Higher Doses of Radiation Often Needed for Obese, Overweight Patients

< Jul. 01, 2009 > -- New research indicates that people who are overweight and obese are usually given higher-than-normal doses of radiation in order to obtain usable X-ray images, even though the long-term effects are unknown.

The findings are reported in the July issue of Radiology.

According to the study's lead author, Jacquelyn C. Yanch, Ph.D., a professor at the Massachusetts Institute of Technology in Boston, a certain amount of X-rays is needed to go through the body "in order to get an informative image, and excess weight impedes that. And there are very few ways around that problem, other than increasing an overweight patient's exposure to radiation to improve the image quality."

"Americans have gotten larger on average over the last half-century, and so as a result, our radiation dosages have gone up," Dr. Yanch adds. "Exposure can be sometimes 20, 30, even 40 times as much for an overweight patient as for a lean person. And in general, we're also getting more exams and more intensive exams."

"But even so, we don't actually know the impact of such high doses over time, or whether they're dangerous, because we simply haven't tracked the effect," Dr. Yanch says. "So, it's very important for us to start monitoring this exposure for each individual patient so we can get a handle on it."

Radiation Dosage Levels Compared

According to the researchers, x-rays account for the majority of radiation exposure in people.

To gauge how high radiation doses must be to get effective X-rays for overweight and obese people, the researchers used computer simulations that delivered X-ray beams at various strengths to so-called "phantom" patients representing five different fat tissue levels, from lean to obese. Different body areas, including the chest and abdominal regions, were X-rayed to see which entry points were most effective in rendering high-quality images.

The researchers then compared the dosage levels, body position options, and body mass distribution numbers with the amount of radiation the computer software indicated that each imaginary patient would have had to absorb to get the desired image.

Overall, they found that directing an X-ray to the thickest part of a person's fat allowed delivery of a lower radiation dose than would be needed if a different area were targeted.

Even so, the dosage needed to get an effective X-ray via the abdominal region of a moderately overweight man was up to 10 times greater than for a lean man, the study found. And for a more severely overweight or obese person, the needed dosage was up to 40 times greater than for someone of normal weight.

Proof Still Lacking

Dr. Yanch and her team point out, however, that the development of adipose tissue cancer from radiation exposure has not been proven. In fact, she says, the issue is not that the jury is still out but that it has not even begun to deliberate.

"For some procedures, the standard doses are very low, and so even 20 times higher than that is likely still too low to be concerned about," she notes. "But for some procedures, the doses to a very overweight person will be quite high. Yet the scientific field does not know what this all means. We don't know if this is anything to be concerned about yet. We have models and prediction, but no real data."

"The way to find out is to begin to pay close attention to what doses are being given over time, patient by patient, and what the outcomes are," she adds.

Risk of Repeated Exposure Not Defined

Dr. Levon Nazarian, a professor of radiology and vice chairman for education at Thomas Jefferson University Hospital in Philadelphia, agrees that the central question is how the risk for health problems goes up with repeated exposure to high-dose radiation.

"It's true that the dose from a typical X-ray is very, very small," he says. "So, yes, 40 times a very small dose is still small and probably not dangerous. However, were you to do repeated X-rays at 40 times the regular dose, eventually the additive effect could be dangerous because your body never forgets an X-ray. It's cumulative over time. So the more you do over a lifetime, the more you have a chance of causing cancer due to radiation exposure."

Dr. Raul N. Uppot, a radiologist at Massachusetts General Hospital and an assistant professor of radiology at Harvard Medical School, notes that physicians dealing with overweight patients are caught between a rock and a hard place because of the absence of definitive information about long-term side effects of high-dose radiation.

"The image quality among obese patients is not sufficient unless something is done to adjust exposure upwards to deal with the problem," he notes. "That is a bottom line. But, of course, we're always trying to balance what's safe with what's needed. So certainly I think, when you have no other option but to increase dosage exposure, you do want to come back and monitor these patients and see if their risk of cancer is any higher. Ultimately, that's the critical information needed to determine what dosages are, in fact, safe."

Always consult your physician for more information.

What Are X-Rays?

X-rays use invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs on film or digital media. Standard x-rays are performed for many reasons, including diagnosing tumors or bone injuries.

X-rays are made by using external radiation to produce images of the body, its organs, and other internal structures for diagnostic purposes. X-rays pass through body structures onto specially-treated plates (similar to camera film) or digital media and a "negative" type picture is made (the more solid a structure is, the whiter it appears on the film).

When the body undergoes x-rays, different parts of the body allow varying amounts of the x-ray beams to pass through. The soft tissues in the body (such as blood, skin, fat, and muscle) allow most of the x-ray to pass through and appear dark gray on the film or digital media.

A bone or a tumor, which is more dense than the soft tissues, allows few of the x-rays to pass through and appears white on the x-ray. At a break in a bone, the x-ray beam passes through the broken area and appears as a dark line in the white bone.

X-ray technology is used in other types of diagnostic procedures, such as arteriograms, computed tomography (CT) scans, and fluoroscopy.

Radiation during pregnancy may lead to birth defects. Always tell your radiologist or physician if you suspect you may be pregnant.

The radiologist is a medical doctor who has completed a four year residency in either diagnostic radiology or radiation oncology. A radiologist may act as a consultant to another physician who is caring for the patient, or act as the patient's primary physician in treating a disease (such as a radiation oncologist).

Following the residency, most radiologists and radiation oncologists become board-certified by the American Board of Radiology. Some go directly into practice, while others enter fellowship programs for additional training in a specialized area, such as neuroradiology or pediatric radiology.

As a result of increasing knowledge and levels of technology in the field, radiology has become highly specialized, as have most other medical and surgical specialties. The current trend is for radiologists to become specialized in a particular discipline, such as cardiology (the study and treatment of the heart) or neurology (the study and treatment of the brain and nervous system).

Board-certified radiologists must adhere to the Practice Standards of the American College of Radiology.

Always consult your physician for more information.