Motion adaptive x-ray therapy: a feasibility study

TLDR

Breathing‑induced intrafraction motion in chest and abdominal radiotherapy necessitates larger treatment margins and can create dose artefacts, while gated or breath‑hold techniques increase treatment time or are poorly tolerated. The study aimed to develop and evaluate a motion‑adaptive x‑ray therapy (MAX‑T) that synchronizes a dynamic multileaf collimator with target motion to reduce margins and artefacts without extending delivery time. MAX‑T achieves this by superimposing respiratory‑induced target motion onto the pre‑planned beam, allowing the dynamic MLC to adjust leaf positions in real time so the beam view remains static, with synchronization performed using respiration‑gated equipment and verified on a mechanical sinusoidal oscillator. Dose measurements for moving targets using MAX‑T were equivalent to those delivered to static targets with a static beam, demonstrating the technique’s feasibility.

Abstract

Intrafraction motion caused by breathing requires increased treatment margins for chest and abdominal radiotherapy and may lead to `motion artefacts' in dose distributions during intensity modulated radiotherapy (IMRT). Technologies such as gated radiotherapy may significantly increase the treatment time, while breath-hold techniques may be poorly tolerated by pulmonarily compromised patients. A solution that allows reduced margins and dose distribution artefacts, without compromising delivery time, is to synchronously follow the target motion by adapting the x-ray beam using a dynamic multileaf collimator (MLC), i.e. motion adaptive x-ray therapy, or MAX-T for short. Though the target is moving with time, in the MAX-T beam view the target is static. The MAX-T method superimposes the target motion due to respiration onto the beam originally planned for delivery. Thus during beam delivery the beam is dynamically changing position with respect to the isocentre using a dynamic MLC, the leaf positions of which are dependent upon the target position. Synchronization of the MLC motion and target motion occurs using respiration gated radiotherapy equipment. The concept and feasibility of MAX-T and the capability of the treatment machine to deliver such a treatment were investigated by performing measurements for uniform and IMRT fields using a mechanical sinusoidal oscillator to simulate target motion. Target dose measurements obtained using MAX-T for a moving target were found to be equivalent to those delivered to a static target by a static beam.