Excretion and whole-body retention of radium-223 dichloride administered for the treatment of bone metastases from castration resistant prostate cancer.

Abstract

OBJECTIVE: The aim of the study was to determine the fraction of administered activity that was excreted and retained by a small cohort of patients who each received treatment with radium-223 dichloride (Ra). Ra is an α-emitting radionuclide that has been approved for use in the treatment of bone metastases that are secondary to castration resistant prostate cancer. PATIENTS AND METHODS: Six patients received two weight-based administrations of Ra 6 weeks apart. Activity excreted in the urine and faeces during the first 48 h following each treatment was assessed by direct counting of the excreta. During the same period the whole-body retention of Ra was also determined using a single probe counting system. The results of the excreta counting and the whole-body counting were compared to determine whether whole-body counting was a suitable surrogate for assessing excretion. Further whole-body retention counts were made at around 3, 4, 7 and 42 days following treatment. RESULTS: Patterns of excretion and retention of Ra varied significantly between patients, but were similar for each patient's pair of treatments. The cumulative maximum activity excreted in the initial 8-h period following the Ra administration was 2.6% that increased to 39% at 48 h. The median excreted activity at ~1 and 6 weeks after treatment was 70 and 86%, respectively. Skeletal retention of Ra at 6 weeks ranged from 11 to 60% of the administered activity.