Top Line: What is the maximum safe dose of fractionated SBRT for inoperable renal cell carcinoma (RCC)?
The Study: The ideal SBRT regimen for RCC is unclear as there are safe and effective options ranging from 1 to 5 fractions. A previous dose escalation study of fractionated SBRT for primary treatment of early stage RCC in medically inoperable patients showed that doses up to 48 Gy in 4 fractions is safe with no dose limiting toxicity (DLT). That trial was then expanded into a second series of patients who were enrolled at three higher dose levels: 48 Gy→ 54 Gy→ 60 Gy, all in 3 fractions. Patients had T1-3N0 tumors, there was no strict renal function criteria for enrollment, and patients could also have just one kidney. All treatments were delivered on the CyberKnife platform with fiducial guidance, and dose was prescribed to the 75-82% isodose line. A total of 11 patients were enrolled, and there were no dose limiting toxicity events. The only grade 3+ event was a pyelonephritis 2 years after SBRT. The 3-year local control rate was 90%. When combined with the first series of patients on the trial, the 5-year local control rate was > 95%. Just under half of patients elected to have post-treatment biopsy. Interestingly, all 5 had residual tumor cells at a median 6 months after treatment. This finding is discordant with the clinical control outcomes, so it’s unclear how to interpret a positive biopsy after ablative dose SBRT.
TBL: Dose escalation up to 60 Gy in 3 fractions for inoperable RCC appears safe and effective with a <10% rate of grade 3+ toxicity and >90% local control. | Grubb, Radiother Oncol 2020