Advances in radiation therapy boost the dose to cancer while reducing the damage to normal cells.
By Kari Bohlke, ScD
Whether it’s given alone or in combination with other treatments such as surgery or chemotherapy, radiation therapy improves outcomes for patients with many different types of cancer. Radiation therapy involves the use of a particular type of energy, known as ionizing radiation, to kill cancer cells.
“It works at the level of the DNA,” explains Anita Pomerantz, MD, assistant member, Department of Breast Oncology at Nevada Cancer Institute. “By damaging the DNA, it doesn’t allow cells to replicate.” Radiation can affect normal cells as well as cancer cells, but normal cells have a greater ability to repair radiation-induced damage. Furthermore, as the technology for radiation therapy has evolved, important advances have been made in the ability of physicians to precisely target the area of the cancer. “The fundamental struggle that we have in radiation oncology is always trying to hit the tumor harder while sparing the normal tissues around it,” says Dr. Pomerantz.
Advances in both external and internal radiation therapy have improved the ability of radiation oncologists to meet this challenge.
Advances in External Radiation Therapy
External radiation therapy refers to radiation that is delivered from a machine outside of the body. One important advance in external radiation therapy is intensity-modulated radiation therapy (IMRT). IMRT starts with a three-dimensional image of the cancer and allows physicians to deliver different doses of radiation to different areas. The potential advantages for patients include both better tumor control and fewer side effects. For patients receiving radiation for head and neck cancer, for example, IMRT may reduce the likelihood of problems such as dry mouth and injury to the jawbone.
Other technology may be combined with IMRT to further improve patient outcomes. Image-guided radiation therapy (IGRT), for example, assesses the exact location of the cancer each day that a patient comes in for treatment. “A CT [computed tomography] scan is taken every day when the patient comes in,” explains Dr. Pomerantz. “The purpose of that is simply to fine-tune the area that you’re going to be irradiating for that particular day.” In the case of prostate cancer, for example, the exact location of the prostate may vary from day to day depending on the contents of the bladder or bowel. IGRT allows physicians to account for these shifts and precisely target the cancer each day.
For patients who are receiving radiation to organs that move during breathing (such as the lungs or liver), technology known as “respiratory gating” can also improve radiation delivery. Respiratory gating follows breathing movements and delivers radiation only at a particular point in the breathing cycle. Once again, this allows the radiation to be targeted to the tumor while minimizing exposure of nearby organs and normal tissue.
Although they play an important role in the treatment of certain types of cancer, these newer approaches to delivering radiation therapy are not necessary or beneficial for all patients. “Head and neck cancer, prostate cancer, lung cancer, and more-complicated sites such as brain tumors—I would say those are the biggest categories that have benefited from these higher doses of radiation and newer technology,” says Dr. Pomerantz.
Advances in Internal Radiation Therapy
Internal radiation therapy—also referred to as brachytherapy—refers to the placement of radioactive material in or near the cancer. “If you can get a radiation source directly into a tumor, you can deliver an extraordinary amount of radiation,” says Dr. Pomerantz.
Brachytherapy is commonly used for prostate cancer and certain gynecologic cancers. Advances have also been made in using brachytherapy for breast cancer. “For the right candidates—and this means patients with earlier-stage tumors—there’s something called partial breast radiation,” says Dr. Pomerantz. “It’s still being studied, but it’s a phenomenal advancement.” Radioactive material is placed directly into the area where the breast tumor was removed. With this approach treatment can be completed in only five days, as opposed to several weeks with conventional external radiation therapy. Asked about the efficacy of this approach, Dr. Pomerantz notes that the results published thus far are quite promising and that additional study results should be available this spring. Regardless of the results, however, she emphasizes that not all breast cancer patients will be candidates for this type of treatment.
Preparing for Treatment
The goals of radiation therapy can vary. Depending on a patient’s circumstances, it may be used to help cure the cancer, or it may be used to help relieve the symptoms of advanced cancer. “When we see patients for the first time, it is our responsibility to discuss with the patient and the family what the role of radiation is for that patient,” says Dr. Pomerantz.
It’s also important that physicians address any fears or misperceptions that the patient may have about treatment. “The word radiation is certainly not the most friendly,” acknowledges Dr. Pomerantz, “and fear of the unknown can be strong.” To overcome this fear, Dr. Pomerantz encourages patients to learn as much as they can about the procedure and to talk with their physician about any concerns. Dr. Pomerantz also notes that patients tend to become more comfortable once they’ve had a few treatments: “They realize that the treatments are painless and relatively fast.”
The advances discussed above are only a sample of what’s happening in the field of radiation oncology. If you need radiation therapy, your radiation oncologist, in collaboration with the other members of the radiotherapy team, will develop a highly individualized treatment plan that addresses your specific needs. No two patients—and no two cancers—are exactly alike.
“Radiation oncology is a very exciting field,” concludes Dr. Pomerantz. “Every day there’s something new and exciting coming around the corner. We hope that radiation will add to the eradication of cancer, perhaps in the next generation.”
1. Nutting CM, Morden JP, Harringon KJ, et al. Parotid-sparing intensity modulated versus conventional radiotherapy in head and neck cancer (PARSPORT): a phase 3 multicentre randomised controlled trial. Lancet Oncology. 2011;12:127-36.
2. Kachnic LA, Winter KA, Myerson RJ, et al. Two-year outcomes of RTOG 0529: A Phase II evaluation of dose-painted IMRT in combination with 5-fluorouracil and mitomycin-C for the reduction of acute morbidity in carcinoma of the anal canal. Paper presented at: Eighth Annual Gastrointestinal Cancers Symposium; January 20-22, 2011; San Francisco, CA. Abstract 368.
Radiation Therapy in the News
Two recent studies evaluated whether intensity-modulated radiation therapy (IMRT) reduces radiation side effects. The first study, published in the journal Lancet Oncology, compared IMRT with conventional external radiation therapy for the treatment of pharyngeal squamous cell carcinoma (a type of head and neck cancer). The primary goal of the study was to determine whether IMRT could reduce the occurrence of severe dry mouth by minimizing radiation to the parotid glands, which produce saliva. By two years after treatment, moderate or severe dry mouth was reported by 83 percent of patients treated with conventional external radiation therapy but only 29 percent of patients treated with IMRT. Patients treated with IMRT reported better recovery of saliva production as well as better quality of life.1
A second study, presented at the Eighth Annual Gastrointestinal Cancers Symposium, evaluated IMRT in combination with chemotherapy for the treatment of anal cancer. The results of the study suggested that IMRT was as effective as conventional radiation therapy but less likely to cause skin and gastrointestinal side effects.2