NaF PET/CT for response assessment of prostate cancer bone metastases treated with single fraction stereotactic ablative body radiotherapy

INTRODUCTION: In prostate cancer patients, imaging of bone metastases is enhanced through the use of sodium fluoride positron emission tomography ((18)F-NaF PET/CT). This imaging technique shows areas of enhanced osteoblastic activity and blood flow. In this work, (18)F-NaF PET/CT was investigated for response assessment to single fraction stereotactic ablative body radiotherapy (SABR) to bone metastases in prostate cancer patients. METHODS: Patients with bone metastases in a prospective trial treated with single fraction SABR received a (18)F-NaF PET/CT scan prior to and 6 months post-SABR. The SUV(max) in the tumour was determined and the difference between before and after SABR determined. The change in uptake in the non-tumour bone was also measured as a function of the received SABR dose. RESULTS: Reduction in SUV(max) was observed in 29 of 33 lesions 6 months after SABR (mean absolute decrease in SUV(max) 17.7, 95% CI 25.8 to − 9.4, p = 0.0001). Of the three lesions with increased SUV(max) post-SABR, two were from the same patient and located in the vertebral column. Both were determined to be local progression in addition to one fracture. The third lesion (in a rib) was shown to be controlled locally but suffered from a fracture at 24 months. Progression adjacent to the treated volume was observed in two patients. The non-tumour bone irradiated showed increased loss in uptake with increasing dose, with a median loss in uptake of 23.3% for bone receiving 24 Gy. CONCLUSION: (18)F-NaF PET/CT for response assessment of bone metastases to single fraction SABR indicates high rates of reduction of osteoblastic activity in the tumour and non-tumour bone receiving high doses. The occurrence of marginal recurrence indicates use of larger clinical target volumes may be warranted in treatment of bone metastases. TRIAL REGISTRATION: POPSTAR, ‘Pilot Study of patients with Oligometastases from Prostate cancer treated with STereotactic Ablative Radiotherapy’, Universal Trial Number U1111-1140-7563, Registered 17th April 2013. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13014-019-1359-0) contains supplementary material, which is available to authorized users.