A Randomized Trial of Stereotactic Body Radiation Therapy vs Radiofrequency Ablation for the Treatment of Small Renal Masses: A Feasibility Study (RADSTER)

OBJECTIVE: To evaluate the feasibility of a trial comparing stereotactic beam radiation therapy (SBRT) and radiofrequency ablation (RFA) for small renal masses (SRM). METHODS: Patients opting for treatment of a SRM at a single center were randomized 1:1 to SBRT or RFA. Crossover if ineligible for treatment after randomization was allowed. Biopsies were completed prior to randomization and 12 months post-treatment. Our primary outcome was feasibility of the trial design. Secondary outcomes included treatment efficacy and safety. RESULTS: Over 18 months, 33 patients were screened resulting in the recruitment and randomization of 24 patients (SBRT = 12; RFA = 12). Fourteen received SBRT, 7 RFA, and 3 dropped out. Crossover occurred from RFA to SBRT due to inability to perform RFA. Mean estimated glomerular filtration rate (EGFR) reduction was similar at 1 year (RFA -3 ml/minutes/1.73 m², SBRT -5.3 ml/minutes/1.73 m², P = .7). One-year biopsies were performed in 95.2% (20/21) of patients receiving treatment. Per protocol analysis demonstrated a higher pathologic response (RFA 100% vs SBRT 33.3.%, P = .01) in patients undergoing RFA compared to SBRT but not in the intention to treat analysis. No patients developed local failure, metastasis or death during the study period. CONCLUSION: Recruitment, randomization, and follow-up of patients with SRMs was feasible and our results support performing a larger randomized trial. Multidisciplinary evaluation of patients before randomization is needed to assess RFA feasibility to reduce crossover. Both treatments have excellent short-term safety profiles. While not a surrogate for clinical response, RFA had a non-statistically significant improvement in pathological response. CLINICALTRIALS: gov: NCT03811665.