IGRT is a tool to enhance IMRT.
Intensity-modulated radiation therapy (IMRT) is a type of therapy used to treat cancerous tumors. This therapy is used alone or in conjunction with other traditional cancer treatments, such as chemotherapy, and is particularly effective in the treatment of tumors in the brain or other areas where surgery is not a first option. Image guided radiotherapy (IGRT) is a companion to IMRT and is used for guiding the IMRT to the target area.
IMRT
Prior to the introduction of IMRT, radiation therapy involved not only the affected (cancerous) areas of a person, but also healthy tissue that was treated unnecessarily. This was due to the fact that, while effective, radiation was at the time not easily contained or directed. Of course, the goal was to treat just the tumor and so the IMRT was developed.
IMRT Limitations
Although vastly improved targeted treatment was now available, the IMRT was still limited and could only reach the general shape and surface areas of a tumor. The nooks, crannies and undulating surfaces were not fully covered because what was being treated was inside the patient and could not be seen. As the delivery method for IMRT got more precise, the need to closely track the tumor location became evident.
IGRT
With advances in radiation therapies came the introduction of IGRT. If IMRT is an effective delivery method for radiation therapy, then IGRT is an advanced method for accurately targeting that radiation. Between treatments a tumor may move slightly in response to the position of other organs or the patient's breathing. Using a computed tomography (CT) scan, the radiation oncologist is able to precisely pinpoint the tumor location immediately prior to treatment. In some instances, small pieces of gold can be placed at points along the edge of a tumor to help identify its shape and location. The imagery from the CT is uploaded to a computer system, and overlapped with previous scans, and the IGRT calculates any changes to the radiation therapy online.
Dose Painting IGRT
Another advance in the use of IGRT is the use of positron emission tomography (PET) to map 3D images of the functional images (the images of cells that show function rather than simple anatomical features) of cells. This imagery shows the benign and malignant areas of the tumor and surrounding tissues, and the IGRT can then "paint" the surface of the areas needing radiation prior to treatment.
IGRT Considerations
Although IGRT does not have any direct contact with the patient, it does have disadvantages. The process is time-consuming and requires a high level of skill. Additionally, the costs can be significant to the individual undergoing treatment. Although minimal, the extra dosages of radiation (in a CT or PET scan) needed to map a tumor are a consideration. Finally, errors in targeting are a possibility and must be guarded against.
Tags: radiation therapy, areas tumor, delivery method, does have, prior treatment, surface areas, therapy used
