Keith Strauss, an emeritus associate professor at the University of Cincinnati School of Medicine, is fully aware of what his well-researched proclamation means for his line of work, all medical technologists, millions of patients, decades of clinical best practices and countless textbooks, exams and course curriculums.
Everything needs to change.
Because the gold standard of medical physics for more than 70 years—gonadal shielding—provides little to no benefit to patients.
“It’s a substantial shift in existing clinical practice,” says Strauss, former head of Clinical Medical Physics within the Radiology Department of Cincinnati Children’s Hospital Medical Center.
Strauss’ position on gonadal shielding—a procedure used to help keep a person fertile by preventing damage to their reproductive organs during radiation therapy via a lead protective shield—is greatly supported by a who’s who of medical physicist leaders.
Medical physics organizations in agreement to limit or phase out gonadal shielding include the American Association of Physicists in Medicine (AAPM), the American College of Radiology (ACR), the Canadian Organization of Medical Physics (COMP), the Health Physics Society (HPS) and the Canadian Association of Radiologists (CAR).
Plus, the National Council on Radiation and Measurements (NCRP) made several recommendations on how to end routine gonadal shielding.
There are quite a few reasons why gonadal shielding is a precaution that provides little to no benefit, says Strauss and colleague Kevin Buckley, a Certified Health Physicist (CHP) and the Radiation Safety Officer (RSO) and Diagnostic Medical Physicist at Lawrence General Hospital in Massachusetts.
Three stand out.
Heritable genetic risks are much less than previously estimated.
It all started with fruit flies.
“There were a few classical experiments done where fruit flies were given various radiation doses,” Strauss says. “Fruit flies multiply very quickly. So you can get through generations in a short amount of time.”
What happened during the experiment?
“The offspring started to have mutations,” Strauss says. “Instead of having a pair of wings, they might have two pairs of wings, or they might have three pairs of wings.”
That was in the 1920s. Fast forward to the 1950s. Many changes in radiotherapy, notably megavoltage therapy, take root. But experts remain uncertain about the long-term effects of radiation exposure on unborn fetuses and reproductive cells.
“We believed that the model we saw with the fruit flies might apply to human beings,” Strauss says.
Gonadal shielding is implemented to minimize the potential for heritable genetic effects from medical exposures. It’s cemented as a standard of practice.
But decades of researching the effects of routine diagnostic imaging exams on humans show gonadal shielding isn’t needed. Case in point: Gonads have sustained a decrease in tissue-weighting factor, which estimates the potential adverse effects of irradiation.
“The tissue-weighting factor for the gonads decreased from 0.2 to 0.08,” Strauss says. “That means we now believe humans are not as susceptible to mutations as previously thought. Meanwhile, the other major organs in the abdomen have retained their same tissue-weighting factor.”
He adds: “Think about it: With gonadal shielding, we are trying to shield one of the body’s least sensitive organs (to radiation). It just doesn’t make sense.”
Technology advancements have decreased risk.
Strauss remembers looking it up to be sure. Sure enough, he was correct.
“The dose associated with a kidney, ureter, and bladder (KUB) x-ray was 20 times greater in the 1950s than today,” he says. “So even without gonadal shielding, patients today are getting significantly less radiation dose to their gonads that they got with shielding back in the ’50s.”
In other words, medical imaging technology has made significant advances.
Today, hospitals and imaging centers have sophisticated imaging devices that can reduce radiation exposure to the reproductive glands during pelvic imaging by as much as 96%, the American College of Radiology (ACR) says.
During gonadal shielding’s infancy, radiographic machines didn’t have automatic exposure control (AEC), an x-ray exposure termination device that did not become widespread until the early 1970s. Today, AEC is always used for adults and sometimes for pediatrics.
“Automatic exposure control uses a sensor usually placed in front of the image receptor,” Buckley says. “A human operator always starts the medical radiographic exposure, but an AEC sensor is calibrated so that when a predetermined amount of radiation has been received, exposure automatically shuts down.”
Except, at times, when paired with gonadal shielding.
“Gonadal shielding can interfere with automatic exposure control and thereby cause an increase in dose to other pelvic and abdominal organs that may be more radiosensitive,” the NCRP remarked in its Statement 13 analysis, which Strauss helped prepare.
“That means the patient could receive a higher dose than prescribed because gonadal shielding can block the AEC’s ability to do its job,” Strauss says. “Gonadal shielding and automatic exposure control should not be coupled together. They don’t play nicely in the same sandbox.”
Gonadal shielding does not cover most ground.
So, was gonadal shielding ever needed? It’s a good question, Strauss says.
But here’s a better question: Did gonadal shielding ever really achieve its intended purpose?
“Despite the careful application of gonadal shielding by technologists, 70% or 80% of the time, it failed to adequately shield the actual location of the patient’s gonads,” said Buckley.
Not even close.
The location of the gonads within the female body varies considerably among patients, the NCRP says. Unlike male gonads, ovaries are not visible and can be located anywhere in a large area across the abdomen and pelvis.
“We now understand the potential location of the ovaries is spread wide across the entire female abdominal region,” Strauss says. “That’s important because we later learned that the small cross-sectional area of the gonadal shield that the technologists are given to use only covers about 10% of that area.”
“So, 90% of the time, the shield probably is not directly over the ovaries,” Strauss says. “There is no way for the technologist to know the location in a given patient.”
The situation is also true for males, although not to the same degree.
“The male gonads are surface located, so we know where they are. But misalignment of surface shields with respect to the male gonads still occurs,” Strauss says. “Gonadal shielding does not shield all the gonads in most patients due to the limited area of the shield and the normal variations in patient anatomy.”
And we can’t give technologists a larger shield, either, in an attempt to improve alignment of the shield with the gonads.
“A larger shield may cover parts of the anatomy the radiologist needs to see,” Strauss says. “The bigger the shield, the greater the risk there’s an important finding in the radiograph that’s masked by the shield.”
“The result is a process given to technologists that too often is unsuccessful through no fault of the technologist,” Strauss said. “We didn’t understand that then. We do now.”
If gonad shielding is eliminated, what’s next?
Technologists have been trained for 70 years that gonad shielding is one of the most important things they can do to foster patient safety, Buckley says.
“For decades, there has been zero tolerance for anybody not using gonadal shields,” Strauss adds. “Now, all of a sudden, we say gonadal shielding, one of their gold standards, should be discontinued during x-ray-based diagnostic imaging?”
Easier said than done.
“A lot needs to change,” Strauss admits. “It’s going to take time.”
While technologists have gradually embraced the transition supported by a mixture of medical physics organizations, two key groups will need the most persuasion: patients and parents.
“If you have had imaging exams with a shield, you may be fearful of having an exam without one,” the American Association of Physicists in Medicine (AAPM) says.
“Pregnant mothers or parents of children being imaged may be especially anxious about this change,” the ACR says.
Furthermore, there are many sources of misinformation about gonadal shielding, making it difficult to find accurate data. And Buckley says not all states have updated their policies, meaning they still require shielding.
These points underscore the importance of taking additional steps to support your radiology department and its technical staff properly. “They’re the ones who must explain why we no longer do gonadal shielding and answer the patient or parents’ questions,” Strauss says.
At Cincinnati Children’s Hospital Medical Center, where gonadal shielding is discontinued, Strauss provided extra support by developing question-and-answer sheets, conducting forums and giving out support hotline numbers that help answer patients’ questions about the now obsolete practice.
“There were times that, despite detailed explanation, parents still pushed back and wanted the gonadal shield on their child. That’s why we made sure gonadal shields were still available in the room to do just that,” Strauss said. “We get it. It’s what everyone has known as best practice for years and decades. Now, we know better through greater health physics research. We’ll get it right.”
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