Purpose: We investigated, for the first time to our best knowledge, the feasibility of integrating a novel quadruple on-board imaging design - including positron emission tomography (PET), single-photon emission computed tomography (SPECT), spectral CT, and cone-beam computed tomography (CBCT) - into a small animal radiation treatment (SART) platform for one-stop preclinical RT studies by using a Monte Carlo (MC) model.
Methods: As a proof-of-concept, the quad-modal image-guided SART system was designed using the GATE MC code. A PET subsystem with dual 90° arcs of symmetrically opposite PET detectors was integrated into our previously proposed SPECT/spectral-CT/CBCT on-board imaging system using a single photon-counting cadmium zinc tellurium imager. The PET scanner was designed based on novel pixelated thallium bromide detectors with a resolution of 1.25 mm × 1.25 mm. The spatial resolution, sensitivity, and scatter fraction of PET imaging was measured mainly by using the methods prescribed by the NEMA NU-4 standard. A simulated phantom with multiple imaging probes, incuding Iodine, ¹⁸F, and ⁹⁹ᵐTc, was imaged to demonstrate the imaging performance of the system. In spectral CT, virtual non-contrast (VNC) electron densities and iodine contrast agent fractions in the Kidney1 inserts within the phantom were decomposed and imaged quantitatively by using the Bayesian eigentissue decomposition and the maximum a posterior estimation methods.
Results: In PET imaging, the absolute peak sensitivity was measured as 18.5% with an energy window of 175–560 KeV; the measured scatter fraction was 3.5% for a mouse phantom with a default energy window of 480–540 KeV; the spatial resolution exceeded 1.2 mm. The system can successfully capture high-quality PET, SPECT, spectral-CT (including decomposed iodine contrast agent fraction and VNC electron density images), and CBCT images of the simulated phantom.
Conclusion: The results demonstrated the feasibility of the highly integrated quad-modal imaging configuration in a SART platform.
Radiation Therapy, PET, Image Guidance
TH- Small Animal RT: Development (new technology and techniques)