Re: Radiopharmaceutical patient release

[isurveyor@vianet.net.au (Ivor Suveyor)]

Dear Radsafers

Below are some notes that I made a few years ago on possible contamination
of patients relatives and friends  following iodine-131 treatment.  The
notes are my summary and interpretation of the literature, I enclose them
because these issues appear to be of current interest to the news group. The
issues have been addressed in the past.  Other related aspects that have
been considered in the literature include, the external radiation field
surrounding the patient, breast feeding (absolutely a contraindication to
therapy) and prospects for future pregnancies (good, provided conception is
postponed until the iodine-131  has cleared from either the potential mother
and or father). 
THE PROBLEM OF CONTAMINATION:
In 1970 Buchan and Brindle(1) measured the 131I content of thyroid glands in
members of the household of out patients treated with 131I at Plymouth
General Hospital, UK.  39 subjects [husbands 19,  wives 7,  sons 9(ages 7-25
y),  daughters 3(ages 11-19 y),  and 1 lodger].   Radioactivity administered
to patients was in the range 3 - 20 mCi (111 - 740 MBq).  The measured
activity was small in all thyroids tested and this was irrespective of
whether  precautions were advised or not, and in 5 cases sexual intimacy
occurred.  It was concluded that save where young children were involved,
advice regarding direct bodily contact, exclusive use of toilets,
segregation of crockery and cutlery was not required.
Greater levels of contamination were found by Jacobson(2) from the
Department of Environment and Industrial Health, University of Michigan.
131I was administered to 7 patients .   The activity administered was in the
range 8 mCi to 20 mCi  or  300 to 750 MBq, except for  their patient number
2 who was given 150 mCi or 5.55 GBq.   17 family members from  the 7
separate families formed the basis of the report.   11 of  their subjects
being children under the age of 16.   Measured thyroid radioactivity ranged
from 92 - 110,000 pCi (3.4 - 4070 Bq) and they estimated the thyroid
absorbed dose as being 
4 - 1330 mrem (4 - 13,300 mSv).   Interestingly, the family members of the
patient who received the large dose, were successful in limiting their
internal exposure from contamination.
O'Doherty(3) measured salivary activity in 30 patients over a 10 day period.
Mean (range) salivary activity in the first 24 h was 86.7(0.6-208) Bq.g-1
MBq-1 of administered activity falling to  a mean value of 27.4 Bq.g-1 MBq-1
of administered activity with an upper 95% confidence interval of 38.8
Bq.g-1 MBq-1.  The addition of carbimazole after treatment with 131I caused
a slight increase in salivary radioactivity. 
Nishizawa(11) studied the rate of iodine excretion in a number of body
secretions following treatment for either thyroid cancer or thyrotoxicosis.
Excretion rate was expressed as ratio of administered dose.  Concentration
in blood decreased rapidly at first with an effective half life of 7.6 ± 0.4
h over the first two days; but thereafter much more gradually.  Salivary
concentration was 30 to 500 times greater then blood concentration, the mean
value being 100.  The maximum excretion ratio for saliva was an average of
6.3 x 10-3.  However, if the salivary effective half life of 8.7 ± 0.34 h is
considered, the salivary concentration will fall within 2-3 days to the same
magnitude as reported by O'Doherty(4).    It was estimated (4) that in order
to transfer 0.1 MBq of 131I,  (one-tenth annual intake for workers under
revised ICRP recommendations guidelines(5),   0.5-2.0 ml saliva would have
to be transferred between persons in first 24 h and 2.0-5.0 ml thereafter.
Thus O'Doherty(4) advised restrain from kissing for 48 h.
In general the question of contamination risk is unanswered as it clearly
has much to do with personal  hygiene of patients and their standard of
living.    Further, special consideration may have to be given to patients
who are demented,  incontinent,  or live in sub standard dwellings including
caravans.    Either in patient treatment should be offered, in wards with
specially trained nursing staff, or it is accepted that these patients are
unsuitable for 131I treatment.

1.	Buchan RCT, and Brindle JM. Radioiodine therapy to out-patients - the
contamination hazard.  Br J Radiol 1970;                         43:479-482.

2.	Jacobson AP, Plato PA and Toeroek MS.  Contamination of the home
environment by patients treated with iodine                    -131: initial
results.  Am J Pub Health 1978;68:225-230.

3.	O'Doherty MJ, Kettle AG, Eustance CNP, Mountford PJ and Coakley AJ.
Radiation dose rates from adult                             patients
receiving 131 I therapy for thyrotoxicosis. Nucl Med Commun 1993; 14: 160-168.

4.	Nishizawa K, Ohara K, Maekoshi H, and Orito T.  Monitoring of I
excretions and materials of patients treated                    with 131I.
Health Phys 	1980;38:467-481.

5.	International Commission on Radiological Protection. Annual limits on
intake of radionuclides by workers based on                         the 1990
recommendations. Annals of the ICRP 1990;  21.   Oxford: Pergamon Press;
ICRP publication 61. 




Ivor Surveyor
Emeritus Consultant Physician, Nuclear Medicine. 
E-mail:    isurveyor@vianet.net.au