Characterisation of cardiac and respiratory motion in cone-beam CT images for cardiac SABR
Daniel, J. Burke, K. Whitehurst, Philip
Daniel, J.
Burke, K.
Whitehurst, Philip
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Abstract
Purpose or Objective
Cardiac SABR is a new treatment technique for ventricular tachycardia which delivers 25 Gy in a single
fraction to the errant substrate in the myocardium. Planning challenges include the motion of both the
diaphragm and the heart. We propose a method to track the heart and diaphragm in order to characterise
motion for radiotherapy treatment planning and to quality assure patient set-up using raw CBCT projection
data.
Materials and Methods
Planar images acquired as part of routine 4D Elekta XVI cone beam CTs included views of the heart and
diaphragm over a range of 200°. The distal electrode (pacing lead tip) of implantable cardioverter devices
(ICDs) were visible in the images and provided a suitable surrogate for target motion. Code written in Python
3 was used to process the images and identify the position of the pacing lead tip and level of the apex of the diaphragm (target and OAR surrogates respectively). Motion traces were reported for the lead tip in the three
cardinal axes and in the sup-inf axis for the diaphragm. Fourier analysis subsequently allowed respiratory
motion to be separated from cardiac motion.
Validation of this process was carried out using a ball-bearing in motion on a moveable platform. Data
tracking accuracy was assessed by manual identification of positions compared with automatic tracking. Data
from three patients treated at our centre were analysed for cardiac and respiratory motion.
Results
Phantom validation measurements showed that motion was quantified to within 0.5 mm for motion amplitudes
over a clinically relevant range. For the three patients included in this study, lead tip displacement was
measured to be on average (± standard deviation) 9.5 ± 2.1 mm (left-right), 9.7 ± 1.8 mm (ant-post) and 12.9
± 2.7 mm (sup-inf). Cardiac motion alone was shown to provide approximately two thirds of the total motion
(see table). Diaphragm positions were between 11 and 19 mm measured as average peak-to-trough
values. The accuracy of lead tip tracking was > 82% and diaphragm tracking was > 94% for each of the
patients. Conclusion
A novel technique for measuring motion in the hearts of patients undergoing radiotherapy has been developed
and validated. A three-patient sample has reported results in-line with motion data measured by other
authors using alternative measurement approaches. Characterisation of motion for radiotherapy treatment
planning and quality assurance of patient set-up have been shown to be possible for cardiac SABR using
routinely acquired cone-beam CT images.
Authors
Description
Date
2021
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Daniel J, Burke K, Whitehurst P. Characterisation of cardiac and respiratory motion in cone-beam CT images for cardiac SABR. Radiotherapy and Oncology. 2021;161:S385-S6.