Stereotactic ablative radiotherapy is emerging as a viable option for managing renal masses, demonstrating promising outcomes in local control and patient safety. Recent data presented at the 2024 South Central American Urological Association (AUA) Annual Meeting and published in Lancet Oncology and other journals, highlight the efficacy and safety of this approach, particularly for patients who are not suitable candidates for surgery.
IROCK Meta-Analysis: Long-Term Outcomes
The International Radiosurgery Consortium of the Kidney (IROCK) group conducted an individual patient data meta-analysis, published in 2023, assessing 5-year outcomes after stereotactic ablative radiotherapy for primary renal cell carcinoma. The analysis included 190 patients from 12 institutions, with a median follow-up of 5.0 years. The mean tumor diameter was 4.2 cm, and 50% of patients had ≥ T1b (≥ 4 cm) primaries. Results showed a local failure rate of 5.5% at 5 years, indicating strong long-term control of the disease. Notably, 75% of patients were deemed inoperable by their urologist, often due to cardiovascular comorbidities.
TROG 15.03 FASTRACK II Trial: High Local Control Rates
The TROG 15.03 FASTRACK II trial, a non-randomized phase 2 study, evaluated stereotactic ablative body radiotherapy for primary kidney cancer. Seventy patients received either a single fraction of 26 Gy for tumors ≤ 4 cm or 42 Gy in three fractions for tumors > 4 cm to 10 cm. The primary endpoint was local control, defined as no progression of the primary renal cell cancer. At a median follow-up of 43 months, the local control rate at 12 months was 100% (p < 0.0001). Grade 3 treatment-related adverse events occurred in 10% of patients, with no grade 4 adverse events reported.
Systematic Review and Practice Guideline
A systematic review and practice guideline published in Lancet Oncology in 2024, assessed 36 articles (23 retrospective, 13 prospective; n = 822 patients) on stereotactic body radiotherapy for primary renal cell carcinoma. The median age was 72 years, 73% were male, and the median tumor diameter was 4.4 cm. The median local control rate was 94.1% (range 70.0-100), the 5-year progression-free survival was 80.5% (95% CI 72-92), and the 5-year overall survival was 77.2% (95% CI 65-89).
Monitoring Post-Treatment
Post-treatment monitoring after stereotactic body radiotherapy differs from that after thermal ablation or partial nephrectomy. Key considerations include:
- Reduction in tumor size by imaging is slow, occurring over years.
- Residual enhancement does not predict local failure.
- A positive biopsy is not uncommon, despite high rates of local control; these biopsies often show decreased cellularity, decreased Ki-67, increased fibrosis, hyalinization, and increased markers of cellular senescence.
Patient Selection
Patient selection is crucial for stereotactic body radiotherapy. This approach is suitable for small peripheral tumors, larger tumors, tumors close to the hilum, and patients who are medically inoperable or at high risk. The data suggest that stereotactic body radiotherapy is a safe and effective alternative to surgery for select patients with renal masses, offering high rates of local control and acceptable toxicity profiles.
