Re: Dose Rates from Patients -Reply

[Kent Lambert <lambert@allegheny.edu>]

I am suprised by the numbers below - by calculation:

   Dose rate = specific gamma ray constant * Activity  / distance ^2

         = 2.2 (R/h)(cm^2/mCi) * 175 mCi / (100 cm)^2

         = 40 mR/h

This does not include shielding provided by the patient, so the actual 
measured value should be significantly less depending on the patient's size.

Also, since the measurements are taken immediately after administration, 
neck and whole body uptakes are NOT a factor.  The capsules or liquid would 
still be in the stomach and thus be close to a point source.  

Perhaps the instrument used was a GM meter calibrated to Cs-137 in which 
case it would over-respond to the lower energy I-131 gamma's.

Connie Ketarkus wrote:
> Dose of 131-I given:            Initial dose-rate: (one meter from anterior
> chest/neck)
> 142mCi                  76mRem/hour
> 145mCi                  70mRem/hour
> 54mCi                   25mR/hr
> 144mCi                  75mR/hr
> 142mCi                  70mR/hr
> 142mCi                  80mR/hr
> 187mCi                  80mR/hr
> 118mCi                  60mR/hr
> 96mCi                   50mR/hr
> 96mCi                   60mR/hr
> 188mCi                 135mR/hr
> 125mCi                  65mR/hr
> 100mCi                  70mR/hr
> 
> you get the idea . . . . . each patient is different.  their initial exposure
> rate depends on their size (fat, skinny,
> tall, short) and, most importantly, their neck and whole-body uptakes.
> 
> note, these are *initial* exposure rates, and these fall very rapidly, usually
> to less than + in the first
> 24 hours due to urinary excretion.

--
Kent Lambert, CHP
lambert@allegheny.edu

All opinions are well reasoned and insightful.
Needless to say, they are not [necessarily] the
opinions of my employer. - paraphrased from Michael Feldman