Intensity-modulated radiation therapy (IMRT) is an advanced mode of high-precision radiotherapy that utilizes computer-controlled x-ray accelerators to deliver precise radiation doses to a malignant tumor or specific areas within the tumor. The radiation dose is designed to conform to the three-dimensional (3-D) shape of the tumor by modulating or controlling the intensity of the radiation beam to focus a higher radiation dose to the tumor while minimizing radiation exposure to surrounding normal tissues. Treatment is carefully planned by using 3-D computed tomography (CT) images of the patient in conjunction with computerized dose calculations to determine the dose intensity pattern that will best conform to the tumor shape. Typically, combinations of several intensity-modulated fields coming from different beam directions produce a custom tailored radiation dose that maximizes tumor dose while also protecting adjacent normal tissues.
||Because the ratio of normal
tissue dose to tumor dose is reduced to a minimum with the IMRT
approach, higher and more effective radiation doses can safely
be delivered to tumors with fewer side effects compared with
conventional radiotherapy techniques. IMRT also has the
potential to reduce treatment toxicity, even when doses are not
increased. There are more studies showing much less toxicity
from using IMRT (go here).
IMRT may be even more effective if special techniques are use to help target the tumor (referred to as Image Guided Radio Therapy or IGRT). The ultimate form of IGRT would be using Tomotherapy. Even more sophisticated tumor targeting is used in high end radiosurgery techniques such as Cyberknife.
IMRT plan for head and neck cancer
|Typical techniques: go here|
|Radiation techniques for
IMRT/IGRT require prescribing doses to the cancer (GTV or gross
tumor volume, CTV or clinical tumor volume or PTV planning tumor
volume) but also require prescribing limiting dose to the normal
tissue or organs (called dose limiting constraints)
IMRT for prostate cancer