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The Impact of Sitting Positioning On Deviations of Neutron Beam Axis From Condition Pre-Planned with Diagnostic Images in Boron Neutron Capture Therapy

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T Motoyanagi

T Motoyanagi1*, K Hirose1 , T Kato1 , T Harada1 , K Arai1 , R Shimokomaki1 , Y Takai1 , (1) Southern Tohoku BNCT Research Center, Koriyama, Fukushima, Japan


SU-I-GPD-T-206 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To assess skin marker positioning errors for incidence and emitting points of neutron beam axis due to differences between patient’s supine position for diagnostic CT and sitting position as a treatment position for boron neutron capture therapy (BNCT) of head and neck cancer.

Methods: Five patients were assumed to receive BNCT for parotid cancer with sitting position. At first, using treatment planning system SERA, lesions were delineated and beam incidence and emitting points on patient skin were preliminarily decided on diagnostic CT images. These points of interests (POIs) were set on a skin surface of the neck. After the first CT scan was performed in normal supine position, patients were immediately setup with a 45-degree neck rotation toward healthy side, followed by the second CT scan. Furthermore, patients were setup in pseudo-sitting treatment position by adding “bending forward” with a 30-degree waist pad, followed by the third CT scan. After matching three CT datasets along with three standard points, such as apex of bilateral mastoid process and dorsum of nose, deviations of each POI between three CT image datasets were evaluated.

Results: The deviations of incidence and emitting points between supine and pseudo-sitting position in the LR or RL (from-diseased-to-healthy direction)/SI/AP (mm) were 5.7±4.0/-3.7±2.7/4.7±9.7, and 18.7±8.6/15.6±11.6/4.5±6.5 with the differences (mm) of 11.1±7.0 and 28.1±5.6, respectively. Roll and pitch angles (degree) of the neutron beam axis relative to skull structure in supine position were 27.6±3.9, and 16.9±12.5, respectively. The deviations in roll/pitch angles (degree) due to change of position into neck rotation and pseudo-sitting were -7.9±1.2/-0.1±1.5 and -10.7±3.2/+2.5±2.4, respectively.

Conclusion: Our results revealed that it is inevitable to perform re-planning with CT images acquired at sitting position as an actual treatment position because of large beam axis deviations derived from the impact of patient positioning in head and neck BNCT.

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