[Paper Review] Technical Note: A prototype clinical proton radiography system

Ethan A. DeJongh, Don F. DeJongh+10 more|arXiv (Cornell University)|Sep 10, 2020

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TL;DR

This paper presents a low-cost, compact proton radiography prototype using fast scintillator technology and multiplexed SiPMs for efficient signal readout. By employing patient-specific scan patterns with multiple input energies and a calibrated 16-PMT residual energy detector, the system achieves accurate proton range imaging with minimal excess dose, enabling clinical translation for proton therapy verification.

ABSTRACT

Purpose: To demonstrate a proton imaging system based on well-established fast scintillator technology to achieve high performance with low cost and complexity, with the potential of a straightforward translation into clinical use. Methods: The system tracks individual protons through one (X, Y) scintillating fiber tracker plane upstream and downstream of the object and into a 13 cm-thick scintillating block residual energy detector. The fibers in the tracker planes are multiplexed into silicon photomultipliers (SiPMs) to reduce the number of electronics channels. The light signal from the residual energy detector is collected by 16 photomultiplier tubes (PMTs). Only four signals from the PMTs are output from each event, which allows for fast signal readout. A robust calibration method of the PMT signal to residual energy has been developed to obtain accurate proton images. The development of patient-specific scan patterns using multiple input energies allows for an image to be produced with minimal excess dose delivered to the patient. Results: The calibration of signals in the energy detector produces accurate residual range measurements limited by intrinsic range straggling. The use of patient-specific scan patterns using multiple input energies enables imaging with a compact range detector. Conclusions: We have developed a prototype clinical proton radiography system for pretreatment imaging in proton radiation therapy. We have optimized the system for use with pencil beam scanning systems and have achieved a reduction of size and complexity compared to previous designs.

Motivation & Objective

• To develop a clinically viable proton radiography system with reduced size and complexity compared to prior designs.
• To leverage well-established fast scintillator technology to ensure high performance and reliability.
• To minimize patient dose through patient-specific scan patterns using multiple input proton energies.
• To enable accurate residual range measurement via robust calibration of PMT signals to energy deposition.
• To streamline signal readout by multiplexing fiber tracker signals into SiPMs and selecting only four PMT outputs per event.

Proposed method

• The system uses two scintillating fiber tracker planes (upstream and downstream of the object) to track individual protons in X and Y directions.
• Fiber signals are multiplexed into silicon photomultipliers (SiPMs) to reduce the number of required electronics channels.
• A 13 cm-thick scintillating block serves as the residual energy detector, with light collected by 16 photomultiplier tubes (PMTs).
• Only four PMT signals are output per event to enable fast readout and reduce data load.
• A robust calibration method correlates PMT signals to residual proton energy, ensuring accurate range measurement.
• Patient-specific scan patterns with multiple input energies are used to reconstruct proton images with minimal dose.

Experimental results

Research questions

• RQ1 Can a compact, low-cost proton radiography system be developed using established scintillator and SiPM technologies for clinical use?
• RQ2 How accurately can residual proton range be measured using a calibrated 16-PMT scintillating block detector?
• RQ3 To what extent can patient-specific scan patterns with multiple input energies reduce dose while maintaining image quality?
• RQ4 Can signal multiplexing via SiPMs and selective PMT output reduce system complexity without compromising performance?
• RQ5 What is the impact of intrinsic range straggling on the accuracy of proton imaging in this prototype system?

Key findings

• The calibration of PMT signals to residual energy enables accurate proton range measurements, limited only by intrinsic range straggling.
• The use of patient-specific scan patterns with multiple input energies allows for high-quality imaging using a compact residual energy detector.
• Signal multiplexing via SiPMs significantly reduces the number of electronics channels, simplifying system design.
• Fast readout is achieved by outputting only four PMT signals per event, maintaining real-time performance.
• The system achieves a notable reduction in size and complexity compared to previous proton imaging prototypes.
• The prototype demonstrates feasibility for pretreatment imaging in proton therapy with minimal excess dose.