RE: Chernobyl thyroid doses ?

[Franta, Jaroslav]

Thanks very much Andrew -- I guess I should have looked there first myself (

I have now).

The thyroid dose figures you cite from UNSCEAR Annex J are about 25 times

higher than the doses used by Dr. Jaworowski in his comparison with "30 000

Swedish patients diagnosed with 131-I, among which no increase but a deficit

of thyroid cancers was found." 



Moreover, included in the group of 4064 children "above 2 Gy," were quite a

few with thyroid doses ten times that figure or more. 



According to the Annex, mean thyroid doses of children less than 3y old were

typically 10 to 20 times the mean for adults over 18y, and even for adults

there were individuals with thyroid doses up to about 10 Gy, or 1000 R (for

example, in the evacuated village of Pogonnoe, according to Fig. XIX on

p.481). 



Annex J doesn't appear to have a graph for children's thyroid dose

distribution comparable to Fig. XIX for adults, but from the above

information, it seems safe to say that there were quite a few with doses of

several thousand rads ( tens of Gy), or 100 to 1000 times the doses used by

Dr. Jaworowski in his comparison with "30 000 Swedish patients diagnosed

with 131-I, among which no increase but a deficit of thyroid cancers was

found." 



I suppose that if one subscribes to the LNT, then the mean thyroid dose

might be the one to use for comparisons with other exposed groups and for

cancer risk estimates. 



But it seems to me that this may well be a case illustrating the threshold

effect, where only the high-dose tail end of the dose distribution is at

significant risk of thyroid cancer. 



I suspect that, in contrast, the Swedish patients had a fairly well

controlled and limited dose range about their mean dose, putting them all

below the cancer threshold (whatever that may be). 



Do you think its possible that all the Chernobyl thyroid cancers may be due

to the high-dose tail end of the dose distribution ? 



Thanks again.



Regards,



Jaro 

 

-----Original Message-----

From: Andrew McEwan [mailto:acmcewan@clear.net.nz]

Sent: Saturday July 05, 2003 12:25 AM

To: Franta, Jaroslav; Radsafe (E-mail)

Subject: Re: Chernobyl thyroid doses ?





Jaro Franta asked about thyroid doses from Chernobyl.  A good reference is

the UNSCEAR 2000 report (Annex J, Vol.2 Effects: Exposures and effects of

the Chernobyl accident.)

 

To cite some figures for the Gomel contaminated region of Belarus 34 % of

children under 1 year were estimated to have received thyroid doses above 2

Gy, and 15 % of all children in the 0-18 years range received doses above 2

Gy (a total of 4064 children out of 27 463). Average absobed doses to the

thyroid of 0-7 year old children in rural Gomel were 1.1 Gy (Table 39). The

mean thyroid dose to children less than 1 year evacuated from Belarusian

villages was 4.3 Gy (Table 22).

 

Clearly there is a lot more information in the report.



Andrew McEwan

acmcewan@clear.net.nz <mailto:acmcewan@clear.net.nz>