Eri Takeshita

Moving target irradiation with fast rescanning and gating in particle therapy.

PURPOSE In moving target irradiation with pencil beam scanning, the interplay effect between the target motion and the scanned beam is a problem because this effect causes over or under dosage in the target volume. To overcome this, we have studied rescanning using a gating technique. METHODS A simulation and experimental study was carried out. In the experiment, we used the fast scanning system developed at the HIMAC to verify the validity of phase controlled rescanning method, in which the time for rescanning irradiation of each slice is matched to the gating duration. RESULTS Simulation and experimental results showed that controlling the scan speed to match the respiration cycle with rescans can deliver the blurred dose distribution. In the comparison between the static measurements and the moving measurements with the phase controlled rescanning method, the dose difference was less than 2% for pinpoint chambers in the target volume. CONCLUSIONS The simulation and experimental results demonstrated that the phase controlled rescanning method makes it possible to deliver the dose distribution close to the expected one. As an experimental result for 3D irradiation, it was estimated that blurring by the probability density function was not only for a lateral distribution, but also for a distal distribution, even in the lateral rescanning.

Performance of the NIRS fast scanning system for heavy‐ion radiotherapy

PURPOSE A project to construct a new treatment facility, as an extension of the existing HIMAC facility, has been initiated for the further development of carbon-ion therapy at NIRS. This new treatment facility is equipped with a 3D irradiation system with pencil-beam scanning. The challenge of this project is to realize treatment of a moving target by scanning irradiation. To achieve fast rescanning within an acceptable irradiation time, the authors developed a fast scanning system. METHODS In order to verify the validity of the design and to demonstrate the performance of the fast scanning prior to use in the new treatment facility, a new scanning-irradiation system was developed and installed into the existing HIMAC physics-experiment course. The authors made strong efforts to develop (1) the fast scanning magnet and its power supply, (2) the high-speed control system, and (3) the beam monitoring. The performance of the system including 3D dose conformation was tested by using the carbon beam from the HIMAC accelerator. RESULTS The performance of the fast scanning system was verified by beam tests. Precision of the scanned beam position was less than +/-0.5 mm. By cooperating with the planning software, the authors verified the homogeneity of the delivered field within +/-3% for the 3D delivery. This system took only 20 s to deliver the physical dose of 1 Gy to a spherical target having a diameter of 60 mm with eight rescans. In this test, the average of the spot-staying time was considerably reduced to 154 micros, while the minimum staying time was 30 micros. CONCLUSIONS As a result of this study, the authors verified that the new scanning delivery system can produce an accurate 3D dose distribution for the target volume in combination with the planning software.

SU-F-J-190: Time Resolved Range Measurement System Using Scintillator and CCD Camera for the Slow Beam Extraction

PURPOSE To investigate the time structure of the range, we have verified the rang shift due to the betatron tune shift with several synchrotron parameters. METHODS A cylindrical plastic scintillator block and a CCD camera were installed on the black box. Using image processing, the range was determined the 80 percent of distal dose of the depth light distribution. The root mean square error of the range measurement using the scintillator and CCD system is about 0.2 mm. Range measurement was performed at interval of 170 msec. The chromaticity of the synchrotron was changed in the range of plus or minus 1% from reference chromaticity in this study. All of the particle inside the synchrotron ring were extracted with the output beam intensity 1.8×108 and 5.0×107 particle per sec. RESULTS The time strictures of the range were changed by changing of the chromaticity. The reproducibility of the measurement was sufficient to observe the time structures of the range. The range shift was depending on the number of the residual particle inside the synchrotron ring. CONCLUSION In slow beam extraction for scanned carbon-ion therapy, the range shift is undesirable because it causes the dose uncertainty in the target. We introduced the time-resolved range measurement using scintillator and CCD system. The scintillator and CCD system have enabled to verify the range shift with sufficient spatial resolution and reproducibility.

The Ion-Beam Radiation Oncology Center in Kanagawa (i-ROCK) Carbon Ion Facility at the Kanagawa Cancer Center

The Kanagawa Cancer Center (KCC) is the core facility for cancer care in Kanagawa Prefecture. It serves a population of more than 9 million people. Planning for the ionbeam Radiation Oncology Center in Kanagawa (i-ROCK) started in 2015. The basic framework and design of i-ROCK was established in 2010, and it is the first cancercenter-based carbon ion radiation therapy facility in the world and the fifth carbon ion radiation therapy facility in Japan. The building was completed in August 2014 (Figure 1). The installation of beam delivery equipment has been completed. The start of clinical operation is planned for December 2015. An overview of i-ROCK is presented in this report.