Children not at increased risk for cancer from routine imaging tests: study
June 09, 2017
by John W. Mitchell
, Senior Correspondent
In a pronouncement sure to add kindling to a long-burning debate, a group of researchers maintain that normal CT and nuclear medicine imaging do not put kids — or adults — at higher risk for cancer.
Furthermore, they assert the premise for such concerns is based on misinterpretation of a foundational study dating back 70 years.
"I really want to stir up and put an end to this controversy," Jeffry Siegel, Ph.D., President and CEO of Nuclear Physics told HCB News. "I can't believe this linear no-threshold model (LNT) debate has been going on for so long ... causing reinforcing radiophobia that has parents telling their pediatrician they don’t want their kid child to have a needed CT scan."
Siegel is lead author on the study just published in the June issue of the Journal of Nuclear Medicine (JNM). The article calls the widely-accepted belief in the LNT model “misguided” and “detrimental” because credible evidence of imaging-related low-dose carcinogenic risk is nonexistent.
"I am a scientist, and I'm going to call out people who make assertions that are not proven," said Siegel. "I always go to the original source study documents and read them myself. Most people don't do this because they don't have or take the time."
The original studies giving rise to LNT over 70 years ago by a Nobel Laureate and others concluded that all radiation was harmful, regardless of the dose and dose rate, down to zero dose. However, the JNM article asserts the studies were not done at low doses, so the conclusions were inaccurate.
Siegel maintains that the resulting current drive for minimal doses as low as reasonably achievable (ALARA) is based on a misinterpretation of these original studies. Also, the study asserts that Japanese survivors of the atomic bomb blasts in World War II — the gold standard in dose-response population according to the article — illustrate the faulty assumptions of LNT and ALARA for both pediatric and adult populations.
Siegel said that Japanese nuclear blast survivors who received low-level radiation exposure have been followed for their lifetime and compared to control groups. This low dose group does not exhibit an LNT dose-response relationship. Rather they exhibit, at the very least, a linear threshold relationship, below which there is no observable harm.
He also said that LNT-based cancer risk predictions related to this data have led to the "outrageous and erroneous conclusion" by one group that two percent of cancers in the U.S. are caused by CT scans. But, he noted, such predictions have never been validated by observations.
"These predictions are simply wrong and have no scientific basis," said Siegel. "CT does not cause cancer, but rather cancer causes people to have CTs. Before CT, patients had to undergo exploratory surgery and many died from the procedure or the accompanying anesthesia."
The study also details the human body's ability to repair or eliminate DNA double strand damage caused by low-level radiation exposure, so that such damage does not go on to cause cancer. Siegel said the human body has a "wonderful" ability to maintain homeostasis and mitigate low-level radiation effects. At high doses, the body is overwhelmed and unable to repair or eliminate radiation damage.
Siegel’s findings will no doubt be front and center at the Society for Nuclear Medicine and Molecular Imaging annual meeting starting in Denver this weekend. An all-day Saturday session is scheduled on optimal pediatric dosing. While Siegel said that he will not be attending the meeting this year, he said a colleague had listed him as a co-presenter for a segment about the "LNT fiction".
"The obsession over lowering radiation dose is a futile and laborious attempt to minimize what is, in fact, a nonexistent risk," said Siegel. "Radiophobia is detrimental to patients and parents, induces stress, and leads to suboptimal image quality or avoidance of imaging. This increases misdiagnoses and consequent harm, while offering no compensating benefits."