Updated long‐term outcomes after carbon‐ion radiotherapy for primary renal cell carcinoma

Long‐term oncological outcomes for primary renal cell carcinoma (RCC) treated with carbon‐ion radiotherapy (CIRT) are poorly understood. Patients with primary RCC were treated with 12 or 16‐fraction CIRT at The Hospital of the National Institute of Radiological Sciences outside of clinical trials. Outcome data were pooled and retrospectively analyzed for toxicity, local control, and disease‐free, cancer‐specific, and overall survival. From 1997 to 2014, 19 RCC patients (11 with T1aN0M0, 4 with T1bN0M0, and 4 with inoperable advanced stage [T4N0M0, T3aN1M0, and T1aN0M1]) were treated with CIRT and followed up for a median of 6.6 (range, 0.7‐16.5) years; 9 of these patients were inoperable because of comorbidities or advanced‐stage disease. Diagnoses were confirmed by imaging in 11 patients and by biopsy in the remaining 8. In 4 of 5 patients with definitive renal comorbidities, including diabetic nephropathy, sclerotic kidney or solitary kidney pre‐CIRT progressed to grade 4 chronic kidney disease (CKD). In contrast, the remaining 14 patients without definitive renal comorbidities did not progress to grade 3 or higher CKD. Furthermore, although 1 case of grade 4 dermatitis was observed, there were no other grade 3 or higher non‐renal adverse events. Local control rate, and disease‐free, cancer‐specific, and overall survival rates at 5 years of all 19 patients were 94.1%, 68.9%, 100%, and 89.2%, respectively. This updated retrospective analysis based on long‐term follow‐up data suggests that CIRT is a safe treatment for primary RCC patients without definitive renal comorbidities pre‐CIRT, and yield favorable treatment outcomes, even in inoperable cases.