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

© Copyright 2000 - 2009 The Hindu

Is work in a nuclear power plant risky?

The Tribune

SCIENCE & TECHNOLOGY Friday, February 12, 2010, Chandigarh, India

Is work in a nuclear power plant risky?
K S Parthasarathy
A 24 year old who is about to join the Department of Atomic Energy (DAE) as a scientific officer, is troubled by what he saw on a TV channel. He is unmarried; his parents are worried about the alleged damage to DNA by radiation. I assured him that there is no such harm. TV channels often go overboard and make unsubstantiated claims.
A 63 year old person asked me whether the throat malignancy, which, his 33 year old daughter is suffering from, is likely due to the possible radiation exposure he might have received while working in a nuclear power plant when he was 28 year old.
Thyroid diseases are not infrequent. No one knows for sure the reason for getting it. But there is no evidence that radiation exposure to father may lead to cancer in their children.
Workers in nuclear power plants will receive some radiation dose. Nuclear Power Corporation of India Limited (NPCIL) has instituted strict procedures to keep the doses to workers within the limits prescribed by the Atomic Energy Regulatory Board (AERB) and to values As Low As Reasonably Achievable (ALARA). Their radiation risk is insignificant.
ALARA committees with Chief Superintendents as chairmen, section heads as members and health physicists as member secretary review radiation work at each station periodically. Sectional ALARA committees plan work involving radiation exposures.
Each Station prepares a work plan, identifies various activities involving radiation exposure and gets AERB's approval for an annual “Radiation Budget”. If any Station exceeds the budget, AERB will not be amused!
The interior areas of the plant buildings are categorised into four zones for radiation and contamination control. Healthphysicists record radiation levels and airborne activity with prescribed frequency. Movement of every worker within the zones is controlled. Before entering Zone 2, 3 &4, they must wear lab coat, gloves and shoe covers and personnel dosimeters. They come out through sensitive portal monitors which will detect contamination, if any, present. They check hands and shoes using special monitors.
Annual reports published at (www.aerb.gov.in) indicate that the compliance with its stipulations is near total. For instance, during 2001 to 2008, among the annual average workforce of about 14,000 workers, one worker each in Rajasthan Atomic Power Station (RAPS) and Narora Atomic Power Station (NAPS) exceeded the limit in 2001; in 2002, one worker each in Madras Atomic PowerStation (MAPS) and NAPS; in 2007, two workers in NAPS exceeded the limits. This is indeed a creditable record.
Dose limits are based on conservative assumptions. It is inconsequential if any one receives, occasionally, a dose above the limit.
The Station managements made improvements in ventilation, reduced heavy water leakages, shielded hotspots, filtered crud from heat transport system, promptly detected and removed failed fuel bundles and used cobalt-free materials (Radiation from Cobalt-60, formed by actrivation of cobalt present in certain reactor components increases the radiation field). Many elegant engineering solutions helped to reduce radiation doses to workers.
Radiation protection standards assume that any dose of radiation, no matter how small, involves a possible risk to human health (World Nuclear Association, November 2009). After reviewing 200 peer-reviewed publications, Electric Power Research Institute (EPRI) concluded that this methodology may have been over-estimating the risks. (World Nuclear News, December 2).
Radiation protection standards are based on studies by scholarly bodies such as the US National Academy of Sciences (NAS)’ Biological Effects of Ionizing Radiation Committee, the International Agency for Research on Cancer (IARC) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). They indicate that at low doses, radiation risks, if there are any, are very small. Negligibly small risks are no risks at all. Work in a nuclear power plant is not a risky occupation.
The writer is Raja Ramanna Fellow, Department of Atomic Energy

Many glaciers, ice caps worldwide in retreat

Date:04/02/2010 URL: http://www.thehindu.com/thehindu/seta/2010/02/04/stories/2010020450051400.htm Back Sci Tech



Many glaciers, ice caps worldwide in retreat

90 per cent of the 612 glaciers across the High Asian region were retreating; this increased to 95 per cent from 1990 to 2005

— Photo: AFP





Core evidence: Ice cores collected in 2006 from the 6050 metre high Naimona’nyi Glacier lack the distinctive nuclear fallout footprints suggesting no net accumulation of ice since at least 1950s. This file picture shows the Khumbu Glacier in the Everest-Khumbu region.

Ice cores drilled from glaciers around the world generally contain elevated levels of beta radioactivity including chlorine-36 and tritium associated with thermonuclear bomb testing in the 1950s and 1960s (Kehrwald, Thompson and others, Geophysical Research Letters, Nov 22, 2008). These researchers found that the ice cores collected in 2006 from the 6050 metre high Naimona’nyi Glacier, in the Himalayas (Tibet), lack the distinctive nuclear fallout footprints suggesting no net accumulation of ice since at least 1950s .

Surprisingly, no one referred to these studies in the recent controversy over the Statement of the Intergovernmental Panel on Climate Change (IPCC) on the Himalayan Glaciers.

Professor Lonnie Thompson a leading glaciologist and a co-author of the paper made similar observations many months earlier (“Missing footprints of A-bomb fallout in Himalayan ice fields,” The Hindu, January 31, 2008).

Responding to my e-mail query, Prof. Thompson wrote that he conducted his research on glaciers across the Tibetan Plateau and on the Tibetan side of the Himalayas.

“From the Qilian Mountains on the northeast side of the Plateau, to the Kunlun Mountains in the west, to the northern slopes of the central and western Himalayas, all the glaciers and ice caps that I have studied are retreating,” he asserted.

He pointed out that all the glaciers he has studied in the Peruvian Andes are also shrinking. The glaciologists at the Institute of Tibetan Plateau Research in Beijing have found that from 1980 to 1990, 90 per cent of the 612 glaciers across the High Asian region were retreating, and from 1990 to 2005, this increased to 95 per cent.

Thompson admitted that meteorological records from the Tibetan Plateau and the Himalayas are scarce and of relatively short duration, most beginning in the mid-1950s to early 1960s; however those that do exist show that surface temperatures are rising, and rising faster at higher elevations than at lower elevations.

According to him, the Tibetan Plateau has been warming at a rate of 0.16 degrees centigrade per decade, with winter temperatures rising 0.32 degrees centigrade per decade.
GRACE data

“A recent paper by Matsuo and Heki in Earth and Planetary Science Letters (time-variable ice loss in Asian high mountains from satellite gravimetry) shows that from 2003 to 2009 the average ice loss from the Asian high ice fields, as measured by GRACE satellite observations, had accelerated twice as fast as the rate over four decades before, but the loss was not consistent over space and time”, he cautioned

He observed that ice retreat in the Himalayas slowed slightly, while loss in the mountains to the northwest increased markedly.

“So, between the surface temperature measurements, the satellite studies, the ground studies on glaciers, and ice core results, a case can be made that glacier retreat at high elevations is indeed occurring concomitantly with increasing temperatures, which is consistent with the IPCC model results which show not only low-latitude warming but an amplification of that warming at higher elevations where these glaciers are located,” he argued

Thompson stated that the rate at which glaciers respond to climate change depends on their size; larger a glacier, the longer it takes to retreat in response to a warmer/drier climate, or grow in response to a cooler/wetter climate.

“Thus, among the 15,000 glaciers in the Himalayas, the largest are currently reacting to changes that happened 100 years ago. However, some of the growing glaciers are in fact surging; that is, they are advancing because of dynamics of ice flow and not because of climate.
Temporal differences

On the short term, glaciers show rapid changes in response to changes in snowfall amounts as well as temperature, but over the long term temperature will dominate,” he clarified.

Prof. Thompson referred to their latest paper titled ‘Glacier loss on Kilimanjaro continues Unabated’ in the Proceedings of the National Academy of Sciences (November 2, 2009) which demonstrates that ice loss on Kilimanjaro is unfortunately right on track as predicted in their 2002 Science paper. New measurements completed on GEOEYE satellite images from July 17, 2009 shows that the loss of ice continues right along the project from their Science paper.

According to Anna Barnet, assistant editor and copy editor of Nature Reports Climate Change (July 9, 2009), Thompson has spent more time above 20,000 ft than any other human being. She noted that by collecting a vast library of ice samples from mountain peaks, he has developed a unique view of past and present-day climate change. Thompson had 7,000 metres of glacial ice in his collection (PNAS, 2006). He is eminently qualified to comment on the topic.

Prof. Thompson noted that the recent document by V.K. Raina, formerly Deputy Director General of the Geological Survey of India, has been catapulted into the fray over the Himalayan glacier retreat.

According to Prof. Thompson Mr. Raina states quite correctly in his report (before going on to present case studies of only 3 glaciers) that “a few glaciers cannot be taken as the representative of around 10,000 glaciers of various sizes that exist in the Indian part of the Himalayas.”

Prof. Thompson clarified that very few solid peer-reviewed papers exist on glacier retreat in this region of the world, and as Mr. Raina would evidently agree, nothing conclusive can be claimed based on studies of a handful of glaciers out of over 15,000 throughout the Himalayas, both on the Indian and the Tibet sides.

Poster child glaciers

Prof. Thompson stated that participants on both sides of the issue are drawing conclusions about what is happening in a very large and climatologically and topographically complex region based on the “behaviour” of a few glaciers that have been adopted collectively as the “poster child” for all the world’s bodies of ice.

He conceded that most glaciologists and climatologists, he included, do not believe that most of the Himalayas will be ice-free by as early as 2035.

‘The provenance of this statistic may not be scientific or peer-reviewed, and the authors and reviewers … may have erred by allowing it to slip past the fact-checking process while the report was being prepared, but it doesn’t invalidate the entire IPCC report.

If any of the report’s authors felt compelled for whatever reason to include such material, as apparently admitted by Murari Lal, one of the lead coordinating authors of the 2007 IPCC report’s chapter on Asia (US News and World Report, Jan 25), then that should be investigated and the current guidelines should be strengthened and more rigorously enforced to prevent future occurrences of non-peer reviewed material slipping through,” he suggested.

“Scientists hold the peer-review process as the “gold-standard” for publication, but as in all human endeavors mistakes are occasionally made.

“In the end, it is the total body of substantiated evidence on global climate change that is important, not occasional errors or miscommunications that provoke unbalanced and hyperbolic reactions,” Prof. Thompson clarified.

K.S. PARTHASARATHY

Raja Ramanna Fellow, Department of Atomic Energy

( ksparth@yahoo.co.uk )

© Copyright 2000 - 2009 The Hindu