STEREOTACTIC BODY RADIATION THERAPY (SBRT) FOR RENAL TUMOURS: A PROSPECTIVE PHASE II STUDY

Abstract

Purpose:

Stereotactic body radiotherapy (SBRT) represents a novel, efficacious treatment for patients with kidney tumours who are medically inoperable or decline surgery. There is limited prospective data on the impact of kidney SBRT on renal function. Herein, we present the primary endpoint of a prospective trial of kidney-directed SBRT.

Materials and Methods:

This is a prospective single-arm Phase II trial of renal-directed SABR including patients with solid kidney mass(es) (primary or metastatic) amenable to SBRT, and who were medically inoperable or declined surgery. Key exclusion criteria included prior kidney radiation exposure, recent nephrotoxic systemic therapy, or end-stage renal failure. SBRT was delivered as 27.5-40 Gy in 5 fractions, delivered on alternate days. Primary endpoint was nephron toxicity, measured by the change in eGFR over 2 years. Secondary endpoints included oncologic endpoints, toxicity, and quality-of-life (QOL), measured by NFKSI-19. The a priori null hypothesis was that eGFR does not decrease over time and was analyzed using a null hypothesis significance test (NHST) Princess Margaret Cancer Centre, University Health Network, University of Toronto, Toronto, Ontario and two one-sided tests (TOST) of equivalence for the paired t-test at α=0.05.

Results:

Thirty patients with 32 renal tumours enrolled, with median (IQR) age 76 years (73-86), Charlson comorbidity index 8 (7-9), 93% had chronic kidney disease Stage >2, and the majority had cT1b disease. Twenty-six patients (87%) had primary kidney cancer, and the remainder had non-kidney cancer metastatic lesions. Median radiation dose was 35 Gy in 5 fractions. Median follow-up was 24.5 months (IQR 20-36.2). Median (IQR) eGFR levels (mL/min/1.73m2) were 47.5 (37.8-64.0) at baseline, 42.0 (35.2-54.2) at 1-year and 39.5 (25.5-54.8) at 2-years. The null hypothesis was rejected (mean difference=8.7, 90% CI [3.4, 14.1]; NHST p=0.011; TOST p=0.71). Local control was 96.7% at 2 years. The cumulative incidence of Grade >2 toxicity was 4.3% (95% CI 0.3, 18.7). There were no acute or late Grade 3+ toxicities. QOL scores did not significantly change following treatment.

Conclusions:

Kidney-directed SBRT results in minimal loss of renal function, comparable to that expected from other treatment options, with high rates of local control, low rates of toxicity, and preservation of QOL. Kidney SBRT should be tested in large, randomized trials to evaluate its outcomes, including efficacy and impact on renal function, relative to other standard-of-care therapies.