Real-time compensation of target motion with a dynamic multileaf collimator

Abstract

Advanced high quality radiation therapy techniques such as IMRT require an accurate delivery of precisely modulated fluence patterns to the target volume. Intrafractional motion, however, may considerably deteriorate the accuracy of the dose delivery. To compensate for these errors, a dynamic real-time capable MLC control system was designed and implemented which compensates during the delivery for the motion and deformation of the target volume. Specialized algorithms were developed which constantly optimize the MLC aperture based on online provided target information allowing the sparing of adjacent organs-at-risk from additional dose. These algorithms were implemented in a dynamic target tracking control system for the Siemens 160 MLC™. Experiments using different phantom setups were performed to assess and quantify the quality of the tracking technique. The results showed that 2-dimensional target motion can be compensated for with the new control system. For a clinical IMRT dose distribution, the congruence within 2 % / 2 mm with a static reference delivery was increased from 18.75% to 76.79 %. Similar improvements were achieved for the delivery of a complete IMRT treatment fraction to a moving lung phantom. However, the quality of the tracking system is limited by the system's latency times. The experiments proved that the tracking concept, the new algorithms and the dynamic control system allow to effectively compensate for target motion in real-time. It therefore can increase the accuracy and the quality of the treatment delivery. © 2009 Springer-Verlag.