Radiation doses of yttrium-90 citrate and yttrium-90 EDTMP as determined via analogous yttrium-86 complexes and positron emission tomography

Yttrium-90 is used for palliative therapy for the treatment of skeletal metastases, but because it is a pure beta(-) emitter, data on the pharmacokinetics and radiation doses to metastases and unaffected organs are lacking. To obtain such data, the present study employed yttrium-86 as a substitute for Y-90, with detection by positron emission tomography (PET). The study compared the properties of two different Y-86 complexes - Y-86-citrate and Y-86-ethylene diamine tetramethylene phosphonate (EDTMP) - in ten patients with prostatic cancer who had developed multiple bone metastases (the ten patients being divided into two groups of five). Early dynamics were measured up to 1 h post injection (p.i.) over the liver region, followed by subsequent whole-body PET scans up to 3 days p.i. Absolute uptake 3 data were determined for normal bone, bone metastases, liver and kidney. Radiation doses were calculated according to the MIRD recommendations. Based on the pharmacokinetic measurements of the distribution of the Y-86 complexes, it was possible to calculate radiation doses for the bone metastases and the red bone marrow delivered by complexes containing Y-90. In 1 cm(3) of bone metastasis, doses of 26 +/- 11 mGy/MBq and 18 +/- 2 mGy/MBq were determined per MBq of injected Y-90-citrate and Y-90-EDTMP, respectively. The doses to the bone marrow were 2.5 +/- 0.4 mGy/MBq for Y-90-citrate and 1.8 +/- 0.6 mGy/MBq for Y-90-EDTMP. Y-86 and PET provide quantitative information applicable to the clinical use of Y-90. This method may also be useful for the design of other Y-90 radiopharmaceuticals and for planning radiotherapy dosages.