[ RadSafe ] Gamma detector proves less invasive, more accurate for seed migra tion

[Roy.Herren at med.va.gov]

The following article appeared today on AuntMinnie.com.  I would appreciate
your thoughts, and feedback on this issue.

Any opinions in this e-mail are solely those of the author, and are not
represented as those of the VA Medical Center San Francisco, CA, the Dept.
of Veterans Affairs, or the US Government.

Roy Herren
Physical Science Technician
Radiation Safety Branch of the Radiology Department
Veterans Affairs Medical Center San Francisco, CA
===================================================================

Gamma detector proves less invasive, more accurate for seed migration
6/15/2005
By: Shalmali Pal


 

Now that scintillator-based detectors are on the scene, x-rays should be
jettisoned for assessing embolized seed migration in the lungs, according to
radiation oncologists in Canada.

"The seed-migration detector appears to be convenient, cost-effective and
noninvasive ... (and) doesn't expose patients to any additional radiation,"
wrote Dr. Janelle Morrier and colleagues in a poster presentation at the
2005 American Brachytherapy Society (ABS) meeting in San Francisco.

For this study, 155 patients (8,717 seeds) at Laval University in Quebec
were scanned for seed migration in a one-year period. The detector was
composed of a gamma scintillation probe and a count rate meter. An in-house
collimation cap was added to the detection window of the probe, the authors
said. Detector response profiles were first taken with and without the
collimator using an iodine-125 seed and a water phantom.

The results showed a seed migration rate of 0.47%, or 41 out of 8,717 seeds.
Twenty-one percent of the patients had at least one embolized seed. The
migration detector found all of the dislodged seeds versus radiographs,
which found 68%, and fluoroscopy, which found 90%. Four seeds were found
with the detector but were not seen with either imaging modality, the
authors stated.

Seed migration based on fluoroscopy alone would have led to a 12.1%
false-negative rate; with x-ray alone, the false-negative rate would have
been 39.4%.

"Moreover, fluoroscopy and radiographs would have required ... an extra
radiation dose," they wrote. "The recommendation to perform chest
radiographs to scan the lung for embolized seeds should be revised as the
scintillator-based seed-migration detection presents a superior efficacy and
a lower false-negative rate." The researchers also suggested that x-ray be
reserved for documentation of positive migration cases. 

By Shalmali Pal
AuntMinnie.com staff writer
June 15, 2005