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This retrospective study assessed the treatment planning data and clinical outcomes for 152 prostate cancer patients: 76 consecutive patients treated by carbon-ion radiation therapy and 76 consequtive patients treated by moderate hypo-fractionated intensity-modulated photon radiation therapy. These two modalities were compared using linear quadratic model equivalent doses in 2 Gy per fraction for rectal or rectal wall dose–volume histogram, 3.6 Gy per fraction-converted rectal dose–volume histogram, normal tissue complication probability model, and actual clinical outcomes. Carbon-ion radiation therapy was predicted to have a lower probability of rectal adverse events than intensity-modulated photon radiation therapy based on dose–volume histograms and normal tissue complication probability model. There was no difference in the clinical outcome of rectal adverse events between the two modalities compared in this study.

Purpose To estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR‐39 plastic detectors. Methods A water phantom was irradiated by a 12C pencil beam with energy of 380 MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR‐39 detectors were exposed to secondary fragments. Because CR‐39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particles were combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by ±10% and ±40%. Results At a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by ±40%, the change of RBE was smaller than 10%. Conclusions RBE of 1.3 was expected for secondary fragments emitted at a small angle. Though, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles.

Production of spin polarized short-lived nucleus 12N (I π = 1 + , T 1/2 = 11 ms) using heavy ion reactions at intermediate energies has been performed. Typical polarization of about −25 % and +10 % through the projectile fragmentation Be(14N, 12N)X and the charge exchange CH2(12C, 12N)X processes, respectively, was obtained. The present study proved that the combination of a 12C beam and a proton target provides a fairly good quality of polarized 12N beam in terms of intensity and energy uniformity, and is promising for materials science use of 12N as a nuclear probe.

A microbeam array was formed with a multi-slit collimator (MSC) for research on radiation therapy (MRT). Kodak EDR2 film was used to measure the dose distribution of the microbeam array. The calibration curve of optical density of the film with respect to a dose was established using a standard Farmer chamber and 60Co gamma-ray source. The peak dose of 3.6 Gy/s at the maximum was derived from the film dosimetry using the calibration curve. The uncertainty was estimated to be 5 % which was mainly attributed to the uncertainty of the calibration. It was found that the ionization chamber used for monitoring the dose during the MRT experiments gave lower dose by about 30 % than the dose derived from the film dosimetry.

Heavy-ion therapy is one of the important methods for the cancer treatment. More than 3400 patients were treated between 1994 and 2007 at Heavy Ion Medical Accelerator in Chiba (HIMAC). For the promotion of carbon-ion therapy, a compact carbon-therapy facility was developed. The size of the new facility is three times smaller, while the accelerator can supply the beams similar to those used at HIMAC. The new irradiation system was developed in order to obtain a precise dose distribution for moving and/or deforming organs.

Clinical trials of carbon radiotherapy started at HIMAC in 1994 using three treatment rooms and four beam ports, two horizontal and two vertical. The broad beam method was adopted to make a three-dimensionally uniform field at an isocenter. A spot beam extracted from an accelerator was laterally spread out by using a pair of wobbler magnets and a scatterer. A bar ridge filter modulated the beam energy to obtain the spread out Bragg peak (SOBP). The SOBP was designed to be flat in terms of the biological dose based on the consideration that the field consisted of various beams with different LET. Finally, the field of 20 cm in diameter with +/- 2.5% uniformity was formed at the isocenter. The width of the maximum SOBP was 15 cm. When treating the lung or liver, organs that move due to breathing, the beam was irradiated only during the expiration period in a respiration-gated irradiation method. This reduced the treatment margin of the moving target. In order to prevent normal tissues adjacent to the target volume from irradiation by an unwanted dose, a layer-stacking method was developed. In this method, thin SOBP layers which have different ranges were piled up step by step from the distal end to the entrance of the target volume. At the same time, a multi-leaf collimator was used to change the aperture shape to match the shape of each layer to the cross-sectional shape of the target. This method has been applied to rather large volume cancers including bone and soft-tissue cancers. Only a few serious problems in the irradiation systems have been encountered since the beginning of the clinical trials. Overall the systems have been working stably and reliably.

Knowledge of electron densities for materials is important for treatment planning for proton and heavier-ion radiotherapy. In order to obtain the electron densities with high precision, we have developed dual-energy X-ray computed tomography using synchrotron radiation. Two monochromatic X-rays with different energies generated from synchrotron radiation enables tomographic imaging which produces a cross sectional image based on electron density plus an additional image based on effective atomic number. Experiments for the dual-energy X-ray CT were made on the BL20B2 beamline at SPring-8. An image intensifier system and a CCD camera were used as the 2-D detectors. The measured electron densities were agreement to within 2% of the theoretical ones. Electron density and effective atomic number provide different contrast in images. Dual-energy X-ray CT can be used for quantitative measurement of the material.

A model for beam customization with collimators and a range-compensating filter based on the phase-space theory for beam transport is presented for dose distribution calculation in treatment planning of radiotherapy with protons and heavier ions. Independent handling of pencil beams in conventional pencil-beam algorithms causes unphysical collimator-height dependence in the middle of large fields, which is resolved by the framework comprised of generation, transport, collimation, regeneration, range-compensation, and edge-sharpening processes with a matrix of pencil beams. The model was verified to be consistent with measurement and analytic estimation at a submillimeter level in penumbra of individual collimators with a combinational-collimated carbon-ion beam. The model computation is fast, accurate, and readily applicable to pencil-beam algorithms in treatment planning with capability of combinational collimation to make best use of the beam-customization devices., 16 pages, 5 figures