Philadelphia Medicine Summer 2018 - 20

p h i l a m e d s o c  .org

FEATURE continued

The direction of the beams and the placement of the focus are
guaranteed by stereotactic measures. A limitation of this machine
when it was first invented was that it could only be used to treat
tumors in the brain. Physicians quickly sought a similar machine
to treat tumors outside the brain.
In order to target a tumor precisely, one had to be able to see it.
Improvements in imaging techniques allowed for better identification
and localization of tumors. Thankfully, the field of radiology was
exploding around this time too with high resolution CT scans being
developed in the late 1970s and MRI in the early 1980s. Now that
tumors could be seen clearly, they could be targeted precisely. This
allowed for the discovery of the CyberKnife in 1990 by Dr. John
Adler, a neurosurgeon at Stanford.

in close proximity to critical structures which must be spared from
radiation. Patients with renal cell carcinoma and melanoma benefit
more from high doses per fraction due to the radiobiology of these
cancer subtypes. Patients who have been previously irradiated may
also be good candidates for CyberKnife as a means of delivering
additional radiation while sparing the normal tissues which were
previously radiated.
Future advances in the field of radiosurgery will be numerous. One
of the most exciting areas of current research is how radiosurgery and
immunotherapy can be coupled to improve cell kill. Immunotherapy
unleashes the body's own immune system to attack the cancer cells
and radiation has been shown to stimulate an immune response;
thus together they may be able to achieve superior tumor responses
than either treatment alone. The best way to sequence them is a
current area of active and very exciting investigation.

The CyberKnife was first used in 1995 to treat a craniopharyngioma
and was then FDA approved in 2001 to treat tumors outside the brain.
The CyberKnife System is a computer-controlled, robotic radiation
I feel fortunate to be practicing radiation oncology in this era
delivery system that treats tumors with high doses of radiation from of rapid evolution and expansion of treatment options, offering
virtually any direction or angle with sub-millimeter accuracy. It many patients hope for a cure that in the past was unattainable. The
uses this information to guide and position the radiation beams to "Shortcut to the Future" that
precisely target the tumor, while carefully sparing the surrounding is hypofractionation that I
healthy tissue.
heard about in a conference
as a resident 11 years ago is
It detects and self-corrects for tumor and patient movements here! *
during treatment, thereby minimizing damage to surrounding
tissues. It operates without the use of bulky frames, thus it is totally Dr. Bowers Hayes is
non-invasive. One advantage that it has over frame-based systems associate professor
is that radiation oncologists can fractionate the treatment, meaning and director of Fox
divide the dose up into several smaller doses if this is felt to be better. Chase Cancer Center
Buckingham.
The newest version of the CyberKnife machine has a multileaf
collimator on the head of the linear accelerator which allows for
treatment of larger targets and a quicker delivery time. It can be used
for moderately hypofractionated courses (2-5 weeks) and potentially
even conventionally fractionated courses (6-8 weeks). The best
candidates for CyberKnife are patients with small tumors which are
20 Philadelphia Medicine : Summer 2018


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