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RE: mystery brachytherapy source
Your mystery source is likely to be either Ta-182, Radium-226 or the
decay product of Radon-222, which were used as brachytherapy sources for
many years before they were replaced by seeds filled with Cs-137,
Ir-192, I-125, etc. Because of it's very long halfl-ife, Ra-226 (usually
encased in platinum and/or 1-2 cm long gold sealed tubes or needles) was
normally used as a temporary implant, to be removed once the desired
dose was delivered. Ta-182 with a half-life of 115 days was usually in
the shape of a wire or hairpin (often used for bladder cancer), not
seeds, and was also used as a temporary source . For other treatments,
where it was preferable to leave the source in place, they used Rn-222
gas-filled gold seeds. The Rn-222 seeds were manufactured by drawing
the radioactive gas up into a long gold capillary tube which was crimped
at regular intervals along its length to seal in the gas, and the
crimped tube containing these Rn-222 gas "pockets" was then cut into
seeds - usually about 5 mm long. Rn-222 has a half-life of 3.7 days,
and the minimal radiological contribution of the eventual long-lived
progeny (Pb-210, Bi-210, etc) was essentially ignored - but that is
probably what you are seeing. You may want to refer to R.F. Mould's 1985
book "Radiation Protection in Hospitals" for more information about the
history of brachytherapy sources.
Four years ago, I was presented with necrotic ulcer chest-wall tissue
specimens from a 64 year-old female patient - and each of these ulcer
specimens contained a tiny radioactive gold bead at it's base.
Apparently these seeds had been implanted in her chest wall shortly
after she was born to treat a port-wine stain birthmark. At about age
40, she developed breast cancer which was treated with a mastectomy and
a course of external radiation therapy (probably about 5000 rads) to her
chest wall. The treatment was successful, as she had no recurrence of
the cancer. Approximately twenty years after her breast cancer
treatment, she started to develop these non-healing small ulcers on her
chest wall (on the mastectomy side), which a plastic surgeon removed
and sent along to me for analysis when the gold seeds were found in each
of the excised lesions.
At first we had a bit of a problem identifying the isotopes, as we were
seeing bremsstrahlung through the the external surface of the gold seed.
We embedded one of the seeds in wax and sliced it open using a
microtome in our electron microscopy laboratory - it was then quite easy
to identify the Lead/Bismuth-210 progeny radioisotopes from Radon-222.
What was quite interesting about this case was the fact that it took 20
years before the skin tissue overlying each of the seeds deteriorated
into a necrotic ulcer, demonstrating the cumulative effect of the
original radiation dose delivered at birth by the Rn-222 (dose unknown)
plus the external beam therapy at age 40 (approximately 5000 rads). The
seeds were still emitting readily detectable low-level radiation 64
years after they were implanted, and I have occasionally wondered how
much additional cumulative long term dose they contributed to the
immediate surrounding tissue over that length of time.
I spoke to the patient several months later to get her radiological
history and find out how she was doing. She told me that after the
necrotic lesions containing the seeds were removed, the excised areas
healed uneventfully.
************************************************************************
************************
Karin Gordon
Radiation Safety Office
Health Sciences Centre
GC-214, 820 SherbrookSt.
Winnipeg, MB
R3A 1R9
KGordon@hsc.mb.ca or KGordon@cc.UManitoba.ca
phone (204) 787-1313
fax (204) 787-1313
>----------
>From: Moroney, Roger W[SMTP:Roger.Moroney@mkg.com]
>Sent: July 31, 1998 6:20 PM
>To: Multiple recipients of list
>Subject: mystery brachytherapy source
>
>I have a coworker who has asked me about some radioactive implants he
>received as an infant. I have been unable to ID the original isotope and I
>have a pretty limited knowledge of brachytherapy so I turn to the
>accumulated wisdom of Radsafe in hopes of enlightenment. Here goes.
>
>This person received these implants at the age of two weeks for treatment of
>hematomas. This was 42 years ago and was performed at a hospital in New York
>City. The sources are just below the surface of the skin and are
>approximately 1/2 inch (1.3 cm) long and about 3/32 inch (0.24 cm) in
>diameter. The sources are located in many parts of the body including one
>near the right eye. Several have been removed over the years as they broke
>through the skin. He said they are a gold color. Unfortunately, he can no
>longer locate the ones which were removed.
>
>A scintillation probe (Ludlum model 44-21) gives 3500 - 4000 cpm on contact
>with a source in his wrist. We managed to get this one positioned near a Ge
>detector. Lines were found at 66.9 keV (area = 1663), 68.7 keV (area =
>3205), 77.7 keV (area = 2009) and 79.9 keV (area = 843). This was for a ten
>minute count. These lines seem to correspond to Hg-194 for energy and
>intensity. The half life for Hg-194 is given as >15 years in Erdtmann &
>Soyka and as 520 years in the 14th edition of the GE Chart of the Nuclides
>(which also says there are no gammas). There was also a nice bremsstrahlung
>spectrum present which appeared to extend to about 500 keV.
>
>I'm guessing the Hg-194 is a contaminant of the original isotope? Would the
>original isotope have been Au-???. If anyone could help out it would be
>appreciated. I'll have to admit to being a little surprised at the amount of
>activity still present after 4 plus years.
>
>********************************************************
>********************************************************
>Roger Moroney
>Technical Director - External Dosimetry Program
>Health Physicist
>Mallinckrodt
>roger.moroney@mkg.com
>314.654.7457 voice
>314.654.7571 fax
>************************************************************************
>The RADSAFE Frequently Asked Questions list, archives and subscription
>information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
>
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The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html