Radiation Therapy for Lung Cancer
Lung cancer is the second most common cancer found in both men and women and comprises 15 percent of all cancers diagnosed. In 2010, it was estimated that 222,520 new cases of lung cancer would be discovered that year (American Cancer Society, 2009).
Lung cancer can be difficult to treat, but fortunately new innovations in radiotherapy are making it easier for clinicians to target lung tumors (Onishi et al, 2004, Timmerman et al 2010).
There are two main types of lung cancer, non-small cell lung cancer and small cell lung cancer. Non-small cell lung cancer is the most common type of lung cancer, accounting for 80 percent of cases, while small cell lung cancer is less common and accounts for 20 percent of cases (National Cancer Institute, 2009)
Treatment for lung cancer may entail surgery, chemotherapy, radiation therapy, or experimental treatments. Surgery is almost always performed on early stage cancers. For late stage or metastatic cancer, radiation therapy might be the first line of treatment.
The way the radiation therapy is given depends on the type and stage of the cancer being treated. Radiation therapy may be used to treat lung cancer in the following ways:
- As the primary treatment
- Before surgery to shrink the tumor
- After surgery to eliminate any cancer cells that remain in the treated area
- To treat lung cancer that has spread (metastasized) to the brain or other areas of the body
Treatment Techniques for Lung Cancer
There are two broad categories of radiation therapy – external beam radiation therapy and internal radiation therapy, or brachytherapy. Both are designed to target the tumor precisely while minimizing exposure to the healthy surrounding tissue. In the first category, external beam radiation therapy (EBRT), the radiation is delivered by a machine called a linear accelerator, or linac, which focuses a high-energy x-ray beam into the tumor site from outside the body. External beam radiation therapy includes radiation therapy (or radiotherapy) and also radiosurgery.
External Beam Radiation Therapy
Radiosurgery for lung cancer is also called SBRT, or stereotactic body radiation therapy. Radiosurgery uses similar technology to other radiation treatment techniques but differs from conventional radiation therapy in one important way: rather than having treatment five days a week for several weeks, radiosurgery is delivered in a few very large radiation doses given in five or fewer sessions.
Until recently, radiosurgery was most often used when the patient could not undergo conventional surgery to remove the tumor(s) because of its size or location, or because the person's health was too poor for surgery. However, some hospitals consider radiosurgery as the first line of treatment for early stage lung cancer.
IG-VMAT, or image-guided volumetric modulated arc therapy, uses special software and an advanced linear accelerator to deliver treatments up to eight times faster than what was previously possible with standard radiation therapy. Unlike conventional treatments, during which the machine must rotate several times around the patient, or make repeated stops to treat the tumor from a number of different angles, VMAT can deliver the dose to the entire tumor in a single rotation — in as little as two minutes.
Image-guidance technology utilizes images taken by several scans, to create a detailed, three-dimensional picture of the tumor. The scans typically are produced by computed tomography (CT scan), magnetic resonance imaging (MRI), or positron emission tomography (PET scan). Image-guidance technology enables the treatment team to view the tumor and its position in the body before and during each treatment. This is made possible by the On-Board Imager (OBI), whereby robotic arms extend out from the sides of the linac to take images of the tumor and its position.
IG-IMRT, or image-guided intensity modulated radiation therapy, is still being studied for lung cancer. This technology involves changing the intensity of the radiation beam at various angles to minimize exposure to your healthy tissues, while giving a full dose to the tumor, or target site. Although IMRT is very effective for some cancer types, the use of IMRT for lung treatments is very rare and there is limited data surrounding its application.
Internal Radiation Therapy – Brachytherapy
In the second treatment category, the radiation is delivered by radioactive material placed inside the body near the cancer cells — a procedure called brachytherapy (also called implant radiation therapy or internal radiation therapy). Brachytherapy may be used to treat lung cancer if a tumor is found in the large airways, or major bronchi. It is most often used as a palliative therapy to relieve symptoms or pain when additional surgery and external beam radiation therapy are no longer good options for the patient. For this procedure, a thin plastic tube is inserted into the lung during a bronchoscopy. A small amount of radioactive material is then passed through the tube, and left near a precise treatment area for about 30 minutes. The tube is removed after treatment. Due to its short treatment distance, brachytherapy minimizes the radiation dose given to sensitive nearby tissues, i.e. heart, esophagus and the spinal cord.
