A carbon CT system: how to obtain accurate stopping power ratio using a Bragg peak reduction technique

Abstract

In this study, we investigate the performance of the Gunma University Heavy Ion Medical Center's ion computed tomography (CT) system, which measures the residual range of a carbon-ion beam using a fluoroscopy screen, a charge-coupled-device camera, and a moving wedge absorber and collects CT reconstruction images from each projection angle. Each 2D image was obtained by changing the polymethyl methacrylate (PMMA) thickness, such that all images for one projection could be expressed as the depth distribution in PMMA. The residual range as a function of PMMA depth was related to the range in water through a calibration factor, which was determined by comparing the PMMA-equivalent thickness measured by the ion CT system to the water-equivalent thickness measured by a water column. Aluminium, graphite, PMMA, and five biological phantoms were placed in a sample holder, and the residual range for each was quantified simultaneously. A novel method of CT reconstruction to correct for the angular deflection of incident carbon ions in the heterogeneous region utilising the Bragg peak reduction (BPR) is also introduced in this paper, and its performance is compared with other methods present in the literature such as the decomposition and differential methods. Stopping power ratio values derived with the BPR method from carbon-ion CT images matched closely with the true water-equivalent length values obtained from the validation slab experiment.

Error on the stopping power ratio of ERKODENT's mouthpiece for head and neck carbon ion radiotherapy treatment

“…To calculate the WEL of each sample, following the methods, 17,20,21 the integral depth dose (IDD) near the Bragg peak was measured using an ionization chamber with concentric electrodes (ICCE) contained in a water tank at the horizontal port of the EJHIC. The IDDs of the Bragg curve were measured with no sample and when a sample was placed vertically in front of the water tank.…”

Calculation of Stopping-Power Ratio from Multiple CT Numbers Using Photon-Counting CT System: Two- and Three-Parameter-Fitting Method

“…It can hold up to seven samples, each with a 5 mm diameter and 65 mm height. Water fills the space surrounding the sample rods [31]. An energy-differentiation-type 64-channel cadmium telluride (CdTe) radiation line sensor module (C10413, Hamamatsu, Japan) was used as the imaging system.…”

“…Seven rod-shaped samples were placed in a water-filled sample holder. The seven materials used for the samples were aluminium, graphite, PMMA, and four types of biological phantom materials (Kyoto Kagaku, Japan), that is, BE-T-10, BE-H-10, BE-N-10, and WD-3010, mimicking the properties of compact bone, cortical bone, internal bone, and water, respectively [31]. For the experimental conditions, the X-ray tube voltage and current were set at 150 kV and 40 µA, respectively, with focal spot sizes of 7 µm.…”

“…A height-adjustable water column was used to measure the SPR. Depth profiles of the Bragg curves from the 290 MeV/u carbon-ion beam were obtained in water only and for each slab absorber using a plane-parallel chamber (PTW, advanced Markus model 34045) [31]. A slab phantom of each material (aluminium, graphite, PMMA, and four biological phantom materials) was placed between water and an ionisation chamber in a water column.…”