EARL-based quantitative evaluation of administered activity reduction for [⁶⁸Ga]Ga-DOTATOC PET/CT on a 32-cm axial...

The increased sensitivity of long-axial field-of-view (FOV) digital PET/CT systems enables potential reductions in administered activity and/or acquisition time with respect to standard-field-of-view systems and established clinical protocols, while preserving quantitative performance. This study aimed to evaluate the feasibility of reducing administered activity for [⁶⁸Ga]Ga-DOTATOC PET/CT on a 32-cm axial FOV digital bismuth germanium oxide (BGO) system using an EARL-based phantom methodology, complemented by a preliminary clinical assessment.

A NEMA IEC body phantom was acquired at progressively decreasing ⁶⁸Ga activity concentrations; recovery coefficients (RC_mean and RC_max) were compared with EARL ¹⁸F Standard 1 limits and published ⁶⁸Ga-specific reference curves. The influence of reconstruction settings on harmonization compliance was investigated. Clinical evaluation was performed in two patients by retrospectively simulating reduced-count conditions and assessing image quality using a 5-point Likert scale evaluated by six experienced readers.

Phantom results demonstrated compliance with EARL ¹⁸F Standard 1 recovery limits down to approximately 1.7 kBq/mL for 2 min/bed acquisitions. At 0.8 kBq/mL, corresponding to an administered activity of 1.5 MBq/kg, background variability remained acceptable despite limited RC_max deviations. Comparison with published reference curves showed good agreement for RC_mean, whereas RC_max compliance was lower. Reconstruction settings substantially influenced harmonization, with no single reconstruction achieving uniform agreement. Clinical analysis showed that count reductions of approximately 12-24 % did not significantly impair perceived diagnostic image quality.

On the evaluated 32-cm axial FOV digital BGO PET/CT system, administered activity reductions toward 2.0 MBq/kg appear feasible while preserving acceptable quantitative performance and clinical image quality.