Re: Radioiodine Treatment of Thyroid Cancer

[John Cormack <rajc@flinders.edu.au>]

>I recall a few listings regarding the safety of thyroid cancer
>patients undergoing radioiodine treatments being released from the
>hospital.  These postings included discussions of exposures to hotel
>workers and family members.  I have had a question posed to me about
>potiental exposure of a 8 month old infant who's mother is recieving
>radioiodine.  Her physician is sending her home to care for the
>infant immediately after the treatment.  Fortunately she is not
>breast feeding so that is not a concern.  Summaries of the discussion
>or opinons would be greatly appreciated.
>Stan H. Harts

Stan

The dose to the child could be quite appreciable, depending on the activity
of radioiodine administered, the clinical status of the patient (which will
relate to the physiological rate of clearance) and how much close contact
care the child needs (for a fretful, "clingy" infant, this could be
considerable). For a young infant requiring a lot of care, doses of up to
20 mSv are possible from patients who have received 600 MBq for
thyrotoxicosis, and up to 45 mSv from patients who have received 2000 MBq
for ablation. This assumes the patient is sent straight home to care for
the infant with no particular instructions regarding the avoidance of close
contact. Avoidance of close contact would be required for up to 24 days
post-administration to restrict the dose to the infant to 1 mSv, or up to
10 days to restrict the dose to 5 mSv. Much depends on the individual
circumstances of each patient, but I would certainly advise a great deal of
caution in cases such as these.

If you want to have a go at estimating these doses yourself, using
information tailored to the specific circumstances of the patient, the
information below might be useful.

Cheers

John Cormack


CLOSE CONTACT DOSE  SPREADSHEET TEMPLATES
_________________________________________________________

Thes spreadsheets calculate the exposure to persons around radioactive
sources or patients.

See extract from the "README" file below for a brief description.

If you want to download these spreadsheets, they are available via
anonymous ftp transfer from ftp.flinders.edu.au, cd  pub/medphys/CCExMac
(Mac version) or pub/Medphys/CCExPC (PC version). Enter "anonymous" for
your ID, and your E-mail address for the password
______________________________________________________

CLOSE CONTACT DOSE  SPREADSHEET TEMPLATES
_________________________________________________________
John Cormack and Jane Shearer
Medical Imaging Division
Flinders Medical Centre
Adelaide
South Australia 5042
Telephone 08 8204-4642
E-mail rajc@gamgee.cc.flinders.edu.au

Version 2, February, 1998

_______________________________________________
HARDWARE AND SOFTWARE REQUIREMENTS, INSTALLATION

To run these spreadsheets, you will need EXCEL 6.0 up for PC, EXCEL 5.0 up
for Mac. Any PC or Macintosh hardware capable of running the above package
will do the job. Simply copy the spreadsheets into any convenient directory
on the hard disk.

EXCEL should be set up to do AUTOMATIC calculations
for these spreadsheet programs.
ITERATION should be ON -  maximum of 1000 iterations
to an accuracy of 0.001
For curve fitting, the SOLVER add-in MUST be available

________________________________________________________
BRIEF INSTRUCTIONS FOR USE OF CLOSE CONTACT DOSE SPREADSHEET TEMPLATES
Use of these spreadsheet templates should be relatively straightforward for
persons who have a general familiarity with the use of spreadsheets. Prior
to use, it should be checked that automatic calculation and iteration are
set as indicated above. The SOLVER add-in must be available if curve
fitting is to be implemented, otherwise the "Fit" procedure will halt with
an error message. A little experimentation should be sufficient to give
most users an indication of how everything works. Since the original
spreadsheet is a template, a new copy is created each time it is opened -
this can be discarded or saved with a selected name after use.

There are two EXCEL workbook templates in the set:

 CCDOSV2.xlt - This workbook template allows you to enter your own (up to
three component exponential) radiopharmaceutical clearance rate and a
diurnal contact pattern. It then works out the radiation dose from
continual exposure to this pattern, plus restriction times required to
reduce the dose and dose rate to specified limits. All of the data and
calculations, including a chart of the contact pattern, can be printed out.
There are four sheets in the workbook -
* CCDOSV2, the main worksheet
* Curve Fit, which allows measured clearance data to be fitted with a
single or dual exponential clearance curve, with subsequent transfer of the
fitting parameters (half-life and percentage of each component) to the main
worksheet for use in the main calculation.
* Contact Patterns, which is a worksheet containing various pre-set contact
patterns which can be transferred to the main worksheet. Users can add
their own set of contact patterns here for future use.
* Radiopharm Data, which is a compilation of physiological clearance data
and dose rates for various radiopharmaceuticals. These data can be
transferred to the main worksheet for incorporation in calculations, and
users can add their own data sets.

CCDOSV3.xlt - This is the more versatile of the two close contact
spreadsheet templates, but  requires most thought in its use. It allows an
exposure pattern of any duration, repeating or non-repeating, to be defined
in terms of a series of contact periods at specified dates and times.
Maximum continuous contact times at specified distances are also computed
in this version of the spreadsheet. There are three sheets in the workbook -
* CCDOSV3, the main worksheet
* Curve Fit, which allows measured clearance data to be fitted with a
single or dual exponential clearance curve, with subsequent transfer of the
fitting parameters (half-life and percentage of each component) to the main
worksheet for use in the main calculation.
* Radiopharm Data, which is a compilation of physiological clearance data
and dose rates for various radiopharmaceuticals. These data can be
transferred to the main worksheet for incorporation in calculations, and
users can add their own data sets

Both workbooks contain sample data which should illustrate their use, and
the templates open with the data input data cells highlighted. Pressing the
<return> key allows the user to step through these cells (note, however,
that this will only work when the original template is opened and before
any other cell has been selected). The workbooks are protected so that,
under normal conditions of use, data entry into the wrong areas should be
prevented.  All of the data and calculations, including a chart of the
exposure pattern, can be printed out. If a positive value is given for the
administered activity, measured close contact radiation exposure rates in
micrograys per hour per MBq will have to be entered. For zero or negative
values of administered activity, total radiation exposure rates in
micrograys per hour will be required (be careful that you have the correct
dose-rate data loaded when using this mode)

For the calculation of close contact doses from I-131 therapy patients
(thyrotoxic, ablation and follow-up) both workbooks are pre-loaded with the
clearance and radiation exposure data of Barrington et al and O'Doherty et
al [1-2]- you can change this for your own ( up to three component
exponential decay) if desired. Diurnal exposure patterns can also be
changed to meet your requirements.

NOTE - The RESET button on both of these workbooks resets the initial
values for the iterative calculations. It will generally have to be used
where errors are flagged in the cells which give the results of these
calculations (restriction times required to limit dose and dose rates,
residual activities and so on).

If you have any problems using these spreadsheets, find any bugs, or have
any suggestions for improvements, please contact the authors.

A paper describing the mathematical rationale and design of the
spreadsheets, and examples of their utilisation, is due for publication in
Physics in Medicine and Biology [3]. Further information is also available
on request form the authors, along with a longer version of the paper with
useful ancillary data incorporated.

[1]	Barrington SF, Kettle AG, O'Doherty MJ, Wells CP, Somer EJR,
Coakley AJ. Radiation dose rates from patients receiving iodine-131 therapy
for carcinoma of the thyroid. Eur J Nucl Med 1996;23:123-130.

[2]	O'Doherty MJ, Kettle AG, Eustance CNP, Mountford PJ, Coakley AJ.
Radiation dose rates from adult patients receiving I-131 therapy for
thyrotoxicosis. Nuclear Medicine Communications 1993;14:160-168.

[3]	Cormack, J and Shearer, J. Calculation of radiation exposures from
patients to whom radioactive materials have been administered. Physics in
Medicine and Biology 1998;43(3)).

____________________________________________________

_____________________________________________________
John Cormack
Chief Medical Scientist
Division of Medical Imaging
Flinders Medical Centre
Bedford Park
South Australia 5042

Ph:08-8204-4642 National, 618-8204-4642 International
Fax:08-8204-5450 National, 618-8204-5450 International