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In this study, we performed on-beam monitoring of 511 keV annihilation gamma emissions using a Compton camera. Beam monitoring experiments were conducted using carbon ion beams of 290 MeV/u irradiated on a polymethyl methacrylate (PMMA) phantom. The intensity of the beams was 3 × 109 particles per pulse, with 20 pulses per minute. A Compton camera based on a silicon/cadmium telluride (Si/CdTe) detector was used to monitor the annihilation gamma rays emitted from the phantom. We successfully reconstructed the energy events of 511 keV annihilation gamma rays and developed Compton images using a simple back-projection method. The distribution of the annihilation gamma ray generation traced the beam trajectory and the peak intensity position was a few millimeters shorter than the Bragg peak position. Moreover, the effect of the beam range shifter with 30, 60, and 90 mm water equivalent thickness (WET) was clearly visualized in the reconstructed Compton images. The experimentally measured values of the corresponding range shifts in the PMMA phantom (28.70 mm, 52.49 mm, and 76.77 mm, respectively) were consistent with the shifts of the Bragg peak position (25.50 mm, 51.30 mm and 76.70 mm, respectively) evaluated by Monte Carlo simulation. The results show that the Si/CdTe Compton camera has strong potential for on-beam monitoring of annihilation gamma rays in particle therapy in clinical situations.

Facilities for heavy ion therapies are steadily increasing in number worldwide. One of the advantages of heavy ions is their high relative biological effect (RBE). In a model used at NIRS (National Institute of Radiological Sciences), linear energy transfer (LET) spectra are required to estimate biological dose (physical dose × RBE). The CR-39 plastic charged-particle detector (CR-39) is suitable for measurement of LET. For the present study, done at the Gunma University Heavy Ion Medical Center (GHMC), we measured LET spectra at 11 depths in spread-out Bragg peak (SOBP) irradiation by a

The aim of this research is to develop a stereotactic-radiosurgery (SRS) technique using carbon beams to treat small intracranial lesions; we call this device the carbon knife. A 2D-scanning method is adapted to broaden a pencil beam to an appropriate size for an irradiation field. A Mitsubishi slow extraction using third order resonance through a rf acceleration system stabilized by a feed-forward scanning beam using steering magnets with a 290 MeV/u initial beam energy was used for this purpose. Ridge filters for spread-out Bragg peaks (SOBPs) with widths of 5 mm, 7.5 mm, and 10 mm were designed to include fluence-attenuation effects. The collimator, which defines field shape, was used to reduce the lateral penumbra. The lateral-penumbra width at the SOBP region was less than 2 mm for the carbon knife. The penumbras behaved almost the same when changing the air gap, but on the other hand, increasing the range-shifter thickness mostly broadened the lateral penumbra. The physical-dose rates were approximate 6 Gy s−1 and 4.5 Gy s−1 for the 10 × 10 mm2 and 5 × 5 mm2 collimators, respectively.

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.

Monochromatic x-ray computed tomography (CT) at two different energies provides information about electron density of human tissue without ambiguity due to the beam hardening effect. This information makes the treatment planning for proton and heavy-ion radiotherapy more precise. We have started a feasibility study on dual energy x-ray CT by using synchrotron radiation. A translation-rotation scanning CT system was developed for quantitative measurement in order to clarify what precision in the measurement was achieved. Liquid samples of solutions of K2HPO4 and solid samples of tissue equivalent materials were used to simulate human tissue. The experiments were carried out using monochromatic x-rays with energies of 40, 70 and 80 keV produced by monochromatizing synchrotron radiation. The solid samples were also measured in a complementary method using high-energy carbon beams to evaluate the electron densities. The measured electron densities were compared with the theoretical values or the values measured in the complementary method. It was found that these values were in agreement in 0.9% on average. Effective atomic numbers were obtained as well from dual-energy x-ray CT. The tomographic image based on each of the electron densities and the effective atomic number presents a different feature of the material, and its contrast drastically differs from that in a conventional CT image.