Intensity-Modulated Radiation Therapy

Intensity-Modulated Radiation Therapy (IMRT) is used primarily for the treatment of prostate, and head and neck cancer, but it has been used in a limited fashion for the treatment of lung-related cancers and for mesothelioma. IMRT is one of three types of radiation treatment used on mesothelioma patients. The other two are Three-Dimensional Radiation Treatment (3D-CRT) and Brachytherapy.

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IMRT makes use of a computer-controlled device called a linear accelerator, which increases the speed by which radiation travels along a straight path. The accelerator makes it possible to deliver precise,high-radiation doses to the whole tumor or to certain portions of the tumor. The precision minimizes the risk of injuring healthy tissue within the vicinity of the irradiation area. Because the beam is released in many short bursts, the dose is more easily conformed to the size and shape of the tumor. Getting rid of the tumor is a significant factor in the life expectancy for a mesothelioma patient.

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IMRT for Pleural Mesothelioma

The standard of care for treating advanced pleural mesothelioma is known as trimodality therapy.

Trimodality may consist of:

  • Neoadjuvant chemotherapy (chemotherapy administered before the primary treatment, which is surgery)

  • Extrapleural pneumonectomy (surgical removal of the diseased lung)

  • Adjuvant radiation (administered after the surgery as a secondary or follow-up treatment)

The form of radiotherapy found to be most effective as part of this treatment is IMRT. Given the toxicity issues associated with this type of treatment, the radiation oncologist must periodically evaluate the effectiveness of it by using an imaging scan created by fluorodeoxyglucose-positron emission tomography (FDG-PET).

This uses a radioactive glucose tracer, a substance that has a radioisotope added to it, which can track the metabolism of glucose within the cancer cell. This provides a clearer picture of whether the cell is still functional or if it is responding to treatment.

Hemithoracic Radiation Therapy

Hemithoracic radiation is a form of IMRT that targets a single portion of the affected chest area. Researchers are finding success utilizing high doses of this therapy, including a trial in which 45 patients who were diagnosed with advanced forms of mesothelioma underwent this treatment with surprising results.

The trial showed that the patients who received high-dose hemithoracic radiation therapy had a median survival rate of 12.4 months with a one-year survival rate around 50 percent. The results were presented at the European Lung Cancer Conference in 2012.

Some medical experts believe hemithoracic radiation may hold opportunities to treat certain cases of mesothelioma, despite previous thoughts that mesothelioma was insensitive to it. Even scientists who are optimistic acknowledge the need for continued research.

Pros and Cons of IMRT

Developing a treatment plan for a mesothelioma patient undergoing IMRT requires the use of data from 3D CT scans and MRIs in addition to computer-calculated radiation doses. Those help determine the level of radiation that best suits the shape of the tumor. Beams are projected from multiple directions to customize the dose and each of these beams is controlled to emit only small, regulated amounts of radiation.

An important benefit of this form of intensity modulation is that the ratio between the dose received by the tumor and the dose received by healthy tissue is significantly reduced. That means higher doses can be applied to the tumor with less chance of normal tissue damage, leading to a patient experiencing fewer severe side effects.

However, it is still possible for patients undergoing IMRT to experience adverse reactions. One of the most severe forms of toxicity is fatal pneumonitis. This is a condition in which the lungs become inflamed. At its most extreme, it can cause irreversible lung damage by making tissue that lines air sacs inside the lung unable to stretch during breathing. As the condition worsens, it can result in heart failure, respiratory failure and death.

Research has shown that using the standard parameter for radiation dose calculation known as V20 (the volume of the lung that will receive 20 Gy or more) is not enough to prevent the patient from receiving too high a dose and developing pneumonitis. To lessen the risk, the radiation oncologist must also consider the Mean (average) Lung Dose and V5 (the volume of lung that will receive 5 Gy or more) to determine just how high a dose a patient can tolerate without serious side effects.

Additional Resources

  1. Allen, AM, et al. (2006). , International Journal of Radiation Oncology, Biology, Physics, 65(3), 640-645. Retrieved from : http://www.mesothelioma-line.com/articles/2006/06/06/fatal-pneumonitis-associated-with-intensity-modulated-radiation-therapy-for-mesothelioma/" title="Permanent Link: Fatal pneumonitis associated with intensity-modulated radiation therapy for mesothelioma
  2. Alexander, et al. (2011). Intensity-Modulated Radiotherapy After Extrapleural Pneumonectomy in the Combined-Modality Treatment of Malignant Pleural Mesothelioma, Journal of Thoracic Oncology, 6(16), 1132-1141. doi: 10.1097/JTO.0b013e3182199819
  3. Intensity –Modulated Radiation Therapy (IMRT) (n.d.). Retrieved September 21, 2011, from: http://www.radiologyinfo.org/en/info.cfm?pg=imrt

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