Image-Guided Radiation Therapy (IGRT)
Image-Guided Radiation Therapy (IGRT) refers to the use of imaging, usually CT scans and X rays, to help precisely target the cancer with radiation therapy. This is another important advance in the radiation therapy technology that improves the chance of killing a cancer whilst reducing the risk of damaging normal body tissues and structures. In IGRT, CT scans or Xrays, or both, are taken every day before each radiation treatment to ensure that the cancer or region to be treated lines up exactly as planned. IGRT is always used when Intensity-Modulated Radiation Therapy (IMRT) is being used.
The patient is ‘set-up’ (usually lying down) on the treatment machine ‘couch’ in the same position every day. A quick Xray or CT scan is taken using special equipment mounted on the treatment machine. Sometimes small markers made of metal (e.g. gold) or other materials seen well on Xrays, are placed inside a cancer or organ. Adjustments can be made prior to each treatment to make certain the cancer is covered by the radiation beams, and to check that surrounding normal tissue or organs are not receiving too much dose.
For example, when radiation therapy is being given for prostate cancer, the position of the prostate gland can change inside the body depending on how full or empty the lower bowel (rectum) and bladder are. Using a mini CT scanner, called a Cone Beam CT, built into the on the treatment machine, any movements of the prostate can be seen prior to each daily treatment.
For cancers located in the lung, the radiation therapists can take images during the delivery of the actual treatment so that they can compensate for the movement occurring during normal breathing. This has been called 4-dimensional radiation therapy (4D-RT) where the fourth dimension is ‘time’. The only disadvantage of IGRT for the patient is that the delivery of each treatment is slightly longer – though still only a few minutes per treatment. This minor ‘down-side’ however, is far outweighed by the improved results using IGRT. This technique, very commonly in conjunction with IMRT, is now standard practice for all treatment centres around Australia and New Zealand.