GENERAL OVERVIEW OF THE ROLE OF RADIATION THERAPY
Radiotherapy is used for the treatment of lung cancers in various ways. In early stage disease, surgery is often considered the first choice, however radiation treatment, particularly with a method known as stereotactic radiosurgery can very successful in disease eradication and is the preferred method for some patients. The system used at Genesis Healthcare is the CyberKnife Radiosurgery System. It delivers a high dose to a small volume, in a very ‘pin point’ fashion to the tumor, causing ablation.
For more advanced disease, such as the situation where the tumor has spread to the lymph nodes in the center of the chest, more broad, yet still highly focussed radiation is preferred, with techniques known as three dimensional conformal radiotherapy, intensity modulated radiation therapy (IMRT) and image guided radiation therapy (IGRT).
Small cell lung cancers are a unique subset handled with a different treatment paradigm. As these tumors are extremely responsive to chemotherapy, treatment is often initiated with chemotherapy, followed by external beam radiotherapy.
In the postoperative setting, radiation is often used as an adjuvant treatment to improve local control.
Radiation therapy is also used for the palliation of advanced and metastatic lung cancer, where the goal is improvement in quality of life, instead of cure.
RADIATION TREATMENT METHODS FOR LUNG CANCER
(3D CONFORMAL, IMRT, IGRT)
The ability to precisely target the tumor volume with highly conformal radiation dose delivery thereby allowing substantial sparing of surrounding normal tissues has improved substantially in recent years. This allows for better tolerance to treatment in addition to giving the ability to increase the dose to improve likelihood of cure.
Three dimensional conformal radiation therapy represented an approach to improve the local outcome of radiotherapy in lung cancer, by computerized planning treatment in all three dimensions, with both the tumor and normal organs imaged in all planes, allowing for more sophisticated beam angles, giving maximum dose to tumor and minimal dose to normal tissues. In traditional 3D approach, each radiation beam is of uniform intensity, which is analagous to the uniform brightness of light emanating from a flashlight.
Intensity modulated radiation therapy (IMRT) improved upon traditional 3D conformal therapy, by varying the intensity of the radiation beam as needed, allowing for even more conformal treatment. Again, by way of analogy, this can be visualized as light coming from a flashlight, but instead of uniform brightness across the beam, there are varying degrees of brightness across the beam. By manipulating the beam intensity, more conformal plans can be created. (see Figure 2)
IGRT or image guided radiation therapy refers to imaging the tumor prior to each treatment, which can be done with a CT scan built into the treatment machine. By visualization each day, the accuracy is improved as adjustments can be done at the time of each treatment, allowing for more accurate delivery, and further sparing of surrounding normal tissue.
IMAGE FUSION TREATMENT PLANNING FOR LUNG CANCER
Multiple radiation beams are used to deliver a high dose of radiation to the tumor while minimizing the dose to normal tissue.
The anatomy of cancers in the chest may be complicated and the interpretation of radiology studies challenging. For example, cancer and pneumonia often coexist in the same patient and it may be difficult to define where one condition stops and the other one starts. The cancer may also involve lymph nodes in the mediastinum (central part of the chest between the lungs), which may be problematical to accurately detect with conventional studies.
The combination of CT and PET imaging has significantly improved the ability to accurately map the distribution of cancer within the chest, and the newest generation of radiation therapy planning computers has the ability to take full advantage of both study types in the treatment planning process. This is done by co-registering or fusing the images from different planning studies in three dimensions on the same display. In this way the anatomic information provided by the CT and the cancer biological information provided by the PET study are combined in the computer. This in turn allows us to design the most accurate possible radiation treatment volume, which means a higher dose of radiation to the target volume, more accurately directed, with better sparing of surrounding tissues. This improves that chance of destroying the tumor without creating too much collateral injury to surrounding tissues.
Images on the right show how the radiation dose conforms to the tumor which appears as a white shadow, which is the PET scan image overlayed on the CT scan image. The area within the green envelope of radiation receives the highest dose.
SIDE EFFECTS OF RADIATION THERAPY FOR LUNG CANCER
It often takes patients several weeks to get back to their normal energy level. During treatment, patients are advised to pace themselves at home and work. They may need to take frequent breaks to avoid overexertion.
The following are the most common side effects, both acute and chronic, resulting from radiation. Unforeseen side effects may occur because of the unique and varied tolerance of individual persons. Late effects of treatment may not always be predictable and may be influenced by concurrent and/or subsequent treatment for this and other diseases. These common side effects include, but may not be limited to the following.
The use of radiation therapy in the treatment of malignant tumors of the lung is a technique used either alone or in conjunction with surgery and/or chemotherapy. The course of treatment may last from 3 to 7 weeks and most often is given in a single treatment each day, five days a week, although two treatments per day are sometimes employed for specific tumors. The side effects may vary substantially depending on the size and location of the treated area and whether or not chemotherapy is also given.
Fatigue is a common radiotherapy side effect. This usually begins during the second or third week of treatment and gradually increases until the treatment series has been completed. Gradual recovery occurs over the following 4 to 6 weeks. This is not normally debilitating and, in itself, should not affect your daily activities or ability to drive. However, you may wish to go to bed earlier or take an afternoon nap during this period. Fatigue and weakness are worse in patients who lose weight. Accordingly, we strongly encourage you to supplement your diet with high calorie foods or commercially available nutritional supplements (for example Ensure Plus, Sustacal, Boost), if necessary to maintain your weight.
Skin changes within the treated area usually include redness of the skin similar to a sunburn. This usually starts during the second or third week of treatment and increases until the treatment series has been completed. Recovery occurs over the following 2 to 4 weeks, although a tanned, dry skin condition may persist to a mild degree as long as 6 to 12 months after treatment. Skin changes may be treated with a variety of measures including aloe vera gel, moisturing lotion, or cortisone cream.
Specific effects related to radiotherapeutic effects upon organs in the chest include cough, usually mild and not productive of sputum, and difficulty swallowing with the feeling of either irritation or the presence of something stuck in the esophagus. There is no actual mechanical impairment to swallowing. There are several measures, including antacids, which may relieve this condition.
Long-term effects of radiation may be serious and involve inflammation or scarring within the lung and possible damage to the spinal cord. Fortunately, serious complications are unusual. Lung injury occurs in 5% or less, and spinal cord injury occurs in approximately 1 in 1,000 patients.