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SU_22_2221 - Identifying Potential Predictors of Late Renal Toxicity After Stereotactic Body Radiation Therapy for Primary Renal Cell Carcinoma: A Prospective Cohort Study

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Identifying Potential Predictors of Late Renal Toxicity After Stereotactic Body Radiation Therapy for Primary Renal Cell Carcinoma: A Prospective Cohort Study
M. Niglas1, P. Cheung2, A. Swaminath3, D. Erler2, R. Korol2, D. Vesprini4, and W. Chu2; 1Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 2Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, ON, Canada, 3Juravinski Cancer Centre, Hamilton, ON, Canada, 4Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada

Purpose/Objective(s): A recent individual patient data meta-analysis of patients treated with stereotactic body radiotherapy (SBRT) for localized renal cell carcinoma (RCC) has shown excellent control rates and acceptable toxicity. However, specific clinical and planning parameters have yet to be well-defined for SBRT fractionations in this setting. This study aims to identify clinical and dosimetric features predictive of late renal toxicity to be assessed in more detail in larger populations.

Materials/Methods: After institutional research ethics board approval, patients with inoperable RCC who were treated with a 5-fraction SBRT protocol between June 2012 and July 2017 were analyzed. Patient characteristics, dosimetric parameters and serum markers were prospectively collected. Toxicity was defined as GFR deterioration crossing at least one chronic kidney disease (CKD) stage. Absolute change in GFR was also examined. Kaplan-Meier estimates and Cox proportional hazards regression were used to examine toxicity outcomes.

Results: Fifty-two patients with a median GFR of 62 mL/min, median Charlson Comorbidity Index (CCI) of 8 and median tumour size of 4.1 cm (range 1.2-14.6 cm) were treated with a median dose of 35 Gy in 5 fractions (range 30-45 Gy). Median follow-up time was 9.4 months. Mean change in GFR at the time of last follow-up was -6.3 mL/min (p=0.02). Fourteen patients (27%) developed a worsening of their CKD stage by the time of last follow-up (median time to toxicity 24.8 months). Those who experienced progression of CKD stage had a mean pre-treatment GFR of 77.2 mL/min, compared to 57.2 mL/min in those who had stable CKD stage (p=0.02). On univariate analysis, higher rates of deterioration in CKD stage were seen in patients with a CCI of less than 8 (HR = 9.01, p=0.004), tumour motion of more than 1 cm (HR = 6.0, p<0.001), baseline stage 1-2 CKD (HR = 5.9, p=0.02), and those with more than 250cc of cortex outside of the 17.5 Gy isodose line (HR = 4.4, p<0.001). No significant effects were seen on multivariate analysis.

Conclusion: The change in GFR after SBRT for primary RCC was similar to that observed in other kidney-directed treatment modalities. Uninvolved renal cortex was the only dosimetric feature related to changes in renal function. Patients with more than 1 cm of tumour motion were also at a higher risk of toxicity, suggesting the importance of motion management in this patient population. Patients with lower burden of comorbidities at the time SBRT are at higher risk of late renal toxicity.

Author Disclosure: M. Niglas: None. P. Cheung: Independent Contractor; Ontario Ministry of Health and Long-Term Care. Research Grant; Sanofi Aventis, Pfizer, Abbvie. A. Swaminath: None. D. Erler: None. D. Vesprini: None. W. Chu: None.

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