Stereotactic Body Radiotherapy for a Sacral Metastasis Clarified by Diffusion-Weighted Whole-Body Imaging With Background Body Signal Suppression in a Patient With Castration-Resistant Prostate Cancer

Diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) is an emerging extended modality of diffusion-weighted imaging for screening malignant lesions in the body. A 70-year-old male was diagnosed with advanced-stage prostate adenocarcinoma with distant metastasis. After hormone therapy, the disease progressed to castration-resistant prostate cancer (CRPC). Serum prostate-specific antigen (PSA) levels increased during androgen deprivation therapy with low serum testosterone levels. 18F-Fluorodeoxyglucose positron emission tomography (FDG-PET) and technetium-99m methylene bone scintigraphy (BS) did not reveal obvious distant metastases; however, we were able to identify distant metastases by DWIBS. We herein report a case in which stereotactic body radiotherapy (SBRT) was performed on target lesions detected by DWIBS and successfully suppressed disease progression.