Monte Carlo simulation of photon emission below a few hundred kiloelectronvolts for beam monitoring in carbon ion therapy.

The purpose of this study is to determine whether the main component of the low-energy (63-68 keV) particles emitted perpendicularly to the 12C beam from the 12C-irradiated region in a water phantom is secondary electron bremsstrahlung (SEB). Monte Carlo simulations of a 12C-beam (290 MeV/u) irradiated on a water phantom were performed. A detector was placed beside the water phantom with a lead collimator between the phantom and the detector. To move the Bragg-peak position, a binary filter was placed in an upper stream of the phantom. The energy distributions of the particles incident on the detector and those deposited in the detector were analyzed. The simulation was also performed with suppressed delta-ray and/or bremsstrahlung generation to identify the SEB components. It was found that the particles incident on the detector were predominantly photons and neutrons. The yields of the photons and energy deposition decreased with the suppression of SEB generation. It is concluded that one of the predominant components of the yields in the regions shallower than the Bragg-peak position is due to SEB generation, and these components become significantly smaller in regions deeper than the Bragg-peak position.

A proton therapy system in Nagoya Proton Therapy Center.

The purpose of this paper is to describe an outline of a proton therapy system in Nagoya Proton Therapy Center (NPTC). The NPTC has a synchrotron with a linac injector and three treatment rooms: two rooms are equipped with a gantry and the other one is equipped with a fixed horizontal beamline. One gantry treatment room has a pencil beam scanning treatment delivery nozzle. The other two treatment rooms have a passive scattering treatment delivery nozzle. In the scanning treatment delivery nozzle, an energy absorber and an aperture system to treat head and neck cancer have been equipped. In the passive treatment delivery nozzle, a multi-leaf collimator is equipped. We employ respiratory gating to treat lung and liver cancers for passive irradiation. The proton therapy system passed all acceptance tests. The first patient was treated on February 25, 2013, using passive scattering fixed beams. Respiratory gating is commonly used to treat lung and liver cancers in the passive scattering system. The MLCs are our first choice to limit the irradiation field. The use of the aperture for scanning irradiation reduced the lateral fall off by half or less. The energy absorber and aperture system in scanning delivery is beneficial to treat head and neck cancer.

Pre-computed system matrix calculation based on a piece-wise method for PET.

A system matrix (SM) is the basic component of iterative image reconstruction algorithms. Calculation of the SM needs a considerable amount of time due to an enormous number of lines of response (LORs) being modeled. In this study, we developed a technique based on a piece-wise calculation method in which symmetry and further division of the voxels are applied. The detector response function for all detectable pairs of photons along certain LORs originating from each voxel is calculated analytically. The total number of LORs in 300 × 300 × 120 voxels (with 2 × 2 × 2 mm(3)) is ~44 billion, and the SM was calculated by the use of three different computers independently; the calculation time was 5 h. The SM took 5 days when calculated by the use of the conventional method (where symmetry and the piece-wise method are not used). The sensitivity correction factor was stored; it had a size of 42 MB in a four-byte computer memory.