(P062) Comparison of Stereotactic Body Radiotherapy (SBRT) and Conventional External Beam Radiotherapy (EBRT) in Renal Cell Carcinoma (RCC)

Christopher L. Tinkle, MD, PhD, Stephen L. Shiao, MD, PhD, Vivian K. Weinberg, PhD, Amy M. Lin, MD, Alexander R. Gottschalk, MD, PhD; University of California, San Francisco; Cedars-Sinai Medical Center

BACKGROUND: Renal cell carcinoma (RCC) is considered a radiation-resistant histology, often with poor response to conventionally fractionated external beam radiotherapy (EBRT). We compared outcomes for patients treated with EBRT vs stereotactic body radiotherapy (SBRT) for RCC.

METHODS: From 2004 and 2012, a total of 89 patients were treated with either EBRT or SBRT and retrospectively reviewed. Patients with locally recurrent RCC, bone or soft tissue RCC metastases, or primary RCC in a solitary kidney were included; 51 patients received EBRT, while 38 patients received SBRT. The median biologically effective dose (BED), assuming an α/β ratio of 10, was 32.6 Gy10 for the EBRT group and 48.0 Gy10 for the SBRT group. Local failure (LC) was defined pathologically or by imaging according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, and toxicity was reported according to Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0) guidelines. Univariable and multivariable analyses using Cox’s regression model was performed to determine predictors of local control.

RESULTS: Median follow-up from radiotherapy was 9.8 months (range: < 1–73 mo) with EBRT and 19.7 months (range: < 1–61 mo) with SBRT (P = .26). EBRT patients were younger (P = .02), and more of them were M1 (P = .04); yet, other baseline features did not differ significantly. Total RT dose, dose/fraction, and BED10 were significantly higher in the SBRT group (P ≤ .002 for each), while number of fractions was significantly lower (P < .001). The 1-year LC estimate was 88% (95% confidence interval [CI], 72%–96%) with SBRT and 50% (95% CI, 32%–65%) with EBRT (P = .001), with no significant difference in rate of distant recurrences (P = .37). The 1-year progression-free survival (PFS) and overall survival (OS) rates between the EBRT and SBRT groups were 17% (95% CI, 8%–29%) vs 39% (95% CI, 24%–54%) (P = .06) and 39% (95% CI, 25%–52%) vs 82% (95% CI, 65%–91%) (P = .002), respectively. The use of SBRT was the most important independent factor that was significantly predictive of local control on multivariable analysis (P = .001, log-likelihood ratio [LLR] test; hazard ratio [HR] = 0.29; 95% CI, 0.13–0.61), while neither age nor metastasis at diagnosis was predictive. No grade 3/4 toxicity was observed in either RT group. 

CONCLUSIONS: The data support that SBRT improves local control over standard fractionation schemes. Higher dose per fraction, with a BED in the range of 48 Gy10, is a safe and effective local treatment modality for RCC.

Proceedings of the 97th Annual Meeting of the American Radium Society- americanradiumsociety.org