Impact of the R.E.N.A.L. complexity score on outcomes of stereotactic ablative body radiotherapy for primary renal cell carcinoma.

Objective: To evaluate the predictive value of the R.E.N.A.L. ([R]adius, [E]xophytic/endophytic properties, [N]earness of tumour to the collecting system or sinus, [A]nterior/posterior descriptor, and [L]ocation relative to polar lines) nephrometry score (RNS) for outcomes following stereotactic ablative body radiotherapy (SABR) for primary renal cell carcinoma (RCC), as the impact of tumour complexity on outcomes following nephron-sparing SABR treatment is unclear.

Patients And Methods: This was a single institutional retrospective analysis of patients with primary RCC receiving SABR between 2012 and 2020. The primary outcome was the change in renal function post-SABR, measured by estimated glomerular filtration rate (eGFR), and the effect of baseline RNS on it was assessed using linear mixed models (LMMs).

Results: A total of 90 patients with a median (interquartile range [IQR]) age of 77 (71-82) years and a median (IQR) follow-up of 4.8 (2.8-7.8) years were included. In all, 52 patients (58%) had T1b disease, nine (10%) had T2 disease, and three (3%) had T3 disease. The median (IQR) maximum tumour size was 4.6 (2.1-8.4) cm. Most patients had moderate-complex renal tumours with a median (IQR) RNS of 9 (7-10). The baseline median eGFR was 53.6 mL/min/1.73 m (95% confidence interval [CI] 49.7-57.5 mL/min/1.73 m). The eGFR declined by -8.1 mL/min/1.73 m (95% CI -6.5 to -9.6 mL/min/1.73 m) at 1 year. The P value for the post-SABR eGFR trajectory according to baseline RNS was P = 0.06. Two patients (2.2%) underwent dialysis. Three patients (3.3%) experienced local progression. The 3- and 5-year estimates for freedom from local failure were 97% (95% CI 89-99%), and 91% (95% CI 68-98%), respectively. Four (4.4%) patients experienced Grade 3 toxicities.

Conclusion: Stereotactic ablative body radiotherapy is an effective treatment option, with acceptable decline in renal function and toxicity for medically inoperable patients with complex primary kidney tumours. The association between baseline RNS and renal function trajectories is worthy of further investigation.