Improvement of ¹⁷⁷Lu-DOTATATE Post-Treatment Protocol.

Purpose

Peptide Receptor Radionuclide Therapy (PRRT) with [¹⁷⁷Lu]-DOTA-TATE is an effective treatment of neuroendocrine tumors (NETs). After each cycle of treatment, patient dosimetry evaluates the radiation dose to "risk organs", kidneys and bone marrow. Absorbed doses are calculated from the radioactivity in blood and Single Photon Emission Computed Tomography (SPECT) images corrected by Computed Tomography (CT) acquired after each course of treatment. The aim of this work is to assess whether the dosimetry along all treatment cycles can be calculated using a single CT. We hypothesize that the absorbed doses to risk organs calculated with a single CT will be accurate enough to correctly manage the patients, i.e., whether or not to continue PRRT.

Methods

Twenty-four patients diagnosed with metastatic NETs undergoing PRRT with [¹⁷⁷Lu]-DOTA-TATE were retrospectively included in this study. We compared radiation doses to kidneys and bone marrow using two protocols. In the "classical" one, dosimetry is calculated based on a SPECT and a CT after each treatment cycle. In the new protocol, dosimetry is calculated based on a SPECT study after each cycle but with the first acquired CT for all cycles.

Results

The decision whether or not to stop PRRT because of unsafe absorbed dose to risk organs would have been the same had the classical or the new protocol been used. The agreement between the cumulative doses to kidneys and bone marrow obtained from the two protocols was excellent with a Pearson’s correlation coefficient r = 0.95 and r = 0.99 (P < 0.0001) and a mean relative difference of 5.30% ± 6.20% and 0.48% ± 4.88%, respectively.

Conclusions

The null hypothesis, supposing no difference in the patients management between the two protocols, cannot be rejected. Dosimetry calculations for a given patient`s can be done using a single CT registered to serial SPECTs. This new protocol would allow, for instance, small local centers equipped with γ-camera only to perform personalized dosimetry using a previous acquired CT.