CHICAGOThe permanent placement of radioactive seeds
in the prostate gland is proving to be equivalent to radical prostatectomy in
the treatment of men with prostate cancer, according to some recently published
data. However, some men have been reluctant to choose this treatment option
because of the chance that the seeds may expose family members to excessively
high radiation doses.
A new study has found that the seeds produce radiation levels
less than one tenth of Nuclear Regulatory Commission (NRC) limits, said Jeff M.
Michalski, MD, assistant professor of radiology, Washington University School
of Medicine, St. Louis. He presented the data at the 86th Annual Meeting of the
Radiological Society of North America (RSNA).
59 Prostate Cancer Patients
The study of 59 prostate cancer patients with radioactive
brachytherapy seeds compared the direct exposure of family members to radiation
from the seeds with the amount of radiation in the everyday environment.
The NRC sets 500 millirem per year as the boundary of safety
for adults who are exposed to radiation in the workplace. For people who are
not in the radiation industry or come into contact with radiation in other
occupational ways, such as radiologists or radiation oncologists, the safe
limit is 100 millirem per year.
The results showed that the average amount of exposure to
radiation for a spouse was only 10 millirem per year, or only one tenth the NRC
limit. At worst, one spouse had a total annual exposure of 55 millirem, which
is still only half the NRC limit.
Exposure to radiation from brachytherapy seeds also is in
keeping with overall background exposure to cosmic and gamma rays, Dr.
He explained that total annual background radiation exposure
from terrestrial gamma rays in rocks and earth varies from 180 millirem for an
individual who lives in St. Louis to 400 millirem for one who resides in
Denver. The average annual background exposure to radiation in the United
States is approximately 300 millirem.
"We can now tell a woman living in St. Louis that the
amount of radiation she will get from her husband in 1 year is less than she
would get from living in Denver for 3 or 4 months," he said.
High-altitude travel is another source of exposure to radiation
from cosmic rays. A round-trip flight from New York to Tokyo, for example, adds
20 millirem of exposure. When Dr. Michalski compiled data from patients and
their families who had the most exposure to radiation, he calculated that the
average annual exposure was 21 millirem.
"So a wife who spends a lot of time with her husband would
be getting no more radiation exposure in 1 year than from an act [a long
roundtrip flight] we accept as being appropriate," he said.
Dr. Michalski recruited 59 patients who consented to wear two
radiation film badges, one on the collar and one at the waist. A badge also was
given to each spouse and every other member of the family or household who
would be in contact with the patient, and a badge was placed in each of four
rooms in the housebedroom, kitchen, bathroom, and family room. Patients were
told to keep the room badges close to the space they normally occupy, for
example, next to the nightstand at the edge of the bed.
The badges, which are sensitive down to 1 millirem, were
assessed 3 weeks after the seeds where implanted when patients returned for a
routine follow-up CT scan of the pelvis to verify that the seeds had been
Although the study accumulated data only on 3 weeks of
radiation exposure. the researchers used information on the half-life and decay
pattern of the radioactive isotopes to extrapolate or amortize the exposure to
which an individual would be subjected over a designated period of time,
assuming the behavior of the patient and the lifestyle of the household would
"We could assume that an iodine implant would deliver 98%
of its lifetime dose in a year, and the palladium implant, which has a shorter
half-life, would deliver nearly 100% of the radiation dose in the first
year," he said.
Based on this information, Dr. Michalski concluded that
radiation exposure to members of the household of a brachytherapy patient are
well within NRC limits. "We found that it is extremely difficult for
anyone to expose a member of the family to amounts of radiation that we can
even detect, and the amounts we can detect are very low," he said.
He noted that radiation oncologists at Washington University
nevertheless caution brachytherapy patients to minimize direct contact with
family members. "The greatest exposure is in the lap; so we recommend that
patients limit direct exposure for their grandchildren, for example, by not
holding them in their lap for long periods of time, because it is a simple
measure they can do," he said.