A novel design of proton computed tomography detected by multiple‐layer ionization chamber with strip chambers: A feasibility study with Monte Carlo simulation

Abstract

Purpose Uncertainty in proton range can be reduced by proton computed tomography (CT). A novel design of proton CT using a multiple‐layer ionization chamber with two strip ionization chambers on the surface is proposed to simplify the imaging acquisition and reconstruction. Methods Two strip ionization chambers facing the proton source were coupled into a multiple‐layer ionization chamber (MLIC). The strip chambers measured locations and lateral profiles of incident proton beamlets after exiting the imaging object, while the integral of depth dose measured in the MLIC was translated into the residual energy of the beamlet. The simulation was performed at five levels of imaging dose to demonstrate the feasibility and performance expectations of our design. The energy of the proton beamlet was set to 150 ± 0.6 MeV. A collimator with a round slit of 1 cm in diameter was placed in the central beam axis upstream from steering magnets. Proton stopping power ratio (SPR) was reconstructed through inverse radon transform on sinograms generated with proton beamlets scanning through an imaging phantom from a half‐circle gantry rotation. The imaging phantom was 10 cm in diameter. The base was made of water‐equivalent material holding 13‐tissue equivalent inserts constructed according to ICRP 1975 (Task Group on Reference Man. “Report of the Task Group on Reference Man: A Report”, Pergamon Press 23, 1975). All inserts were 1 cm in diameter with materials ranging from lung to cortical bone. Percentage discrepancies were reported by comparing to the ground truths. The imaging dose and quality were also evaluated. Results The maximum deviation in reconstructed proton SPR from the ground truths was reported to be 1.02% in one of the 13 inserts when the number of protons per beamlet passing through the slit dropped to 103. Imaging dose was correlated linearly to incident protons and was determined to be 0.54 cGy if 5 × 102 protons per beamlet were used. Imaging quality was acceptable for planning purpose and held consistently through all levels of imaging dose. Spatial resolution was measured as five line pairs per cm consistently in all simulations varying in imaging dose. Conclusions Proton CT using a multiple‐layer ionization chamber with two strip ionization chambers on the surface simplifies data acquisition while achieving excellent accuracy in proton SPR and acceptable spatial resolution. The imaging dose is lower compared to kV CBCT, making it potentially a great tool for localization and plan adaption in proton therapy.

A reconstruction approach for proton computed tomography by modeling the integral depth dose of the scanning proton pencil beam

“…The maximum SPR deviation in one of the 12 inserts was 1.02% in our previous work. 19 The uncertainties of SPR and WEPL determined through this approach were also on the same magnitude as those reported by the experimental studies of the proton tracking system. (Accuracy in SPR ≤ 1.6% for all inserts 40 ; accuracy in WEPL about 3.0 mm per proton in the 260 mm range.…”

“…In the previous study, only the peak location of the IDD was used to determine the WEPL, 19 while the approach developed in this study utilized the IDD values at all depths of the MLIC to determine the WEPL. In this way, the contribution of protons covering different lateral positions of the imaging object can be separated, and thus the spatial resolution was improved without confining the proton spot size.…”

“…The effective detector area is $$25.6 \times 25.6\ {\rm{c}}{{\rm{m}}^2}$$, thus the maximum volume of the object for scanning is $$1.68 \times {10^4}\ {\rm{c}}{{\rm{m}}^3}$$. Additional details of the detector design can be found in our previous publication 19 . In this study, the source to isocenter distance and the source to detector center distance were set to be 184 and 224 cm, accordingly.…”

“…Additional details of the detector design can be found in our previous publication. 19 In this study, the source to isocenter distance and the source to detector center distance were set to be 184 and 224 cm, accordingly.…”

“…Our group's previous simulation study validated the feasibility of a novel design of a proton CT system equipped with a multilayer ionization chamber (MLIC) and two strip ionization chamber plates. 19 The MLIC was designed to measure proton residual dose at different depths. The two strip ionization chamber plates in front of the MLIC were designed to determine positions and lateral profiles of the exiting proton beams, which can provide information to further improve SPR accuracy.…”