The aim of this proof-of-concept study is to propose a simplified personalized kidney dosimetry procedure in ¹⁷⁷ Lu peptide receptor radionuclide therapy (PRRT) for neuroendocrine tumors and metastatic prostate cancer. It relies on a single quantitative SPECT/CT acquisition and multiple radiometric measurements executed with a collimated external probe, properly directed on kidneys.
We conducted a phantom study involving external count-rate measurements in an abdominal phantom setup filled with activity concentrations of ^99m Tc, reproducing patient-relevant organ effective half-lives occurring in ¹⁷⁷ Lu PRRT. GATE Monte Carlo (MC) simulations of the experiment, using ^99m Tc and ¹⁷⁷ Lu as sources, were performed. Furthermore, we tested this method via MC on a clinical case of ¹⁷⁷ Lu-DOTATATE PRRT with SPECT/CT images at three time points (2, 20 and 70 hrs), comparing a simplified kidney dosimetry, employing a single SPECT/CT and probe measurements at three time points, with the complete MC dosimetry.
The experimentally estimated kidney half-life with background subtraction applied was compatible within 3% with the expected value. The MC simulations of the phantom study, both with ^99m Tc and ¹⁷⁷ Lu, confirmed a similar level of accuracy. Concerning the clinical case, the simplified dosimetric method led to a kidney dose estimation compatible with the complete MC dosimetry within 6%, 12% and 2%, using respectively the SPECT/CT at 2, 20 and 70 hrs.
The proposed simplified procedure provided a satisfactory accuracy and would reduce the imaging required to derive the kidney absorbed dose to a unique quantitative SPECT/CT, with consequent benefits in terms of clinic workflows and patient comfort.