Feasibility of fiducial-free prone-position treatments with CyberKnife for lower lumbar/sacral spine lesions

Christoph Fürweger,Christian G Drexler,B Wowra,Markus Kufeld

doi:10.7759/cureus.21

Abstract

Objective: For spinal CyberKnife (CK) treatments, prone patient position can yield a dosimetric advantage for posterior lesions, but the target can be subject to respiratory motion. We treated 17 lower lumbosacral lesions in prone position using CK fiducial-free XsightTM spine tracking and analyzed motion data in order to establish an adequate margin concept. Methods: The lumbar spine and pelvis were elevated and stabilized to decouple the target from respiration. The tracking region of interest was centered at the lumbar vertebrae L4/L5. Pairs of X-ray images were taken periodically (1.4 per minute) during treatment. Tracking data from two periods of 6 to 15 minutes per treatment were analyzed to assess the extent of breathing-induced motion. Results: Stochastic motion in left/right and superior/inferior direction was small, with peak amplitudes of 0.40±0.20 mm and 0.58±0.31 mm. Anterior/posterior spine motion was significantly increased with a peak amplitude of 1.27±0.50 mm, and was positively correlated with a head-down/-up tilt of the spine due to breathing. Conclusions: Fiducial-free prone treatments of the lower lumbar and sacral spine are feasible using XsightTM spine tracking and proper immobilization. The residual impact of respiratory motion can be compensated with an additional PTV margin of 3 mm.

Highlights

Spinal stereotactic radiosurgery is an increasingly adopted technique [1] that relies on highly accurate delivery of large radiation doses to spinal lesions
Xsight spine tracking could be performed with no indication of a regional mismatch
In terms of the stochastic component, prone patient position resulted in substantial amount of motion in anterior/posterior direction, which significantly exceeded movement along the left/right (p=7.4x10-5, paired student t-test) and superior/inferior (p=9.1x10-7, paired student ttest) axes

Summary

Introduction

Spinal stereotactic radiosurgery is an increasingly adopted technique [1] that relies on highly accurate delivery of large radiation doses to spinal lesions. For this purpose, different imageguidance methods are applied in order to minimize the geometric targeting error. The current CyberKnife version (CK, Accuray Inc., Sunnyvale, CA) has recently been described in a comprehensive review [6]. It is comprised of a compact linear accelerator mounted on a robotic arm, and a stereoscopic kV imaging system. For image-guided delivery of CK treatments, different software applications are used to identify the target and to correct the

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Conclusion