Carbon Ion Radiation Therapy for Nonmetastatic Castration-Resistant Prostate Cancer: A Retrospective Analysis

Abstract

PurposeTreatment outcomes of definitive photon radiotherapy for nonmetastatic castration-resistant prostate cancer (nmCRPC) are reportedly unsatisfactory. Carbon ion radiotherapy (CIRT) has shown favorable tumor control in various malignancies, including radioresistant tumors. Therefore, we retrospectively evaluated the clinical outcomes of CIRT for nmCRPC. Methods and MaterialsPatients with nmCRPC (N0M0) treated with CIRT at a total dose of 57.6 Gy (relative biological effectiveness; RBE) in 16 fractions or 51.6 Gy (RBE) in 12 fractions were included. The castration-resistant status was diagnosed based on prostate-specific antigen kinetics showing a monotonic increase during primary androgen deprivation therapy (ADT) or the need to change ADT. Clinical factors associated with patient prognosis were explored. Twenty-three consecutive patients were identified from our database. The median follow-up period was 63.6 months (range, 14.1–120). ResultsSeven patients developed biochemical relapse, six had clinical relapse, and four died from the disease. The 5-year overall survival, local control rate, biochemical relapse-free survival, and clinical relapse-free survival were 87.5%, 95.7%, 70.3%, and 75.7%, respectively. One patient with diabetes mellitus requiring insulin injections and taking antiplatelet and anticoagulant drugs developed grade 3 hematuria and bladder tamponade after CIRT. None of the patients developed grade 4 or worse toxicity. ConclusionsThe present findings indicate the acceptable safety and favorable efficacy of CIRT, encouraging further research on CIRT for nmCRPC.