IBIC2012 - List of Authors (Iwata, Y.)

Paper	Title	Page
MOPA37	Reliable Beam-Intensity Control Technique at the HIMAC Synchrotron	143
	K. Mizushima, T. Furukawa, Y. Hara, Y. Iwata, K. Katagiri, K. Noda, S. Sato, T. Shirai NIRS, Chiba-shi, Japan
	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.

Paper

Title

Page

Reliable Beam-Intensity Control Technique at the HIMAC Synchrotron

143

K. Mizushima, T. Furukawa, Y. Hara, Y. Iwata, K. Katagiri, K. Noda, S. Sato, T. Shirai
NIRS, Chiba-shi, Japan

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.