Abstract
INTRODUCTION: Radiotherapy for widespread bone metastasis results in severe hematological toxicity. CASE PRESENTATION: A 71-year-old male was diagnosed with metastatic hormone-sensitive prostate cancer (cT4N1M1b) and treated with apalutamide and degarelix. Concurrently, palliative radiation therapy was sequentially initiated for the 1st, 5th, and 10th thoracic vertebrae and right femur. On day 35 after treatment, severe neutropenia necessitated treatment interruption and required 23 days for neutrophil recovery with a granulocyte colony-stimulating factor agent. CONCLUSION: Owing to the severe hematologic toxicity caused by extensive radiation therapy for multiple bone lesions, treatment prioritization by lesion and avoiding irradiation of the red bone marrow is essential.