Nearly 70 percent of women over the age of 40 received a mammogram to screen for breast cancer in the past two years, according to a 2010 Centers for Disease Control and Prevention study. But exactly how much radiation was each individual woman exposed to during her exam?
An Emory medical physicist received a $1 million grant from the Susan G. Komen Foundation in June to study that question.
Ioannis Sechopoulos, assistant professor of radiology at Emory University School of Medicine, has been studying breast-imaging radiation for nine years now. He plans to use the new grant to develop a more individualized method for measuring the amount and location of radiation delivered to a woman's breast during an imaging exam.
"We'll be able to answer our patients' questions if they ask us," Sechopoulos said. "People want to know how much radiation they are getting."
The new Monte Carlo method that Sechopoulos will be using for the study will first be developed using "phantom images," with breast-like objects. Then, Sechopoulos plans to use real patient images to further test these methods. The Monte Carlo method involves simulating what takes place during an imaging test through a computer program. The computer will use this simulation to predict the path of each x-ray and where the x-ray radiation will deposit energy in the breast.
After researchers test the methods, any patient image can be fed into the simulation, and a doctor can see a personalized estimation of the radiation dose for each patient.
The current method of determining the radiation dose models all patients' breasts as if they were the same, Sechopoulos said. However, the structure of tissue within the breast differs for every woman.
According to Sechopoulos, the amount and exact location of glandular tissue, usually concentrated in the center of the breast, makes a major difference in how much radiation is absorbed by a patient during an imaging test.
Last year, Sechopoulos conducted a study that compared the traditional way scientists measure radiation dose in mammography and the new patient-specific method he is developing. He said scientists have been overestimating the radiation dose from mammography – a dose said to be about two weeks worth of natural background radiation per image.
"In general, the glandular tissue absorbs less radiation dose than the numbers we've been using," Sechopoulos said. "So that's good because if we're going to be wrong, then we might as well be wrong on the conservative side, overestimating."
One of the larger implications of collecting patient-specific data could be the creation of "dose registries," Sechopoulos said. These would allow institutions like Emory to send in data on the radiation dose used for its mammograms and compare its numbers to those of other places over time.
"If we had national registries of real patient-specific dose, we would have a better understanding of how [dosage] trends are moving in time," Sechopoulos said. "And if ... we're reducing dose too much or not enough, you can make technology advancements."
These technology changes could include adjusting the number of x-rays used in a breast imaging exam and the energy levels to either increase or decrease the radiation dose delivered to a patient, Sechopoulos said. To lower the dose of radiation to the breast, some technology improvements in the past have included using better digital detectors for digital mammograms, according to Sechopoulos.
In this study funded by the Komen foundation, Sechopoulos will be testing the Monte Carlo method for a new breast screening technology, tomosynthesis. This technique is similar to acquiring many mammograms from different angles. Then the computer renders a 3D representation of the breast from these images so doctors can better visualize the tissue.
"There are many screening centers around the country that are starting to use [tomosynthesis] in addition to mammography," Sechopoulos said. "In the future, I predict that we will start using it in replacement of mammography for screening."
Sechopoulos said the Emory Breast Imaging Center will be receiving a tomosynthesis machine soon but is not yet sure of an exact date.
In the meantime, Sechopoulos will begin conducting this new study at the Winship Cancer Institute with collaborators at the University of Pennsylvania, the University of Chicago and the Technical University of Varna in Bulgaria.
– By Nisha Giridharan
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