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A Feasibility Study On Molecular-Imaging-Based Real-Time Tumor Tracking for Gated Radiotherapy

M Ishikawa

M Ishikawa1*, S Tanabe2, S Yamaguchi3, N Ukon1, T Yamanaka1, K Sutherland1, N Miyamoto1, R Suzuki4, N Katoh4, K Yasuda4, H Shirato1, (1) Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, (2) Keiyuukai Sapporo Hospital, Sapporo, ,(3) Iwate Medical University, Iwate, ,(4) Hokkaido Univesity Hospital, Sapporo,

SU-E-J-57 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Molecular imaging is one of the important modalities in delineating tumors particularly in radiotherapy treatment planning. If the real-time tumor position can be detected using molecular imaging during radiotherapy, it may be helpful for gated irradiation. A feasibility study on a beam gating system for radiotherapy using real-time molecular imaging was conducted by the prototype and simulating a parallel plane PET system.

Methods: Assuming that the motion of the positron source is constrained to the central plane, the source position can be calculated from a cross point of the Line of Response (LOR) and the central plane between detector surfaces. If a positron source is located at the ISO center, distribution of the cross points might be blurred due to random/scattered coincidence. Center Located Ratio (CLR) was defined as a ratio of LORs passing through the ISO center divided by the entire LORs. When dislocation for perpendicular direction is occurred, a distribution of cross points will be spread out and associated decrease of CLR value will be expected.

Results: The behavior between real measurement and simulation was similar on proto-type experiments, however, the result from simulation for demonstrator might be different from actual measurement. RTRT system recognizes the position of a gold marker in the rate of 30 fps using two X-ray television systems. It is shown that 15,000 events per second will be needed for an appropriate gating irradiation to recognize discrepancy over 2mm of time resolution in the parallel plane PET system demonstrator.

Conclusion: A feasibility study was carried out to verify the potential for gating irradiation of tumors with real-time molecular imaging using a parallel plane PET system.
For an parallel plane PET system demonstrator, the possibility of detecting the tumor position with an accuracy of 2 mm from the ISO center with 500 events.

Funding Support, Disclosures, and Conflict of Interest: This research was a part of the "Innovation COE Program for Future Drug Discovery and Medical Care" project and partially supported by the Grant-in-Aid for Project for Developing Innovation Systems of the Japanese Ministry of Education, Culture, Sports, Science and Technology.

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