EVALUATION OF THROMBOCYTOPENIA IN PATIENTS TREATED WITH RHENIUM-186-HEDP - GUIDELINES FOR INDIVIDUAL DOSAGE RECOMMENDATIONS

A potential limitation of rhenium-186-1,l-hydroxyethylidene diphosphon ate (Re-186-HEDP) therapy in patients with painful bone metastases is thrombocytopenia. Given the palliative character of this therapy, it i s essential to be able to predict the degree of thrombocytopenia befor e therapy. Methods: Thus far, 39 prostatic cancer patients with multip le painful bone metastases were treated. Twenty-one patients underwent the therapy twice, resulting in 60 therapies. From the pre-therapy Tc -99m-HDP scintigram, the bone scan index (BSI) was determined as an in dex of the extent of bone involvement. Results: The administered activ ity ranged from 1104 to 3479 MBq Re-186-HEDP. The platelet count was l owest 4 wk following therapy. From this value and the pretreatment lev el, the percentage decrease in the platelet count was determined (47% +/- 19%, range 14%-89%). The BSI ranged from 8 to 93. Regression analy sis showed a functional relation (R = 0.78; p < 0.001) of the percenta ge of platelet decrease with BSI and administered activity normalized to standard body surface area. Conclusion: Using this relation, it is possible to predict thrombocytopenia by pretreatment bone scintigraphy and to adjust the dosage to each patient to avoid unacceptable toxici ty.