Twins in spirit part IV – [177Lu] high affinity DOTATATE

Abstract

Summary Aim: Besides the use of somatostatin analogues, small molecules like sunitinib and everolimus as well as conventional chemotherapy, peptide receptor radiotherapy (PRRT) using radiolabelled somatostatin analogues has gained an important role in the treatment of inoperable, metastasized neuroendocrine tumours (NET). There are various radiotracers in use. Based on our experience with the PET tracer [68Ga]DOTA-3-iodo- Tyr3-octreotate ([68Ga]HA-DOTATATE), a DOTATATE derivative with an increased binding affinity to hsst5, the current retrospective analysis is exploring the therapeutic potential of [177Lu]HA-DOTATATE. Methods: Eighteen patients with metastatic NET (G1/G2) were treated using [177Lu]DOTATATE and/or [177Lu]HA-DOTATATE, and dosimetric results of both tracers were compared. Results: Using [177Lu]HA-DOTATATE, a mean tumour dose of 5.34 Gy/GBq (median 2.53 Gy/ GBq; range 0.89-33.3 Gy/GBq) was achieved, while [177Lu]DOTATATE delivered a tumour dose of 5.53 Gy/GBq (median 2.70 Gy/GBq; range 0.44-15.3 Gy/GBq). Organ doses for [177Lu]HA-DOTATATE vs. [177Lu]DOTATATE were as follows: kidney 2.31 ± 0.85 vs. 2.03 ± 0.96 Gy/GBq, liver 1.6 ± 0.79 vs. 1.67 ± 1.73 Gy/GBq, spleen 3.89 ± 4.04 vs. 4.50 ± 3.69 Gy/GBq and whole body 0.16 ± 0.10 Gy/GBq vs. 0.15 ± 0.08 Gy/ GBq. Tumour-to-kidney dose ratio was slightly higher for [177Lu]DOTATATE (2.4 ± 5.6) compared to [177Lu]HA-DOTATATE (1.5 ± 3.6). Conclusion: Both tracers showed marked inter-patient variation in their dosimetry, and no significant differences in dosimetry of [177Lu]HA- DOTATATE and [177Lu]DOTATATE were observed when taking all patients into account. Thus, [177Lu]HA-DOTATATE appears viable for PRRT, although it was marginally inferior regarding kidney dose and tumour-to-kidney dose ratio compared to the established [177Lu]DOTATATE.