Assessing Ultra-low Dose PET/CT and CT-less PET Using a Long Axial Field-of-view PET/CT System

Assessing the Clinical Acceptability of Ultra-low Dose PET/CT and CT-less PET Using a Long Axial Field-of-view PET/CT System: a Single-centre, Single-blinded Method Agreement Study

Latest generation extended axial field-of-view (FOV) PET/CT systems offer the potential for substantial reductions in applied radiopharmaceutical necessary for a clinical scan. However, such low-dose examination protocols have yet to be robustly tested or demonstrated to be non-inferior. Furthermore, extended FOV scanners offer the potential for CT-less attenuation correction of the PET emission data, making clinically acceptable ultra-low dose examination protocols with radiation exposures of < 1 millisievert possible for the first time. The aim of this study is to demonstrate the clinical acceptability of such low and ultra-low dose scanning protocols in a head-to-head prospective study against a full-dose scan using a regular FOV system

The first installation of a long-axial field-of-view (LAFOV) PET/CT system occurred in October 2020 at the department for nuclear medicine in Bern. This scanner along with recently introduced total-body scanners (TB-PET/CT) represent a substantial step forward in terms of nuclear medicine imaging technology. In conjunction with recent improvements in time-of-flight resolution and fully-digital detection technology, such systems offer surpassed sensitivity with improvements in image quality, lesion detection and diagnostic certainty. In contrast to LAFOV systems, standard axial field of view (SAFOV) scanners suffer from limited detection efficiency, where 90% of emitted photons go undetected owing to the ability to capture signal from only a small portion of the body (termed "bed position" or "bp").

However, while a number of studies are able to simulate lower applied radiopharmaceutical activities through the re-sampling of PET-sinogrammes or the rebinning of list-mode data, few studies adequately test the application of lower radiopharmaceutical activities, where limited data are available to justify the deviation from clinical routine. The clinical acceptability of such low-dose scans, in terms of lesion detection, image quality and lesion quantification is yet to be determined, which this study aims to address.

Inclusion Criteria:

• Adults (>18 years) able to provide informed consent for inclusion, willing and able to undergo a PET/CT for the detection or staging of cancer.
• Individuals undergoing a PET/CT with 18F-FDG for the investigation of known or suspected NSCLC.
• Upper fasting plasma glucose levels of <8.3 mmol/L (<150 mg/dL) (as measured >30 mins prior to the administration of the radiopharmaceutical).

Exclusion Criteria:

• Patients who are unable to consent to a second study-specific examination
• Patients with claustrophobia requiring medication.
• Patients who commence active treatment of a cancer or other pathology between scans.
• Patients who have not fasted for > 4 hours prior to the study.
• Insulin dependent diabetics.