Image-guided radiation therapy (IGRT) uses high-tech imaging to guide the application of radiation when treating cancers like mesothelioma. IGRT provides greater accuracy and less damage to healthy tissue. It is often used along with chemotherapy or surgery.[1]
About Radiation Therapy
Radiation therapy, or radiotherapy, is a cancer treatment that uses beams of high energy to target and kill cancer cells. There are a few types of radiotherapy:
- External beam radiation. The radiation beam is external and directed to a point, or points, on the outside of the patient’s body. The radiation penetrates the skin and other tissue to kill cancer cells in an underlying tumor.[2]
- Brachytherapy. Brachytherapy involves the implantation of a radioactive device inside the body near the tumor. The device might be placed temporarily or permanently.
- Intensity-modulated radiation therapy. IMRT uses radiation that varies in intensity in order to better conform to the shape of individual tumors. This minimizes damage to nearby healthy tissue.
- Image-guided radiation therapy. IGRT uses imaging before and sometimes during therapy to target the tumor precisely and to avoid damaging healthy tissue.
The best type of radiation depends on each patient’s unique situation. Oncologists and radiologists work within the medical team to determine the best option for every patient, including those with mesothelioma.
What Is Image-Guided Radiation Therapy?
Image-guided radiation therapy is an important development in cancer treatment that relies on CT scans, PET scans, and other images to improve precision.
IGRT is a type of external beam radiation therapy that uses images to guide radiation treatment. Before beginnning IGRT, a patient must undergo several imaging scans. The medical team uses the images to create a specific radiation plan for the patient.
Images may also be taken and used during radiation treatment to change the dosing and the focus of the beam. The result is radiation therapy that more precisely targets the tumor. It also allows for higher radiation doses and better protection of healthy tissue.[1]
What Does Image-Guided Radiation Therapy Treat?
IGRT can be used to treat any type of cancer. Doctors often choose IGRT for patients with tumors located close to more sensitive or vulnerable tissue and organs. It is also useful for tumors that might move during radiotherapy.
IGRT is often used for mesothelioma or asbestos-related lung cancer. The greater precision of this type of radiation therapy helps limit damage to the lungs.
Types of Images Used in IGRT
Types of imaging scans for IGRT depend on the medical team and the equipment available:
- CT scans (computer tomography scans) use several X-ray images to create a cross-sectional image or a three-dimensional image of the tumor.
- PET scans (positron emission tomography) scan a radioactive material that has been injected into the body. As the radioactive material collects in cancer tumors, it allows it to appear clearly in imaging scans.
- MRI (magnetic resonance imaging) uses magnetic fields to create a three-dimensional image.
- Ultrasound uses sound waves to create a two- or three-dimensional image of soft tissues, like tumors.
4D Radiation Therapy
4D radiotherapy is a variation of IGRT. It involves taking images during the therapy session so that the machine can adjust its position in real-time. It will even turn off if necessary.
Cancers in the chest cavity, like pleural mesothelioma, tend to move when the patient breathes. The 4D technique minimizes accidental damage to the lungs as the tumors shift.
Does Image-Guided Radiation Work for Mesothelioma?
Radiation alone is rarely a useful treatment for mesothelioma. Most patients undergo multimodal treatment with some combination of chemotherapy, surgery, radiation therapy, and immunotherapy.
Because it provides greater accuracy and protection of sensitive tissue, like lung tissue, IGRT is often chosen for pleural mesothelioma patients who can benefit from radiation.
The National Cancer Institute Thoracic Malignancy Steering Committee published an expert opinion on using radiation to treat patients with pleural mesothelioma in 2019. The statement includes the recommendation that radiation be image-guided for the best results.[3]
A 2017 study of pleural mesothelioma patients found good results with IGRT. The patients underwent extrapleural pneumonectomy first, a surgery that removes one entire lung. The researchers found that following the surgery with IGRT helped spare the remaining lung.[4]
How to Prepare for IGRT
IGRT begins with a preparatory session, sometimes called a simulation. During the planning stage, the patient is imaged with one or more imaging scans, which are fed into the computer that will direct the radiation treatment.
The medical team creates a treatment plan using the computer and images of the tumors. Images may also be taken during treatment to change the direction or dosage of the radiation as necessary.
The technicians may insert metal markers near the tumor to help identify it on imaging scans.[2] Preparation may also include fitting molds or masks for the patient to wear or be situated with during the treatment. These molds are designed to keep the patient properly positioned, protect healthy tissue, and help guide the radiation beam.
During Treatment
Preparation for IGRT often takes longer than the actual treatment. Once planning is complete, the patient is positioned on a table or bed, with molds placed if necessary.
The technicians and doctors then retreat to another room to avoid radiation exposure during treatment. The procedure takes about fifteen to thirty minutes and is not painful. A patient may require several treatment sessions.
Benefits of Using IGRT for Mesothelioma Patients
Using images to guide radiation therapy is beneficial in multiple ways:[1]
- One important benefit is increased accuracy. Without image guidance, there is a greater risk of the beam missing cancerous tissue and harming healthy cells. Using multiple images improves the definition and monitoring of the shape, size, and location of the tumor.
- Because this technique is more accurately directed, it allows for a larger and more powerful dose of radiation. This increased dosage can improve treatment effectiveness.
- Because radiation treatment harms healthy tissue, patients often experience painful or uncomfortable side effects. With image-guided radiation, this harm is minimized, as are side effects for most patients.
Risks and Side Effects of IGRT
Radiation therapy often causes side effects. IGRT causes fewer and milder side effects than non-guided radiation. This is because radiation in IGRT is focused precisely on the shape and size of individual tumors. Because of this increased focus, healthy tissue is less likely to be affected.
Side effects are still possible, including irritation, swelling, or hair loss at the beam site. Fatigue is also a common side effect that occurs with radiation therapy, though it improves after the completion of treatment.
Depending on the treatment location, mesothelioma patients may experience other side effects. For example, with pleural mesothelioma, radiation is aimed at the chest. This may cause swelling or inflammation in the heart or lungs. This inflammation can cause difficulty breathing, which may be temporary and mild or permanent and more severe.
For peritoneal mesothelioma, potential side effects are caused by damage to the bowels and bladder, resulting in digestive issues or incontinence.
Image-guided radiation therapy is an important treatment for many patients with mesothelioma. IGRT protects healthy organs and tissue while attacking tumors in sensitive locations. It can be used before surgery to shrink tumors or after surgery to reduce the chances that tumors will return.
