Integration of Real-Time Internal Electromagnetic Position Monitoring Coupled With Dynamic Multileaf Collimator Tracking: An Intensity-Modulated Radiation Therapy Feasibility Study
Received 11 August 2008; received in revised form 22 January 2009; accepted 25 January 2009. published online 24 April 2009.
Purpose
Continuous tumor position measurement coupled with a tumor tracking system would result in a highly accurate radiation therapy system. Previous internal position monitoring systems have been limited by fluoroscopic radiation dose and low delivery efficiency. We aimed to incorporate a continuous, electromagnetic, three-dimensional position tracking system (Calypso 4D Localization System) with a dynamic multileaf collimator (DMLC)–based dose delivery system.
Methods and Materials
A research version of the Calypso System provided real-time position of three Beacon transponders. These real-time three-dimensional positions were sent to research MLC controller with a motion-tracking algorithm that changed the planned leaf sequence. Electromagnetic transponders were embedded in a solid water film phantom that moved with patient lung trajectories while being irradiated with two different plans: a step-and-shoot intensity-modulated radiation therapy (S-IMRT) field and a dynamic IMRT (D-IMRT) field. Dosimetric results were recorded under three conditions: no intervention, DMLC tracking, and a spatial gating system.
Results
Dosimetric accuracy was comparable for gating and DMLC tracking. Failure rates for gating/DMLC tracking are as follows: ±3 cGy 10.9/ 7.5% for S-IMRT, 3.3/7.2% for D-IMRT; gamma (3mm/3%) 0.2/1.2% for S-IMRT, 0.2/0.2% for D-IMRT. DMLC tracking proved to be as efficient as standard delivery, with a two- to fivefold efficiency increase over gating.
Conclusions
Real-time target position information was successfully integrated into a DMLC effector system to modify dose delivery. Experimental results show both comparable dosimetric accuracy as well as improved efficiency compared with spatial gating.
Reprint request to: Parag J. Parikh, M.D., Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Saint Louis, MO 63110. Tel: (314) 747-9614; Fax: (314) 362-8521
Conflict of interest: Drs. Parag J. Parikh and Paul J Keall receive funding from Varian Medical Systems and Calypso Medical Technologies.
ABSTRACT