Intensity Modulated Radiation Therapy (IMRT) is a method of 3-D conformal therapy using a computer controlled multi-leaf collimator.
Intensity Modulated Radiation Therapy (IMRT) is a method of 3-D conformal therapy using a computer controlled multi-leaf collimator. The benefit of this type of therapy over fixed-leaf collimators is the improved conformality of dose distribution across the field do to the ability to divide each beam into segments. This proves particularly helpful when treating tumors that in the past have been poor to minimally responsive to radiation therapy due to the presence of critical structures within the field and their associated dose-limiting parameters. Utilization of IMRT changes how radiation therapy treatments are planned, helps to improve treatment outcomes, and assists in decreasing patient side effects.
Treatment planning involves the use of advanced imaging such as computed tomography (CT). Patients are placed on the CT couch in an appropriate positioning device in the exact position they will receive their therapy. Once completed, the images are sent to the treatment planning computer where regions of interest are highlighted and the tumor is prescribed by the radiation oncologist and/or physicist. The computer can then do the dose calculations to determine how much radiation will be received by normal and affected tissue alike. Appropriate adjustments can be made accordingly prior to the start of therapy, assuring adequate dose to the tumor and acceptable dose to surrounding tissue.
IMRT plans use multiple beams circling the patient around a 360-degree arc. IMRT can specifically control ("modulate") the weights of portions within each individual radiation beam. This is called " intensity distribution" and is how the beam is shaped into the complex three-dimensional form of the tumor volume being targeted. This further allows for non-uniform fluence (beam intensity) to the patient, so critical structures/tissues may be spared while malignant tissue may receive the optimal treatment dose.