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.
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 radiation 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.
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.
A 2017 study published in Acta Oncologica evaluated the safety and efficacy of IMRT following extra-pleural pneumonectomy (EPP) procedures on pleural mesothelioma patients. The study showed IMRT contributed to excellent local control after EPP, suggesting IMRT may lead to longer survival for select patients.
However, 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).
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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 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.
Volumetric Modulated Arc Therapy (VMAT) is a new form of IMRT that combines rotational — also known as arc — delivery with MLC-based IMRT. MLC stands for multileaf collimator, which is a device comprised of individual “leaves” that move in and out of the path of a radioactive beam to conform the beam to the shape of a tumor.
The combination of rotational delivery with MLC allows for better tumor targeting and preservation of healthy tissue around the tumor compared to MLC alone. Other techniques, known as step-and-shoot or static techniques, aren’t as dynamic as VMAT and don’t conform as closely to the shape of the tumor.
VMAT is better at sparing healthy tissue from radiation than traditional IMRT and other forms of radiation therapy.
VMAT also takes less time to deliver than traditional IMRT, which reduces the likelihood of patient movement. When a patient moves during radiation therapy the beam of radiation can miss the tumor target and end up hitting healthy tissue.
The reduced delivery time makes the radiation therapy process easier and less stressful on patients. For example, traditional IMRT may take eight to 12 minutes of actual delivery time, while VMAT may take as few as two minutes.
Studies involving VMAT in pleural mesothelioma patients have proven the therapy to be safe and effective. It works well as a form of follow-up therapy after surgery because of its accuracy and ability to provide a relatively low dose of radiation to the thoracic cavity.
VMAT is a relatively new, cutting-edge form of radiation therapy, and that means not every hospital and cancer center have the equipment to offer this therapy.
Some renowned mesothelioma cancer centers that offer VMAT include:
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.
Karen Selby joined Asbestos.com in 2009. She is a registered nurse with a background in oncology and thoracic surgery and was the director of a tissue bank before becoming a Patient Advocate at The Mesothelioma Center. Karen has assisted surgeons with thoracic surgeries such as lung resections, lung transplants, pneumonectomies, pleurectomies and wedge resections. She is also a member of the Academy of Oncology Nurse & Patient Navigators.
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