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 radiotherapy (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). 14 received SBRT, 7 RFA, and 3 dropped out. Crossover occurred from RFA to SBRT due to inability to perform RFA. Mean EGFR reduction was similar at 1 year (RFA -3 ml/min/1.73 m2, SBRT -5.3 ml/min/1.73 m2, p=0.7). 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 = 0.01) 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.