Technical Note: A fast and monolithic prototype clinical proton radiography system optimized for pencil beam scanning

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. We measured the water‐equivalent thickness (WET) of a block of solid water (physical thickness of 6.10 mm) with a proton radiograph. The mean WET from all pixels in the block was 6.13 cm (SD 0.02 cm). 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.

Costs of Definitive Chemoradiation, Surgery, and Adjuvant Radiation Versus De-Escalated Adjuvant Radiation per MC1273 in HPV+ Cancer of the Oropharynx

“…For a voxel-wise SPR validation in patients, proton CT would be one possible method. Recently, improvements have been made and clinical prototype systems have emerged [38,39]. However, its potential benefit over dual-energy CT has yet to be demonstrated in clinical application [5,15,40].…”

Analysis of characteristics of images acquired with a prototype clinical proton radiography system

“…For example, the pediatric head phantom presented in Section 3.C has variations in WET between 0 and 20 cm and requires three scans of different energies to ensure that each (X, Y) position in the image has protons that pass completely through the phantom and also stop in the scintillating block. For more detailed information on the detector hardware and calibration procedure, we refer the reader to the technical note by DeJongh, et al 9…”

“…Therefore, a single energy scan with a field size of 20 × 20 cm 2 at the isocenter plane delivers between 16 and 32 million protons, which results in a dose of 0.06 to 0.12 mGy. 9 To achieve the low beam intensity, we reduced the proton current at the cyclotron source as well as increased the beamline collimation of the momentum and divergence slits. The cyclotron current and the collimator slit positions are then maintained constant for each energy during the imaging runs.…”

“…ProtonVDA LLC developed a clinical prototype proton radiography system, shown in Fig. 1, with design considerations to easily transition into a proton treatment room as described by DeJongh, et al 9 The associated image reconstruction software, as described by Ordoñez, et al, 10 produces clinical proton radiographic images with less than 1 minute of reconstruction time. In order for the clinical implementation to be successful, the proton radiographic images need to possess good and useful image quality while maintaining a low dose to the patient.…”

Relative stopping power precision in time-of-flight proton CT

“…Proton CT scanner prototypes proposed and developed so far rely either on a calorimeter, e.g. a scintillator, to measure the energy deposited by a proton therein (Civinini et al, 2013;Johnson et al, 2016;DeJongh et al, 2021) or a range telescope (Taylor et al, 2016;Alme et al, 2020;Pemler et al, 1999). An alternative measurement principle determines the proton's time of flight (TOF) between two or more sensor planes from which the velocity and thus the kinetic energy can be calculated.…”