MEASUREMENT OF PHARMACOKINETICS OF YTTRIUM-86 RADIOPHARMACEUTICALS WITH PET AND RADIATION-DOSE CALCULATION OF ANALOGOUS Y-90 RADIOTHERAPEUTICS

This study was performed to demonstrate the quantitative in vivo asses sment of human pharmacokinetics of Y-90-radiotherapeuties using the po sitron-emitting substitute Y-86 and PET. This technique is illustrated in a patient with disseminated bone metastases from breast cancer who was injected with 100 MBq of Y-86-citrate as an analog of the commerc ially available radiotherapeutic Y-90-citrate. Whole-body distribution was measured with a PET camera 4, 10, 21, 23 and 45 hr postinjection. Uptake data were determined from reconstructed transverse PET images by regions of interest placed in normal bone tissue, liver and metasta ses. Images of coronal and sagittal whole-body sections were obtained by reformatting the transverse PET images. The ratio of activity conce ntration in metastases to that in normal bone ranged from 1.5:1 to 3.5 :1. Of the injected tracer, 13.4% was found in the skeleton and 0.43% in the metastasis with the highest Y-86 concentration. Radiation doses per 1 MBq of injected Y-90-citrate were calculated from Y-86-citrate data and data from MIRD pamphlets 5 and 11. The doses were 1.01 MGy/MB q for red marrow, 593 mu Gy/MBq for the liver and similar to 3.5 MGy/M Bq for the most conspicuous metastases. This study demonstrates that t he use of PET via Y-86 allows an individual in vivo quantification of activity uptake and radiation dose of both normal tissue and tumor in pain treatment with Y-90-labeled radiotherapeutics.