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Substantial advances have occurred in the field of radiation oncology, resulting in much faster, more flexible and very precise delivery of radiation. Playing a key role in the latest technology is a treatment called Intensity-Modulated Radiation Therapy (IMRT). It’s one of the most precise forms of external beam radiation therapy available, and it can be found at Mount Auburn Hospital.

“IMRT is a highly technical, computer-based method of delivering standard linear accelerator photon radiation, but it allows for more precision while sparing normal tissues that are nearby,” says Carolyn Lamb, M.D., a radiation oncologist at Mount Auburn Hospital in Cambridge, a teaching hospital of Harvard Medical School.

IMRT allows more controlled dosing and needs to be used in conjunction with methods to verify tumor position, such as online-portal imaging and gold seeds.

IMRT uses a highly sophisticated computer program to vary the size and shape of the radiation beam, customizing it for each patient. Dr. Lamb says radiation oncologists and physicists work together to develop a plan of treatment, using the IMRT. A number of imaging devices, including CT scans, are used to plot the site of the tumor, three dimensionally. Once the tumor and surrounding tissue have been mapped out, the oncologist must decide how much radiation certain areas of the target site will receive.

“We can sculpt the dose better now,” says Dr. Lamb. “We can control how much radiation goes to a specific area – a higher dose to this spot, a lower dose to that spot. The goal of IMRT is to target the cancerous tissue while sparing the healthy tissue.” This has led to an improved cure rate in prostate cancer since doctors can deliver a higher dose of radiation to the prostate while minimizing exposure to surrounding structures.

Dr. Lamb says using the IMRT gives radiation oncologists more degrees of freedom when targeting the x-ray beam at a patient’s tumor. That’s because of a unique leaf-like feature, called multi-leaf collimator. There are up to 120 little ‘leaves’ or shields that move during treatment. These leaves block and conform the beam to each patient’s tumor and spare more normal cells.

“Think of it as a radiation beam with a grid placed over top of it,” says Dr. Lamb. “Each square on that grid will have the radiation streaming through it. But by using the multi-leaf collimator, you can block certain squares from letting the radiation through. The multi-leaf collimator is constantly moving, adjusting the amount of radiation that hits certain areas.” Before the IMRT, oncologists could only give a single dose of radiation to the target area.

Dr. Lamb says currently, prostate, head and neck, and certain breast cancers benefit the most from using IMRT.

“Patients with head or neck cancer in the past would usually experience permanent dry mouth after going through radiation. But with IMRT, we can figure out various beam arrangements to try and spare the salivary glands, so they have better salivary function,” Dr. Lamb says.

Prostate cancer works very well with IMRT because doctors are able to track the prostate on a daily basis. The size of a walnut in a healthy younger man, the prostate can move around, depending on how full the bladder or bowel are. Doctors insert gold seeds into the prostate, which highlight the prostate on an X-ray. Another new piece of technology available at Mount Auburn Hospital, called online-portal imaging, allows doctors to take snap shots of the prostate. Because it’s digital, doctors and the treating therapists see their pictures right away and can make sure the beam tracks with the daily position of the prostate.

Dr. Lamb says the linear accelerator treatment machine at Mount Auburn Hospital produces the highest energy of all the linear accelerators in the Boston area, which enables doctors to treat deeper inside the body with improved safety and efficacy.

For a free Mount Auburn Hospital cancer education packet, please call us at 617-499-5094.