89Sr radionuclide therapy: dosimetry and haematological toxicity in two patients with metastasising prostatic carcinoma.

We present dosimetry for spinal metastases and red bone marrow in two patients who received 89Sr therapy for disseminated prostatic carcinoma. Absorbed dose to metastases was estimated by combining 85Sr gamma camera studies with computed tomographic measurements of bone mass, and doses of 20 cGy/MBq and 24 cGy/MBq were found for vertebral metastases that uniformly involved the bodies of L3 and D12 respectively. Absorbed dose to red bone marrow was estimated from total body strontium retention studies using the ICRP model for bone dosimetry, and a ratio of metastatic to marrow dose of around 10 was found in each patient. Although they received comparable treatment activities of around 200 MBq, the patients showed markedly different haematological response, this difference being confirmed when each received a second 89Sr treatment 6 months after the first. As a result, clinically significant thrombocytopenia occurred in one patient which prevented further radiostrontium therapy being given.