Final outcome of²²³Ra-therapy and the role of¹⁸F-fluoride-PET in response evaluation in metastatic castration-resistant prostate cancer–a single institution experience

Background:²²³Ra was the first therapeutic alpha-emitting radionuclide registered for clinical practice. This radionuclide is targeting actively bone-forming cells, and it is approved for treating metastatic skeletal disease in prostate cancer.¹⁸F-PET is used to detect skeletal metastatic disease based on osteoblastic activity. The aim of this study was to analyze, if¹⁸F-PET can be used assessing the results of²²³Ra therapy, and to report final median overall survival in a total of 773 therapy cycles. Methods: A 161 men with castration-resistant prostate cancer were included in a single institution study (Protocol#: PA14-0848) and they received a total of 773²²³Ra therapy cycles. Results: The median overall survival (95% CI) was 12.4 (9.1, 16.1) months in patient population. Interim Na¹⁸F-PET imaging was applied in 14 patients at baseline, after 3 cycles and after 6 cycles. TLF₁₀ (skeletal disease burden at SUV-values >10 on Na¹⁸F-PET) were calculated in all these PET studies, and there was no significant association between change in TLF₁₀ after 3 cycles and TLF₁₀ after 6 cycles (p=0.20). Conclusion: From these results, we conclude that interim imaging does not help in assessing the final outcome of²²³Ra therapy. The survival benefit of²²³Ra therapy alone is more than a year in a high-risk group of advanced prostate cancer.