Predictive value of interim ¹¹C-choline PET/CT for response to radium-223 in metastatic castration-resistant prostate cancer.

Abstract

BACKGROUND: Radium-223 (Ra-223) has been approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC) with predominant osseous metastases. PSA flare phenomenon with Ra-223 limits its use as a prognostic tool to predict treatment response. Currently, there is a lack of diagnostic tools to predict treatment response to Ra-223. Therefore, we sought to investigate the role of mid treatment C-11 choline PET/CT scan in predicting overall response to Ra-223. In a single institute retrospective study, we identified 32 patients who were treated with a full course of 4–6 cycles of Ra-223 and were evaluated with PSA, and C-11 choline PET scan before treatment, at mid-treatment point, and after complete course of Ra-223 between 2013 and 2018. Ra-223 was used as a salvage therapy for their predominant bone disease after failing chemotherapy and 2nd generation hormone therapy. Blind repeat radiographic evaluation of patients’ scans has been done by a radiologist specialized in nuclear medicine. Favorable response was defined by achieving partial response or stable disease on imaging, while unfavorable response was defined by showing progressive disease on imaging. RESULTS: Mean age (± SD) at starting Radium223 was 67.6 (± 7.1) years, median (IQR) primary Gleason score was 9 (8–9), and median (IQR) pretreatment PSA was 13.5 (5.4–39.6) ng/ml. 78% of the patients (n = 25) completed 6 cycles of Ra-223, and 15% of the patients (n = 5) completed 5 cycles while 6% (n = 2) received only 4 cycles. At mid treatment scanning, 25% of the patient (n = 8) showed favorable response (Group A), while 75% of the patients (n = 24) showed unfavorable response (B). After complete course of treatment, 50% of patients (n = 4) in Group (A) continued to show favorable response, versus only 8.3% of patients (n = 2) in Group (B) showed favorable response (p-value = 0.023). CONCLUSION: Mid treatment evaluation with C-11 choline PET/CT scan can predict overall response to Radium 223. Patients with progressive disease at mid- treatment evaluation are very likely not going to respond to their treatment. Further studies and clinical trials are warranted.