Is RCC truly radioresistant? Local control rates of metastatic renal cell carcinoma (RCC) to the lung using stereotactic radiotherapy (SBRT).

Abstract

445 Background: The use of radiation therapy (RT) for renal cell carcinoma (RCC) is controversial because RCC has traditionally been considered to be “radioresistant”. Based on this concern, current studies have suggested the need for higher doses with conventional fractionation (CF) or the use of SBRT with RCC. The purpose of this study is to determine the efficacy of these modalities by comparing the radiographic and symptomatic local control (LC) rates in patients with metastatic RCC to the lung. Methods: We retrospectively analyzed the radiographic and symptomatic RT response in 27 consecutive RCC patients with 37 RCC lung lesions treated between 2005 to 2014. Twenty-six (70.2%) were treated with SBRT and eleven (29.8%) with CF. Only 9 patients (33.3%) had symptoms prior to RT. Median SBRT dose and fraction was 50 Gy (range 25-60) and 3 (range 1-6) versus CF 30 Gy (range 20-55) and 10 (range 5-22) respectively. Toxicity was evaluated by CTCAE 4.0. Results: Median follow up was 16 months (range 1-102). Rates of radiographic local control with SBRT and CF were 92.3% vs. 55.4% respectively (p=0.0016). Under univariate analysis, predictors for radiographic LR were gross tumor volume (GTV) > 20 cc (p < 0.0001), planned tumor volume (PTV) of > 100 cc (p < 0.0001), and biologic effective dose (BED) < 70 Gy (p=0.0001). Subanalysis of CF demonstrated that a BED < 54 Gy was also a strong predictor for LR (p=0.0012). Under multivariate analysis, PTV was a strong predictor for radiographic LR (odds ratio [OR] = 42.2, p=0.0492). For the 9 symptomatic patients, 3 of 4 (75%) patients in the CF arm and 4 of 5 (80%) in the SBRT arm experienced partial or complete symptomatic relief. The median time to relief of symptoms in the SBRT and CF arms were 0.5 and 2 months, respectively. All patients receiving CF had symptomatic LR compared to none in the SBRT arm (p=0.0124). One patient in the SBRT arm had grade 2 hiccups and one with grade 2 pneumonitis in the CF arm. There were no other grade 2 toxicities or higher. Conclusions: SBRT demonstrated an encouraging local control rate and was capable of safely providing symptomatic relief to patients. The traditional view of radioresistance in RCC may not apply in the era of SBRT.