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Re: I-131 Therapy Dose Limits
I can help with these parts of the query:
> 1. Has the NRC open-source radiotherapy limit for I-131 in the been
> raised to 100 mCi from 30 mCi?
> 2. What are the maximum allowable doses for open-source radiotherapy in
> the USA?
> 4. What are the patient release criteria in the USA, once these patients
> received high-dose radionuclide therapy?
The NRC changed 35.75 last week (5/29/97 effective date). The basis for
release is now the dose likely to be received at 1 meter < 0.5 rem.
This is a change from the old 30 mCi or 5 mrem/hr @ 1 m. There are
requirements for instructing patients and maintaining records in the new
reg, and there are also requirements to provide instruction to
breastfeeding women re Dx level activities.
The new regs allow taking into account shielding (important for I-125
permanent implants, for example), occupancy factor at 1 meter (e.g. 0.25
or perhaps lower), and effective vs. physical half life. Reg Guide 8.39
gives some examples for calculations to release patients at
substantially higher activities. Specifically, there are 2
multi-compartment example calculations using generic (& conservative)
uptake & elimination data for I-131 (NaI) therapy for hyperthyroidism
and thyroid carcinoma (post thyroidectomy). These show that the patient
did not require hospitalization after therapeutic doses of 55 mCi
(hyperthyroidism) and 200 mCi (thyroid CA).
So in sum:
1 The release criterion is dependent on integerated exposure at 1 meter,
and can be higher than 100 mCi for I-131, on a per case basis.
2 See 1
4 See 1
MY QUESTION TO THE LIST:
Does anyone see a problem with 1.0 mR/hr @ 1 meter criterion for I-125
permanent implants ??
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/ /
/ Chris Hawkins chawkins@inet.guthrie.org /
/ Radiation Oncology /
/ Guthrie Clinic - RPH 717.882.4048 /
/ Sayre, PA 18840 fax 717.882.5166 /
/ /
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