GFR Measured with Computed Tomography for Platinum Treatment Decision-Making in Urothelial Carcinoma: A Retrospective Cohort Study

BACKGROUND: Accurate assessment of glomerular filtration rate (GFR) is essential for cisplatin eligibility and carboplatin dosing. We recently demonstrated that GFR measured using iodinated contrast agent clearance derived from 4-phase CT urography (CT-mGFR) showed good agreement with iohexol clearance in both healthy individuals and patients with chronic kidney disease. We aimed to evaluate the impact of CT-mGFR on platinum selection and whether CT-mGFR-based carboplatin dosing might reduce toxicity in urothelial carcinoma. METHODS: This single-center retrospective cohort study included patients with urothelial carcinoma treated with platinum-based chemotherapy who had 4-phase CT urography within 6 months before cancer treatment and stable estimated GFR (eGFR). Primary endpoints were, first, the proportion of patients in whom CT-mGFR would have changed the choice between cisplatin and carboplatin compared with 2009 CKD-EPIcr based decision-making (equation used in routine clinical practice in France) using a 60 ml/min/1.73m2 threshold, and second, the association between grade 3-4 carboplatin-related hematologic toxicity and the relative dose difference between CT-mGFR-predicted and administered doses. Relative dose differences within ±15% were considered concordant. Severe hematologic toxicity was defined as Common Terminology Criteria for Adverse Events grade 3-4. Associations were assessed using Fisher's exact test and logistic regression. RESULTS: Forty-seven patients were included (79% male), with a median age of 69 years (IQR, 62-75). CT-mGFR and 2009 CKD-EPIcr-based eGFR led to discordant platinum treatment decisions in 10 patients (21%). The sensitivity and specificity of 2009 CKD-EPIcr for identifying CT-mGFR <60 mL/min/1.73m2 were 68.4% and 85.7%, respectively. CT-mGFR-based carboplatin dosing identified potential overdosing in 4 patients, 3 of whom developed severe hematologic toxicity, compared with 1 of 9 patients with concordant dosing and none of 6 with underdosing (p=0.02). CONCLUSIONS: CT-mGFR may help optimize platinum treatment decision-making and carboplatin dosing in urothelial carcinoma. These findings should be confirmed in larger prospective multicenter studies.