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Validation of Beam Accuracy of a Gated Spot-Scanning Proton Therapy System with Real-Time Tumor-Tracking at Hokkaido University

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T Yamada

T Yamada1*, T Matsuura1 , C Toramatsu1 , S Takao1 , H Nihongi1 , N Miyamoto1 , S Shimizu1 , t takayanagi2 , M Umezawa2 , K Matsuda2 , K Umegaki1 , H Shirato1 , (1) Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido, (2) Hitachi, Ltd., Hitachi Research Laboratory, Hitachi, Ibaraki, (3) Hitachi, Ltd., Hitachi Works, Hitachi, Ibaraki, (4) Department of Engineering, Hokkaido University, Sapporo, Hokkaido


SU-E-T-346 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

At Hokkaido University, we have developed a gated spot scanning proton beam therapy system with real-time tumor-tracking under collaborative work with Hitachi Ltd. This system has the ability to gate proton beams from the synchrotron, turning the beam on only when the actual positions of inserted fiducial markers monitored by two fluoroscopic X-ray systems are within the planned positions [Shirato, 2012]. In this research, we validated the accuracy of the proton beams while utilizing external gating signals.

The accuracy of spot positions, spot dose, absolute dose at the center of the SOBP, and range were measured while utilizing external gating signals. The following external gating signals were generated by an arbitrary waveform generator: (1) ON at all times (without gating), (2) an OFF period of 4 s followed by an ON period of 1 s, (3) two ON periods of 0.5 s with a 0.15 s OFF interval, (4) signals recorded during the treatment of real-time tumor-tracking X-ray therapy in Hokkaido University. The spot positions and spot dose were measured by beam monitors in the nozzle. The ranges were measured with a multi-layer ion chamber made by Hitachi Ltd. The absolute dose was measured with a Farmer ionization chamber and a RFA300 water phantom system.

The maximum error of the beam position in the isocenter plane was 0.8 mm without the gating signal and 1.0 mm with the gating signal. The maximum error of the spot dose was 0.0029 MU, below the criterion of 0.0032 MU. The maximum error of the absolute dose was 0.4% and the maximum variation of the range was 0.1 mm.

It was confirmed with measurements of the beam that the accuracy of the proton beam met the criteria with external gating signals.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by the Cabinet Office, Government of Japan and the Japan Society for the Promotion of Science (JSPS) through the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program), initiated by the Council for Science and Technology Policy (CSTP).

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