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Improvement of the Positional Reproducibility of Head and Neck Cancer Patient Using the Orbitomeatal Angle in Radiotherapy

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T Aoyama

T Aoyama1*, H Shimizu1 , M Ando2 , T Isomura1 , K Nakashima1 , K Yokoi1 , T Iwata1 , H Tachibana1 , T Kodaira1 , (1) Aichi Cancer Center Hospital, Nagoya, Aichi, (2) Aichi Medical University Hospital, Nagakute, Aichi,


SU-I-GPD-J-28 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The purpose of this study is to improve the reproducibility of patient positions in radiotherapy for the head and neck cancer by considering the angle of orbitomeatal (OM) line on the planning CT.

Methods: Nineteen patients with the head and neck cancer were included in the retrospective analysis. Relative setup error between daily megavolt CT image and the planning CT image was assessed at each cervical spine (C1, C2, C3, C5 ,C6 and C7) position for reference one (C4). The setup error was calculated for 3 rotation angles (pitch, roll, and yaw). We analyzed the relation between the setup error for each cervical spine and the angle of OM line on the planning CT.

Results: The errors of pitch and roll in the patient group with the OM angle less than 25 degrees (OM≤25) were significantly smaller than those of the patient group with the OM angle more than 25 degrees (OM>25): especially, the errors of pitch for C2, C3, C5, and C6 in OM≤25 and OM>25 groups were 1.5 vs. 4.7 degrees (p < 0.01), 1.8 vs. 3.1 degrees (p = 0.017), 2.1 vs. 3.8 degrees (p = 0.013), and 2.5 vs. 4.4 degrees (p = 0.028), respectively; the errors of roll for C1, C2, C3 in the both groups were 1.2 vs. 3.1 degrees (p = 0.028), 1.7 vs. 3.0 degrees (p = 0.022), and 1.5 vs. 3.2 degrees (p < 0.01) , respectively. There was no significant difference in yaw.

Conclusion: The OM angle less than 25 degrees on the planning CT can improve the setup error in pitch and roll rotation.

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