The
result of my first PSA test—after 15 IMRT sessions—was encouraging. Given
I was warned that the PSA during treatment can be artificially elevated, the
drop from 34 to 24 was a huge relief to me. There’s no way of knowing, during
the IMRT sessions, what effect the radiation is having, whether or not it is
killing the cancer. So PSA is the only clue you get.
The
staff at St. John’s--especially James, the oncology tech, and oncology nurses,
Jan and Janet--have been very patient with me, going over the details, helping
me understand why IMRT trumps conformal beam radiation.
IMRT
is an advanced form of 3D radiation using a huge
computer-driven machine that actually moves around the patient as it delivers
radiation. In addition to shaping the beams and aiming them at the prostate
from multiple, laser guided angles, the intensity (strength) of the beams can
be adjusted to minimize the dose reaching the most sensitive normal tissues,
while permitting delivery of a higher dose to the cancerous areas. As of 2013,
most major hospitals and cancer centers now include IMRT in the protocols they
offer. But that may soon stop.
The St. John’s machine is a state-of-the-art Varian Trilogy,
and costs several million dollars. The machine.
called RapidArc, provides access to a variety of small fields
that allow the beam to be shaped, and the dose to be modified to get better
distribution with a minimum of side effects.
The
maximum total safe dose, measured in “rads”—units
of energy produced by photons, and/or light particles—is eighty-one hundred
“rads.” So I must receive no more than 180 rads a day for the 45 days of
treatment. That is a therapeutic dose given only to a small area, in my case,
the prostate gland plus lymph nodes. You wouldn’t give that dose to the entire
body. When I asked James about the effective limit with rads, he told me,
“We know that the prostate has what’s known as ‘a dose response curve,’ meaning
simply that the higher the dose the better response.
In the St. John’s unit, I lie in my form-fitted nest while the ion chamber passes
overhead like a planetary formation from another universe. I confess, I love
it! It’s a piece of major magic working for my benefit: pain free, and to date,
free of all negative side effects.
One
day, after my treatment when James allowed me to peer into the ion chamber through a metal flap, it was like
finding myself in the contemporary version of Stanley Kubrick’s 1968 space age
chronicle, “2001.” I was looking at “multileaf collimators”—computer controlled
mechanical devices that use up to 120 moveable tungsten “leaves” that conform
the shape of the radiation beam to the shape of the tumor from any angle. and
can move independently in and out of the path of a particle beam in order to
block it. There is now software for calculating the number of beam angles, beam
shapes, exposure times, and the treatment schedule needed to deliver the
prescribed dose to the targeted area while minimizing exposure to surrounding
healthy tissue.
Concerns
over IMRT include a higher risk of error due to the extreme complexity of
planning and delivery, as well as difficulties in quality assurance, radiation
safety, and portal verification. IMRT is expensive, complex, and
time-consuming, and will not—for some patients-- necessarily offer an advantage
over more conventional techniques such as conformal beam radiation. Long-term
follow-up of patients treated with IMRT is necessary to resolve these issues.
That lack, plus the astonishing cost, are responsible for a trend to reduce
IMRT usage.
Meanwhile
I consider myself fortunate to be getting this advanced image-guided radiation
treatment, and Dr. Chaiken’s team is undoubtedly among the best.
After
30 sessions, I got my second PSA reading. To my profound relief, it registered another
downward shift—this time from 24 to 16.5—with only one more cycle to go!
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