Final Results from a Prospective Randomized Pilot Trial of Stereotactic Body Radiation Therapy vs. Radiofrequency Ablation for the Management of Small Renal Masses (RADSTER)

Abstract

The benefits of stereotactic body radiation therapy (SBRT) as a primary treatment modality for small renal masses (SRMs) ≤4cm are unclear. Our objective was to evaluate both SBRT and radiofrequency ablation (RFA) for SRMs to determine the utility of a future Phase III randomized controlled trial (RCT). Patients with SRMs who declined active surveillance, surgery or were deemed inoperable were recruited at a single tertiary academic center. After meeting inclusion/exclusion criteria, participants were assigned 1:1 to SBRT or RFA, with crossover allowed if technical or patient factors precluded either treatment. SBRT included an initial simulation and a single delivered fraction of 25 Gy to the planning target volume. RFA was conducted percutaneously with 2 cycles of up to 8 minutes each upon reaching target temperature. Renal protocol imaging (CT or MRI) was completed q3 months (up to 1 year) post-procedure. Diagnostic and 1-year renal biopsies were also required. The objective of this trial was feasibility of randomization, with the aim of recruiting 24 patients based on this assumption. From January 2020 to June 2021, 33 patients were screened, with 24 recruited and initially randomized (SBRT = 12; RFA = 12). Median age was 67 years (53-85) and 17/24 were male. Seventeen patients had clear cell renal cell carcinoma (RCC), 6 had papillary RCC, and 1 had chromophobe RCC. Following randomization, a total of 14 patients had SBRT, 7 had RFA, and 3 declined treatments. Crossover mainly occurred from RFA to SBRT due to technical inability to perform RFA. One grade 2 acute pain flare occurred in the SBRT group (none in the RFA group). No late toxicity up to 1 year was reported in either group. At 1 year, no radiographic local failure (RECIST) was observed, although RFA patients were more likely to have loss of arterial enhancement (83.3% vs 23%, p = 0.041). Mean reduction of estimated glomerular filtration rate was similar at 1 year (RFA -3 mL/min, SBRT -5.3 mL/min, p = 0.7). Biopsies were performed in 20/24 patients at 1 year, on per-protocol analysis 7/7 (100%) of RFA patients had no evidence of residual RCC, whereas with SBRT 4/13 (31%) patients had no evidence of residual RCC, 2/13 (15%) had scant/minimal residual disease, and 7/13 (54%) had evidence of RCC. No patients developed distant failure or death from RCC during follow-up. Recruitment, randomization and follow-up of patients with SRMs was feasible in this study. More patients received SBRT compared to RFA, highlighting the need for thorough multidisciplinary evaluation prior to randomization. Both treatments have excellent safety profiles, with RFA demonstrating initial higher rates of pathological/radiologic response, however long-term follow-up is required. This trial supports the need for a large scale RCT with appropriate radiographic and pathological endpoints built in.