Session Item

To evaluate oncologic and renal function outcomes of stereotactic body radiotherapy (SBRT) for medically inoperable patients with localized renal cell carcinoma (RCC). 

With institutional ethics review board approval consecutive patients with medically inoperable localized RCC treated with curative intent SBRT (30-45 Gy in 5 fractions or 42 Gy in 3 fractions) were included. Local control (RECIST v1.1), distant metastasis, and impact on eGFR, ipsilateral and contralateral renal functions were collected. To compare pre- and post-SBRT renal function, general linear mixed model was performed. To adjust for multiplicity, Bonferroni adjusted p-value <0.007 was considered statistically significant. Univariate and multivariable linear mixed model was performed to search for predictive factors of each renal function metric over time. P-value <0.05 was considered statistically significant. Akaike Information Criterion was estimated for each model. Univariate and multivariable analyses were conducted to determine association of variables with oncologic and renal function outcomes.

Seventy-four patients were analyzed. Median follow-up was 27.8 months (IQR 17.6-41.7). Fifty-seven percent of patients had tumours T1b or greater (median size 4.6 cm, 3.0-5.6cm). One, two and four-year cumulative incidence of local failure was 5.85%, 7.77% and 7.77%, respectively. Cumulative incidence of distant metastasis and survival at 2 years was 4.24% and 100%, respectively. On multivariable analysis, lower PTV mean dose (HR 0.68, 95% CI 0.49-0.94, p=0.019) and larger PTV volume (HR 6.93, 95% CI 1.82-26.45, p=0.005) were significantly associated with risk of developing local failure. Lower PTV maximum dose (HR 0.71, 95% CI 0.51-0.98, p=0.039) was significantly associated with risk of developing distant metastasis. The median change in eGFR (mL/min) from pre-SBRT levels was -7.0 (IQR -14.5 to -1.0) at 1-year and -11.5 (IQR -19.5 to -4.0) at 2-years. The proportion of ipsilateral renal function decreased significantly over time from 47% pre-SBRT to 36% at 2-years, while the proportion of contralateral renal function correspondingly increased from 53% pre-SBRT to 64% at 2-years. On multivariable analysis, lower Charlson comorbidity score (p<0.0001), higher PTV mean dose (p=0.003) and higher uninvolved renal cortex volume (p<0.0001) were significantly associated with higher eGFR values over time. 

Oncologic outcomes with RCC SBRT were favorable in this large institutional cohort. There was a longitudinal decline in renal function in the ipsilateral kidney with a compensatory increase in the contralateral kidney. Overall renal function decline over time is comparable to existing data. Clinical and dosimetric factors were significantly associated with oncologic and renal function outcomes.