title: Relative biological effectiveness of 99mTc radiopharmaceuticals.
abstract: The radiotoxicity of three 99mTc-labeled compounds is investigated using spermatogenesis in mouse testis as the experimental model, and spermatogonial cell survival as the biological end point. The radiopharmaceuticals studied are pertechnetate (99mTcO4-), pyrophosphate (99mTc-PYP), and hydroxyethylene diphosphate (99mTc-HDP). The mean lethal doses at 37% survival (D37) are 0.70 +/- 0.06, 0.84 +/- 0.13, and 0.59 +/- 0.08 Gy for 99mTcO4-, 99mTc-PYP, and 99mTc-HDP, respectively. When these results are compared with the D37 value obtained with external x rays or internal gamma rays, the relative biological effectiveness (RBE) of these compounds are 0.94 +/- 0.09, 0.79 +/- 0.13, and 1.1 +/- 0.16, respectively. These results show that the radiotoxicity of 99mTc in mouse testis is essentially similar to that of low-LET radiations (i.e., RBE approximately 1). To understand these results, the distribution of these radiocompounds in the testis is determined and correlated with the observed RBE values. The expected range of RBE values for 99mTc radiopharmaceuticals in organs is 0.95 to 1.5, depending on the fraction of organ activity that is bound to DNA. This suggests that the Auger electrons emitted in the decay of 99mTc are not capable of causing extreme toxicity in vivo. These results provide further support for 99mTc as the radionuclide of choice for imaging in nuclear medicine.
authors.affiliation: Department of Radiology, University of Medicine and Dentistry of New Jersey, Newark 07103.
authors.forename: V R
authors.initials: VR
authors.lastname: Narra
authors.forename: K S
authors.initials: KS
authors.lastname: Sastry
authors.forename: S M
authors.initials: SM
authors.lastname: Goddu
authors.forename: R W
authors.initials: RW
authors.lastname: Howell
authors.forename: S E
authors.initials: SE
authors.lastname: Strand
authors.forename: D V
authors.initials: DV
authors.lastname: Rao
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002470:Cell Survival / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D012968:Etidronic Acid / Q000493:pharmacokinetics / Q000633:toxicity; D006801:Humans; D008297:Male; D051379:Mice; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics / Q000633:toxicity; D012062:Relative Biological Effectiveness; D013670:Sodium Pertechnetate Tc 99m / Q000493:pharmacokinetics / Q000633:toxicity; D013091:Spermatogenesis / Q000528:radiation effects; D013667:Technetium / Q000633:toxicity*; D016698:Technetium Tc 99m Pyrophosphate / Q000493:pharmacokinetics / Q000633:toxicity; D013737:Testis / Q000166:cytology / Q000528:radiation effects
chemical_list: D015609:Organotechnetium Compounds; C019561:technetium Tc 99m etidronate; D016698:Technetium Tc 99m Pyrophosphate; D013667:Technetium; D013670:Sodium Pertechnetate Tc 99m; D012968:Etidronic Acid