Impact of stereotactic radiotherapy on kidney function in primary renal cell carcinoma: Establishing a dose–response relationship

Abstract

Background and purposeTo evaluate renal dysfunction after stereotactic ablative body radiotherapy (SABR) for inoperable primary renal cell carcinoma (RCC) using nuclear medicine assessments. Materials and methodsIn a prospective clinical trial, patients received single fraction renal SABR (26Gy) for tumours <5cm, or fractionated SABR (3×14Gy) for tumours ⩾5cm. Global and regional glomerular filtration rate (GFR) was calculated through 51Cr-EDTA and 99mTc-DMSA SPECT/CT, respectively, at baseline and post-treatment (14, 90days and at 1-year). Regional loss in function was correlated to the absolute and biologically effective doses (BED) delivered. ResultsIn 21 patients the mean (range) tumour size was 48mm (21–75mm). The mean±SD GFR at baseline was 52±24ml/min. Net change in mean GFR was +0.6±11.3, +3.2±14.5 and −8.7±13.4 ml/min (p=0.03) at 2weeks, 3months and 1year, respectively. For every 10Gy of physical dose delivered, an exponential decline in affected kidney GFR was observed at 39% for 26Gy/1 fraction and 25% for 42Gy/3 fractions. When normalised to BED3Gy, the dose–response relationship for each treatment prescription was similar with a plateau beyond 100Gy. The R50% conformity index correlated with GFR loss (p=0.04). No patient required dialysis. ConclusionsSABR results in clinically acceptable and dose-dependent renal dysfunction at 1-year. Sparing functional kidney from high-dose regions (>50% isodoses) may help reduce risk of functional loss.