T. Shirai

Implementation of a triple Gaussian beam model with subdivision and redefinition against density heterogeneities in treatment planning for scanned carbon-ion radiotherapy.

Challenging issues in treatment planning for scanned carbon-ion (C-ion) therapy are (i) accurate calculation of dose distribution, including the contribution of large angle-scattered fragments, (ii) reduction in the memory space required to store the dose kernel of individual pencil beams and (iii)xa0shortening of computation time for dose optimization and calculation. To calculate the dose contribution from fragments, we modeled the transverse dose profile of the scanned C-ion beam with the superposition of three Gaussian distributions. The development of pencil beams belonging to the first Gaussian component was calculated analytically based on the Fermi-Eyges theory, while those belonging to the second and third components were transported empirically using the measured beam widths in a water phantom. To reduce the memory space for the kernels, we stored doses only in the regions of interest considered in the dose optimization. For the final dose calculation within the patients whole body, we applied a pencil beam redefinition algorithm. With these techniques, the triple Gaussian beam model can be applied not only to final dose calculation but also to dose optimization in treatment planning for scanned C-ion therapy. To verify the model, we made treatment plans for a homogeneous water phantom and a heterogeneous head phantom. The planned doses agreed with the measurements withinxa0±2% of the target dose in both phantoms, except for the doses at the periphery of the target with a high dose gradient. To estimate the memory space and computation time reduction with these techniques, we made a treatment plan for a bone sarcoma case with a target volume of 1.94u2009l. The memory space for the kernel and the computation time for final dose calculation were reduced to 1/22 and 1/100 of those without the techniques, respectively. Computation with the triple Gaussian beam model using the proposed techniques is rapid, accurate and applicable to dose optimization and calculation in treatment planning for scanned C-ion therapy.

Power Model of Biperiodic DAW Cavity

A high power model of the biperiodic L-support DAW for electron acceleration is fabricated and under test. Two 1.2m long accelerating tubes are coupled by a bridge coupler, which has an RF coupler, a vacuum port, and three frequency tuners. Each end of the bridge-coupled tube set is terminated by a full-cell endplate for the accelerating mode. The operating frequency is S-band so that the DAW accelerating tube can replace a conventional disk-loaded-waveguide accelerating tube for high power tests. The mechanical design and the measured parameters are described.

Fabrication of biperiodic DAW cavity

Fabrication techniques for the biperiodic DAW cavity have been investigated for these years. The basic dimensions are optimized by computer simulations and cold model tests. According to results of material tests, all of the parts facing to the inside are made of OFC. In order to improve the properties of a bridge coupler, which is installed between two 1.2-m long accelerating tube, choke structure is implemented.

Present status of the electron linac as the injector for KSR

At Kyoto University, a 300 MeV electron storage ring, KSR, has been constructed for the research of the synchrotron radiation light. As an injector of the ring, an S-band electron linac with the energy of 100 MeV was constructed in October, 1995, and have been operated since then. We measured the transverse emittance of the 100 MeV electron beam using a profile monitor made of a fluorescent screen and quadrupole lenses. The horizontal and vertical ones are 0.44 /spl pi/.mm.mrad and 1.3 /spl pi/.mm.mrad, respectively. The beam from the linac is being used for the experiment of the parametric X-ray radiation from the silicon crystal at rather low duty factor.

Very high-field short-pulse dipole magnet for compact proton synchrotron

Design of a short-pulse dipole magnet for a compact proton synchrotron dedicated for cancer therapy is presented. Its pulse width and maximum magnetic field are 7 [ms] and 4 [T], respectively. Sextupole coefficient is reduced to 4/spl times/10/sup -4/ (32 [T/m/sup 2/]) at 4 [T] by the optimization of the magnet geometry, which is estimated to be sufficiently small for beam acceleration. Laminated silicon steel ( thickness of 1 [mm]) is enough to suppress the eddy current effect in the yoke and B-constant shape rather than Rogowskis curve is adopted at the end of the magnet.

Measurement of the Beam Distribution of 433 MHz Proton Linac in Longitudinal Phase Space

We measured the longitudinal phase space distribution of the proton beams provided by the 433 MHz linac at ICR, Kyoto University, by means of a new monitor which consists mainly of a thin gold target, a deflector cavity, a position sensitive detector (PSD) and three permanent magnet quadrupole lenses. Protons are scattered by the target are guided into cavity, then focused by the PMQs, deflected by the cavity, then focused by the deflector electrodes, and finally reach the PSD. The position and energy data from the PSD are employed to reconstruct the phase space configuration of the beam before hitting the target. The longitudinal emittance of the ICR linac was measured with the present monitor system under some different operating conditions. The obtained measurement results were used to optimize the RF condition. Introduction At the Institute for Chemical Research, Kyoto University, a 433 MHz proton linac has been operated. The linac mainly consists of 50 keV Ion source, and low energy beam transport, 2 MeV Radio Frequency Quadrupole (RFQ) linac, Beam Matching Section (BMS), and 7 MeV Drift Tube Linac (DTL)[1]. In order to measure the longitudinal beam emittance of the 7 MeV proton beam, we developed a new beam monitor [2]. The monitor enables us to measure the beam distribution in the longitudinal beam phase space. The longitudinal beam distribution of the proton linac is obtained by measuring the position and energy of the protons which are scattered at the target and then deflected by an rf field whose frequency is the same as those of RFQ linac and DTL. The figure of the longitudinal emittance monitor is shown in Fig.1. The position and energy of a proton measured by Position Sensitive Detector (PSD) depend on the phase and energy when it is scattered at the target. By calculating the orbit of the deflected proton, the coordinates of the proton in the phase space can be obtained. In this way, a beam distribution in the longitudinal phase space is reconstructed from the measured position and energy distribution. When we accelerate the proton beams, how we control the rf condition is large problem. Then the variations of the longitudinal beam distribution at different rf conditions were measured, in order to examine the effect of the rf condition to the longitudinal beam dynamics. Target PMQ 2 PMQ 1 Baffle Slit Proton Beam

Performance of the 100 MeV Injector Linac for the Electron Storage Ring at Kyoto University

An electron linear accelerator has been constructed as an injector of a 300 MeV electron storage ring (Kaken Storage Ring, KSR) at Institute for Chemical Research, Kyoto University. The output beam energy of the linac is 100 MeV and the designed beam current is 100 mA at the 1 μsec long pulse mode. The transverse and longitudinal emittance are measured to evaluate the beam quality for the beam injection into the KSR. They are observed by the profile monitors combined with quadrupole magnets or an RF accelerator. The results are that the normalized transverse emittance is 120 π.mm.mrad. The longitudinal emittance is 15 π.deg.MeV and the energy spread is +2.2 %. Introduction A compact electron storage ring (Kaken Storage Ring, KSR) is now under construction at the Institute for Chemical Research, Kyoto University [1]. The layout of the accelerators is shown in Fig. 1. The KSR has a race track shape and its maximum beam energy is 300 MeV. It will be used as the synchrotron radiation source from the dipole magnet and the insertion device. The critical wave length of the synchrotron radiation is 17 nm. It will be also used for the research of the free electron laser. The construction of the linac had been finished and we succeeded to accelerate the electron beam of 140 mA in October, 1995. The design beam energy is 100 MeV and the pulse width is variable from 10 nsec to 1 μsec. Table 1 shows the main linac parameters. The linac will be also used for the experiments of the coherent X-ray generation by the election beam. Especially, the parametric X-ray radiation (PXR) experiment has been already started. Accelerator The electron gun has the Pierce electrode and the cathode assembly is the Y-796 (Eimac). The maximum extraction voltage is -100 kV. The pre-buncher is a single reentrant cavity. It is designed to bunch the beam within the phase spread of 60 degree. The buncher is a disc-loaded and 3 step constant gradient structure. It has 21 cells and the total length is 777 mm. The designed phase spread is within 3 degrees at the beam current of 100 mA when the input power is 12 MW. There are three main accelerating structures. The main characteristics of the accelerating structure are also listed in Table 1 Beam parameters and main specifications of the linac. Output Electron Beam Energy 100 MeV Max. Pulse Width 1 μsec Max. Repetition 20 Hz Electron Gun Cathode Assembly Y-796 (Eimac) Max. Extraction Voltage -100 kV DC Accelerating Structure Bore Radius 11.74 13.4 mm Length 3 m Operating Frequency 2857 MHz Maximum Electric Field 15 MV/m at 20 MW Figure 1 Layout of the electron accelerator. table 1. The maximum electric field is 45 MV per an accelerating structure without beam loading at the input power of 20 MW. The doublets of the quadrupole magnets are used as focusing elements between the accelerating structures. Klystron There is a klystron for each accelerating structure. The total number of the klystron is 4 including the buncher, prebuncher system. The klystron is ITT-8568. The maximum output power is 21 MW and the pulse width is 2 μsec. We are going to replace the klystron with Mitsubishi PV3030A2. The present modulators and the focusing coils are reused for the new klystrons so that the replacement cost and time can become minimum. The solenoid is a single electromagnetic coil and generates the magnetic field of 0.9 kGauss on the axis. Figure 2 shows the relation between the cathode voltage and the output power. The output power of 30 MW is available at the cathode voltage of 250 kV. The power efficiency is 48 %. Beam Measurement The beam emittance and the energy is measured downstream of the linac. Figure 3 shows the schematic view of the beam monitor section. The beam current is measured by the current transformer (CT) with ferrite core. The main components in this section are two profile monitors (PM1, PM2). They consist of screens, CCD cameras and an image memory unit. The image data is analyzed by the computer in the control room. The material of the fluorescence screen is an alumina ceramic in which a little chromium oxide is homogeneously doped (Desmarquest, AF995R). PM1 is used for the measurement of the transverse beam profile and the emittance. PM2 is used for the measurement of the energy spread and the longitudinal emittance. Transverse Beam Profile and Emittance The shape of the beam distribution in the transverse phase space is assumed, γ α β ε x xx x 2 2 2 + + = , (1) where α, β, γ are Twiss parameters and ε is the transverse emittance. The Twiss parameters are transformed from QD to PM1according to the following equation.