Is interim (18)F-fluoride PET/CT a predictor of outcomes after radium-223 therapy?

OBJECTIVE: To determine whether an interim (18)F-fluoride positron-emission tomography/computed tomography (PET/CT) study performed after the third cycle of radium-223 dichloride ((223)RaCl(2)) therapy is able to identify patients that will not respond to treatment. MATERIALS AND METHODS: We retrospectively reviewed 34 histologically confirmed cases of hormone-refractory prostate cancer with bone metastasis in patients submitted to (223)RaCl(2) therapy. All of the patients underwent baseline and interim (18)F-fluoride PET/CT studies. The interim study was performed immediately prior to the fourth cycle of (223)RaCl(2). The skeletal tumor burden-expressed as the total lesion fluoride uptake above a maximum standardized uptake value of 10 (TLF(10))-was calculated for the baseline and the interim studies. The percent change in TLF(10) between the baseline and interim studies (%TFL(10)) was calculated as follows: %TFL(10) = interim TLF(10) - baseline TLF(10) / baseline TLF(10). End points were overall survival, progression-free survival, and skeletal-related events. RESULTS: The mean age of the patients was 72.4 ± 10.2 years (range, 43.3-88.8 years). The %TLF(10) was not able to predict overall survival (p = 0.6320; hazard ratio [HR] = 0.753; 95% confidence interval [CI]: 0.236-2.401), progression-free survival (p = 0.5908; HR = 1.248; 95% CI: 0.557-2.797) nor time to a bone event (p = 0.5114; HR = 1.588; 95% CI: 0.399-6.312). CONCLUSION: The skeletal tumor burden on an interim (18)F-fluoride PET/CT, performed after three cycles of (223)RaCl(2), is not able to predict overall survival, progression-free survival, or time to bone event, and should not be performed to monitor response at this time.