Fwd: prostate rad safety

[Ccja@aol.com]

Incidentally, those of you on the MEDPHYS list, who have an interest in these
sorts of topics, should also try posting your questions/answers on the
RADSAFE list (radsafe@romulus.ehs.uiuc.edu), where the health physicists hang
out. There are lots of smart folks there, with good ideas.

chris alston
ccja@aol.com
---------------------
Forwarded message:
From:	oncology@hgo.net (Wayne Butler)
Sender:	medphys@LISTS.WAYNE.EDU (Medical Physics Listserver)
Reply-to:	oncology@hgo.net
To:	MEDPHYS@LISTS.WAYNE.EDU (Multiple recipients of list MEDPHYS)
Date: 97-02-25 22:16:27 EST

Janelle A. Williams wrote:
>
> Question regarding prostate implants:
>
> The new NRC regs scheduled to take effect May 29 of this year
> state that licensees may not authorize the release of patients
> if the estimated dose to anyone in contact with the patient
> would be greater than 500 millirems.  500 millirems to total
> decay for I125 implies an initial exposure rate of 0.24 mR/hr.
> I would appreciate it if people from clinics which have been
> doing these implants for some time could let me know what some
> typical measured exposure rates at one meter are for both I and
> Pd implants.

We find considerable variation between patients in the dose rate at 1m
following prostate implants.

For I-125 implants giving and mPD of 160Gy, a typical implant of 43mCi
total activity results in 0.09mR/h, a 120Gy I-125 boost with 32mCi
produces 0.06mR/h, and a 90Gy boost using 130mCi of Pd-103 produces an
initial dose rate of 0.25mR/h at 1m.  Using a modified uniform loading
procedure to provide homogeneous coverage, a 40g prostate requires about
135 seeds.

Although most prostates (and the number of seeds) range within 40% of
these values, the dose rate may occasionally be a factor of four greater
than the typical one meter values due to pronounced tissue attenuation
effects (or lack thereof).  Even at the high end, however, the lifetime
dose will be within the 500mR/yr limit using reasonable assumptions
about proximity and recommending that spouses sleep in separate beds for
the first few weeks after the implant.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Wayne Butler, Ph.D.
Oncology Center
Wheeling Hospital
Wheeling,  WV  26003

Phone:    304-243-3983
Fax:      304-243-5047
E-mail:   oncology@hgo.net
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~