GaN-Based Readout Circuit System for Reliable Prompt Gamma Imaging in Proton Therapy

Prompt gamma imaging is one of the emerging techniques used in proton therapy for in-vivo range verification. Prompt gamma signals are generated during therapy due to the nuclear interaction between beam particles and nuclei of the tissue that is detected and processed in order to obtain the position and energy of the event so that the benefits of Bragg’s peak can be fully utilized. This work aims to develop a gallium nitride (GaN)-based readout system for position-sensitive detectors. An operational amplifier is the module most used in such a system to process the detector signal, and a GaN-based operational amplifier (OPA) is designed and simulated in LTSpice. The designed circuit had an open-loop gain of 70 dB and a unity gain frequency of 34 MHz. The slew rate of OPA was 20 V/μs and common mode rejection ratio was 84.2 dB. A simulation model of the readout circuit system using the GaN-based operational amplifier was also designed, and the result showed that the system can successfully process the prompt gamma signals. Due to the radiation hardness of GaN devices, the readout circuit system is expected to be more reliable than its silicon counterpart.

Prompt gamma imaging for the identification of regional proton range deviations due to anatomic change in a heterogeneous region

Objectives: Prompt gamma (PG) imaging has previously been demonstrated for use in proton range verification of a brain treatment with a homogeneous target region. In this study, the feasibility of PG imaging to detect anatomic change within a heterogeneous region is presented. Methods: A prompt gamma camera recorded several fractions of a patient treatment to the base of skull. An evaluation CT revealed a decrease in sinus cavity filling during the treatment course. Comparison of PG profiles between measurement and simulation was performed to investigate range variations between planned and measured pencil beam spot positions. Results: For one field, an average over range of 3 mm due to the anatomic change could be detected for a subset of spots traversing the sinus cavity region. The two other fields appeared less impacted by the change but predicted range variations could not be detected. These results were partially consistent with the simulations of the evaluation CT. Conclusion: We report the first clinical application of PG imaging that detected some of the expected small regional proton range deviations due to anatomic change in a heterogeneous region. However, several limitations exist with the technology that may limit its sensitivity to detect range deviations in heterogeneous regions. Advances in knowledge: We report on the first detection of range variations due to anatomic change in a heterogeneous region using PGI. The results confirm the feasibility of using PG-based range verification in highly heterogeneous target regions to identify deviations from the treatment plan.