Intensity Modulated Radiation Therapy IMRT

IMRT is a relatively recent refinement of three-dimensional conformal techniques that uses treatment fields with highly irregular radiation intensity patterns to deliver exquisitely conformal radiation distributions. These intensity patterns are created using special inverse and optimization computer planning systems. Rather than define each shape and weight as is done in conventional treatment planning, planners of IMRT treatment specify the desired dose to the target and normal tissues using mathematical descriptions referred to as constraints or objectives [4]. Sophisticated optimization methods are then used to determine the intensity pattern for each treatment field that results in a dose distribution as close to the user-defined constraints as possible. IMRT delivery is significantly more complex than conformal delivery as well. Delivery of an IMRT intensity pattern requires a computer-controlled beam-shaping apparatus on the linear accelerator known as a multi-leaf collimator (MLC). The MLC consists of many small individually moving leaves or fingers that can create arbitrary beam shapes. The MLC is used for IMRT delivery in either a static mode referred to as step and shoot, which consists of multiple small, irregularly shaped fields delivered in sequence, or a dynamic mode with the leaves moving during treatment to create the required irregular intensity patterns [5]. Since its inception, IMRT has become a common and important method for treating prostate cancer and has facilitated an escalation in dose.

0 0

Post a comment