Post-treatment renal function deterioration following radiation therapy: implications for SABR in primary renal cell...

Definitive renal stereotactic ablative radiotherapy (SABR) is gaining momentum, with promising data showing excellent local control and short-term renal function comparable to surgery. However, data on late radiation-associated kidney injury and renal safety remain limited. We therefore assessed post-treatment renal outcomes and dose-response after kidney irradiation to inform nephron-sparing SABR for primary renal cell carcinoma (pRCC).

We conducted a retrospective cohort study of trunk radiotherapy patients at a tertiary university cancer center, with incidental kidney exposure (EQD2 ≥10 Gy) and longitudinal renal function follow-up. Of 731 screened patients, 232 met inclusion criteria. Chronic-kidney-disease (CKD) deterioration was analyzed against renal dose using multivariable Cox, cut-off, and spline analyses.

During median follow-up of 170 days (IQR 60-541), CKD worsening occurred in 46.98% of patients, at a median of 173 days (IQR 55-423). Mean and maximum kidney doses (EQD2) were 14.2 Gy (SD 4.68) and 14.6 Gy (SD 4.86), respectively. Higher renal dose independently predicted renal function decline (HR 1.04/Gy; p=0.028 for mean; p=0.014 for max). Female sex was a risk factor (HR 2.08; p<0.001). Cut-offs were 18.7 Gy (mean) and 19.0 Gy (max), with monotonic dose-response. Retrospective design limits causal inference; constraints remain exploratory; validation required.

Within low-to-moderate dose ranges to non-tumorous kidney tissue, irradiation was associated with a dose-dependent post-treatment decline in renal function, while severe toxicity was rare. Nephron-sparing SABR is a safe treatment option for pRCC, informing risk-adapted dose constraint refinement to minimize late injury.