Targeted radionuclide therapy (TRT) is recognized as an effective means for treating a variety of cancers (1), ranging from conventional 131I-radioiodine for differential thyroid carcinoma (DTC), 223Ra-Dichloride for bone metastasis of castration-resistant prostate cancer (CRPC), 90Y microspheres for hepatic cancers, to newly EMA (Europe) and FDA (USA) approved 177Lu-DOTATATE Peptide Receptor Radionuclide Therapy (PRRT) for neuroendocrine tumors. Furthermore, several other therapeutic agents including 177Lu-PSMA for prostate cancers and alpha-particle emitters for treating different cancers are in clinical trial or are being developed and evaluated (2). Personalized treatment planning can ensure TRT efficacy while avoiding potential toxicity to critical organs by considering patient-specific pharmacokinetics. Sequential radionuclide imaging following a pre-therapy tracer administration can serve as a non-invasive tool for predicting the radiation absorbed doses delivered to tumor and critical organs by the therapy. In the case of therapies administered over multiple cycles, such as 177Lu-DOTATATE, imaging-based dosimetry after one cycle can be used to predict the absorbed doses that will be delivered by subsequent cycles for consideration of potential dosage adjustment. Quantitative emission computed tomography (ECT), i.e., single photon emission computed tomography (SPECT) and positron emission tomography (PET), provides 3-dimensional (3D) activity distributions for voxel-level dosimetry, which is of increasing research and commercial interest in TRT (3,4). Sequential ECT images can be directly converted to dose-rate maps or a time integrated activity (TIA) map, which can then be converted to an absorbed dose map.
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