Prognostic Impact of Biologically Equivalent Dose in Stereotactic Body Radiation Therapy for Renal Cancer.

Abstract

PURPOSE/OBJECTIVE(S)\nSurgical resection is standard of care for initial management of localized renal cell cancer (RCC). Stereotactic body radiation therapy (SBRT) is an emerging therapy that has seen increased utilization for unresectable RCC. Due to the low α/β ratio of RCC, an improved therapeutic ratio would be predicted with the use of hypofractionated radiation treatment. While different SBRT fractionation schemes are utilized with a wide range of biologically equivalent dose (BED) for management of RCC, there is an absence of data evaluating the prognostic impact of BED for disease control.\n\n\nMATERIALS/METHODS\nThe National Cancer Database (NCDB) was queried (2004-2017) for patients with RCC (ICD C64.9) who did not have surgical resection but received definitive SBRT (defined as > 400 cGY/ fraction) to the kidney. BED was calculated using an α/β ratio of 3. Patients with a BED3 > 60 Gy were included. Kaplan-Meier analysis with log-rank test was used to evaluate overall survival (OS). Univariable (UVA) and multivariable (MVA) analysis were conducted using cox proportional hazard models to determine which clinical and treatment factors were prognostic for overall survival.\n\n\nRESULTS\nA total of 344 patients with median age 77 (IQR 70 - 85) were included in this study. Histology was clear cell in 72.7%, papillary in 6.4%, transitional in 14.2%, and other/unknown in 6.7%. T stage was cT1a in 46.8%, cT1b in 25.9%, cT2 in 4.9%, cT3 in 6.1%, and cT4 in 1.2%. A total of 2.3% of patients were cN1, 6.1% of patients were cM1, and 7% received systemic therapy either before (72.7%), after (22.7%), or concurrent (4.5%) with radiation. Median BED3 was 180 Gy (IQR 126.03 - 233.97). Median OS was 90 months in the highest quartile compared to 36 - 52 months in the lower three quartiles (P\u202f=\u202f0.007). On UVA, higher BED3 was a positive prognostic factor both as a continuous variable (HR 0.99, P\u202f=\u202f0.001; CI 0.99 - 0.99) and as a categorical variable when stratifying patients by a BED3 of 180 Gy (HR 0.67, P\u202f=\u202f0.008; CI 0.51 - 0.91). On MVA, higher BED3 measured as a continuous variable (HR 0.97, P\u202f=\u202f0.005; CI 0.95 - 0.99) was a positive prognostic factor, while age (HR 1.03, P\u202f=\u202f0.005; CI 1.01 - 1.04), transitional cell histology (HR 2.49, P\u202f=\u202f0.004; CI 1.34 - 4.64), T stage (cT1b) (HR 1.69, P\u202f=\u202f0.009; CI 1.14 - 2.51), and M stage (HR 14.01, P < 0.001; CI 5.90 - 33.27) were negative prognostic factors.\n\n\nCONCLUSION\nThis is the first study investigating the prognostic impact of BED for renal cancer SBRT. Higher BED is associated with improved OS. Prospective investigation is needed to clearly define optimal BED for SBRT used to treat RCC.