Total ablative stereotactic body radiotherapy to primary and oligometastatic renal cell carcinoma in medically inoperable cases: An institutional analysis

Introduction: Stereotactic body radiotherapy (SBRT) has been found to be an effective and safe modality with excellent oncological outcome in medically inoperable primary renal cell carcinoma (RCC) and oligometastases. There is scarcity of data on the synchronous delivery of SBRT to primary and oligometastatic RCC in patients unfit for nephrectomy. Here, we report the findings of a retrospective study of prospectively collected data on "total ablative SBRT." Methods: Oligometastatic RCC patients with intact primary tumors were enrolled between May 2021 and June 2022. SBRT was synchronously delivered to the primary tumor and metastases. Demographics, treatment, oncologic outcomes, and toxicity were assessed. Kaplan-Meier estimates were generated for oncologic outcomes. The primary endpoint of this study was feasibility and tolerability. Results: Eleven patients were enrolled between May 2021 and June 2022. One patient died at 2 months after SBRT due to viral pneumonitis (possibly COVID pneumonia). Nine patients (82%) had metastatic disease, while 2 (18%) were stage II. The average maximal diameter of primary was 68.7 mm (range, 23-128 mm). The SBRT doses for primary and metastasis ranged from 40 to 55 Gray (Gy) in 5 to 7 fractions and 22 to 40Gy in 2 to 5 fractions, respectively. The median follow-up period was 10.5 months (Range: 4-15 months). Response assessment was available for ten patients. Local control, marginal control, regional control and initial oligometastatic control (OMC) rates were 100%. OMC declined to 87.5% as one patient had recurrence in irradiated subcarinal lymphnode at 7 months. The metastatic control rate was 80% and loco-regional progression-free survival was 8 months (range, 4-15 months). Toxicities were minimal and manageable. At the last follow-up, 7 of 11 patients were alive with an overall survival of 63.5%. Six patients received systemic therapy after SBRT. Conclusions: Synchronous delivery of SBRT to primary and oligometastatic sites in patients unfit for nephrectomy was feasible and tolerable with good locoregional control. The total ablative SBRT strategy needs to be explored in similar cohorts.