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What is Intensity-Modulated Radiation Therapy?

IMRT is an advanced type of radiation therapy. Like many types of radiation therapy, it uses a linear accelerator, or linac machine, to aim high-energy X-rays at a tumor site inside a patient’s body.

The difference with IMRT is the linac machine is designed to move around the patient and hit the tumor site from multiple directions. A computer controls exactly how much energy the machine uses at each angle, based on imaging scans taken of the patient’s body.

In treatment for pleural mesothelioma, doses of radiation must be tailored to the exact size and shape of the tumor site. This is because pleural mesothelioma develops near the lungs and heart, which are very sensitive to radiation damage.

IMRT may be safer to use on pleural mesothelioma patients than older methods of radiation therapy. It is one of the most sophisticated forms of external beam radiation therapy.

IMRT Facts

  • Advanced form of external beam radiation therapy
  • Safer to administer near vital organs in the chest
  • May be combined with other cancer treatments
  • Requires highly specialized equipment and expertise

Doctors can use IMRT as a palliative treatment, intended to relieve a patient’s chest pain and improve quality of life. IMRT typically causes only mild side effects on its own, and it is safe to combine with chemotherapy or immunotherapy.

IMRT is also an important part of the established multimodal treatment approach to helping patients live longer with pleural mesothelioma. In this approach, radiation therapy is usually the last step after surgery and chemotherapy.

When a patient undergoes surgery to remove a lung and all the cancer around it, doctors often use IMRT to try to kill any cancer cells left behind in the patient’s chest. A 2021 study concluded extrapleural pneumonectomy after IMRT can be done with good early and long-term results.

Some recent studies also support using IMRT after surgery on patients who still have both their lungs.

Types of Intensity-Modulated Radiation Therapy

One of the latest advances in external beam radiation is arc-based IMRT. It is designed to improve on the conventional “step and shoot” or “static fields” technique.

Arc-based IMRT delivers radiation continuously as the machine rotates in an arc around the patient. It controls its accuracy using a multileaf collimator. This device has individual “leaves” that move in and out of the radiation’s path to make the beam the same shape as the tumor site.

Companies have developed different types of arc-based IMRT technology.

Helical Tomotherapy (HT)

In helical tomotherapy, the patient lies on a table that slides through a donut-shaped machine. The machine contains a linear accelerator that can revolve all the way around the patient.

In 2014, a study in the journal Lung Cancer reported on 20 pleural mesothelioma patients who underwent lung-sparring surgery and then received a high dose of radiation through tomotherapy.

This led to a median survival time of almost three years, which is far beyond the usual life expectancy.

However, a 2015 study of 62 patients found helical tomotherapy was not significantly more effective than conventional IMRT for treating pleural mesothelioma.

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Volumetric Modulated Arc Therapy (VMAT)

VMAT also uses a linear accelerator that can rotate itself around a patient. It is much faster than other IMRT techniques, though, which reduces the risk of error because of the patient moving.

In 2012, doctors from the Memorial Sloan-Kettering Cancer Center reported the initial results of a VMAT technique they developed for pleural mesothelioma and tested on 36 patients.

The median survival time was 26 months for patients who received radiation after surgery. The patients ineligible for surgery had a median survival time of 17 months.

Based on this research, the doctors went on to develop the intensity-modulated pleural radiation therapy (IMPRINT) technique.

In a 2016 article in the Journal of Clinical Oncology, they reported the results of a phase II clinical trial combining IMPRINT with lung-sparring surgery.

Previous research had already shown that patients could benefit from radiation therapy after having a lung removed. The IMPRINT study supports the idea that radiation therapy can also be tailored for patients who undergo lung-sparring surgery.

Because VMAT is a cutting-edge technology, though, not every hospital and cancer center is equipped to offer it.

Some renowned mesothelioma cancer centers that offer VMAT include:

Pros and Cons of IMRT

IMRT treatment relies on careful planning and complex imaging techniques. With the right preparation, a computer can control exactly how much radiation each part of the patient’s body receives.

IMRT maximizes radiation exposure in the tumor site and minimizes exposure in healthy cells. This allows doctors to administer higher doses of radiation even when the tumor site is next to a sensitive organ such as a lung.

Of course, no treatment is 100 percent safe. Some patients do experience adverse reactions to IMRT.

Radiation toxicity can lead to inflammation in lung tissue, or pneumonitis. At its most extreme, it can cause irreversible damage by hardening the lung’s air sacs, which prevents them from inflating. This makes it impossible for the patient to breathe. Radiation can also damage the muscle in the heart.

Fortunately, improvements in IMRT techniques have reduced the risk of severe side effects. This has played a role in the rise of lung-sparring surgery in multimodal treatment.

A 2015 study published in the International Journal of Radiation Oncology compared two groups of pleural mesothelioma patients. The groups were balanced in terms of health factors and treatment plans. Patients in both groups received IMRT after surgery.

Patients in one group had lung-sparring surgery, and patients in the other group had a lung removed. The patients who kept both lungs had a median survival time of 28.4 months, compared to 14.2 months for the other group.

However, the study’s authors also warn IMRT can lead to long-term, progressive decline in lung function, even if it does not cause any immediate problems.

Radiation is not part of every mesothelioma patient’s treatment plan. Each patient must discuss with a mesothelioma specialist whether this treatment is appropriate for them.


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