Breathing motion
Multiple breath-hold CBCT for online image guided radiotherapy of lung tumors: Simulation with a dynamic phantom and first patient data

https://doi.org/10.1016/j.radonc.2011.01.019Get rights and content

Abstract

Background and Purpose

Computer controlled breath-hold effectively reduces organ motion for image-guided precision radiotherapy of lung tumors. However, the acquisition time of 3D cone-beam-CT (CBCT) exceeds maximum breath-hold times. We have developed an approach enabling online verification using CBCT image acquisition with ABC®-based breath-hold.

Methods

Patient CBCT images were acquired with ABC®-based repeat breath-hold. The clinical situation was also simulated with a Motion Phantom. Reconstruction of patient and phantom images with selection of free-breathing and breath-hold projections only was performed.

Results

CBCT-imaging in repeat breath-hold resulted in a precisely spherical appearance of a tumor-mimicking structure in the phantom. A faint “ghost” structure (free-breathing phases) can be clearly discriminated. Mean percentage of patient breath-hold time was 66%. Reconstruction based on free-breathing-only shows blurring of both tumor and diaphragm, reconstruction based on breath-hold projections only resulted in sharp contours of the same structures. From the phantom experiments, a maximal repositioning error of 1 mm in each direction can be estimated.

Discussion and Conclusion

CBCT during repetitive breath hold provides reliable soft-tissue-based positioning. Fast 3D-imaging during one breath-hold is currently under development and has the potential to accelerate clinical linac-based volume imaging.

Section snippets

Patient treatment planning and cone-beam volume acquisition

Treatment planning CT was acquired during one moderately deep inspiratory ABC®-based breath-hold and the CT data was exported to the XVI® system [38]. The depth of inspiration was determined during a patient training session with ABC® and was typically set at approximately 70% of vital capacity. The treatment was delivered during the ABC®-inspiration breath hold. The linac and ABC® interface were not connected and so, when either the treatment beam finished or the breath hold had completed the

Phantom data: image interpretation

CBCT imaging of the simulation of “free breathing” in the dynamic thorax phantom (CIRS; Fig. 2. A–C) resulted in blurred “tumor” contours especially in the craniocaudal direction. CBCT imaging during the simulation of the repeat breath-hold situation (free breathing 8 mm, breath-hold 24 mm Fig. 2. D–F) resulted in images which replicated the tumor position in breath-hold. Fig 2 clearly shows the blurred appearance of the lung-tumor mimicking moving phantom insert during free breathing and the

Discussion

Several techniques compensate for breathing motion. Free breathing planning and irradiation result in motion artefacts and potential insufficient dose coverage [41], [42], [43]. Non-monitored breath hold approaches represent a possible means to reduce the margin, which accounts for margin between CTV and PTV safety margins but comparison of noncontrolled and controlled approaches indicate superior results with controlled approaches [32], [44], [45]. Controlled breath-hold approaches such as

Conclusions

Cone beam CT acquisition with ABC®-based repeated breath-holds including free breathing between breath-hold is a feasible approach for image-guided extracranial precision lung radiotherapy and allows on-line 3D–3D soft-tissue-based matching to be performed.

Conflict of interest statement

This work was in part supported by a Grant of Elekta, Crawley, UK.

Acknowledgements

Parts of these studies were supported by a research grant from Elekta Inc. The first author is supported by the “Ministerium für Bildung und Forschung, Baden-Württemberg“ and the ESF (European Social Fonds).

The work undertaken at The Royal Marsden NHS Foundation Trust received a proportion of its funding from the NHS Executive; the views expressed in this publication are those of the authors and not necessarily those of the NHS Executive. This work was supported by the Institute of Cancer

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