Optimization of high precision, hypo-fractionated radiotherapy for moving targets

Abstract

Respiratory-induced motion of tumours located in the thorax can significantly degrade the
geometrical accuracy of radiotherapy and as such result in lower tumor control and higher soft
tissue complication probabilities. Therefore, several motion management strategies have been
developed and clinically implemented, which can typically be categorized in passive and active
strategies. Using passive strategies, the extent of the respiratory-induced motion is measured
once, pre-treatment, and motion encompassing volumes are defined to ensure the tumour
receives sufficient dose. On the contrary, with active motion management, the tumour location
and motion is monitored in real-time and treatment parameters are updated as such.
The first aim of this thesis was to quantify breathing-induced motion variability, to evaluate the
robustness of passive motion management strategies and the reliability of a single pre-
treatment measurement. Second, the aim was to develop a markerless tumor tracking
framework, applicable on conventional radiotherapy systems, which would enable active motion
management, but also real-time monitoring during passive motion management, on a broad
scale. The studies performed in this thesis showed that breathing-induced motion variability is
large for lesions moving with higher amplitudes, and so passive motion management is only
advisable for those tumours moving with smaller amplitudes. Further, a framework for
markerless tracking was developed based on three pilars ; the visibility of tumours on real-time
images was improved through the development of dual-energy imaging techniques, a robust
tracking algorithm was translated from computer vision to the medical imaging domain, and a
framework was developed to make optimal use of pre-treatment information.

Date of Award	8 Oct 2020
Original language	English
Awarding Institution	Vrije Universiteit Brussel
Supervisor	Dirk Verellen (Promotor), Jef Vandemeulebroucke (Co-promotor), Johan De Mey (Co-promotor), Andre Dekker (Jury), Jenny Bertholet (Jury), Charlotte Billiet (Jury), Bart Jansen (Jury) & Guy Nagels (Jury)