The following information was provided by the State of
Wisconsin via facsimile:
On Thursday, February 17, 2005 at approximately 3:45p.m. [CST], the Wisconsin Radiation Protection Section (RPS) received a telephone call from the Marshfield Clinic, Marshfield, WI (license number 141-01162-001) informing the section of a medical event involving a therapeutic radiation dose from a gamma knife exposing a site outside the intended treatment volume to a level greater than 50% of the expected dose. (HFS 157.72 (1) (a) 3.)
Preliminary Information From the Licensee:
On Wednesday, February 16, 2005, the Marshfield Clinic had scheduled a therapeutic radiation treatment of 18 Gray (1800 Rads) using a gamma knife. During the process of manually programming the positioning system, the y and z coordinates were transposed. The error was not noticed during a double check of the treatment coordinates. As a result, a site outside the intended treatment volume received an estimated dose of 5.06 Gray (506 Rads) instead of the originally estimated 0.4 Gray (40 Rads). The volume of the unintended treatment site was 0.7 cubic centimeters. The treatment duration was 2.42 minutes. The prescribed dose of 18 Gray was delivered and the patient treatment was completed.
The attending neurosurgeon and radiation oncologist believe there will be no medical consequences to the patient from the unintended exposure. The referring physician has been notified.
[State of Wisconsin] is reporting this event under:
HFS 157.72 (1) (a) 3. requires a licensee to report an event where there is 'A dose to an organ outside the intended treatment volume that exceeds the expected dose to that organ by 0.5 Sv (50 Rem) where the excess dose is greater than 50% of the expected dose to that organ. . . '
DHFS, RPS staff have been dispatched on Friday, February 18, 2005 to investigate.
Wisconsin Incident No: 20