Motion adaptive x-ray therapy: a feasibility study

Intrafraction motion caused by breathing requires increased treatment margi ns for chest and abdominal radiotherapy and may lead to 'motion artefacts' in dose distributions during intensity modulated radiotherapy (IMRT). Techn ologies 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 distr ibution artefacts, without compromising delivery time, is to synchronously follow the target motion by adapting the x-ray beam using a dynamic multile af 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 respirati on onto the beam originally planned for delivery. Thus during beam delivery the beam is dynamically changing position with respect to the isocentre us ing a dynamic MLC, the leaf positions of which are dependent upon the targe t position. Synchronization of the MLC motion and target motion occurs usin g respiration gated radiotherapy equipment. The concept and feasibility of MAX-T and the capability of the treatment machine to deliver such a treatme nt 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 b e equivalent to those delivered to a static target by a static beam.