Re: Boice, Rad Research, 1/96 -Reply

[FRAMEP@ORAU.GOV]

John Moulder wrote, in part, wrt the Hall, Mattsson and Boice article
in Rad Res:
>Excess incidence confined to patients referred because of suspected
>thyroid tumors, and not related to radiation dose, time since
>exposure or age at exposure.
>"the slight excess of thyroid cancer thus appeared to be due to the
>underlying thyroid condition and not the radiation exposure"

As I read it, this study cannot be taken to suggest that there is no
risk of radiation/I-131 induced thyroid cancer in the ONLY age group
of concern: those exposed under 20 years of age.

The authors point out "No dose-response relationship has been
[previously] reported after adult exposure" although "substantial
excesses of thyroid cancer have been [previously] reported among
children"  This particular study of 34,104 only included 2,408 who
were administered I-131 before 20 years of age. In this younger group
of 2,408 there was an excess relative risk of 0.25 per Gy which could
not be attributed to the underlying thyroid condition. However, the
results were not statistically significant. The paper's concluding
remark was "Contrasting studies of childhood exposures, I-131 appears
considerably less (2 to 10 times) effective [note, they do not say
ineffective] in inducing thyroid cancer than brief exposures to
external radiation". 

Studies regarding external radiation thyroid exposures to children,
such as that by Shore et al, Am J. Epid 1993, V 137 #10, p1068  and
Ron et al Rad Res 1989 Vol. 120 p 516, show significant excess risk
of thyroid cancer. The paper by Shore et al even states that "the
dose response relationship was essentially linear" and that "Thyroid
cancer rates were elevated even at low doses i.e. a dose response
analysis over the range of 0-0.3 Gy showed a significant positive
slope". 

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov