[18F]AlF-NOTA-octreotide PET imaging: biodistribution, dosimetry and first comparison with [68Ga]Ga-DOTATATE in neuroendocrine tumour patients

Purpose The widespread use of gallium-68-labelled somatostatin analogue (SSA) PET, the current standard for somatostatin receptor (SSTR) imaging, is limited by practical and economic challenges that could be overcome by a fluorine-18-labelled alternative, such as the recently introduced [F-18]AlF-NOTA-octreotide ([F-18]AlF-OC). This prospective trial aimed to evaluate safety, dosimetry, biodistribution, pharmacokinetics and lesion targeting of [F-18]AlF-OC and perform the first comparison with [Ga-68]Ga-DOTATATE in neuroendocrine tumour (NET) patients. Methods Six healthy volunteers and six NET patients with a previous clinical [Ga-68]Ga-DOTATATE PET were injected with an IV bolus of 4 MBq/kg [F-18]AlF-OC. Healthy volunteers underwent serial whole-body PET scans from time of tracer injection up to 90 min post-injection, with an additional PET/CT at 150 and 300 min post-injection. In patients, a 45-min dynamic PET was acquired and three whole-body PET scans at 60, 90 and 180 min post-injection. Absorbed organ doses and effective doses were calculated using OLINDA/EXM. Normal organ uptake (SUVmean) and tumour lesion uptake (SUVmax) and tumour-to-background ratio (TBR)) were measured. A lesion-by-lesion analysis was performed and the detection ratio (DR), defined as the fraction of detected lesions was determined for each tracer. Results [F-18]AlF-OC administration was safe and well tolerated. The highest dose was received by the spleen (0.159 +/- 0.062 mGy/MBq), followed by the urinary bladder wall (0.135 +/- 0.046 mGy/mBq) and the kidneys (0.070 +/- 0.018 mGy/ MBq), in accordance with the expected SSTR-specific uptake in the spleen and renal excretion of the tracer. The effective dose was 22.4 +/- 4.4 mu Sv/MBq. The physiologic uptake pattern of [F-18]AlF-OC was comparable to [Ga-68]Ga-DOTATATE. Mean tumour SUVmax was lower for [F-18]AlF-OC (12.3 +/- 6.5 at 2 h post-injection vs. 18.3 +/- 9.5; p = 0.03). However, no significant differences were found in TBR (9.8 +/- 6.7 at 2 h post-injection vs. 13.6 +/- 11.8; p= 0.35). DR was high and comparable for both tracers (86.0% for [Ga-68]Ga-DOTATATE vs. 90.1% for [F-18]AlF-OC at 2 h post-injection; p= 0.68). Conclusion [F-18]AlF-OC shows favourable kinetic and imaging characteristics in patients that warrant further head-to-head comparison to validate [F-18]AlF-OC as a fluorine-18-labelled alternative for gallium-68-labelled SSA clinical PET.