metabolic safety.Materials/Methods:
Forty-one SFRT courses were delivered in 28 patients (2021–2026) with advanced malignancies, including multifocal disease. Single-fraction doses of 15 Gy (n=9) or 20 Gy (n=32) were delivered to vertices using cross-firing or VMAT. The peak-to-valley ratio ranged from 1.7 to 2.0. The median GTV volume was 1173 cc (mean: 1568 cc; range: 146–5881 cc) Histopathological diagnoses included mostly sarcomas (60.5%), adenocarcinomas (11%), melanomas (7%), and single cases of other carcinomas. Twelve treatments were re-irradiations (EORTC category 1), with a median interval of 16.5 months. Tolerance was assessed by physicians and patients using a 5-point scale (very good, good, fair, acceptable, unacceptable). Subjective clinical response was assessed by patients using an analogous scale. Serum potassium and uric acid levels were measured before and after treatment; TLS prophylaxis was administered in 15 cases.Results:
Median follow-up was 8.9 months (range, 0–39). Median overall survival was 5.5 months (2.5 months in patients with multifocal disease). Physician-assessed and patient-reported tolerance were rated as 'good' or 'very good' in 78% and 75% of cases, respectively. Subjective improvement occurred in 58%, no change in 29%, and deterioration in 7%. Imaging within 3 months (n=26) demonstrated stable disease in 46%, partial response in 34%, and progression in 15%. Among 23 cases with confirmed progression, mean time to progression was 2.6 months (range, 0.3–11 months). Ongoing stabilization was observed in 10 cases. No clinical TLS occurred. Median pre- and post-treatment potassium levels didn’t changed and was 4.3 mmol/L, median uric acid levels changed from 353 to 362 µmol/L. TLS prophylaxis did not significantly influence metabolic parameters. In 5 cases, the treated region underwent subsequent re-irradiation (median interval, 22 months). Three patients underwent repeat SFRT. Four serious events (intratumour haemorrhage, skin abscess,vesicoureteral fistula, sepsis) were observed but were considered more likely to be disease-related.Conclusion: Palliative SFRT is safe and provides meaningful symptomatic relief in patients with bulky, advanced malignancies. The single-fraction approach is highly suitable for end-of-life care. The absence of tumor lysis syndrome or significant metabolic disturbances, even in large-volume tumors, confirms the metabolic safety of the procedure. However, the occurrence of SAEs emphasizes the need for rigorous patient selection in the palliative setting.