Jans Hans-S, Stypinski Daria, Kumar Piyush, Mercer John R, McQuarrie Stephen A, McEwan Alexander J B, Wiebe Leonard I
Department of Oncology, University of Alberta, Edmonton, AB T6G 1Z2, Canada.
Pfizer Inc., New York, NY 10017, USA.
Pharmaceutics. 2022 Aug 9;14(8):1655. doi: 10.3390/pharmaceutics14081655.
Theragnostic pairs of isotopes are used to infer radiation dosimetry for a therapeutic radiopharmaceutical from a diagnostic imaging study with the same tracer molecule labelled with an isotope better suited for the imaging task. We describe the transfer of radiation dosimetry from the diagnostic radioiodine isotope I, labelled for the hypoxia tracer molecule iodoazomycin arabinoside ([I]IAZA), to isotopes I (therapeutic) and I (PET imaging). Uncertainties introduced by the dissimilar isotope half-lives are discussed in detail. Radioisotope dosimetries for [I]IAZA were obtained previously. These data are used here to calculate residence times for I and I and their uncertainties. We distinguish two cases when extrapolating to infinity: purely physical decay (case A) and physical decay plus biological washout (case B). Organ doses were calculated using the MIRD schema with the OLIDNA/EXM code. Significant increases in some organ doses (in mSv per injected activity) were found for I and I. The most affected organs were the intestinal walls, thyroid, and urinary bladder wall. Uncertainty remained similar to I for case A but considerably greater for case B, especially for long biological half-lives (GI tract). Normal tissue dosimetries for IAZA must be considered carefully when substituting isotope species. A long biological half-life can significantly increase dosimetric uncertainties. These findings are relevant when considering PET imaging studies with [I]IAZA or therapeutic administration of [I]IAZA.
治疗诊断同位素对用于通过使用标记有更适合成像任务的同位素的相同示踪分子进行诊断成像研究来推断治疗性放射性药物的辐射剂量学。我们描述了辐射剂量学从标记用于缺氧示踪分子碘氮霉素阿拉伯糖苷（[I]IAZA）的诊断放射性碘同位素I，转移到同位素I（治疗用）和I（PET成像）的情况。详细讨论了由不同同位素半衰期引入的不确定性。先前已获得[I]IAZA的放射性同位素剂量学数据。此处使用这些数据来计算I和I的驻留时间及其不确定性。在外推至无穷大时，我们区分两种情况：纯物理衰变（情况A）和物理衰变加生物清除（情况B）。使用带有OLIDNA/EXM代码的MIRD模式计算器官剂量。发现I和I的某些器官剂量（每注射活度的mSv）有显著增加。受影响最大的器官是肠壁、甲状腺和膀胱壁。情况A的不确定性与I相似，但情况B的不确定性要大得多，尤其是对于长生物半衰期（胃肠道）。在替代同位素种类时，必须仔细考虑IAZA的正常组织剂量学。长生物半衰期会显著增加剂量学不确定性。在考虑使用[I]IAZA进行PET成像研究或[I]IAZA的治疗给药时，这些发现具有相关性。
