Computational model for detector timing effects in Compton-camera based prompt-gamma imaging for proton radiotherapy

Area of Science:

• Medical Physics
• Nuclear Instrumentation
• Radiation Oncology

Background:

• Proton therapy requires accurate range verification.
• Prompt gamma (PG) imaging offers a potential method for real-time range verification.
• Compton cameras (CCs) are used for PG detection, but their performance at clinical dose rates is not fully understood.

Purpose of the Study:

• To simulate and experimentally validate a Compton-camera based prompt-gamma imaging system for proton range verification.
• To investigate the impact of varying clinical dose rates on PG detection and image quality.
• To assess the accuracy of PG measurements using a Monte Carlo plus Detector Effects (MCDE) model.

Main Methods:

• Developed a Monte Carlo plus Detector Effects (MCDE) model to simulate PG production and energy deposition in a CC.
• Simulated PG emission from a polyethylene phantom irradiated with a 150 MeV proton beam at three dose rates.
• Incorporated realistic detector timing effects and acquired experimental PG data using a pre-clinical CC at the same dose rates.

Main Results:

• Increased dose rates led to reduced detected events due to dead-time, increased false-coincidence events, and loss of spectral peaks.
• Simulation showed a significant increase in false scatter events (double and triple) with rising dose rates (22-70% for double, 3-35% for triple).
• High percentages of false scatter events were identified as a major limitation for usable PG imaging with the prototype CC.

Conclusions:

• The MCDE model accurately simulated the effects of dose rate on PG detection.
• High dose rates significantly degrade PG imaging data quality by introducing noise from false scatter events.
• Further development is needed to overcome limitations in prototype Compton cameras for clinical prompt gamma imaging.