Optimization and evaluation of multiple gating beam delivery in a synchrotron-based proton beam scanning system using a real-time imaging technique.
OBJECTIVE
To find the optimum parameter of a new beam control function installed in a synchrotron-based proton therapy system.


METHODS
A function enabling multiple gated irradiation in the flat top phase has been installed in a real-time-image gated proton beam therapy (RGPT) system. This function is realized by a waiting timer that monitors the elapsed time from the last gate-off signal in the flat top phase. The gated irradiation efficiency depends on the timer value, Tw. To find the optimum Tw value, gated irradiation efficiency was evaluated for each configurable Tw value. 271 gate signal data sets from 58 patients were used for the simulation.


RESULTS
The highest mean efficiency 0.52 was obtained in TW=0.2s. The irradiation efficiency was approximately 21% higher than at TW=0s, which corresponds to ordinary synchrotron operation. The irradiation efficiency was improved in 154 (57%) of the 271 cases. The irradiation efficiency was reduced in 117 cases because the TW value was insufficient or the function introduced an unutilized wait time for the next gate-on signal in the flat top phase. In the actual treatment of a patient with a hepatic tumor at Tw=0.2s, 4.48GyE irradiation was completed within 250s. In contrast, the treatment time of ordinary synchrotron operation was estimated to be 420s.


CONCLUSIONS
The results suggest that the multiple gated-irradiation function has potential to improve the gated irradiation efficiency and to reduce the treatment time.
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan; Hitachi Ltd., 1-1 7-chome, Oomika-cho, Hitachi-shi, Ibaraki 319-1292, Japan.
Takahiro
T
Yamada
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan. Electronic address: miya-nao@med.hokudai.ac.jp.
Naoki
N
Miyamoto
Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, North13 West8, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Taeko
T
Matsuura
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Seishin
S
Takao
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Yusuke
Y
Fujii
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Yuka
Y
Matsuzaki
Department of Medical Physics, Graduate School of Medicine, Hokkaido University, North15 West7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Hidenori
H
Koyano
Hitachi Ltd., 1-1 7-chome, Oomika-cho, Hitachi-shi, Ibaraki 319-1292, Japan.
Masumi
M
Umezawa
Hitachi Ltd., 1-1 7-chome, Oomika-cho, Hitachi-shi, Ibaraki 319-1292, Japan.
Hideaki
H
Nihongi
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan; Global Station of Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, North15 West7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Shinichi
S
Shimizu
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan; Global Station of Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, North15 West7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Hiroki
H
Shirato
Proton Beam Therapy Center, Hokkaido University Hospital, North14 West5, Kita-ku, Sapporo, Hokkaido 060-8638, Japan; Global Station of Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, North15 West7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan; Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, North13 West8, Kita-ku, Sapporo, Hokkaido 060-8638, Japan.
Kikuo
K
Umegaki
D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D061766:Proton Therapy / Q000295:instrumentation*; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation*; D017356:Synchrotrons; D013997:Time Factors
Gated irradiation; Respiratory motion; Spot scanning; Tumor tracking