Context: The use of stereotactic ablative radiotherapy for recurrent and metastatic renal cell carcinoma (RCC) is not yet standard treatment due to uncertainties regarding its efficacy and safety. Objective: The objective of the systematic review and meta-analysis was to assess the efficacy and safety of stereotactic radiotherapy for metastatic RCC. Evidence acquisition: A Population, Intervention, Control, Outcome, Study Design (PICOS)/Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)/Meta-analysis of Observational Studies in Epidemiology (MOOSE) protocol was utilized to select studies published during 1998–2019. The primary outcome was 1 year local control and 1 year overall survival; the secondary outcome was Common Terminology Criteria for Adverse Events grade 3–4 toxicity. Weighted random-effect meta-analyses were conducted using the DerSimonian and Laird method, heterogeneity was evaluated using the I2 statistic and Cochran Q test, and the Egger test assessed publication bias. Evidence synthesis: A total of 265 studies were screened and 28 studies were included. There were 1602 mutually exclusive patients (679 extracranial/923 intracranial) and 3892 lesions (1159 extracranial/2733 intracranial). The median age was 62 yr. The median treatment volume was 59.7 cc for extracranial (interquartile range: 31.1–71.4) and 2.3 cc for intracranial (interquartile range: 1.3–4.3) lesions. Under the random-effect model, the summary effect size for 1-yr local control was 89.1% (95% confidence interval [CI]: 83.6–93.7%, I2 = 71%) and 90.1% (95% CI: 83.5–95.3%, I2 = 74%) for extracranial and intracranial disease, respectively. The 1-yr survival rates were 86.8% (95% CI: 62–99.8%, I2 = 95%) and 49.7% (95% CI: 41.1–58.3%, I2 = 74%) for extracranial and intracranial disease, respectively. The incidence of any grade 3–4 toxicity was 0.7% (95% CI: 0–2.1%, I2 = 0%) for extracranial disease and 1.1% (95% CI: 0–7.4%, I2 = 53%) for intracranial disease. Conclusions: Stereotactic radiotherapy is safe and efficacious for RCC oligometastases, with local control at 90% and any significant toxicity at 1%, reported at 1 yr. Further prospective studies are needed. Patient summary: Stereotactic radiotherapy is safe and effective in treating kidney cancer that has spread to other parts of the body: 90% of cancers do not progress in the treated region and <1% of patients have side effects at 1 yr. Stereotactic radiotherapy is safe and efficacious in the management of extracranial and intracranial renal cell oligometastases, with local control at 90% and any significant toxicity at 1%.
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