Dosimetric correlation of radiation-induced chronic kidney disease (CKD): a competing risks analysis.

BACKGROUND AND PURPOSE: To determine the competing risks (CR) cumulative incidence of radiation-induced chronic kidney disease (CKD) and identify independent dosimetric predictors in patients receiving radiotherapy (RT) involving the para-aortic lymph nodes (PALNs), providing evidence to refine kidney dose constraints in contemporary RT planning. MATERIALS AND METHODS: From November 2000 to September 2023, 126 patients with gynecological malignancies receiving extended-field RT (EFRT) or salvage PALN RT were retrospectively analyzed. The planned PALN dose was 39.6-62 Gy/22-31 fractions. Patients with baseline estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m2 were excluded. CKD was defined as stage 3A (eGFR < 60 ml/min/1.73 m2) or stage 3B (eGFR < 45 ml/min/1.73 m2). Mean kidney dose (MKD) groups: Group 1 (<5 Gy), Group 2 (5-9.9 Gy), and Group 3 (≥10 Gy). CR analysis with Gray's test and the Fine-Gray subdistribution hazard model accounted for the competing risk of death without CKD. RESULTS: After a median follow-up of 55 months, 7-year CR cumulative incidences of stage ≥ 3A CKD were 17.0 %, 20.9 %, and 55.7 % in Groups 1, 2, and 3 (p = 0.008), respectively; corresponding rates for stage ≥ 3B CKD were 0 %, 13.9 %, and 26.4 % (p = 0.041). Patients with pre-RT eGFR < 75 ml/min/1.73 m2 had significantly higher 7-year CR rates of stage 3A (57.1 % vs. 23.2 %; p < 0.001) and stage 3B CKD (37.2 % vs. 7.6 %; p = 0.005). Multivariate CR analysis identified MKD group (p = 0.012) and pre-RT eGFR < 75 ml/min/1.73 m2 (p = 0.023) as independent predictors of stage 3B CKD. CONCLUSIONS: Radiation-induced CKD is significantly correlated with MKD and baseline eGFR. Even MKD values of 5-9.9 Gy carry measurable risk of stage 3B CKD-below the QUANTEC-recommended ceiling of 15-18 Gy-suggesting that stricter MKD constraints (< 5 Gy) are warranted, particularly in patients with pre-RT eGFR < 75 ml/min/1.73 m2.