I–131 THERAPY
FOR THYROID CARCINOMA
Patient receiving more than 30 mCi I–131
must be hospitalized. In the case of thyroid carcinoma treatment, doses range
from 50–150 mCi. Before radioiodine administration, the patient, nursing staff
and the isolation room must be prepared to minimize radioactive contamination
and unnecessary radiation exposure.
Patient preparation
1. Children
and pregnant women should not be allowed to visit the patient.
2. Some
patients may have difficulty being confined to a small area. They should be
encouraged to bring materials to provide some diversion during their
confinement. However, patients should also be informed that these materials may
become contaminated so that it may be necessary to hold them for decay in
storage following the patient’s discharge.
3. Large
amount of radioiodine will be excreted in the urine. Human excreta may be
disposed of through the sewer system. The patient should be instructed to flush
the toilet three or four times after each use to remove and dilute the
radioactivity.
4. The
patient should fast before the radioiodine is administered to enhance its
absorption from the stomach. The technologist should ascertain that the patient
has no difficulty swallowing by asking the patient to drink a small amount of
water.
Preparation of the isolation
room
1. To
facilitate decontamination of the treatment room, floors, countertops and other
porous surfaces should be covered with plastic backed absorbent paper. Plastic
covers should be placed over chairs. The use of plastic mattress cover is
recommended. Plastic wrap can be used to cover knobs, handles, and telephone
receiver and the toilet.
2. The
patient linen should be kept in a container in the isolation room and monitored
for contamination before it is sent to the hospital laundry. Likewise, the
patient’s disposable eating utensils and uneaten food should be collected for
monitoring before disposal.
3. After
administration of the radioiodine, the isolation room should be posted with
“Caution: Radioactive Material.”
Instructions to Hospital
Personnel
1. All
nursing personnel should be issued film badges and instructed on how to wear
them.
2. No
pregnant personnel should be assigned to care for the therapy patient
Patient monitoring
1. The
patient is monitored by Health Physicist with a portable ionization chamber at
3 meters to determine safe exposure times to nearby patients and when the
patient can be released from isolation
Calculation of
retained dose of I–131 for patient for discharge:
Initial dose
rate = Subsequent
dose rate
mCi administered mCi retained
Example, a
patient receives 100 mCi of I–131. Immediately following administration, the
dose rate at 3 meters measures 150 mrem/hr. 24 hours later, the dose rate at 3
meters measures 50 mrem/hr. how many mCi remain in the patient?
150 mrem/hr = 50
mrem/hr
100 mCi (n) mCi
n = 100
mCi (50 mrem/hr)
150 mrem/hr
n = 33.3
mCi
Therefore, the
patient must remain in isolation (cut – off is 30 mCi)
2. The
radiation exposure limit for visitors and nursing personnel is 2 mrem in any
one hour. If the measured dose rate exceeds 2 mrem/hr, the length of time that
visitors or nursing personnel can remain in the room must be calculated by a
Health Physicist.
Calculation of
length of stay in a radiation room:
If the survey
meter measurement at bedside is 15 mrem/hr, how long can a visitor or nurse
remain at the point where the reading was made?
15 mrem = 2
mrem
60 mCi n
n = 2 mrem
(60 min)
15 mrem
n = 8
minutes
Discharge Instructions
Therapy patients continue to excrete
radioiodine into their saliva, urine and perspiration for about 1 week
following discharge from the isolation room. The patient should be instructed
of techniques that will minimize the radiation dose to family members or other
individuals with whom therapy patients may come in contact. The most likely
routes of radioiodine transfer should be reviewed with the patient along with
the following guidelines:
1. Intimate
personal contact should be avoided. The patient should not share a bed with
anyone. Close contact with children, such as holding or kissing should be
avoided.
2. The
patient should use separate bathroom, if one is available, from other household
members. The toilet should be flushed twice after each use.
3. The
patient should not share eating utensils, cups, glasses or towels.
4. The
patient should wash hands thoroughly after using the bathrooms.
PHOSPHOROUS–32
THERAPY
Phosphorous–32 is a pure beta emitter.
Beta particles are effectively shielded by the glass vial or plastic syringe
containing the radionuclide. Once the radionuclide has been introduced into the
patient, there is no external radiation hazard. Therefore, 32P does
not require the patient be placed in isolation.
Sodium phosphate
1. Sodium
phosphate is a clear, colorless solution intended for intravenous
administration. Dose range from 1 to 2 mCi depending on the pathology being
treated.
2. Sodium
phosphate is used for the treatment of polycythemia vera and the control of
bone pain resulting from metastatic disease in the skeleton.
Chromic phosphate
1. Chromic
phosphate suspension is a blue green colloidal solution intended for
intracavitary use only. If this agent is mistakenly administered intravenously,
the colloidal particles will be taken up by the Kuppfer cells of the liver,
thereby causing severe localized radiation damage. Doses range from 6 to 20
mCi.
2. Colloidal
chromic phosphate is introduced into the peritoneal or pleural cavities. Once
administered, the agent remains in the cavity into which it was introduced.
However, drainage from the installation site or dressing covering the site
should be considered radiation hazards and handled appropriately. Likewise,
materials used during the installation should be disposed of as radioactive
material.
STRONTIUM–89
THERAPY
1. Strontium–89
chloride is administered to treat bone pain caused by metastatic bone disease.
The goal of this type of therapy is to relieve pain and restore the patient’s
daily routine.
2. Strontium–89
is an analog of calcium that is rapidly cleared from the blood and localizes in
the bone.
3. Strontium–89
chloride is administered intravenously. The recommended unit dose is 4 mCi or
40–60 µCi/kg based on the patient’s body weight. Depending on the patient’s
response to therapy, 89Sr may be administered at 3 months interval.
4. Strontium–89
is a beta emitter with a 50 day half–life. Appropriate shielding material,
plastic rather than lead, should be used to avoid the production of
bremsstrahlung radiation.
5. Greater
uptake of the tracer occurs in sites of osteogenesis, which means that areas of
bony metastases will concentrate 89Sr to a greater extent than areas
of normal bone. It also remains in the metastatic sites longer than in normal
bone (about 50 days compared to 14 days).
6. Infiltration
of 89SR during intravenous administration could lead to localized
irradiation of soft tissue at the injection site. It is necessary that a free
flowing intravenous line is established prior to tracer administration.
7. Approximately
two thirds of the administered dose is excreted in the urine and the remainder
in the feces. Urinary excretion is greatest in the first two days following
administration.
8. Licensee
must assay 89Sr directly or using special instrument capable of the
assay or assay them using a combination of measurements and calculations with
available instrumentation.
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