Radiation Dosimetry of Theragnostic Pairs for Isotopes of Iodine in IAZA

Abstract

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 123I, labelled for the hypoxia tracer molecule iodoazomycin arabinoside ([123I]IAZA), to isotopes 131I (therapeutic) and 124I (PET imaging). Uncertainties introduced by the dissimilar isotope half-lives are discussed in detail. Radioisotope dosimetries for [123I]IAZA were obtained previously. These data are used here to calculate residence times for 131I and 124I 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 131I and 124I. The most affected organs were the intestinal walls, thyroid, and urinary bladder wall. Uncertainty remained similar to 123I 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 [124I]IAZA or therapeutic administration of [131I]IAZA.

Comparisons between Criteria for Successful Radioiodine Remnant Ablation in a cohort of Patients with Papillary Thyroid Carcinoma

“…Firstly, unlike thyroid carcinoma, which exhibits varying degrees of cellular differentiation (19), thyroid remnant maintains a su cient to capture and retain 131 I, owing to the relatively intact structure and function pertaining to thyroid hormone synthesis (20). Secondly, bene ting from the proper physical halflife and the availability, 131 I has emerged as the preferred radiotracer in detecting for residual thyroid within a much longer period of time when the accumulation of iodine peeks (nearly 24 hours post oral administration), compared to its intravenous injected isotopes, 124 I and 123 I (21,22). Thirdly, advancements in SPECT technology, particularly in the e ciency of photon detection, coupled with the integration of CT component, have rendered DxWBS conducted 24 h after the administration of as low as 74 MBq of 131 I feasible and reasonable (16).…”

Peelable Nanocomposite Coatings: “Eco-Friendly” Tools for the Safe Removal of Radiopharmaceutical Spills or Accidental Contamination of Surfaces in General-Purpose Radioisotope Laboratories

“…The primary goal of radiopharmacy in nuclear medicine is to use radiolabeled compounds for diagnostic [1] and therapeutic [2] purposes. Because the treatment frequently targets life-threatening diseases, the benefits of using radionuclides exceed the risks.…”