Abstract
INTRODUCTION: Although cone-beam computed tomography (CBCT) is essential for tumor positioning in image-guided radiotherapy, its diagnostic application is limited by low image quality. This report highlights a case where CBCT unexpectedly detected osteoblastic bone metastasis during radiotherapy for prostate cancer. CASE PRESENTATION: A 65-year-old man with recurrent prostate cancer underwent postoperative intensity-modulated radiotherapy of 66 Gy in 33 fractions. Two months after treatment, an increase in prostate-specific antigen (PSA) levels led us to perform imaging that revealed a new osteoblastic metastasis in the left acetabulum. A retrospective review of the CBCT scans obtained during radiotherapy showed progressive osteoblastic changes that were not visible on pre-treatment imaging. CONCLUSION: The progressive changes in osteoblastic bone metastases on CBCT highlight its potential usefulness in daily monitoring and evaluation during radiotherapy.