Journals Watch - CT scans, memory loss and H1N1

Too busy to keep up with new research? Let Dr Bryan Palmer update you on the latest papers.

A study into the radiation doses and cancer risks of CT scans produced a wide variation in results
A study into the radiation doses and cancer risks of CT scans produced a wide variation in results

Radiation exposure from CT scans - Arch Intern Med 2009; 169: 2078-86

I am fortunate that here in Australia I have open access to CT, but Australia is second in the world to the US for average ionising radiation dose per capita.

It has been suggested that a third of CTs are unnecessary but little is known about the consequences. This US study aimed to clarify doses of radiation from common types of CT (including head, chest and abdomen) and estimate cancer risk due to exposure.

The authors conducted a retrospective cross-sectional study describing radiation dose associated with the 11 most common types of diagnostic CT studies performed on 1,119 consecutive adult patients at four institutions between 1 January and 30 May 2008.

They found not only a wide variation between different types of CT but also a variation in dosages across different providers of the same examination. Sex and age also made a difference to risk with young women having the highest lifetime cancer risk from exposure.

A single head CT gives a 40-year-old woman about a one in 8,000 lifetime risk of developing cancer. Perhaps doctors who have access to CT should have ongoing training on its indications, benefits and risks.

Can Ginkgo biloba reduce cognitive decline? - JAMA 2009; 302: 2663-70

Most (but I admit not all) studies into complementary medicines continue to show their worthlessness. This study, which had a good enough methodology to reach JAMA, investigated Ginkgo biloba and the belief that it reduces cognitive decline.

The Ginkgo Evaluation of Memory study was a randomised, double-blind, placebo-controlled clinical trial of 3,069 people aged 72-96 years with a median follow-up of 6.1 years in the US. Participants were either on twice daily ginkgo or placebo.

Using various scales there was no measurable difference in memory between the two groups at the end of the study.

The authors concluded that compared with placebo, the use of Ginkgo biloba 120mg twice daily did not result in less cognitive decline in older adults with normal cognition or with mild cognitive impairment. We will see many more negative studies but whether we will we see a reduction in sales I don't know.

Protection due to the paediatric H1N1 vaccine - JAMA 2009; 303:doi:10.1001/jama.2009.1911

We are awaiting the next wave of pandemic flu down under and it was noteworthy that the paediatric vaccine was released the week before Christmas with a correspondingly low uptake rate. This randomised, observer-blind, age-stratified, parallel group study of 370 children aged six months to nine years aimed to determine the dosage, timing and safety of the vaccine.

Following the first vaccination, 92 per cent demonstrated an adequate protective threshold titre and this became 100 per cent after a second dose (although I note seroconversion was 87 and 95 per cent, respectively).

Reported adverse events were deemed mild to moderate with pain the most noted feature followed by fever. As this cohort is the most likely to be hospitalised, the hardest battle is convincing parents there is still a threat.

Sick of sick notes - Fam Pract 2009 doi:10.1093/fampra/cmp096

GPs typically sanction absence from work by issuing sickness certificates. This is also true for those of us who work in the southern hemisphere.

In the UK, there has been debate about changing the way sickness certificates are issued. Change for the better is unlikely to occur unless greater understanding of the process is reached.

This study comprised a cross-sectional postal survey of 2,154 UK GPs. They were asked about perceived certification practices, training in sickness certification, their opinions about the certification process and potential to improve the system.

A response of 42 per cent was achieved and the main issues brought up were a lack of training and the idea that other health professionals could issue sick certificates. GPs felt there was scope to improve training and the system in general.

As a comparison, I write fewer certificates here and for shorter duration because people are often self-employed and want to get back to work.

Lowering the speed limit reduces road injuries - BMJ 2009;339:b4469

'Speed kills' and the slogan 'every K over is a Killer' are routine public announcements in Australia, where the road accident toll is higher than the UK. This study from the BMJ goes to prove those points.

It looked at the effect of 20mph zones in London with regard to collisions, injuries and fatalities using an observational study based on analysis of geographically coded police data on road casualties in 1986-2006. Not only did the number of road injuries fall by almost 42 per cent in those 20mph areas but also by 8 per cent in surrounding areas.

The main beneficiaries were younger children and those in the killed or seriously injured category rather than minor injuries. I would call this a resounding success. It will no doubt lead to further speed restrictions but this study can quickly silence any doubters.

  • Dr Palmer is a former Hampshire GP currently working in Australia, and a member of our team who regularly review the journals

The quick study

  • Lifetime cancer risk is one in 8,000 for a 40-year-old woman after a single head CT.
  • Memory loss is not prevented by Ginkgo Biloba.
  • Paediatric H1N1 vaccine in two doses gives 95 per cent seroconversion.
  • Sickness certification could be carried out by health professionals other than GPs.
  • Road injuries fell by 42 per cent when 20mph zones were introduced.

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