Rapid Responses to:
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Rapid Responses: Rapid Responses published:
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![[Read Rapid Response]](/icons/misc/sectionDOWN.gif)
keep it in perspective
- Bob Bury (2 January 2004)
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Wrong impression created by study publicity
- Sanjay P Prabhu (3 January 2004)
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Paediatric CT Is Higher Than We Thought
- Lynn H. Ehrle (3 January 2004)
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Author’s response.
- Per Hall, Per Hall (4 January 2004)
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Re: Author’s response.
- Sanjay Prabhu (5 January 2004)
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why blame the radiation?
- Bob Bury (5 January 2004)
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Radiation doses in infancy and cognitive function in later life, response from the National Radiological Protection Board (NRPB).
- JR Meara, Gerry Kendall, Colin Muirhead and Barry Wall (6 January 2004)
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Do not confuse radiations
- Leon, G Rausin (7 January 2004)
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Radiation Semantics & Scientific Obfuscation
- Lynn H. Ehrle (8 January 2004)
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Does the radiation solely explain the later cognitive function ?
- Rainer Fogelholm (13 January 2004)
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Radiation-induced thyroid dysfunction as a cause of low intelligence?
- Philippe P. Hujoel, Mark Drangsholt (25 January 2004)
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No link exists between CT and cognitive function deterioration
- Nchimi Alain (27 January 2004)
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further exposures in radiation awareness
- peter shortt, richard wilson,declan hughes,sinead fitzpatrick (29 January 2004)
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Bob Bury, consultant radiologist Leeds General Infirmary LS1 3EX
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There is no doubt that the rapid growth of CT technology has not always been accompanied by a parallel increasing concern with the radiation doses resulting from examinations. This is particularly true for paediatric patients, where doses are relatively higher than for adults, and the sensitivity of the tissues to the effects of radiation is greater. It is therefore important that CT technique is tailored to these young patients, and that CT is only used where there are good clinical indications. However, these authors quote doses from head CT as high as 100mGy, and the abstract in 'this week in the BMJ' irresponsibly gives the impression that this is a standard dose for a head CT scan. The quoted average dose for head CT is usually given as 2mSv (mSv being the units normally used to express effective dose - it is not clear from the article exactly what dose parameters are being quoted), and even for a neonate, the dose is unlikely to be more than 30mSv, assuming correct technique is used. It is therefore unlikely that a child having a CT scan of the head would be exposed to the sort of dose required in this study to produce a measurable effect on cognitive function. Repeated CT scans could soon add up, but these would only be done (hopefully) if the child were suffering from a severe intracranial problem of some kind. So what it boils down to is a small risk of losing a few IQ points if young children are subjected to repeated head CT examinations. Against this you have to set the near certainty of significant morbidity or mortality in many of these patients if the scans are not carried out (assuming, as always, that the requests are properly justified clinically). However, as always in these shock/horror situations, the impression given to parents is that subjecting their child to a head CT will condemn them to a lifetime of imbecility. It would help if the BMJ would make some attempt to put the claims of this type of paper into perspective. But I don't suppose the media would pay any attention if they did. Competing interests: Rapidly increasing frustration with the inability or disinclination of media/politicians/public to understand the simplest principles of risk/benefit analysis. |
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Sanjay P Prabhu, Specialist Registrar in General and Radionuclide Radiology Royal United Hospital, Bath, UK BA1 3NG
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The study in the BMJ is flawed for a number of reasons: 1. Radiation exposure in 1930-1960 was without adequate collimation, shielding and the machines used were far less accurate than in recent years. 2. The X ray treatments mainly involved contact therapy at low (60 kVp) voltage, which means less penetration and lower energy photons which are absorbed more in tissue. Some children were treated more than once, either by receiving several treatments for one hemangioma or by receiving individual treatments for several haemangiomas. This would obviously have an stochastic effect which is a fact well known to all radiologists today. We do not expose the average patient today to anything resembling what the paper quotes. 3. "No consistent difference was seen between the two lowest dose categories (1-20 mGy and > 20-100 mGy); however, the increment of exposure was limited, with median values of only 0 and 30-40 mGy." These are the maximum levels of exposure on CT scans and this is further reduced on newer scanners with dose reduction protocols based on infant age and body weight. CT dose varies with both equipment related and operator dependent factors. The mean CTDIw in various studies is reported to be between 45-60 mGy. Radiologist in the UK work with the mSv units ( millisievert) to quantify dose as Dr. Bury correctly puts it in his rapid response. 4. There is no mention of the fact that in the United Kingdom, at least, there is careful discussion based on national and international guidleines (e.g. in the UK previously jointly agreed by the RCPCH and RCR and recently published by NICE) before deciding on CT scans for young children. Radiologists and paediatricians are striving to minimise dose levels by scanning at lower mAs and there has been wide debate about this in recent radiological literature. Because some data already indicate that low-dose radiation (such as that in CT) may have a significant risk of cancer, especially in young children, we know it is important to limit CT radiation by following the ALARA (as low as reasonably achievable) principle. There are a variety of strategies to limit radiation dose, including performing only necessary examinations, limiting the region of coverage, and adjusting individual CT settings based on indication, region imaged, and size of the child. However, it would be far preferable to have a CT scan to rule out serious intracranial pathology than worry about loss of couple of IQ points in later life in a child with signs of raised intracranial pressure/ dropping GCS/ GCS score of 12 or lower/presence of focal neurological deficits/loss of consciousness/ amnesia/ drowsiness/ seizure or vomiting. Thsi fact must be highlighted rather than extrapolate high dose radiation effects to low dose CT scans. I feel that this paper is only another example of the BMJ having stooped to publish an article for gaining publicity in the media by sensationalising an issue. I believe that all radiologists and paediatricians should register our concern at the way the article has been publicised. References: 1.Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort study Per Hall, Hans-Olov Adami et al BMJ 2004;328:19 2.Brenner DJ, Ellis CD, Berdon WE. Estimated risks of radiation induced fatal cancer for pediatric CT. AJR Am J Roentgenol 2001; 1176:289- 296. 3..Frush DP. Pediatric CT: practical approach to diminish radiation dose. Pediatr Radiol 2002; 32:714-717.[Medline] 4. The ALARA concept in pediatric CT intelligent dose reduction. Multidisciplinary conference organized by the Society of Pediatric Radiology. August 18-19, 2001. Pediatr Radiol. 2002 Apr;32(4):217-313. 5. Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? Am J Roentgenol 2001;176:297–301. Competing interests: Radiologist with paediatric training- advocate of best possible care for children |
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Lynn H. Ehrle, Senior Policy Analyst, National Association for Public Health Policy(US) 8888 Mayflower Dr., Plymouth, MI 48170
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In his response to the Per Hall et al paper on paediatric head CT at low dose(Jan. 3), Bob Bury notes "these authors quote doses from head CT as high as 100mGy[10 rad]...The quoted average dose for head CT is usually given as 2mSv" [0.2rad]. A study by medical physicist Edward Nickoloff supports the authors' estimate. In fact, 10rad may be on the low side. Writing in the April 2002 issue of Pediatric Radiology, Nickoloff, working with acrylic phantoms, found the typical pediatric head CT dose ranged from 7.8-15.2rad at settings of 350-560mAs. He discovered that neuroradiologists like to have noise-free images; "they like to scan at high mAs...a generic thing." Is the internal dose accurate when using phantoms? Nickoloff states, "as the diameter of the phantom decreases to a small size, the dose at the center is nearly the same as the surface." He also graphs the results from several different scanners and deals with technical issues that should be instructive for all radiologists. Three issues in need of further clarification are 1)the cumulative impact of multiple scans, 2)a comparative analysis of current practices in the US, the UK and Europe, and 3)the hiring of technologists in jurisdictions where licensure is not required. A Summer 2002 bulletin published by the US National Cancer Institute and the Society for Pediatric Radiology identified pediatric CT as "a public health concern." This medical writer concurs. Competing interests: None declared |
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Per Hall, Associate Professor Karolinska Institutet, Per Hall
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I would like to comment on Dr Prabhu recent response to our paper on the adverse health effects of ionising radiation. Firstly, I am convinced that radiologists aim at the best possible care for children. Dose estimations were performed on an individual basis using a phantom of a child’s head, old treatment protocols, and even the old equipment. I believe that the dose estimates are as valid as they can get but it could of course be argued that different dose rates, fractionation, etc. have dissimilar effects. Things we know very little about. The comment on fractionation, dose and deterministic effect is unclear to me. Cancer induction is considered stochastic (which is of course wrong, we all have different susceptibility to ionising radiation) and skin burns, lens opacification, and, possibly, mental dysfunction, are considered deterministic. Type of effect has nothing to do with fractionation or dose. A Swedish survey of the equivalent to NRPB found brain doses after a CT scan of a child's skull to be on average 68 mGy, with a maximum of 130 mGy. The study was performed in 2001. British radiologists seem to be far better than their Swedish colleagues when it comes to minimize doses. Swedish doses are closer to those delivered in the US, please see the paper by Brenner (1) and the Rapid Response by Lynn H. Ehrle, where it is stated that 100 mGy per examination could be an underestimation! I am indeed sorry for not sharing your belief that we only do - necessary examinations, limiting the region of coverage, and adjusting individual CT settings. I have had a couple of e-mail responses where radiologists share their frustration of, what the radiologists perceive as, unnecessary examinations. Not all children receiving a CT scan after falling of the bike have "signs of raised intracranial pressure/ dropping GCS/ GCS score of 12 or lower/presence of focal neurological deficits/loss of consciousness/ amnesia/ drowsiness/ seizure or vomiting". These patients are not the problem, a scan is needed and is a fantastic and very important tool. The major problem is the unnecessary use. Today, Sunday, I have received several mails, two mails from parents. One had her 2-year- old child doing a CT scan after 2 weeks of headache. The other person had her newborn examined since his brother had a brain injury at delivery a couple of years earlier. Without having any more details, the indications seems questionable to me. You state that you think that all radiologists and paediatricians should register their concern at the way the article has been publicised. I think that you should register your concern about reducing doses and unnecessary examinations. There is a lot of work left to be done, at least in Sweden, regardless of our results. Competing interests: None declared |
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Sanjay Prabhu, Specialist Registrar in Clinical Radiology Royal United Hospital, Bath, U K BA1 3NG
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I agree with the author's assertion that "one should register your concern about reducing doses and unnecessary examinations". I have indeed done that in my letter. I also agree that unnecessary examnations are to be avoided at all costs. In the UK, with radiologists as gatekeepers to CT examinations, the number of unnecessary exminations is reduced, although, by no means, totally eliminated. Also, I believe that dose reduction practices are regularly implemented in many places as at my institutions in Bristol and Bath after regular audit and lower mAs studies have been shown to equally diagnostic in many cases. In our institution-based audit in 2001, we found that radiographers were failing to change parameters to infant settings in a significant number of cases leading to higher doses. Once a system for dose reduction was strictly implemented, the mAs and effective dose fell sharply for head, abdominal and chest CT. You state that one of the patients in her e-mail had her newborn examined since his brother had a brain injury at delivery a couple of years earlier. What was the indication for interaction with healthcarers on this occasion? No well-meaning radiologist or paediatrician will scan a well newborn infant. Did the mother raise concerns and bring pressure upon the clinician/radiologist? Though this is no excuse, it is in many cases the reason for unnecessary scan examinations in children. Litigation levels are higher in the United States and is a causative factor for higher number of CT examinations. Then there is the point of utilising MRI examinations instead of CT as first line in selected cases, thereby reducing radiation exposure. The problems with this are need for sedation and availabilty. Finally, we should strive to limit the region of coverage and adjust individual CT settings. I have not said that this is always done in all cases. But it is what all of us should aim for. I completely agree with the author that there is a lot of work left to be done in this field. A more pertinent study would be to study children who had diagnostic scans in 1990-1998 and look at the developmental and IQ scores compared to controls. I would be happier accepting results from such a study rather than extrapolated data from radiation in the 1930's to the 1950's. As diagnositic radiologists and responsible clinicians we have to try and to make CT examinations as safe as possible by minimizing dose without losing out on diagnostic accuracy. Radiologists in particular have to guide and teach clinicians the appropriate use of CT. The other important role we have is to identify a reasonable balance between diagnostic benefit and radiation dose, and provide understandable measures of outcome. Competing interests: Radiologist with paediatric training- advocate of best possible care for children |
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Bob Bury, consultant radiologist Leeds LS8 2JX
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Firstly thanks to Per Hall for his response, and for emailing me to point out that mGy are the correct units to use for organ-specific doses - I should have known that! These responses have already demonstrated the fact that Europe, and the UK in paticular, have been more proactive than some other parts of the world in limiting radiation exposure in paediatric imaging, although we shouldn't be complacent. My assumption that we only expose children to CT when it is likely to bring real benefits is, I hope, justified in this country. However, if radiologists elsewhere are concerned that children are being irradiated unnecessarily, and using high-dose protocols, surely the answer is in their hands? We are the gatekeepers of the technology, and we are the people who have to justify the exposures. Also, since my first response, a radiological colleague has pointed out another flaw in the paper, namely that the authors have assumed that the changes in cognitive functioning must be due to the radiation. These are patients with vascular malformations of the head and neck. Is it not at least possible that both the malformation and the intellectual changes are due to the same underlying (possibly dysplastic) process? What would be needed is a comparison of patients with haemangiomas treated with radiation and those either left untreated, or treated without the use of ionising radiation. Competing interests: None declared |
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JR Meara, Deputy Director NRPB, Chilton, DIDCOT, OXON OX11 0RQ, Gerry Kendall, Colin Muirhead and Barry Wall
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The new study from Sweden has reported adverse effects on cognitive function in adulthood among males treated with radiation for skin haemangioma during infancy (Hall et al, BMJ, 328, 19-21, 2004). The proportion of boys who attended high school decreased with increasing radiation dose to the brain. Furthermore, there was a negative trend with dose to the brain for three cognitive tests for learning ability and logical reasoning, but not for a test of spatial recognition. The mean brain dose was 50 mGy. The evidence for the effects reported was strongest among those males who received the highest doses, and it is unclear whether there was a dose threshold below which no effects occurred. This appears to be a well-conducted study, based on a sizeable cohort. Data on exposures and outcomes were collected in an objective manner, so reducing the possibility of bias. In such studies it is always necessary to consider whether factors relating to the original condition may have driven the findings. However in this study, comparisons were made of cognitive function amongst haemangioma patients with differing levels of brain dose, rather than using an external comparison group. Confounding would seem plausible only if the severity of the clinical condition both affected IQ AND was correlated with the brain dose. Comparison of these results with previous studies is not straightforward, since many of these studies had considered higher doses, exposures received in utero rather than in infancy, or may have been subject to confounding by the clinical condition that gave rise to the exposure. However, there does appear to be consistency across studies, in indicating adverse effects of radiation on intellectual development. Established principles of radiation protection call for unnecessary exposures to be avoided and for all exposures to be kept as low as reasonably practicable. This is to control well-established risks, largely of radiation-induced cancers. Much the commonest significant doses to infants are from medical procedures. Ordinary X-rays give low doses, but Computed Tomography (CT), which can give more detailed clinical information, involves higher doses. However, CT of the head is not a first line examination for children except in the case of severe head injury. In the UK, guidelines have been produced by the Royal College of Radiologists and by the National Institute for Clinical Excellence. These guidelines specify that CT head scans are not appropriate for minor head injuries, but only in those few cases where there are specific clinical symptoms suggesting the possibility of significant brain injury which may require neuro-surgical intervention. Nevertheless, if stringent efforts are not made to adjust the CT scanning protocol to the small size of very young patients, the dose to the brain from localised head exposure can possibly exceed 100 mGy, and would fall within the upper range of doses encountered in the Swedish study. Therefore, the results of this study reinforce the need for optimising CT scan protocols to minimise the dose to the patient without losing essential diagnostic information and for restricting such examinations to those cases where there is a clear clinical indication. Note The Swedish study discussed the consequences of doses to the brain; where the head is irradiated the doses to other organs and tissues of the infants concerned will generally be much lower. For protection purposes it is common to express the potential harm from inhomogeneous partial body exposures in terms of the “effective dose”, a weighted sum of doses to many organs and tissues. The dose to the brain will be much higher than the effective dose from a CT brain scan, since (as the most highly irradiated “remainder” organ) dose to brain is multiplied by a tissue weighting factor of 0.025 to form the major contributor to the effective dose. Provisional NRPB calculations of organ doses from CT head scans on infants suggest that effective doses of about 5 mSv and corresponding brain doses of about 100 mGy would be possible if adult CT scanning protocols were applied to infants aged below 18 Competing interests: The authors all work for the National Radiological Protection Board (NRPB). NRPB has a statutory duty in the UK to advise on protecting the public from the harmful effects of radiation. This response will also appear on the NRPB website |
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Leon, G Rausin, Pediatric Radiologist CHR Citadelle Liege 4000 Belgium
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As a pediatric radiologist, i read your article with great attention. I think radiation therapy for scalp hemangioma is by no mean comparable to that of CT scanners. The quality of the rays employed is completely different from the Xrays used in CT. You pointed out that the technique used was a "contact therapy " application. In this technique, the radiation is completely absorbed by the subject. Every pediatric radiologist knows that he has to avoid radiation of less than 65 Kv in order to deliver a "safe" radiation , minimally absorbed by the child. In CT scanner, and above all for head scanners, we need an energetic radiation wich can hit the detectors and give a signal strong enough to be distinguished from the noise. In your article , i notice three main bias:
I think it is dangerous to publish such a bare article without any discussion about the quality of the radiation. I am conscious of my responsability when i realise CT scanner in children , but i am convinced that the ionising radiation you speek about has nothing to do with Xrays used for diagnostic purposes. Competing interests: None declared |
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Lynn H. Ehrle, Senior Policy Analyst, National Association for Public Health Policy(US) 8888 Mayflower Dr., Plymouth, MI 48170
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After reading radiation research for over 30 years I have discovered one universal principle--PRACTITIONERS ACROSS RADIATION DISCIPLINES SPEAK IN DIFFERENT LANGUAGES. Not only that but radiation research is highly susceptible to scientific obfuscation. Interviews with over 50 medical physicists and radiologists have revealed little agreement on low dose risk, and its definition is all over the map. The Per Hall et al paper(3 Jan.)claims "existing data are based mostly on high doses of ionizing radiation(>1Gy), therefore little is known about the effects of low doses of radiation or a threshold value." Actually, there is a large body of literature on the subject, particularly if you define low dose as anything under 1Gy[100rad). The conventional wisdom has held that the benefit from diagnostic and therapeutic X ray procedures always exceeds the risk and some practitioners even preach The Hormesis Thesis(small doses are beneficial). Independent scientists have long disputed these claims and have presented scientific evidence that there is no safe dose(threshold), whereas others proclaim that radiation is a weak carcinogen. This latter proposition does not hold up under the glare of the historical record. Within a year of Wilhelm Roentgen's discovery of X ray in 1895, laboratories popped up in every major city, advertising cures for every manner of illness, and despite medicine's conservative reputation and the admonition "to, first do no harm," physicians embraced "the ray" with reckless abandon. Even though over 100 deaths of radiologists and patients were recorded in those early years and unusual illnesses began to present, few medical histories appeared in the early journals. Denial was the order of the day. Out of the ashes of Hiroshima and Nagasaki, the Cold War and nuclear power emerged, and-- scientific obfuscation. In the U.S., Great Britain, and France, huge amounts of money began to flow to academic research centers and the nuclear industry was able to extract government subsidies for power plant construction Radiation research, much of it related to the weapons program, was often relegated to RESTRICTED DATA files. Then came the human radiation experiments and above ground atomic tests, always under the rubric of "national security," a justification for avoiding the Nuremberg requirement for informed consent. In 1958, Alice Stewart presented the first human radiation data, the Oxford Survey of Childhood Cancer, demonstrating excess cancers and leukemias in children before age 10, whose mothers had received in utero X ray(1). Her work was roundly criticized at the time, in part because it was a retrospective study, but the critics would have a hard time with the prospective study, by Brian MacMahon, whose work four years later supported Stewart's Oxford Survey. Since those early studies much has transpired and new evidence of genomic instability and the bystander effect has added to our understanding of radiation's powerful mutagenic effects at low dose. A recent study,authored by 15 cancer rssearchers, concludes there is good epidemiological data supporting cancer risk in humans from acute exposures of10-50mSv and protracted exposure in the 50- 100mSv range(3). It is now time to address the profusion of terms and equations that litter the radiation landscape, making it difficult if not virtually impossible for members of the broader medical community, not to mention informed citizens, to traverse the journal entries. Excess relative risk(ERR), excess absolute risk(EAR), sievert, rem, gray, and rem; relative biological effectiveness(RBE), single radiation track, dose rate effectiveness factor(DREF), internal organ dose, skin dose. The need for clarity is self-evident. As to the claim by Sanjay Prabhu that BMJ is "sensationalizing" the issue--nonsense! This journal is acting in the highest interest of public discourse, with open dialog and effective peer review, the very anthesis of the closed shop approach we so often encounter at conferences and in many journals. References 1. Stewart Am, Webb JW, Hewitt D, 1958. A survey of childhood malignancies. Brit Med J 2:1495-1508. 2. MacMahon B,1962. Prenatal x-ray exposure and child-hood cancer. J Natl Cancer Inst 28:1173-1191. 3. Brenner DJ, Doll R, Goodhead DT, Preston DL, Ron E, et al, 2003. Cancer risks attributable to low doses of ionizing radiation:assessing what we really know, 2003. Proc Natl Acad Sci 100:13761-13766. Competing interests: None declared |
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Rainer Fogelholm, neurologist (retired) -
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In media all "bad news" have always been the most selling stuff. So were also the results of this study. Because of the publicity of the study by Hall et al., I read the paper with a great interest. The crucial point to my response is the lack of a more detailed description of the patients; the boys had cutaneous haemangiomas in the head region, and they were in 1930-59 younger than 18 months. As a neurologist, my first question was how many of these boys had Sturge-Weber syndrome with cutaneous AND cerebral haemangiomas. In a typical case, the cutaneous lesions are in the territory of the trigeminal nerve and the cerebral in the haemispheral cortex of the same side. There are, however, many variations. The neurological symptoms, if present, include epileptic seizures, hemiparesis and some mental retardation. In skull X-ray cortical calcifications may be seen. I am afraid that the diagnosis of possible cortical haemangioma has not been made at the time of radiation therapy. In 1930-59 none of the current neuroradiological examinations was available, and skull x-rays, if performed, were of little help because cortical calcifications are rare at such a young age. The study found an inverse association between the estimated radiation dose and high school attendance, and frontal radiation dose and military test results. In Sturge-Weber syndrome the cutaneous lesions are predominantly in the forehead, and the sizes of the cutaneous and cortical lesions are often correlated. Therefore, one can expect that large frontal radiation doses are associated with larger cerebral cortical lesions. I am sure, that Sturge-Weber syndrome is only a part of the mix of boys who had radiation treatment for cranial haemangiomas, but they can explain the poorer (mean) results in both high school attendance and military tests. This probability should be examined before scaring the laypersons more about the hazards of CT and other x-ray examinations. Competing interests: None declared |
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Philippe P. Hujoel, Professor University of Washington, Seattle, WA 98105, Mark Drangsholt
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The study by Drs. Hall et al. has contributed significantly to the growing body of evidence that low-dose head-and-neck radiation may not be as harmless as current guidelines suggest. Low dose ionizing radiation has now been associated with thyroid disease, lowered IQ, low birth weight, and small stature and cranial size (1, 2). The key to understanding these disparate epidemiological observations may be that radiation is primarily affecting thyroid function which, in turn, leads to a variety of systemic effects that include both abnormal growth and impaired mental development. This explanation is consistent with the finding that frontal skull radiation was more harmful than posterior skull radiation for intelligence (where skeletal tissues provide a more effective barrier against thyroid radiation), and that the strong association was observed when radiation occurred in infancy, when thyroid susceptibility to radiation is high (4). Extensive evidence supports the susceptibility of the thyroid to very -low dose radiation. Low dose ionizing radiation from diagnosticl X-rays, fall-out at Chernobyl, or housing construction materials contaminated with radioactive materials all have been associated with thyroid pathology ranging from subtle, subclinical auto-immune thyroiditis to thyroid carcinoma (3). Subtle subclinical thyroid maternal dysfunction has been associated with a lowered IQ of the offspring (5) and it is not such a large leap of faith to hypothesize that subtle infant thyroid dysfunction has a similar impact on intelligence. An attractive feature about the thyroid hypothesis is that it provides a simple, unifying, biologically plausible hypothesis for the variety of systemic effects reported to occur when the head-and-neck region is exposed to low-dose ionizing radiation. Also, further evaluation of the thyroid hypothesis is important because it would imply that sensitivity to radiation is strongly dependent on age and gender (which would have significant consequences for establishing diagnostic radiation guidelines), and that possibly, interventions can be designed to counteract a radiation-damaged thyroid gland. References: 1. Miller RW, Blot WJ. Small head size after in-utero exposure to atomic radiation. Lancet 1972;2(7781):784-7. 2. Goldberg MS, Mayo NE, Levy AR, Scott SC, Poitras B. Adverse reproductive outcomes among women exposed to low levels of ionizing radiation from diagnostic radiography for adolescent idiopathic scoliosis. Epidemiology 1998;9(3):271-8. 3. Pacini F, Vorontsova T, Molinaro E, Kuchinskaya E, Agate L, Shavrova E, et al. Prevalence of thyroid autoantibodies in children and adolescents from Belarus exposed to the Chernobyl radioactive fallout. Lancet 1998;352(9130):763-6. 4. Ron E, Lubin JH, Shore RE, Mabuchi K, Modan B, Pottern LM, et al. Thyroid cancer after exposure to external radiation: a pooled analysis of seven studies. Radiat Res 1995;141(259-77). 5. Haddow JE, Palomaki GE, Allan WC, Williams JR, Knight GJ, Gagnon J, et al. Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child. N Engl J Med 1999;341(8):549-55. Competing interests: None declared |
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Nchimi Alain, Radiologist Medical Imaging Dep. Centre Hospitalier Chrétien, B-4000 Liège (Belgium)
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Dear Sir, I read with interest, in a recent issue of BMJ(1), the study published by Hall and colleagues, in which an adverse effect on the intellectual development was found related to ionising radiation exposure at doses reportedly equivalent to those of head computed tomography (CT). Although I believe that the paper serves the ongoing debate over the adverse effects of CT, the debate itself requires strong evidences and serenity, both of which did not clearly appear in the paper. As the result, this paper might rise considerable amount of suspicion and anxiety over CT, in parents and paediatric healthcare workers. Moreover, considering this paper, no one would be surprised to see the debate over the adverse effects of CT move from inside the journals to inside the courts in the next few years. With your indulgence, I would like to express below an opinion, of which I respectfully suspect, you are aware. The relationship between head CT and adulthood intellect as established by the authors was based on the fact that some sources reported head CT doses in infants as high as 100 mGy (1, 2). Indeed, in their study, adverse effects on high school attendance was evident for groups at radiation doses higher than 100mGy. No such effects was evidenced in groups with lower doses (1-20 mGy). However, the doses discussed in the paper of Brenner et al. (2) resulted from a national trial in Britain, that taken in account adult scanning protocols. Current, paediatric head CT effective doses as recently measured in a Belgian multicentre study ranged from 0.4 to 2.3 mSv*(3). These values are dramatically lower than those cited by Hall et al (1). Moreover, the authors did not discuss important points that could alter the credibility of their caculated doses. The bias related to retrospective dosimetry, which I suppose (considering both the administration method and the ancillary equipment used) was high, was not taken in account. Also, the differences between administered doses and absorbed doses were not discussed. To conclude, Hall et al. are acknowledgeable for reminding that indications for CT should be taken cautiously, especially in children. However we should consider that they had link adulthood cognitive retardation to unknown-dose head irradiation, yet, not to CT. Though if such a link was necessary, a study of the intellect of the young adults who had undergone head CT, as children, in the early 80’s, might serve the purpose. References 1. Hall P, Adami HO, Trichopoulos D et al. Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort study. BMJ 2004; 328 :19. 2. Brenner DJ, Ellis CD, Berdon WE. Estimated risks of radiation induced fatal cancer for pediatric CT. AJR Am J Roentgenol 2001; 1176:289- 296. 3. Pages J, Buls N, Osteaux M. CT doses in children: a multicentre study. Br J Radiol. 2003; 76: 803-811. *One mSv represents the effective radiation dose that equals one mGy for photon irradiation Competing interests: None declared |
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peter shortt, sho a&e a&e department royal victoria hospital,belfast bt12 6ba, richard wilson,declan hughes,sinead fitzpatrick
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Dear Sir, We note that in recent editions of your Journal you have published two papers directly concerned with aspects of exposure to ionizing radiation. Most recently Hall et al (1) discussed the adverse effects of low dose ionizing radiation to cognitive development while previously Shiralkar et al (2) highlighted the lack of awareness among doctors to the degree of exposure to ionizing radiation from common radiological examinations We recently carried out a telephone audit regarding the awareness amongst Emergency Department SHOs in Northern Ireland of their responsibilities under the Ionizing Radiiation (Medical Exposure) regulations (3). These regulations were introduced in March 2000 by the U.K. Departmnet of Health. These are legal requirements to ensure patients have the appropriate radiological procuedure performed given the appropriate clinical indication and that there is no unnecessary exposure to ionizing radiation. We questioned forty ED SHOs on their awareness and udnerstanding of these regulation. Of these SHOs only six were aware of the regulations. The other thirty-four SHOs stated they had never heard of them. Of all the SHOs questioned twenty-one stated they had received a general induction course on starting their posts in ED. However, only nine recalled part of this being dedicated to the appropriate use of the Radiology Department and only one recalled the regulations ever being mentioned. We feel this demonstrates a surprising finding among medical practitioners who have direct access to a range of radiological investigations on a daily basis. We are forced to question whether this level of awareness is reflextive of SHOs in other medical specialties/regions. Yours faithfully References: (1) Hall et al. Effect of low doses of ionizing radiation in infancy on cognitive function in adulthood: Swedish Population based cohort study. BMJ 2004; 328:19-21 (2) Shiralkar et al. Doctors knowledge of radiation exposure: questionnaire study. BMJ 2003: 327:391-402 (3) The Ionizing Radiation (Medical Exposure) Regulations 2000. www.doh.gov.uk/irmer Competing interests: None declared |
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