[Radiopharmacokinetic and gammagraphic studies for calculating personalized dosimetry]

In nuclear medicine radiation absorbed doses are important in the patient's risk/benefit evaluation and are estimated by means of biological and complex mathematical models. The biological model includes radiopharmacokinetic data obtained through blood and urine samples taken at given intervals. A useful mathematical model is the MIRD model and with the value for the time of residence tau the MIRDOSE3 computer program uses several anatomic models and calculates radiation absorbed dose for 25 organs. At the Radiopharmacy Unit of the Nuclear Medicine Department at INCMNSZ two new bone seeking radiopharmaceuticals, 99mTc-ABP and 188Re-ABP, have been designed, characterized and animal-tested. Radiopharmaceutical parameters and sequential scanning were obtained for diagnostic 99mTc-ABP in 10 normal subjects and the aim was to use % 24 hour urine elimination and % bone uptake to calculate radiation absorbed dose and extrapolate the values to 188Re-ABP as the basis for a therapeutic treatment. 99mTc-ABP was eliminated in women's urine 63.2 +/- 7.3%/activity and 70 +/- 11%/activity in men. In women 36.8 +/- 7.3% of the radiopharmaceutical remains on the bone surface and in men 30 +/- 11%. ROIs were drawn on the images and the time-integrated renal cpm/pixel/ROI gave a residence time tau = 0.52 h. Cumulative bone activity A calculated with A = 1.443 (T1/2) A0 was 2358 +/- 469 MBq h for women and 1923 +/- 707 MBq h for men. Residence time tau was 3.19 +/- 0.63 h in women and 2.6 +/- 0.95 h in men. Radiation absorbed dose for the whole body was 0.0020 +/- 0.0004 mGy/MBq for women and 0.0013 +/- 0.0005 mGy/MBq for men. For women's bone marrow it was 0.0063 +/- 0.0013 mGy/MBq and for men 0.0041 +/- 0.0015 mGy/MBq. 188Re-ABP behaves as 99mTc-ABP therefore, the effective dose given by 188Re, a beta emitter, would be for women 0.0936 mSv/MBq and for men 0.0608 mSv/MBq. These characteristics and the radionuclidic characteristics of 188Re indicate that 188Re-ABP might be a good bone metastases pain palliation radiopharmaceutical.