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Development of a Detection System for Intra-Fractional Motion in Intracranial Treatment Using Patient Surface Pressure

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H Inata

H Inata1, 2*, F Araki1, Y Nakaguchi1, S Nakayama2, Y Itoh2, K Uwatsu2, O Nishizaki2, (1) Kumamoto University, Kumamoto, Kumamoto, Japan (2) Saiseikai Imabari Hospital, Imabari, Ehime, Japan

SU-E-T-360 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
To develop a dedicated real-time monitoring system to detect intra-fractional motion in intracranial radiotherapy using patient surface pressure.

Methods:
The motion for two volunteers was analyzed by a new type of immobilization system that detect load given to a patient head. The immobilization system consists of sensors with a thickness of 0.55 mm and a radius of 9.1 mm, a thermoplastic mask, a vacuum bag, and an acrylic baseplate. The four pieces of sensors were positioned at left-right sides, superior-inferior sides on the vacuum bag, respectively. The other four pieces of sensors were positioned at up-down sides, left-right sides of chin just under the thermoplastic mask, respectively. The load given to the volunteer was detected by the immobilization system that the eight sensors were attached. The pressures for sensors were calculated using a measuring resistor in a voltage divider configuration. The three pieces of light-emitting diodes (LEDs) were located on the thermoplastic mask at the chin and the pair of cheeks to detect the volunteer motion. The three-dimensional positions of LEDs were continuously detected using the Cyberknife Synchrony system. The sensor's pressures were compared with the root mean square (RMS) of LEDs displacement during the 30 min interval.

Results:
The RMS values of LEDs displacement within 1 mm or less were almost related to the pressures of sensors at left and superior sides on the vacuum bag. The pressures of other sensors were not detected or no relationship with the RMS values of LEDs displacement in two volunteers.

Conclusion:
The dedicated real-time monitoring system using patient surface pressure can detect intra-fractional motion in intracranial treatment with high precision of 1 mm or less.

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