Endocrine Abstracts

Background: Currently there is limited availability of ⁶⁸Ga-DOTATATE in the UK due to limited radiopharmaceutical production. New whole-body PET/CT scanners with higher sensitivity may allow administered activities lower than the recommended 100-200MBq by international guidelines, potentially allowing more patients to be imaged from an elution vial.

Aim: To evaluate the feasibility of reducing administered tracer activity on a whole-body scanner in patients undergoing ⁶⁸Ga-DOTATATE somatostatin receptor scintigraphy for Neuroendocrine Tumours

Methods: Following preliminary re-binning of twenty patient data in those administered 100-150MBq of ⁶⁸Ga-DOTATATE, we established 0.75MBq/Kg would be potentially be feasible on the whole-body Siemens Biograph Quadra camera (minimum of 50MBq was selected). We evaluate the images of 10 consecutive patients who had previously undergone ⁶⁸Ga-DOTATATE PET/CT on Siemens Biograph Vision camera (4minutes/bed position+5mins for bed over liver) reconstructed with TrueX +TOF (UltraHD-PET) and subsequently had a follow-up ⁶⁸Ga-DOTATATE PET/CT on the wholebody Siemens Biograph Quadra camera (10 minutes vertex to thighs acquisition) reconstructed with TrueX +TOF. We compared the injected activity, weight, body mass index (BMI) and liver signal to noise ratio (SNR) between these two studies.

Results: The mean injected activity was 58MBq (range 48-82MBq) on Quadra and 129MBq on the Biograph. The mean BMI was 28 and 26 at the time of the Biograph and Quadra study respectively. Semiquantitative analysis showed an improvement in mean SNR of 56% (range 33%-93%) on the Quadra.

Conclusion: Administered activity of 0.75MBq/kg on the Quadra results in superior liver SNR ratio (vs. standard administered activities on Vision) translating to better images. In general, limited availability of ⁶⁸Ga-DOTATATE doses results in long waiting times for patients referred for ⁶⁸Ga-DOTATATE imaging. Therefore, reduced administered tracer activity and faster imaging times would potentially allow imaging of 1-2 additional patients per ⁶⁸Ga elution, helping in reducing waiting times. There are added benefits of better image quality and reduced patient dose.