Stereotactic ablative body radiotherapy (SABR) uses high doses of radiation directed at the tumour to destroy the cancer. SABR can be used to treat small primary tumours in the kidney or, more commonly metastases found in the liver, lung and pancreas, and brain. because SABR uses radiotherapy that is focused at the area of the body containing the tumour, it avoids damaging as much healthy tissue as possible.

Rarely, kidney cancer can grow in people born with only one kidney or in the remaining kidney in people who have had a kidney surgically removed. The aim of this study was to compare kidney function up to 5 years after SABR in patients who have kidney cancer and only one kidney compared to patient who have kidney cancer in one of their two kidneys.

190 patients were included in the study; 56 had only one kidney, 134 had two kidneys. Patient had their primary tumour treated with SABR and were followed for an average of 5 years. Before SABR, kidney function (estimated glomerular filtration rate, eGFR) was similar in patients with one (61 ml/min) compared to two kidneys (58 ml/min). Average tumour size was 3.7 cm and 4.35 cm, respectfully.

After SABR, there was a compensatory increase in eGFR in both groups of patients at 1 year (in 22.7% of patients with one kidney and 17.7% of patients with two kidneys). This increase continued for 5 years in a 5th of patients with two kidneys, but not those with one kidney. Five years after SABR, eGFR decreased by and average of -14.5 ,l/min in patients with one kidney and -13.3 ml/min in patient with two kidneys. At all timepoints assessed, there were no significant differences in eGFR decline between patients with one kidney compared to those with two. There were also no significant differences in end-stage kidney disease (7.1% versus 6.7%) or dialysis (3.6% versus 3.7%) in patients with one compared to two kidneys, respectively.

There was no observed difference between kidney function in patients with one kidney compared to two kidneys during 5 years after SABR. While larger tumours may increase the risk of eGFR decline following SABR, treatment of a single kidneys does not appear to increase the risk of decline in kidney function long-term.

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