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

ObjectiveThe 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-223). Ra-223 is an -emitting radionuclide that has been approved for use in the treatment of bone metastases that are secondary to castration resistant prostate cancer.Patients and methodsSix patients received two weight-based administrations of Ra-223 6 weeks apart. Activity excreted in the urine and faeces during the first 48h following each treatment was assessed by direct counting of the excreta. During the same period the whole-body retention of Ra-223 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.ResultsPatterns of excretion and retention of Ra-223 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-223 administration was 2.6% that increased to 39% at 48h. The median excreted activity at similar to 1 and 6 weeks after treatment was 70 and 86%, respectively. Skeletal retention of Ra-223 at 6 weeks ranged from 11 to 60% of the administered activity.