False-Positive Findings on Bone Scintigraphy After MRI-Guided Stereotactic Ablative Radiotherapy for Osseous Oligometastasis.

Radical radiation therapy for oligorecurrent prostate cancer is considered to improve both overall and disease-specific survival. Therefore, accurate diagnosis by imaging is important when considering the indications for radiation therapy. We present a case of marginal recurrence of bone metastases from castration-resistant prostate cancer previously treated with radical radiation therapy, which could not be detected by bone single photon emission computed tomography/computed tomography (SPECT/CT) but could be diagnosed by 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT). Bone SPECT/CT showed false-positive tracer uptake in the lesion previously irradiated. 68Ga-PSMA PET/CT scan showed no abnormal uptake in the previously irradiated lesion, but showed intense uptake in the newly developed metastasis near the irradiated site. 68Ga-PSMA PET/CT scan may be able to diagnose marginal recurrence after radiation therapy more accurately than bone SPECT/CT.