Radiation therapy is also called radiotherapy and x-ray therapy. It is one of the major modes of cancer treatment (the others being surgery and chemotherapy). Doctors administer radiation, in carefully controlled amounts, to specific areas of the body in hopes of destroying cancerous cells. Radiation therapy for mesothelioma is a challenge, because the pleura is large and spread out. Aiming the radiation at the pleura often results in radiation to the lungs and rest of the thorax. This is why brachytherapy is often preferred for mesothelioma.
Practice guidelines published by the National Comprehensive Cancer Network in 2010 laid out recommended doses for conventionally fractionated radiation therapy in pleural mesothelioma:
| Treatment Type | Total Dose | Fraction size | Treatment Duration |
| Postoperative | 45-50 Gy | 1.8-2 Gy | 4 to 5 weeks |
| Postoperative – Negative Margins Microscopic-macroscopic positive margins |
20-40 Gy 30 Gy |
4 Gy or more 3 Gy |
1 to 2 weeks 2 weeks |
| Palliative – Chest wall pain from recurrent nodules Multiple brain or bone metastasis |
20-40 Gy 30 Gy |
4 Gy or more 3 Gy |
1 to 2 weeks 2 weeks |
| Prophylactic radiation to prevent surgical tract recurrence | 21 Gy | 7 Gy | 1 to 2 weeks |
Gy=Grays, a unit of energy used to describe the quantity of ionizing radiation applied.
How does radiation therapy work?
The effects of radiation therapy come from the damage that targeted radiation does to the genetic structure of malignant cells. Beams of radiation alter the atoms that constitute the cancer cell’s DNA helix. Since cells have processes for healing damaged genetic material, the most effective technique has been to attempt to break both strands of the helix molecule. Also, malignant cells lack the ability to heal their DNA as fast as healthy cells, thus they carry their now-defective DNA as they reproduce. Such an alteration inhibits the cancer cell’s ability to sustain the malignancy, causing the tumor to shrink and die. Radiation is commonly used in the diagnostic x-rays, CT scans and dental x-rays. However, radiation therapy uses much higher x-ray energy to deliver a many times stronger dose to treat cancer. These high doses can wipe out abnormal cells by destroying the genetic material that controls the growth of these cells. Some healthy cells will also be destroyed but the goal of this treatment is to kill off as many of the cancerous cells while minimizing its impact on the healthy cells. Cancer cells are more susceptible to radiation therapy because they divide more rapidly than healthy cells and are vulnerable to damage while dividing. It helps in this fight against cancer that healthy cells can recover from the treatment faster and more effectively than the cancer cells can.
How is radiation therapy delivered?
Radiation therapy is used in two ways; externally and internally.
Externally – is the most common form of radiation therapy. External methods are used to both lessen the size of tumors and alleviate the pain associated with them, typically in an outpatient setting. This technique uses a large machine, a linear accelerator, to deliver high doses of radiation to the specific location. This machine delivers the radiation in a continuous stream of fast-moving subatomic particles. Generally, this treatment is done on a daily basis for around four – six weeks, depending on the individual case.
Internally – this treatment process is also known as brachytherapy, meaning short distance therapy, and includes both interstitial and intracavitary radiation. This treatment uses special radioactive substances about the size of grain of rice, called seeds or pellets. Wires, tubes or containers may also be used. Internal procedures usually require a hospital stay as the insertion of implants, catheters or radioactive “seeds”, along with the surgical procedures needed to install the device, takes some measure of recovery time. Also, internal treatments can be administered by infusion through the bloodstream.
Intracavitary radiation is when a container of radioactive material is placed in a specific body cavity. In order to place these radioactive sources in the right place, the physicians use x-rays, ultrasound or CT scans. These implants, depending on the treatment plan, can be either permanent or temporary.
* Permanent – involves low dose radiation placing these pellets or seeds directly into tumors using very fine hollow needles. Once in place, the pellets give off radiation for several weeks or months. Due to their tiny size, these implants are left in place even after their radioactive material is used up.
* Temporary – involves high dose radiation where hollow needles, tubes, or balloons filled with fluid are placed into the area to be treated. These are left in for a short period of time and then removed. This process will be repeated over several days to weeks. Lying calm and still during treatment is required to stop the implant from shifting.
* Radiopharmaceuticals – These are drugs that contain radioactive materials. These drugs can be given through an IV line, orally, or into a body cavity. Depending again on the drug and how it is given to the patient, these radioactive materials travel to various parts of the body. This method is used extensively for some conditions, such as bone pain and thyroid cancer. Examples of these drugs are:
Phosphorus 32 – infused through a catheter in the space in the abdomen or between the linings around the lungs. It can also be injected directly into certain tumors.
* Strontium 890 and samarium 153 – both used for tumors that have spread to the bone. Can be given through an IV and will travel to areas of the bone where there is cancer
* Iodine 131 – destroys cancer cells in the thyroid gland with limited damage to the rest of the body.Doses for radiation therapy are measured in Grays (Gy), where 1 Gray equals 100 rads. Depending on the level of radiation required to treat the tumor, doses may total between 60 and 80 Grays over the course of a treatment schedule. Due to the care taken to avoid irradiating surrounding healthy tissue, treatment specialists spread out doses over the course of numerous sessions spread out over several weeks, usually in doses of one-and-a-half to two Grays per session.
Researchers have developed a wide variety of delivery methods and discovered numerous radiation sources that are effective in cancer treatment. X-rays, gamma rays and proton beams are all employed in different areas of cancer radiation therapy. Techniques such as stereotactic radiotherapy and three-dimensional conformal radiotherapy allow doctors to target the tumor cells without impacting the surrounding normal tissue.
Radiation is not part of the standard mesothelioma treatment, but it may be used if an oncologist feels it is appropriate for any patient. It can be useful for palliative reasons.
Another concern is that radition therapy may actually trigger mesothelioma. If a patient is being treated for another form of cancer, but has been exposed to asbestos in the past, there is a danger that mesothelioma may form. Here is a report from The Netherlands about a patient being treated for lymphoma where radiation treatment seemed to cause mesothelioma.
How is radiation therapy used in cancer treatments?
Multimodality therapy for mesothelioma
Adaptive Radiation Therapy for Localized Mesothelioma with Mediastinal Metastasis Using Helical Tomotherapy – Abstract of clinical work
