Image-Guided Radiation Therapy
Image-guided radiation therapy, or IGRT, is a type of radiation therapy used to treat cancers like mesothelioma that uses imaging scans to guide and direct the radiation to the tumor. Like any kind of radiation therapy, this treatment uses a beam of high-energy radiation aimed at tumors to kill cancer cells and shrink tumors. It may be used alone, but more often IGRT is used before or after surgery or in conjunction with chemotherapy.
The process of IGRT begins with taking images of the patient’s body where the tumors are located. The images may be taken with CT scans, MRIs, or PET scans, and multiple images are likely to be made. These images help the radiation oncologist, the technicians, and the computer generating the radiation beam better direct the treatment at the cancer cells while minimizing contact with healthy cells and tissue.
What is IGRT?
IGRT is a type of radiation therapy that uses images to guide the treatment. It is a type of external beam radiation therapy, which means that the radiation used to treat the cancer is a beam created by a linear accelerator machine. That beam is then directed to a point, or points, on the outside of the patient’s body. The radiation penetrates the skin and other tissue to get to the tumor where it kills cancer cells.
Before beginning IGRT a patient must undergo several imaging scans. These are then used by the medical team that will be delivering the treatment to make a specific radiation plan for the patient. The images may also be taken and used during the delivery of radiation to guide and change the dosing of radiation and the focus of the beam. The end result is radiation therapy that more precisely targets the tumor with higher doses and better protection of healthy tissue.
IGRT is often used as a type of radiation therapy for mesothelioma or asbestos-related lung cancer. Tumors in these types of cancer are close to vital organs and having a more targeted and precise type of radiation therapy is important for protecting them, minimizing damage, and avoiding serious side effects.
Types of Images Used in IGRT
The types of imaging scans created for the patient undergoing IGRT depend on the medical team and the equipment. CT scans, MRIs, and PET scans are typically used, and sometimes, ultrasound images are also used. Computer tomography scans, or CT scans, use several X-ray images to create a three-dimensional or cross-sectional image of the tumor. Magnetic resonance imaging, or MRI, is an imaging technique that uses magnetic fields to create a three-dimensional image. A positron emission tomography, or PET, scan involves giving the patient a radioactive injection followed by a scan that images the radioactive material that collects in the tumor. An ultrasound uses sound waves to create a two- or three-dimensional image of soft tissues, like tumors.
Preparation for IGRT
IGRT begins with a preparatory session, sometimes called a simulation. The patient is imaged with one or more types of imaging scans during the planning stage. These are fed into the computer that will direct the radiation. The medical team will use this computer and the images to create a plan for treatment, although images may also be taken during the treatment to change the direction or dosage of the radiation as necessary.
The technicians may mark the patient’s skin to make sure the radiation beam is directed at the right spot on the body. The preparation may also include fitting molds or masks for the patient to wear or be situated with during the treatment. These protect healthy tissue, help keep the patient in the correct position, and help guide the radiation beam.
The preparation step for IGRT often takes longer than the actual treatment. Once all the planning is done the patient will be situated on a table or bed in the correct position, with the use of molds as needed. The technicians and doctors will retreat to another room to monitor the treatment and to avoid being exposed to the radiation. The procedure will not hurt and takes about 15 to 30 minutes. A patient may go through several of these treatment sessions on different days, or sometimes two in one day.
Benefits of Using IGRT
Guiding radiation therapy with images is beneficial in multiple ways. One very important benefit is that this technique provides greater accuracy for the delivery of radiation. Without guidance there is a greater risk the beam will hit and harm healthy tissue and miss cancerous tissue or part of a tumor. The use of multiple images of the patient’s body and the tumor improves the definition and monitoring of the shape, size, and location of the tumor.
Because this technique is guided and more accurately directed at the tumor it allows for a larger and more powerful dose of radiation to be given, which can improve the effectiveness of the treatment. Harm to healthy tissue is what causes side effects with radiation treatment, and with image-guided radiation this harm is minimized. Side effects, in turn, are also minimized for most patients.
Risks and Side Effects
Radiation therapy may cause side effects, but IGRT causes fewer and milder side effects than radiation that is not guided by images. This is because the radiation is focused more precisely on the particular shape and size of individual tumors. Healthy tissue is less likely to be affected as a result. Side effects still may be possible, including irritation, swelling, or hair loss at the place on the body where the beam has been directed. Fatigue is also a common side effect that occurs with radiation therapy, but it should improve after treatment is finished.
For mesothelioma patients, there may be other side effects because of where the radiation is focused. For instance, with pleural mesothelioma the radiation is aimed at the chest. This may cause swelling or inflammation in a lung or even in the heart. This can cause symptoms like difficulty breathing, that may be mild and temporary or that may be more severe and permanent. For peritoneal mesothelioma, potential side effects are related to damage to the bladder and bowels which may cause digestive issues or incontinence.
Image-guided radiation therapy is an important type of treatment for many patients with mesothelioma. It helps protect healthy organs and tissue, while attacking tumors in sensitive locations in the body. It can be used before surgery to shrink tumors or after surgery to reduce the chances that tumors will return after treatment.
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