Abstract
By adapting to the actual patient anatomy during treatment, tracked multi-leaf collimator (MLC) treatment deliveries offer an opportunity for margin reduction and healthy tissue sparing. This is assumed to be especially relevant for hypofractionated protocols in which intrafractional motion does not easily average out. In order to confidently deliver tracked treatments with potentially reduced margins, it is necessary to monitor not only the patient anatomy but also the actually delivered dose during irradiation. In this study, we present a novel real-time online dose reconstruction tool which calculates actually delivered dose based on pre-calculated dose influence data in less than 10 ms at a rate of 25 Hz. Using this tool we investigate the impact of clinical target volume (CTV) to planning target volume (PTV) margins on CTV coverage and organ-at-risk dose. On our research linear accelerator, a set of four different CTV-to-PTV margins were tested for three patient cases subject to four different motion conditions. Based on this data, we can conclude that tracking eliminates dose cold spots which can occur in the CTV during conventional deliveries even for the smallest CTV-to-PTV margin of 1 mm. Changes of organ-at-risk dose do occur frequently during MLC tracking and are not negligible in some cases. Intrafractional dose reconstruction is expected to become an important element in any attempt of re-planning the treatment plan during the delivery based on the observed anatomy of the day.
Highlights
Dynamic multi-leaf collimator (MLC) tracking is an emerging form of adaptive radiotherapy suitable for tumours which are affected by intrafractional motion
The benefit of applying MLC tracking to more mobile tumour sites such as lung is hypothesised, but as of today not demonstrated in clinical studies
A finer sampling in the direction orthogonal to the MLC leaves could increase the accuracy for beamlets partially covered by the Y collimators, but was not tested as it is not expected to be beneficial for the majority of MLC leaves as beamlets and leaves both have a 5 mm width and are perfectly aligned
Summary
Dynamic multi-leaf collimator (MLC) tracking is an emerging form of adaptive radiotherapy suitable for tumours which are affected by intrafractional motion. MLC tracking, in its currently prevalent form, is focussed on dynamically reshaping the treatment field in the beam’s-eye-view according to the actual recorded target motion. This is sometimes referred to as translational or centroid tracking. Non-invasive and yet largely untested (in the context of radiotherapy) target detection techniques are ultrasound imaging (Schlosser et al 2010) and magnetic resonance (MR) imaging (Crijns et al 2012, Yun et al 2013). The latter technique holds a lot of promise when available on a MR-guided delivery machine. Due to their superior soft-tissue contrast, MR images are expected to visualise target translations, and target rotations and deformations as well as organ-at-risk (OAR) motion
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
