Radiation dose reduction in medical imaging needed

Of late there has been renewed interest in reducing radiation doses from medical imaging procedures.This has been partly due to extensive media coverage of a few over exposure incidents

K.S.Parthasarathy

Date:18/02/2010 URL: http://www.thehindu.com/thehindu/seta/2010/02/18/stories/2010021850111500.htm Back Sci Tech



Radiation dose reduction in medical imaging needed

CT scans involve extended exposure to radiation, and hence higher radiation dose



















— Photo: K. R. Deepak

Overdose: The adult effective dose from a CT exam of the head is equivalent to the adult effective dose from roughly 100 chest X-rays.

On February 9, 2010, the US Food and Drug Administration (FDA) published a white paper titled “Initiative to reduce unnecessary radiation exposure in medical imaging.” FDA found out several instances of radiation over exposures; some of them were as appalling as the ones reported within a few months of the discovery of X rays!

The new FDA initiative promotes safe use of medical imaging devices, supports informed clinical decision making and offers measures to increase patient awareness.

On October 8, 2009, FDA issued a radiation alert when it discovered that 206 patients who underwent CT perfusion studies in a hospital may have received 6 to 8 times more dose than what is necessary.
Media coverage

Some patients suffered hair loss and reddening of the skin indicating high radiation doses. The Agency found out that the overexposures were more wide-spread. Media covered these excesses extensively.

In January 2008, 23 month old Jacoby Roth fell out of bed; his doctor ordered a CT scan to find out damage, if any, to his spine.

A technologist carried out 151 scans in 68 minutes. Within a few hours, the child developed a bright red ring around his head from the massive overdose of radiation (AuntMinnie.com, 2009).

The dose to the child may have been about 2800 mSv to 11,000mSv. (mSv is a unit of radiation dose, the dose in a normal paediatric study of the entire spine may be about 1.5 to 4 mSv). The California Department of Public Health (CDPH) imposed a fine of $25,000 on the hospital. The technologist is fighting to retain her licence. Parents are suing the hospital.

Clinically indicated computed tomography (CT), nuclear medicine procedures and fluoroscopy carry immense benefits for patients when they are executed by trained professionals using optimally adjusted equipment. Misadministrations are rare.
The assertion

FDA asserted that there must be appropriate justification for ordering and performing each procedure, and careful optimization of the radiation dose used. International Commission on Radiological Protection (ICRP) upholds these basic principles.

“Because CT, fluoroscopy, and nuclear medicine procedures involve repeated or extended exposure to radiation, these types of exams are associated with a higher radiation dose than projection radiography.

For example, the adult effective dose from a CT exam of the head is equivalent to the adult effective dose from roughly 100 chest X-rays. The adult effective dose from a CT exam of the abdomen is roughly equivalent to the adult effective dose from roughly 400 chest X-rays”, the FDA paper cautioned.

FDA may require that CT and fluoroscopic devices display, record, and report radiation dose and alert users when the dose exceeds a diagnostic reference level, a peak skin-dose threshold for injury, or some other established value.

The Atomic Energy (Radiation Protection) Rules, 2004 (RPR2004) require that the licensee “shall for optimising the medical exposure ensure that performance of the equipment is verified periodically by appropriate quality assurance tests.”

The licensee shall also “ensure that any accidental medical exposure is investigated and a written report submitted to the competent authority.” The Atomic Energy Regulatory Board (AERB) has not so far received any report of accidental exposures in medical imaging, though there is anecdotal evidence of their occurrence.

RPR 2004 requires that the licensee shall maintain the records of radiation doses received by therapy patients and activities administered to patients in diagnostic and therapeutic nuclear medicine procedures. The rules need amendment to make recording of diagnostic X-ray dose mandatory in line with recent trends.

Inputs from an AERB funded safety research project indicate that at least 1.5 lakhs of children are found to be receiving excess radiation exposure because some of the CT Centres do not follow paediatric protocols. Parents should insist that the physicians should refer their children to only centres which follow appropriate protocols.

AERB’s effort to enforce strict compliance of rules in an area which grew unbridled for the past several decades is a daunting task.

ksparth@yahoo.co.uk

(The author is Raja Ramanna Fellow, Department of Atomic Energy)

K.S. PARTHASARATHY

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