NIRS, Chiba-shi
Construction of new treatment facility as an extension of the existing HIMAC facility, in which all treatment room will be equipped with a 3D pencil beam scanning system, is in progress at NIRS. The challenge of this project is to realize treatment of a moving target by scanning irradiation, because pencil beam scanning is more sensitive to organ motions compared with the conventional broad-beam irradiation. To accomplish practical moving target irradiation, a prototype of the scanning irradiation system was constructed and installed into existing HIMAC physics experiment course. One of the most important features of the system to be tested is fast scanning toward moving target irradiation with a relatively large number of rescannings within an acceptable irradiation time. Commissioning of the prototype is successfully in progress cooperating with highly stabilized beam provided by the HIMAC accelerator complex. We will report the design of the system and the status of the beam study.
NIRS, Chiba-shi
AEC, Chiba
Tumor therapy using energetic carbon ions, as provided by the HIMAC, has been performed since June 1994, and more than 5000 patients were treated until now. With the successful clinical results over more than ten years, we are constructing a new treatment facility. The new facility would have three treatment rooms; two of them have both horizontal and vertical fixed-irradiation-ports, and the other has a rotating-gantry-port. For all the ports, a scanning irradiation method is applied. The new facility is constructed in conjunction with the HIMAC, and heavy-ion beams will be provided by the HIMAC accelerators. To fulfill requirements for the scanning irradiation, we proposed multiple-energy operation with the quasi-DC extension of a flat top. With this operation, the beam energy can be successively varied within a single synchrotron-cycle, and therefore no energy degrader or the range shifter is required. The beam acceleration and extraction tests of the multiple-energy operation were successfully made. We will present the development of this operation as well as results of the beam acceleration tests.
NIRS, Chiba-shi
For the beam profile diagnosis of heavy ion cancer therapy in HIMAC (Heavy Ion Medical Accelerator in Chiba), a MWPC (Multi-Wire Proportional Counter) detector is employed as a beam profile monitor. Due to the high rate beams (~ 108 pps), a gain reduction of output signals, which is caused by space charge effects, have been observed in the scanning beam experiments at HIMAC. In order to reduce the gain reduction by optimizing the parameters of MWPCs including anode radius, and distance between electrodes, a numerical calculation code was developed by employing two-dimensional fluid model. In order to understand the relations between the gain reduction and space charge distribution, the temporal evolution of the ion/electron distribution were calculated for several hundredμseconds, which is significantly longer than the time period required for ions to travel between the electrodes. The output signal was also evaluated by the current flux into the anode and compared with that obtained by the beam experiment at HIMAC. The dependence of the gain reduction on the MWPC parameters was analyzed from these calculation results.
NIRS, Chiba-shi
AEC, Chiba
Based on more than ten years of experience of the carbon cancer therapy with HIMAC, we have proposed a new treatment facility for the further development of the therapy with HIMAC. This facility will consist of three treatment rooms: two rooms equipped with horizontal and vertical beam-delivery systems and one room with a rotating gantry. For the beam-delivery system of the new treatment facility, a 3D hybrid raster-scanning method with gated irradiation with patient's respiration has been proposed. A R&D study has been carried out toward the practical use of the proposed method. In the R&D study, we have improved the beam control of the size, the position and the time structure for the proposed scanning method with the irradiation gated with patient's respiration. Further, owing to the intensity upgrade of the HIMAC synchrotron, we can successfully extend the flattop duration, which can complete one fractional irradiation with one operation period. The building construction of the new treatment facility will be completed at March 2010 and treatment of 1st patient is scheduled at March 2011. We will report the recent progress on the new treatment facility project at HIMAC.
NIRS, Chiba-shi
The development of the screen monitor system (SCN) at the Heavy Ion Medical Accelerator in Chiba (HIMAC) comprises the surveillance of the carbon beam. In the three-dimensional scanning system for the carbon therapy, the beam qualities, i.e., position, size and intensity of the beam, play a significant role for the patient's treatment. Therefore, we designed a semi-nondestructive monitoring system located on the the high-energy beam transport line to monitor the beam qualities by using a thin fluorescent screen and a high-speed charge-coupled device. The beam position and profile were obtained from the light emitting distribution of the screen. The SCN was checked on the prototype scanning system at HIMAC and succeeded to monitor the beam real-time in steps of about 10 msec, corresponding to a 100 Hz sampling rate. The developments steps will focus toward a operation at HIMAC's new therapy facility extension, recently. In the conference, we would like to report on details of the automatic beam tuning before starting the treatment and the interlock system during therapy using the SCN.
NIRS, Chiba-shi
The betatron tune fluctuation due to the current ripple of power supplies brings the beam spill ripple through the stable area variation in resonant slow extraction. The effect becomes dominant especially in the case of the low beam rate extraction. The RF-knockout slow extraction method is insensitive to the tune ripple compared to the ordinary one because it uses the diffusion with the transverse RF field. However, the ripple effect appears even in the beam spill extracted by it. The amount of the separatrix fluctuation due to the tune ripple depends on the difference between the bare and the resonant tune, and the sextupole magnetic strength. We measured the correlation between the beam spill and the tune ripple which was the artificially generated with low and high frequency components of 67 Hz and 1167 Hz near those of the real current ripple. We confirmed the reduction of the beam spill ripple by setting the tune away from the resonance while keeping the separatrix area. The comparison between the experimental results, the analytical calculation and the simulation will be reported.