L. Zhao1, D. Keilty2, M. Levesque1, M. Stein3, A. Christie1, A. Garant3, J. Brugarolas4, R. D. Timmerman5, and R. Hannan3; 1University of Texas Southwestern Medical Center, Dallas, TX, 2Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 3Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 4Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, 5Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):Stereotactic ablative radiation (SAbR) to metastatic lesions from renal cell carcinoma (mRCC) has been shown to delay systemic therapy initiation/rotation, but there is little long-term data on SAbR in this disease long thought to be radio-resistant,impacting its widespread clinical uptake. We undertook a detailed retrospective review of long-term local control rates and toxicity afterSAbR for mRCC.Materials/
Methods: We retrospectively reviewed 354mRCC patients who received SAbR to 902lesions between 2010and 2022. Acute and late adverse events and their Common Terminal Criteria for Adverse Events (CTCAE) v. 5.0 grades were collected. RECIST v. 1.1 was used to evaluate treatment response. Local control (LC) was estimated using the cumulative incidence function, with death as a competing risk.To rule out pseudo-progression, localfailure was defined as growth on two sequential imaging results at least 3 months after SAbR. We assigned radiation toxicity attributions for each CTCAE adverse event; thoseclassified asprobable/likely/definite were included in toxicity analysis. Results: Lesions were followed for a median of 2 years; 195 lesions had > 3 years of follow-up. The most common radiation prescription was 36 Gy in 3 fractions, and the median biological effective dose was 72 Gy10.The overall 3-year local control rate was 81.3% (95% CI 68.2, 83.0); 3-year LC differed according to lesion location, ranging from 67.9% (95% CI 55.3, 77.6) in the spine to 95.5% (95% CI 83.0, 98.8) in lymph nodes. Radiation-induced adverse events were experienced by 113 patients: 62 (17.5%) had anacute (= 90 dayssince SAbR) grade 1-2 toxicity; 10 (2.8%) had an acute grade 3-4 toxicity; 49 (13.8%) had a late grade 1-2 toxicity; 12 (3.4%) had a late grade 3-4 toxicity. The most common acute grade 1-2 toxicity was nausea(n=25), followed by pain(n=14) and fatigue (n=12). There were 6patientswith acute grade 3-4 pain, 4 withfractures, and 3 withnausea. The most common late grade 1-2 toxicity was pneumonitis or fibrosis (n=20), followed by pain (n=10) and fractures (n=9). Hyperglycemia was the only late grade 3-4 toxicity that occurred more than once (n=2).60% of patients who experienced an acute reactionwitha subsequenttreatment had previously experienced an acute reaction, while70% of patients with late reactions did not experience an acute side effect. Conclusion: SAbR offers durable LC of mRCC lesions with an acceptable toxicity profile. LC was affected by treated lesion location, with bone (including long bones and ribs) and spine locations experiencing less durable LC, corresponding to locations that received lower-BED treatments.
