Sci‐AM1 Sat ‐ 04: Gamma‐camera verification of breast brachytherapy seed distributions

Abstract

Objective: To assess whether a proposed SPECT device could resolve implanted breast brachytherapy seeds within an acceptable imaging time for correction of misplaced seeds. Method: Monte Carlo simulations of a cadmium zinc telluride crystal‐based gamma camera were used to assess whether the detection of 22 keV photons emitted from seeds was feasible. A 5×5 cm detector, fitted with a hexagonal parallel hole collimator (hole length 38 mm, diameter 1.2 mm, septa 0.2 mm) was modeled. Projections were taken every 7.5 degrees, with a radius of rotation of 10 cm, and images reconstructed using an OSEM algorithm. The phantom modeled consisted of an 8 cm diameter sphere of breast tissue containing a central, 1 cm cubic distribution of 8 seeds, which were each 5 mm long and 0.8 mm wide titanium tubes with an inner radius of 0.32 mm. Results: An acquisition duration of 24 seconds yielded images with a FWHM of 6.0 mm and a scatter fraction of 8.2%. The error between the center of mass of the reconstructed image and the physical seed location was 0.81 ± 0.16 mm, when the phantom was imaged for 24 seconds. Conclusion: The online gamma‐camera approach to imaging the seeds is feasible for a simple seed distribution. The high contrast between the seeds and the non‐radioactive background allow a practical acquisition time of a minute or less. Additional simulations will be required to assess the system design for more realistic seed distributions in a geometry more closely modeling a patient.