No shield needed for mammograms, says radiologist

Gillian McAinsh

A MISLEADING e-mail about mammograms which incorrectly advises patients to use a “thyroid shield” has been circulating among women in Nelson Mandela Bay.

Port Elizabeth radiologist Dr Phil Pretorius, of Greenacres Hospital, said a thyroid shield was not necessary and could even camouflage cancer.

“Wearing a thyroid shield during mammography will compromise the mammogram as a portion of breast tissue deep against the chest wall may not be included in the mammogram image,” he said in response to whether or not the e-mail was valid.

“This may lead to a cancer being hidden and consequently missed on the mammogram – a far greater risk to health than scatter radiation to the thyroid.” He said dental x-rays were of even lower doses than mammograms.

“During any x-ray, the beam of radiation is directed to the part of the body and is accurately focused and ‘coned-off’ to prevent unwanted radiation to adjacent tissues,” he said.

“Small amounts of radiation are scattered to the adjacent tissue outside the area being x-rayed. This is called ‘scatter radiation’ and in the case of most x-ray procedures, including mammography, this is negligible.

“This scatter radiation is the radiation to the thyroid that is ‘hyping’ Dr Oz up.”

In fact, said Pretorius, the radiation dose exposure to the thyroid gland after 40 years of annual mammograms would be less than the background radiation received by sitting in a television studio for 60 minutes.

“For further context, a dose of 0.01 mGy is typical of the background radiation dose obtained every day from the sun, buildings, garden, and so on, surrounding you every day. So each full mammogram (four views – giving a dose of about 0.04mGy) will give you the same radiation exposure to the breasts as just living for four months.

“These doses are even smaller now, with new modern equipment in use, which reduce the radiation compared with the older machines.”

He also said that patients who had received radiation doses to thyroid of up to 600mGy showed no increase in thyroid nodules, even though this dose was 15000 times the dose of a mammogram.

“Beware of unscrupulous media presenters who take small facts out of context and sensationalise them to ‘make a show’.

“They do not have the public’s real interest at heart – only their show’s ratings.”

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