Development and Evaluation of a Target-tracking Radiation-therapySystem Using a Multileaf Collimator (MLC) Synchronized with MovingOrgans

Abstract

A target-tracking radiation-therapy (RT) system that tracks the movement of a treatment target resulting from internal organ movement has been developed, and the system was evaluated for effectiveness. The developed radiation-therapy system determines the limit of the MLC (multileaf collimator) movement range with an acquired maximum displacement value of target movement during the radiotherapy planning stage and moves the MLC to continuously detect and synchronize the displacement of the abdominal by using a CCD camera monitoring system during real-time RT treatment. The system consists of a Co-60 teletherapy unit, an abdominal displacement detection system to correlate the movement of internal organs, and a MLC moving stage synchronized with the abdominal displacement. The effectiveness of the RT system was evaluated by analyzing the beam penumbra from the dose distribution on films (Gafchromic EBT) installed within a moving phantom. Penumbra widths (80%/20%) were measured for the nominal left (perpendicular to leaf motion) and right (parallel to leaf motion) directions of the x-axis and the y-axis for a fixed phantom and fixed MLC (3.3 mm/3.5 mm and 3.7 mm/3.1 mm), a moving phantom and a fixed MLC (9.0 mm/8.2 mm and 9.1 mm/8.8 mm), and a moving phantom and a moving MLC (3.7 mm/3.5 mm and 3.7 mm/3.8 mm). Percent area deviations of the 100% to 80% field of the maximum dose for the exposure condition of a fixed phantom and a fixed MLC were a relatively low value of 0.64% and a relatively high value of 15.04%, as compared to the values for a moving phantom and a fixed MLC and for a moving phantom and a moving MLC. With the method to move the MLC by passive synchronization with organ motion, the target-tracking radiation-therapy system was successfully implemented and was evaluated for performance. In future studies, various verification processes should be performed prior to the application of the system in a clinical situation.