Contraindications To The Use Of Radiopharmaceuticals For Pain Relief
A single site of bone pain should receive teletherapy. Metastatic disease detected radiographically where there is no osteoblastic response (i.e., a bone scan showing no abnormality in the painful site) as, for example, in about half of the myeloma patients, should not be treated with these agents, as there will be no localization where the Tc-99m medronate or oxidronate bone scan shows no increased uptake. In painful sites where marked osteolysis (over 50% of the cortex destroyed by tumor) is radiographically apparent, teletherapy is required, often accompanied by prophylactic orthopedic intervention, to avoid pathologic fracture. A pathologic fracture is quite painful and will, of course, not respond to radiopharmaceutical therapy despite the abnormal bone scan at the site. Cord compression and epidural metastases should be dealt by employing teletherapy and/or surgery but not with beta emitters. Nonosseous sources for pain referred to bony sites must be carefully excluded, as clearly these radiopharmaceuticals will be ineffective in this clinical setting.
There are also hematologic contraindications to the use of these radiophar-maceuticals. Significant cytopenias (pretreatment leukocyte count below about 2500-3000/ul, absolute neutrophil count below 1000/ul, platelet count below 60,000-100,000/ul) raise the risks for infection and bleeding. It should be recalled that there are other reasons for pancytopenia in cancer patients, including recent or concurrent chemotherapy or radiotherapy, marrow involvement by tumor, and disseminated intravascular coagulation.
Disseminated intravascular coagulation (DIC) is usually subclinical and has been reported in up to 10% to 20% of prostate cancer patients. In this entity, megakaryocyte production and turnover are greatly increased to provide the maximum platelet supply possible, and these platelets have very short half-lives as they participate in the ongoing clotting process. In this disorder, suppression of megakaryocyte production by these beta emitters can lead to precipitous and life-threatening thrombocytopenia, so very active DIC is a relative contraindication to the use of these radiopharmaceuticals. A search for fibrin split products is a far more sensitive test for DIC than the platelet count.