An even better question is why was the scan being done. It is not common to perform a diagnostic scan on a euthyroid patient, adult or child. If the suspision is that the thyriod is cancerous, the thyroid would have been surgically removed and I-131 given to destroy any remenants that remained.
Before jumping in with all kinds of dose estimations and presumptions of misconduct with the physicians, I would try and determine if there is any MEDICAL significants of the dose. Apparently the child's physician concluded that the dose was not significant based on the future health of the patient.
By the way, a good reference for determinating radionuclide doses to children receiving medical scans can be found at http://www.orau.gov/ehsd/pedose.doc For a 10 year old child, which is close to a 9 year old, the thyroid dose 880 mSv/MBq of I-131. The effective dose equivalent is 27 mSv/MBq. For a dose of 400 uCi or 14.8 MBq, the thyroid dose is 13037 mSv or 130.4 rem, and the EDE is 3.99 rem.
It beats making calculations using NRC regulations.
William V Lipton <liptonw@DTEENERGY.COM> wrote:
Is the MIRD dose factor for normal thyroid uptake. If the patient was being
scanned because of a suspected hyperthyroid condition, it seems that the uptake
and dose would be higher.
Second question. Would prompt intervention, eg, administration of stable iodide
have been effective in reducing the dose?
It seems that even late intervention would be helpful in reducing the dose from
recycled iodine.
. . .