Low dose radiation 'likely helps
prevent' cancer: experts
prevent' cancer: experts
Experts assert no evidence links X-ray or CT to future cancer diagnoses
January 11, 2017
By Lauren Dubinsky and Gus Iversen
By-and-large, the health care industry is on a mission to reduce radiation exposure to the bare minimum and avoid it entirely whenever possible — but some experts have taken the position that this attitude is misguided and potentially hazardous to patients.
An article published this month in The Journal of Nuclear Medicine makes the case that the nature of radiation exposure is fundamentally misunderstood.
The confusion goes back at least as far as Hermann Muller's 1946 Nobel Lecture, in which he claimed, “all radiation is harmful, regardless of how low the dose and dose rate.” This way of thinking is known as the linear no-threshold hypothesis (LNTH) and this isn't the first time it's come under fire.
Study author, Jeffry A. Siegel — who is the president and CEO of Nuclear Physics Enterprises, an international nuclear physics consulting firm specializing in clinical trial design for radionuclide therapy agents, regulatory issues, quantitative diagnostic imaging acquisition and analysis, and radiation dosimetry — makes the case that Muller's argument is scientifically invalid.
Although it has repeatedly been shown that the dose-response relationship may reasonably be considered to be linear down to a certain threshold, (i.e. "half as much is half as bad") Siegel and the other authors argue, at a certain point this relationship changes.
"Credible evidence of imaging-related low-dose (<100 mGy) carcinogenic risk is nonexistent; it is a hypothetical risk derived from the demonstrably false LNTH," they wrote. "On the contrary, low-dose radiation does not cause, but more likely helps prevent, cancer."
Some evidence toward the possible benefits of very low radiation dose exposure was published in 2015 in PLOS ONE, where researchers showed that exposing fruit flies to radiation could actually make them live longer.
As Low As Reasonability Achievable, or ALARA, refers to the widely accepted principle that using the minimum necessary radiation dose for CT, X-ray and nuclear medicine imaging exams is the best medicine — and despite a lack of evidence regarding the dangers of low dose — many regulatory policies are based on it.
Siegel's team points to studies that demonstrate the LNTH and ALARA philosophies focus solely on molecular damage and disregard the protective, biological responses that can take place on a very low level.
They assert that low doses of radiation stimulate protective responses and help the body prevent additional damage over time, including that of subsequent, higher radiation exposures.
A study on the life spans of Japanese atomic bomb survivors, which the article cites as "the gold standard for estimating radiation effects in humans" found that low-dose carcinogenicity predicted with the LNTH is invalid below about 200 milligray (mGy). The doses of typical imaging exams can range from a fraction of a millisievert (mSv) for regular X-ray to 15 mSv for whole-body FDG PET/CT. One mSv is the dose produced by exposure to 1 mGy of radiation
The American College of Radiology recommends limiting lifetime diagnostic radiation exposure to 100 mSv. That is equal to 10,000 chest X-rays, or up to 25 chest CTs, according to Harvard Medical School.
The study authors argue that the real danger is when these valuable diagnostic exams are avoided due to "radiophobia."
An opinion piece published in the June issue of the American Journal of Roentgenology discussed the difference between the public’s perception of radiation risk and the actual risk from low doses of ionizing radiation.
Dr. Cynthia H. McCollough of Mayo Clinic explained that if the exam is needed, the benefit will outweigh “any small or potentially nonexistent risk.” She also noted the importance of adjusting the delivered dose to the patient size and to the diagnostic task.
“There have been too many polarizing articles on the topic of radiation dose in CT. These articles serve only to perpetuate the discussion, leaving patients and their families with the impression that this issue is a deeply concerning one,” she said in a statement.
The authors of the JNM article believe that the medical profession must be properly re-educated, starting with diagnostic radiologists and nuclear medicine physicians, then the public can be given valid information that they can trust.
By-and-large, the health care industry is on a mission to reduce radiation exposure to the bare minimum and avoid it entirely whenever possible — but some experts have taken the position that this attitude is misguided and potentially hazardous to patients.
An article published this month in The Journal of Nuclear Medicine makes the case that the nature of radiation exposure is fundamentally misunderstood.
The confusion goes back at least as far as Hermann Muller's 1946 Nobel Lecture, in which he claimed, “all radiation is harmful, regardless of how low the dose and dose rate.” This way of thinking is known as the linear no-threshold hypothesis (LNTH) and this isn't the first time it's come under fire.
Study author, Jeffry A. Siegel — who is the president and CEO of Nuclear Physics Enterprises, an international nuclear physics consulting firm specializing in clinical trial design for radionuclide therapy agents, regulatory issues, quantitative diagnostic imaging acquisition and analysis, and radiation dosimetry — makes the case that Muller's argument is scientifically invalid.
Although it has repeatedly been shown that the dose-response relationship may reasonably be considered to be linear down to a certain threshold, (i.e. "half as much is half as bad") Siegel and the other authors argue, at a certain point this relationship changes.
"Credible evidence of imaging-related low-dose (<100 mGy) carcinogenic risk is nonexistent; it is a hypothetical risk derived from the demonstrably false LNTH," they wrote. "On the contrary, low-dose radiation does not cause, but more likely helps prevent, cancer."
Some evidence toward the possible benefits of very low radiation dose exposure was published in 2015 in PLOS ONE, where researchers showed that exposing fruit flies to radiation could actually make them live longer.
As Low As Reasonability Achievable, or ALARA, refers to the widely accepted principle that using the minimum necessary radiation dose for CT, X-ray and nuclear medicine imaging exams is the best medicine — and despite a lack of evidence regarding the dangers of low dose — many regulatory policies are based on it.
Siegel's team points to studies that demonstrate the LNTH and ALARA philosophies focus solely on molecular damage and disregard the protective, biological responses that can take place on a very low level.
They assert that low doses of radiation stimulate protective responses and help the body prevent additional damage over time, including that of subsequent, higher radiation exposures.
A study on the life spans of Japanese atomic bomb survivors, which the article cites as "the gold standard for estimating radiation effects in humans" found that low-dose carcinogenicity predicted with the LNTH is invalid below about 200 milligray (mGy). The doses of typical imaging exams can range from a fraction of a millisievert (mSv) for regular X-ray to 15 mSv for whole-body FDG PET/CT. One mSv is the dose produced by exposure to 1 mGy of radiation
The American College of Radiology recommends limiting lifetime diagnostic radiation exposure to 100 mSv. That is equal to 10,000 chest X-rays, or up to 25 chest CTs, according to Harvard Medical School.
The study authors argue that the real danger is when these valuable diagnostic exams are avoided due to "radiophobia."
An opinion piece published in the June issue of the American Journal of Roentgenology discussed the difference between the public’s perception of radiation risk and the actual risk from low doses of ionizing radiation.
Dr. Cynthia H. McCollough of Mayo Clinic explained that if the exam is needed, the benefit will outweigh “any small or potentially nonexistent risk.” She also noted the importance of adjusting the delivered dose to the patient size and to the diagnostic task.
“There have been too many polarizing articles on the topic of radiation dose in CT. These articles serve only to perpetuate the discussion, leaving patients and their families with the impression that this issue is a deeply concerning one,” she said in a statement.
The authors of the JNM article believe that the medical profession must be properly re-educated, starting with diagnostic radiologists and nuclear medicine physicians, then the public can be given valid information that they can trust.