Jennifer R. Bellon, M.D.Dept of Radiation OncologyDana-Farber Cancer Institute and Brigham and Women's HospitalHarvard Medical School
Following lumpectomy, radiation therapy lowers the risk of cancer recurring in the breast, and also improves the chance of cure. Standard radiation includes radiation to the entire breast, but it is designed to minimize treatment to the heart and lungs. Sometimes, the lymph nodes underneath the arm and around the collarbone are also included. Radiation is typically given in small daily doses which allow the normal tissue a chance to heal in between treatments. Modern advances in technology have also greatly improved the safety and accuracy of radiation therapy planning and delivery. Central to these advances is the use of CT-based treatment planning which allows customization of the radiation therapy to the unique anatomy of each individual person. Intensity modulated radiation (IMRT) is a further improvement in treatment planning which uses a computer-based algorithm to ensure uniform distribution of the radiation therapy throughout the breast. Other improvements include respiratory gating, which can turn the radiation machine on and off at different points in the respiratory cycle. During a deep inspiration, the heart moves away from the chest and the radiation field. By controlling when the radiation is delivered during respiration, long-term injury to the heart can be minimized.
While standard whole breast radiation is highly effective, it is inconvenient, and carries a small risk of long-term injury to the normal underlying organs. Several recent advances have been made to shorten the radiation course. One approach is to give a higher daily dose of radiation over fewer total weeks. The most experience with this approach is from Canada, where a three–week regimen has been found to have similar efficacy and safety as the standard six week course. Until there is more information available, shorter course radiation is most appropriate for older women with early-stage disease.
Over the last five years there has also been increasing interest in partial breast irradiation. Recurrences in the breast occur most often at the site of the original tumor. Based on this observation, many physicians believe that it may be possible to limit the radiation to the site of the original tumor, and spare the rest of the breast. Because a smaller amount of breast is treated, the amount of radiation given with each treatment can be higher. Typical regimens consist of 10 treatments given twice a day over five days. There are multiple techniques for giving radiation to only part of the breast. The technique with the longest track record involves inserting multiple evenly-spaced plastic tubes into the breast. Each of the tubes becomes a conduit for a temporary radiation source. This technique has not gained wide popularity because it is quite invasive, and involves considerable specialized expertise. It is also possible to insert an inflatable balloon into the surgical cavity (either at the time of surgery, or afterwards with local anesthesia). A rubber tube extends outside the body, and a small source of radiation (approximately the diameter of a pencil lead) is inserted in the balloon for approximately ten minutes, and then it is withdrawn. At the end of the week, the balloon is deflated, and can be easily removed. Other techniques include using standard external radiation confined to the lumpectomy site, or delivering the radiation directly to the surgical site at the time the primary tumor is removed (more common in Europe and the UK). Partial breast irradiation is an attractive alternative to standard whole breast radiation because it is convenient, and may be less toxic to the normal organs. At present, however, we have much more experience with standard whole breast radiation, and as a result, we have a much better sense of its effectiveness and long-term side effects. It may be that partial breast is just as effective and safe, but this remains to be proven. Multiple comparative studies in the US, Canada, UK and Europe are currently ongoing. In the meantime, it is prudent to limit partial breast radiation to a small subset of women with breast cancer, such as older women with early –stage breast cancer and favorable pathologic features. In the next several years, we will have far more information on the role of partial breast irradiation that we do today.