A comparison of simplified protocols of personalized dosimetry in NEN patients treated by Radio Ligand Therapy (RLT) with [177Lu]Lu-DOTATATE to favour its use in clinical practice.

The role of internal dosimetry is usually proposed for investigational purposes in patients treated by RLT; while the application in clinical practice is still very restricted. The limited application is partially justified by the use of fixed doses, the lack of well established methods to calculate absorbed doses to organ at risk and tumours, the time consuming needed for imaging and calculations, the lack of trained, highly-specialized personal, and the discomfort to the patients for the numerous and prolonged sessions of imaging. Methods: In our series thirty patients with NENs, candidate to RLT with Lutathera®, dosimetry was performed after each of the four cycles and used as reference method (M0). Data were then used to assess the feasibility of simplified, lighter, protocols: defining the dosimetry after the first cycle only (M1) and after the first and last cycles (M2). Results: The mean difference, comparing the cumulative absorbed dose (cAD) obtained with M1 and M0, was: -10% for kidneys, -5% for spleen, +34% for liver, +13% for red marrow and +37% for tumour lesions. Such differences decreased comparing cAD obtained with M2 and M0: -3% for kidneys, -0,3% for spleen, +6% for liver, +3% for red marrow and 6% for tumour lesions. Conclusions: The dosimetry established by M2 protocol was not statistically different from that calculated by M0; while M1 overestimates for all OARs but spleen