Author: Jorge Naoki Dominguez Kondo, Qihui Lyu 👨🔬
Affiliation: University of California San Francisco, Department of Radiation Oncology, University of California, San Francisco 🌍
Purpose:
Targeted alpha therapy (TAT) has emerged as a highly potent therapeutic method in oncology, but its development is limited by the lack of imaging methods to quantify its dosimetry. Conventional gamma imaging methods, such as Single-photon emission computed tomography (SPECT), result in low signal-to-noise ratios (SNR) due to the photon rejection by the collimators. Compton camera using electronic collimation is a promising imaging modality for TAT to improve the SNR, but its image quality is compromised by the inability to distinguish between back-scatter and forward-scatter events. In this study, we investigate the impact of misinterpreted back-scatter and forward-scatter events on the calculation of Compton scatter angles.
Methods:
We used the OpenTOPAS toolbox for the Monte Carlo simulation of a Compton Camera. The Compton camera include two detector layers: a scatterer and an absorber. High energy photons interact with the scatterer and the absorber through Compton scattering interactions and photoelectric interactions. The energy deposition and location of the event were recorded. Qualified Compton events were filtered according to the total energy, number of events, and the coincidence detector arrival. For each qualified detector event, the Compton scattering angle were computed and the deviation from the ground-truth scattering angle was evaluated. The simulation was performed with and without backscatter filtering, with primary photon energies ranging from 100 keV to 1 MeV.
Results:
Without backscattering photons, assuming ideal detector energy resolution and positioning accuracy, Compton camera can recover the scattering angle with less than 0.4 degrees deviation, for both 500keV and 1MeV primary. With backscattering photons, the mean angular deviation can be higher than 50 degrees.
Conclusion:
Identifying back scattering photons is crucial to improve the image quality of Compton cameras.