Advances in Radiation Therapy

Doctors first began using X-rays to treat cancer in the early 1900s. Since then, the field of radiation therapy has grown tremendously in its use to treat cancer patients. Today, radiation therapy is considered a standard treatment for cancer and its symptoms.

Nancy Daly, Director of Government Relations for the American Society for Therapeutic Radiation and Oncology (ASTRO), estimates that about 60 to 70% of people with cancer are treated with radiation therapy at some point during their cancer care.

Dr. Norman Coleman from the Radiation Oncology Science Program at the National Cancer Institute adds, “Seventy percent or more of those patients treated with radiation are being treated radically, that is, for cure. About 30% are treated for palliation (to ease pain and other symptoms). Depending on the stage of cancer at diagnosis, many people are cured using radiation."

Who's on Your Radiation Team?

The goal of radiation is to kill cancer cells by directing strong X-rays at the site of the tumor. A person undergoing radiation will see a radiation team including a:

• Radiation Oncologist -- a doctor specifically trained in this area who will prescribe the patient's treatment plan. This includes what kind of radiation is needed, what part of the body will be treated, how much radiation to give at each treatment, and how long the treatment should be given.

• Radiation Nurse -- educates the patient about the treatment, how to manage unpleasant side effects, and coordinates the patient's care.

• Radiation Physicist -- works with the radiation oncologist to prescribe the correct dose of radiation and programs the radiation machines.

• Dosimetrist -- calculates the amount of radiation to be directed at the tumor, and helps develop the treatment plans.

• Radiation Therapist -- treats the patient according to the oncologist's prescription and operates the radiation equipment.

“Radiation can be used as the main treatment to cure the tumor, as part of combined treatment with surgery or chemotherapy, or to prevent recurrence. It can also be palliative for both defined tumors and those that have spread,” says Coleman. “It uses ionizing radiation to kill cancer. This energy is about 1000 times higher than in a diagnostic X-ray because the radiation dose is so concentrated.” Ionizing radiation is short waves of energy that deeply penetrate tissues in the body before releasing the energy.

New Methods of Delivering Radiation Therapy

Researchers are looking for new ways of delivering radiation that can better treat the cancer and to decrease toxic side effects to healthy tissue near the tumor. Large doses of radiation are often needed to kill a tumor but also kill many healthy cells. The challenge is to restrict the radiation to the tumor and ensure that all the cancer cells receive the right dose of radiation. Daly notes the recent changes in radiation, “There is a difference between advances in chemotherapy and radiation therapy. We don't come up with ‘new radiation' like we come up with new chemotherapy drugs. But, in radiation therapy, new technologies are always evolving.” These advancements allow radiation oncologists to improve care by delivering radiation more precisely.

Three-Dimensional Conformal Radiation Therapy and Intensity Modulated Radiation Therapy

Three-Dimensional Conformal Radiation Therapy (3D-CRT) allows radiation to be delivered to tumors in higher doses more accurately. 3D-CRT uses computerized tomography (CT) scanners to produce images of the tumor area. These images are transferred to a computer that measures the size and location of the tumor and nearby healthy tissue. From there, the amount of radiation targeted at the tumor is determined. “3D-CRT uses images from CT scans, but information may also be used from magnetic resonance imaging (MRI) and positron emission tomography (PET) scans for treatment planning. It is a more precise way of defining the tumor target,” Coleman says.

Tumors that are irregular in shape, found in a delicate area such as the brain, or surrounded by normal tissue highly sensitive to radiation may benefit from 3D-CRT. Parts of the body commonly treated with 3D-CRT include the prostate, brain, lung, head, and neck. New computer programming and careful review of the patients' treatment plans are helping to improve this therapy.

Intensity Modulated Radiation Therapy (IMRT) is a new form of 3D-CRT. The difference between IMRT and 3D-CRT is that IMRT treats the tumor with small beams of different strengths of radiation, but 3D-CRT uses beams of the same strength. Older treatment methods give the same radiation dose across the tumor, but tumors often vary in thickness. This may create “hot spots,” or areas of the tumor that receive more radiation than others. IMRT is a technique in which higher doses of radiation are applied to certain tissues. It also supplies a more consistent dose of radiation aimed at the tumor while sparing healthy tissue.

Coleman reports that hospitals are just starting to use IMRT, and its use is still in the early phases. “It requires very complex technology, as does 3D-CRT.”

Stereotactic Radiosurgery and Stereotactic Radiotherapy

Another recent advance in radiation using the 3D technique is stereotactic radiosurgery (SRS). SRS applies a single large dose of radiation with a gamma knife or linear accelerator. Coleman says, “It is mostly used for brain tumors, but the general technique can be used elsewhere in the body.” Stereotactic radiosurgery is best used in organs that do not move, such as the brain, to allow for more accurate delivery of radiation to the tumor and limit exposure to normal tissues. Tumors that respond best to SRS are three centimeters or smaller and evenly round in shape.

Stereotactic radiosurgery also uses a “fixed head frame.” Graeme Fisher, Radiation Oncologist and Assistant Professor at the University of Massachusetts Medical Center, explains, “There is typically a fixed head frame attached to the patient's skull to provide accurate markers for the tumor target. The frame is bolted to the table or something stationary because the dose is given within millimeters.” The fixed head frame is important because the patient must remain still.

Stereotactic radiotherapy (SRT) delivers multiple smaller doses of radiation and uses a non-fixed frame. It is more ideal to use on organs that move, such as the lung. Coleman adds, “New techniques are being developed so that the treatment machine can go on and off to adjust for basic body movements like breathing.”

Other Advances in Radiation Therapy

Additional advances, according to Coleman, include hyperfractionated and accelerated radiation therapy, imaging, proton beam therapy, combination therapies, and brachytherapy.

Two new methods of delivering radiation are hyperfractionated radiation therapy, or hyperfractionation, and accelerated radiation therapy. Coleman explains that hyperfractionation uses a smaller individual dose (fraction size), but the patient is treated twice or more per day instead of the usual once per day treatment. More treatments are needed due to the lower dose. The lower fraction size helps spare injury to healthy tissues. Accelerated radiation also uses fraction-size doses, but more doses are given overall per week. So the total treatment time is shortened.

Molecular imaging helps the doctor better define the tumor area, similar to what MRIs, PET scans, and CT scans do. Molecular imaging produces images of the tumor at a level not visible to the human eye--the molecule. Molecular imaging will help scientists understand how the tumor behaves and responds to different treatments.

Proton beam therapy is a different type of ionizing radiation using tiny particles called protons, which target small, well-defined tumors. Proton therapy causes minimal damage to healthy tissue but is effective at killing target tumor cells. It requires precise imaging and the patient must remain still. Coleman states that the therapy is very expensive compared to X-ray and gamma-ray radiation, and more research is needed for what cancers would most benefit, but it may be useful in highly specialized settings. Proton therapy has been used to treat rare tumors around the eye and spine and advanced prostate cancer.

Combining radiation with other treatments, such as chemotherapy, is called combined modality therapy. Chemotherapy or radiation used alone may not produce the desired effect, and trying to increase the dose may result in worsened side effects. Combining different therapies can increase the effectiveness of the treatment while saving normal tissue. For example, chemotherapy may be given before radiation to help shrink a tumor, or after radiation treatments to prevent the spread of remaining cancerous cells. This method of treatment is becoming standard in many cancers including those of the cervix, lung, head and neck.

“The use of radiation plus new biological agents, such as the anti-angiogenesis agents, is also very exciting,” says Coleman. Studies in animals have found that endostatin and angiostatin, naturally occurring proteins in the body, can shrink tumors by stopping growth of the blood vessels that nourish them. Because there are few side effects and normal cells are not damaged, long-term use of this therapy in addition to chemotherapy or radiation shows promise.

Brachytherapy has been used for over 100 years. It is a treatment that places radiation in direct contact with the tumor, usually through temporary or permanent implants. The implants may be seeds or needles. Treatment with implants is classified as low dose rate (LDR) or high dose rate (HDR) brachytherapy. LDR brachytherapy applies continuous low doses of radiation with implants placed in the body for several days or permanently. HDR brachytherapy uses higher amounts of radiation than LDR, but is given in smaller, repetitive doses. HDR implants are removed immediately after treatment. Brachytherapy is typically used for cancers of the prostate, mouth and throat.

Overcoming Fears About Radiation

Daly, who believes that the word “radiation” may carry with it some negativity, believes the public needs education about the importance of radiation in treating cancer. “Some may not understand how it works and just how many people are cured with radiation,” Daly says.

“Radiation is so stigmatized,” she continues, noting that ASTRO is working to correct this problem. Daly says one fear may be that people hear of childhood cancer survivors who develop secondary cancers as a result of treatment with radiation therapy.

Fisher agrees these side effects are an important consideration but notes that without the use of radiation therapy in treating and curing some childhood cancers, the children with those cancers could die. In addition, says Fisher, “We need to educate people and let them know that the side effects from radiation are not necessarily debilitating, and more patients do extremely well with it than those who have significant side effects. Also, many of our advances have been to help reduce the side effects.”

Coleman adds that the risk of secondary cancer is quite low except in certain high-risk groups. These may include young adolescent women receiving radiation to the breast during breast development, and patients undergoing intensive combined modality therapy with a large amount of chemotherapy and radiation.

Coleman says, “There is a fear of radiation because it is silent--that is, it is not tangible so it can be seen, felt, or heard.” He believes health professionals can work with patients to overcome these fears by helping them to realize that doctors, radiation therapists, and nurses closely monitor radiation.