| Paper | Title | Page |
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| MOPA37 | Reliable Beam-Intensity Control Technique at the HIMAC Synchrotron | 143 |
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| The carbon-ion beam is slowly extracted from the Heavy Ion Medical Accelerator in Chiba (HIMAC) synchrotron using the third-order resonance with the RF-knockout method for scanned carbon-ion therapy. However, an overshoot of the beam spill at the start of extraction is often induced by a slight variation of the beam emittance in operation cycles. It brings dose hot spot inside the target volume, because the tolerable beam-intensity in scanning irradiation is low. We have added short extraction, called preliminary extraction, before irradiation in order to remove the uncontrollable spilled particles. During preliminary extraction, it is necessary to prevent the beam delivering to the patient. Therefore, a fast beam shutter on which an ionization chamber is mounted was developed, and it was installed in the extraction line. The fast shutter enables us to switch from preliminary extraction to irradiation within 100 ms, and the reliability of the beam-intensity control system was drastically improved by the preliminary extraction technique. | ||
| MOPB51 | Beam Monitors of NIRS Fast Scanning System for Particle Therapy | 182 |
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| At National Institute of Radiological Sciences, more than 6500 patients have been successfully treated by carbon beams since 1994. The successful results of treatments have led us to construct a new treatment facility equipped with three-dimensional pencil beam scanning irradiation system. The commissioning of NIRS fast scanning system installed into the new facility was started in September 2010, and the treatment with scanned ion beam was started in May 2011. In the scanning delivery system, beam monitors are some of the most important components. In order to measure and control the dose of each spot, the main and the sub ionization chambers are placed separately as flux monitors. For monitoring of the scanned beam position, a beam position monitor, which is multi-wire proportional chamber, is installed just downstream from the flux monitors. This monitor can output not only the beam position but also the 2D fluence distribution using dynamic fast convolution algorithm. In this paper, the design and the commissioning of these monitors are described. | ||
| MOPB76 | Evaluation of a Fluorescent Screen with a CCD System for Quality Assurance in Heavy-Ion Beam Scanning Irradiation System | 249 |
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| The precise heavy-ion therapy such as the scanning irradiation system necessitates the precise quality assurance (QA) procedures to verify the performance of therapeutic scanned ion beams. To evaluate the uniformity of the 2D field, radiographic film is used due to its high spatial resolution and suit for the measurements of the integral dose. However, this technique is time consuming. Thus, we developed the QA tool with high spatial resolution to verify accuracy of the lateral size, position and uniformity of scanned ion beams in clinical application at the HIMAC, which we called the QA-SCN. The QA-SCN consists of a fluorescent screen, a CCD camera, a mirror, camera controllers and a dark box to protect against surrounding light. In this paper, to evaluate the performance of the QA-SCN, we compared the results obtained by using it with the measurements by radiographic film performed in the same experimental conditions. Also, we verified several types of corrections about errors, e.g. background, vignetting, to distort the measurement results. As a result, we confirmed that the QA-SCN can be used as the system for QA procedures of therapeutic scanned ion beams. | ||
| MOPB78 | Beam Spot Measurement using a Phosphor Screen for Carbon-Ion Therapy at NIRS | 256 |
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| A two-dimensional beam imaging system with a terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) phosphor screen and high-speed charge coupled device (CCD) camera has been used to measure the beam spot for scanned carbon-ion therapy at National Institute of Radiological Sciences (NIRS). The system enables us to obtain one image of the beam spot every 20 milliseconds. The fluctuation of the unscanned-beam spot size and position was observed in the isocenter to verify the time stability of the delivered beam for scanning irradiation. The beam imaging system also functions as a beam alignment adjustment system by setting a steel sphere at the isocenter. For quality assurance, the beam alignment is routinely checked by observing a shadow of the steel sphere on the beam spot image, and it is confirmed that the misalignment of the beam is smaller than the tolerance of 0.5 mm. | ||
| TUPB69 | Numerical Analysis on the Gain-reduction Characteristics of Multi-wire Proportional Chambers | 502 |
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| Several MWPC (Multi-Wire Proportional Chamber) monitors are installed to diagnosis the beam profiles in the high-energy beam transport at HIMAC (Heavy Ion Medical Accelerator in Chiba) synchrotrons. When the intensity of the incident beams are much high, the gain reduction of the output signal from the MWPC monitor occurs due to the space charge effect of positive ions around the anode wires. The gain reduction is expected to be improved by changing geometric parameters, such as anode radius and distance between electrodes. In order to investigate the gain-reduction characteristics for different geometric parameters, we performed numerical simulation using a numerical code. The numerical code was developed using a two-dimensional drift-diffusion model to evaluate the gas gain including the reduction effect caused by the space charge effect of the moving positive ions. We investigate the gain-reduction rate for several parameters of the anode distance when changing the beam intensity. From these results, we discuss desirable distances between the anode wires to improve the gain reduction. | ||
| TUPB73 | Development of a Beam Profile Monitor using Nitrogen-Molecular Jet for Intense Beams | 511 |
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Funding: This work was supported by MEXT/JSPS KAKENHI Grant Number of 24310079 (Grant-in-Aid for Scientific Research(B)). A non-destructive beam profile monitor using a sheeted jet beam of nitrogen molecular as a target has been developed for intense ion beams. The pressure of the sheeted molecular beam was 5 x 10-4 Pa at the beam collision point. A light emitted from excited nitrogen by an ion beam collision is measured by a high sensitive camera with a radiation resistant image intensifier. Verification of such a principle was already demonstrated with low-energy ion beams[1]. In this paper, some actual designs for intense beams of the J-PARC MR will be discussed mainly as bellow, intensity upgrade of the jet beam production, configuration of the detection chamber and its apparatus placed beam collision point, and the optical system for the light detection. *[1] Y. Hashimoto, et al., Proc. of IPAC'10, Kyoto, Japan, p.987-989. |
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