Comparative accuracy and resolution assessment of two prototype proton computed tomography scanners

Abstract

BackgroundImproving the accuracy of relative stopping power (RSP) in proton therapy may allow reducing range margins. Proton computed tomography (pCT) has been shown to provide state‐of‐the‐art RSP accuracy estimation, and various scanner prototypes have recently been built. The different approaches used in scanner design are expected to impact spatial resolution and RSP accuracy. PurposeThe goal of this study was to perform the first direct comparison, in terms of spatial resolution and RSP accuracy, of two pCT prototype scanners installed at the same facility and by using the same image reconstruction algorithm. MethodsA phantom containing cylindrical inserts of known RSP was scanned at the phase‐II pCT prototype of the U.S. pCT collaboration and at the commercially oriented ProtonVDA scanner. Following distance‐driven binning filtered backprojection reconstruction, the radial edge spread function of high‐density inserts was used to estimate the spatial resolution. RSP accuracy was evaluated by the mean absolute percent error (MAPE) over the inserts. No direct imaging dose estimation was possible, which prevented a comparison of the two scanners in terms of RSP noise. ResultsIn terms of RSP accuracy, both scanners achieved the same MAPE of 0.72% when excluding the porous sinus insert from the evaluation. The ProtonVDA scanner reached a better overall MAPE when all inserts and the body of the phantom were accounted for (0.81%), compared to the phase‐II scanner (1.14%). The spatial resolution with the phase‐II scanner was found to be 0.61 lp/mm, while for the ProtonVDA scanner somewhat lower at 0.46 lp/mm. ConclusionsThe comparison between two prototype pCT scanners operated in the same clinical facility showed that they both fulfill the requirement of an RSP accuracy of about 1%. Their spatial resolution performance reflects the different design choices of either a scanner with full tracking capabilities (phase‐II) or of a more compact tracker system, which only provides the positions of protons but not their directions (ProtonVDA).

Characterization of the INFN proton CT scanner for cross-calibration of x-ray CT

“…This is a finer check of the calibration procedure than the one described in Scaringella et al (2023). In addition, the MAPE values, although achieved with a small number of materials, are lower than the one reported in Dedes et al (2022) and Götz et al (2022) with the same reconstruction algorithm, demonstrating a praiseworthy response of our detectors and calibration procedure.…”

“…Finally, the results obtained in this study, through the updated calibration and reconstruction procedures, placed our pCT system among the others currently working with above-average RSP accuracy values and no clearly visible artefacts. The acquisition rate of 80-90 kHz is lower than the one achieved by other systems (Dedes et al 2022) and, together with a limited FOV, it makes direct patient application of the INFN pCT impractical. However, we are working on introducing the INFN pCT scanner as a clinical tool for a novel verification and cross-calibration approach in the proton treatment planning (Farace et al 2021), acquiring both pCT and xCT tomographies on heterogeneous biological phantoms.…”

A review of the clinical introduction of 4D particle therapy research concepts

“…Proton CT systems have been developed in research projects over the past two decades [151] , [152] , [153] . However, the current systems have faced challenges in their clinical implementation due to technical issues in delivering an ultra-low intensity beam consisting of a single proton or ion per radiofrequency bunch but also related to accuracy and resolution [154] . Ideally, if both imaging and treatment beams are used in the same session, they should be mixed or delivered in a rapid sequence.…”

Integrated-mode proton radiography with 2D lateral projections

“…Alternatively, radiographic images representing the water equivalent thickness (WET) of traversed tissues can be acquired. Proton imaging may be helpful for accurate treatment planning in proton therapy by limiting uncertainties in RSP estimation (Schneider and Pedroni 1995, Schaffner and Pedroni 1998, Schneider et al 2005, Paganetti 2012, Yang et al 2012, Dedes et al 2022. Furthermore, as the treatment and imaging sources are the same, proton imaging creates images that are fully registered with the treatment beam, and enables a direct measurement of the residual proton range in the treatment room, right before delivery.…”