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Dosimetric impact of angular deviations in positioning for spinal radiosurgery
Jinkoo Kim, Jian-Yue Jin, Ning Wen, Samir H. Patel, Benjamin Movsas, Jack Rock, Indrin J. Chetty, and Samuel Ryu

Purpose: During image-guided radiosurgery, it is common to account only for translational shifts while leaving rotational deviations uncorrected. The aim of this study is to investigate the rotational setup deviations and estimate the dosimetric impact in spinal radiosurgery.

Materials and methods: Stereoscopic image registrations of 711 spine radiosurgery procedures (546 patients) were retrospectively reviewed and classified to cervical (C), thoracic (T), and lumbar (L) spines. The probability of rotational deviations were estimated in three orthogonal axis. In order to investigate the dosimetric impact, the original simulation CT images were rotated in the range of ±5 deg in each axis. Then, the dosimetric changes were recorded; including the coverage (V90) and minimum dose (Dmin) to the target, and the dose of 10% volume (D10) and maximum dose (Dmax) to the spinal cord.

Results: Target rotations of >5 deg and >3 deg occurred respectively in 1% and 8% of cases. The mean rotations were small (|μ|

Conclusion: Large target rotations occurred in a small percentage of patients. The overall dosimetric impact on target coverage and cord D10 was small. However larger effects were observed on the target Dmin and cord Dmax. Special care must be taken for targets of elongated shapes involving multiple vertebrae.

Keywords: Spinal radiosurgery; image-guided radiation therapy; angular deviation; dosimetric impact; spinal cord dose

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