[ RadSafe ] Article: Radiation oncology saves lives, but at what cost?
crispy_bird at yahoo.com
Mon Aug 21 08:15:58 CDT 2006
>From another list server:
Radiation oncology saves lives, but at what cost?
By: Wayne Forrest
Successful radiation treatment for cancer can prolong
life by 15 to 40 years. However, with that reward
still comes risk, and researchers are trying to
determine to what degree radiation therapy may create
new cancers later in a patient's life.
Dr. Herman Suit, chief of the department of radiation
oncology at Massachusetts General Hospital in Boston,
said there are three certainties about radiation
therapy. One fact is that radiation is carcinogenic,
even in a weakened state.
"Two, the effects of the radiation appear quite late,
maybe 15 to 40 years after the treatment, and we have
very little data on that," he added. "Three, there is
a substantial number of patients who are being cured
and can expect to live 30 to 40 years after
At the 2006 American Association of Physics in
Medicine (AAPM) meeting in Orlando, Suit and
colleagues presented their analysis of studies that
examined the radiation effects on cancer patients,
atom-bomb survivors, individual mammalian cells, and
animals, such as mice and rhesus monkeys. The report
found no uniform relationship between radiation
exposure and secondary cancer incidence, but there
were areas of concerns.
Patients who received relatively high radiation dose
to the stomach, while being treated for another
cancer, increased their chance of developing stomach
cancer from approximately 1% to approximately 4% for
the rest of their lives. The analysis, however, also
found no significant increase in the risk of bladder
or rectal cancer over the dose range of 1 to 60 Gy to
those nearby organs.
While research has not conclusively found a concrete
link between radiation dose and cancer risk, Suit said
that one thing is clear -- radiation exposure, except
at low dose levels (0.01 Gy for a routine diagnostic
x-ray exam), is known to heighten cancer risk.
The debate over whether prostatic irradiation is a
catalyst for rectal cancer recently rekindled. A 2005
University of Minnesota Medical School study reviewed
approximately 85,000 U.S. men with prostate cancer but
no previous history of colorectal cancer. The men
received either surgery or radiation and lived at
least five years.
The Minneapolis-based research found that colorectal
cancers developed in 1,437 patients, 267 of which were
in irradiated sites, 686 in potentially irradiated
sites, and 484 in nonirradiated sites. In addition,
radiation was independently associated with cancer
development over time in irradiated sites, but not in
the remainder of the colon. The conclusion was that
the adjusted hazards ratio for developing rectal
cancer was 1.7 for the radiation group, compared with
the surgery-only group.
Thus, the study found what it described as "a
significant increase in development of rectal cancer
after radiation for prostate cancer." "Radiation had
no effect on development of cancer in the remainder of
the colon, indicating that the effect is specific to
directly irradiated tissue," the authors wrote
(Gastroenterology, April 2005, Vol. 128:4, pp.
Upon further review
Dr. Wayne Kendal, Ph.D, a radiation oncologist at
Ottawa Hospital Regional Cancer Center in Ontario,
Canada, recently took the Minnesota study one step
further with a sample of 285,000 men, including the
85,000 men in the Minnesota report. Both research
ventures used information from the Surveillance,
Epidemiology, and End Results (SEER) database at the
U.S. National Cancer Institute.
Of the men who had radiation for prostate cancer
(33,831 in Kendal's sample), 0.7% developed rectal
cancer, while those who did not have radiation or
surgery (36,335) had a 0.8% rectal cancer rate,
according to the results published in the
International Journal of Radiation Oncology, Biology,
Physics. Men who underwent a prostectomy (167,607) had
a rectal cancer rate of 0.3%. The numbers led Kendal
to conclude that the effect of radiation is minimal
and that age may have played a role in the results
(IJROBP, July 1, 2006, Vol. 65:3, pp. 661-668).
"We know that the incidence of rectal cancer on its
own will increase with age," Kendal said in an
interview with AuntMinnie.com. "When we did our
analysis, using these types of methods and these three
groups, there was no increased rate of rectal cancer
in those who had radiation. We thought this was an
important result, because this would tend to put to
rest many men's fears" of developing radiation-induced
rectal cancer after prostatic radiotherapy.
Kendal currently has a second paper in peer review,
which takes into consideration potential confounding
factors and may produce more evidence for his
Beware the scatter
In radiation therapy, the basic principle is to direct
as much dose as possible into the target organ.
Typically, oncologists prescribe 76 Gy for conformal
treatment, though Kendal said the amount "does not
control all the disease all the time." "The main
limitation is the tolerance of the surrounding tissue.
You don't want to cause a complication, and that's why
we use 76 (Gy) with our conformal treatment," he
While Suit readily noted that the benefit of radiation
therapy outweighs the risks, oncologists must take
every precaution to concentrate dose on the targeted
cancer tissues. "When you do radiation treatment, you
have low doses scattered and you radiate (other
areas)," he said. "It is extremely low, but it isn't
Suit cited several improved techniques and
technologies that are having a positive effect to
minimize secondary cancer risks. Specifically, he
mentioned intensity-modulated radiotherapy (IMRT) --
which, he said, "clearly reduces scattered dose" -- as
well as intraoperative electron beam therapy,
image-guided brachytherapy, and 4D treatment planning
and delivery, which adjusts radiation therapy to the
motion of the cancerous organ.
By Wayne Forrest
AuntMinnie.com staff writer
August 16, 2006
US Oncology, Molecular Profiling Institute form cancer
venture, August 4, 2006
NAS nets FDA nod, July 25, 2006
Strict protocol increases efficacy of CT screening for
lung cancer, July 18, 2006
Mayo Lung Project: Lung cancer screening leads to
overdiagnosis, June 9, 2006
U.K. group finds high miss rate for lung cancers on
chest x-rays, June 9, 2006
Copyright © 2006 AuntMinnie.com
>From an article about physicians doing clinical studies:
"It was just before an early morning meeting, and I was really trying to get to the bagels, but I couldn't help overhearing a conversation between one of my statistical colleagues and a surgeon.
Statistician: "Oh, so you have already calculated the P value?"
Surgeon: "Yes, I used multinomial logistic regression."
Statistician: "Really? How did you come up with that?"
Surgeon: "Well, I tried each analysis on the SPSS drop-down menus, and that was the one that gave the smallest P value"."
John Jacobus, MS
Certified Health Physicist
e-mail: crispy_bird at yahoo.com
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