Imaging device functions in PTSIM for irradiation field reconstruction in particle therapy

PTSIM is a particle therapy system simulation framework based on Geant4 Monte Carlo simulation toolkit. It was originally developed as a reliable dose calculation tool to verify dose distributions inside patient and dose calculation algorithms in treatment planning systems. Besides such a reliable dose calculation, an irradiation field monitoring is desirable for delivering dose with more ideal distribution. It realizes a concept of a tailor-made proton therapy which performs a specially optimized treatment for each patient. The irradiation field monitoring is performed by reconstructing images by detecting prompt gamma rays and annihilation gamma rays from produced radionuclides by nuclear interactions. The PTSIM has an important role to identify the mutual relationship among dose and radionuclide distributions inside a patient, and reconstructed images from signals in imaging devices. We previously reported on the relevant extending functions in PTSIM such as a pencil beam scanning, a material mapping of CT images and a data output interface for a hospital information system, and proposed the software design for imaging systems. In this paper, we report on the development of imaging device functions in PTSIM according to the software design in the previous work. The implementation provides functional capabilities for a flexible scoring and a detector signal flow. Because of the modulated structure, these functions are handled by users through online commands. For example, a user can choose score quantities and specify a signal flow for emulating a detector response. These capabilities were demonstrated with a simple tubular detector for a flexible scoring function and a signal flow function in PET detectors, respectively. The simulated results show the correlation among dose, radionuclides, and coincide signals in PET detectors.