Assessing a small field of view hybrid gamma camera for perioperative iodine-125 seed localisation

To examine the imaging capability of a novel small field of view hybrid gamma camera (HGC) using ¹²⁵I seeds prior to surgical use.

The imaging performance of the camera system was assessed quantitatively and qualitatively at different source depths, source to collimator distances (SCD), activity levels, acquisition times and source separations, utilising bespoke phantoms.

The system sensitivity and spatial resolution of the HGC for ¹²⁵I were 0.41 cps/MBq (at SCD 48 mm) and 1.53 ± 0.23 mm (at SCD 10 mm) respectively. The camera was able to detect the ¹²⁵I seed at a SCD of 63 mm (with no scattering material in place) in images recorded within a 1-min acquisition time. The detection of the seeds beneath scattering material (simulating deep-seated tumours) was limited to depths of less than 20 mm beneath the skin surface with a SCD of 63 mm and seed activity of 2.43 MBq. Subjective assessments of the hybrid images acquired showed the capability of the HGC for localising the ¹²⁵I seeds.

This preliminary ex vivo study demonstrates that the HGC is capable of detecting ¹²⁵I seeds and could be a useful tool in radioactive seed localisation with the added benefit of providing hybrid optical γ images for guiding breast conserving surgery.

The SFOV HGC could provide high resolution fused optical-gamma images of ¹²⁵I radioactive seeds indicating the potential use in intraoperative surgical procedure such as RSL.