Re: Embryo/fetal doses

["Lindsay Tremethick" <lindsay@gh.vic.gov.au>]

> RAY FONG wrote:
> > 
> > Radsafers,
> > I am looking for actual (hi-profile) cases where developing
> > embryo/fetus
> > inadvertently received a relatively significant dose from radiographic
> > imaging sources (e.g., CT, Fluoro, Abd exams, even radiopharmaceutical
> > administration). Any current references/sources?
> > Ray
> -------------------------------------------------------------
 
> Ray - don't send your digest next time, please. Anyway on to the
> story...
> I'm sorry this wasn't high profile but it was an interesting case I
> worked on in 1985. On 1/8/85 a patient was given a hysterosalpingogram
> (x-ray exam of uterus & etc. other bits) to diagnose possible causes of
> infertility) at the West London Hospital. Subsequent to the
> investigation it was discovered that at the time she had been nine weeks
> pregnant. 
> Our original fetal dose estimate using TLDs and a pelvic phantom was
> based on 5 mins flouro screening and 5 spot films and worked out to be
> in the region 4 - 15 cGys (I think these are still rads in the US).
> Later it was discovered from the radiologist that the screening time was
> probably only about 1 min (records of routine screening times were not
> kept at this hospital). Our revised dose estimate was thus reduced to 1
> - 3 cGy.
> Based on the original estimate we did not advise any intervention in the
> course of the pregnancy. The patient was counselled and went on, I
> believe, to give birth to a healthy child, or though no follow up was
> carried out. 
> I've got a feeling that at the time there was something called the
> "Danish Rule" which I think quoted a therapeutic termination dose of 10
> rads, but I could be well wide of the mark here - anybody heard of this?
> Cheers
> Andy Hancock

Can't comment on the danish rule, but I tend to use the 
recommendations of the AAPM Task Group 6 report on Fetal dose from 
radiotherapy with photon beams, Medical Physics Vol 22 No 1. 
They have included a good summary of effect by gestation age and 
include some doses to work by.

A very brief summary of risk as a function of dose
DOSE(Gy)                        RISK
<0.05                                  little
0.05-.10                              uncertain
0.1-0.5                                significant risk 1st trimester
>0.5                                   high risk all trimester

Have a look at the article to get a better idea of the risks. There 
are of course several references that make good reading as well

cheers
All the standard disclaimers!!
Lindsay Tremethick
Radiation Oncology
Geelong Hospital
Geelong, Victoria, Australia
Lindsay@gh.vic.gov.au