Guidelines for outpatient I-131 radioablation therapy:
From Associates in Medical Physics, LLC
On May 29, 1997, the NRC amended their regulations regarding the criteria for the
release of individuals containing radioactive substances (10CFR35.75).
Previously, the criteria for release was when either (1) the dose rate from the patient
was <5 mrems/hr at 1 meter, or (2) the retained activity in the patient was <30 mCi.
This was an activity-based release limit and it was deemed faulty because different
radionuclides with the same activity will give different doses depending upon the
effective half-life of the radionuclide in the body, as well as other factors that vary
for different materials. The current regulation reflects a dose-based release limit
because it reflects a greater concern for public health and safety (i.e: new limits for
I-131 NaI is <33 mCi or less than 7 mrems/hr at 1 meter). The new criteria is based on
an exposure limit of 0.5 rem (5 mSv) total effective dose equivalent in any year to any
individual exposed to the released patient (1 mSv if the individual is pregnant or is 8
years old or less [1]). This could allow for the release of a patient with greater than 30
mCi or a dose-rate of greater than 5 mrems/hr (at 1 meter). In fact, when using
appropriate guidelines limiting individual exposures, patients receiving as much as 200
mCi of I-131 can be managed on an outpatient basis [1]. NOTE: State imposed nuclear
regulations may be more stringent than federal guidelines and need to be reviewed.
The new regulations indicate that patients should receive verbal and written instructions
to inform them as to how they can reduce the radiation exposure to others, if the total
effective dose equivalent to any other individual exposed to the patient is likely to
exceed 1 mSv (patients receiving between 7 and 30 mCi may receive only verbal
instructions). The patient should be made aware that in addition to radiation emitted
directly from them, radioiodine is also excreted in body fluids such as sweat, saliva,
urine, and feces [2]. The physician should be reasonably certain that these instructions
can and will be followed. A record documenting justification of the assigned occupancy
factors and the effective half-lives used in the exposure calculations must be maintained
for 3 years after the date of patient release [1].
This new regulation also discusses the dose to the breast-feeding infant or child. If that
dose is likely to exceed 0.1 rem (1 mSv) - assuming no interruption of breast-feeding -
instructions are required to address guidance on the interruption or discontinuation of
breast-feeding and on the consequences if the patient refuses to follow the guidance. This
is of particular concern with I-131 for both diagnostic and therapeutic administrations
(e.g.:more than 0.4 uCi I-131). If the mother does not cease breast-feeding for this
infant or child, particularly in the case of therapeutic administrations, the internal
dose to the breast-feeding infant could be large enough to cause hypothyroidism or total
ablation of the infant's thyroid gland. If either one of these conditions went undetected
and untreated, severe mental retardation could result.
If the mother agrees to cease or interrupt breast-feeding, the new regulation indicates
the time periods that breast-feeding should be interrupted for significant radionuclides
(e.g.:>30 mCi Tc-99m pertechnetate - interrupt breast feeding for 6 hrs.). In
the case of I-131 NaI, complete cessation for this child is recommended.
The last part of this new regulation (35.75(d) indicates that, even though instructions
must be given if the dose exceeds 0.1 rem (1mSv), records of those instructions must be
maintained only if the dose to the infant or child would exceed 0.5 rem (5 mSv) -
(e.g.:>200 uCi Ga-67 Citrate). These records must be maintained for a period of 3 years
after the release date of the patient.
[Code of Federal Regulations]
[Title 10, Volume 1, Parts 1 to 50]
[Revised as of January 1, 2000]
From the U.S. Government Printing Office via GPO Access
[CITE: 10CFR35.75]
[Page 549]
TITLE 10--ENERGY
COMMISSION
PART 35--MEDICAL USE OF BYPRODUCT MATERIAL--Table of Contents
Subpart C--General Technical Requirements
Sec. 35.75 Release of individuals containing radiopharmaceuticals
or permanent implants.
(a) The licensee may authorize the release from its control of any
individual who has been administered radiopharmaceuticals or permanent
implants containing radioactive material if the total effective dose
equivalent to any other individual from exposure to the released
individual is not likely to exceed 5 millisieverts (0.5 rem).\1\
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\1\Regulatory Guide 8.39, ``Release of Patients Administered
Radioactive Materials,'' describes methods for calculating doses to
other individuals and contains tables of activities not likely to cause
doses exceeding 5 millisieverts (0.5 rem).
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(b) The licensee shall provide the released individual with
instructions, including written instructions, on actions recommended to
maintain doses to other individuals as low as is reasonably achievable
if the total effective dose equivalent to any other individual is likely
to exceed 1 millisievert (0.1 rem). If the dose to a breast-feeding
infant or child could exceed 1 millisievert (0.1 rem) assuming there
were no interruption of breast-feeding, the instructions shall also
include:
(1) Guidance on the interruption or discontinuation of breast-
feeding and
(2) Information on the consequences of failure to follow the
guidance.
(c) The licensee shall maintain a record of the basis for
authorizing the release of an individual, for 3 years after the date of
release, if the total effective dose equivalent is calculated by:
(1) Using the retained activity rather than the activity
administered,
(2) Using an occupancy factor less than 0.25 at 1 meter,
(3) Using the biological or effective half-life, or
(4) Considering the shielding by tissue.
(d) The licensee shall maintain a record, for 3 years after the date
of release, that instructions were provided to a breast-feeding woman if
the radiation dose to the infant or child from continued breast-feeding
could result in a total effective dose equivalent exceeding 5
millisieverts (0.5 rem).
[62 FR 4133, Jan. 29, 1997]
REFERENCES:
(1) J Nucl Med 2001; Coover LR, et al. Therapeutic 131-I in outpatients: A simplified method conforming to the code of federal regulations, Tital 10, Part 35.75. 41: 1868-1875
(2) J Nucl Med 2001; de Klerk JMH. 131-I therapy: Inpatient or outpatient? 41:
1876-1878
