Biomedical Engineering Reference
In-Depth Information
another in that respect. One can also include in such a table, of
course, the values predicted by any biophysical models of interest.
Combining all the factors
Just as for plan assessment, but even more so for plan comparison, the
job of pulling together the many disparate data into an overall
judgment is an excruciatingly difficult task. I have no guidance to
offer concerning it.
P
OST
-
PLANNING
A
CTIVITIES
Finally, just a very few words about the activities that take place after
a satisfactory treatment plan has been arrived at. These include the
following.
Simulation of treatment
A
simulator
is a machine that simulates the features and geometry of
a treatment machine, but substitutes a diagnostic X-ray tube for the
therapeutic source of photons. Simulators were introduced as an aid
to designing a treatment plan
and for efficiency, so as to avoid tying
up a valuable treatment machine (Karzmark and Rust, 1972). In days
of yore, the plan was often designed on the simulator by adjusting
field sizes and shapes until the target coverage and normal tissue
−
avoidance of each beam was deemed satisfactory as seen on radio-
graphs and/or fluoroscopy.
The role of the simulator has vastly changed. Modern treatment
planning systems act as “virtual simulators,” allowing plans to be
developed after the patient has gone home, leaving only his or her
planning CT study and other images behind. However, the treatment
planning systems only partially represent reality, especially so far as
both patient and treatment machine geometries are concerned. Once a
plan has been arrived at, it is usually tried out on a simulator or for
complex equipment on the treatment machine itself, to see if there are
any unanticipated interferences between the patient and the treatment
equipment and to make sure that the geometry embodied in the CT
and other studies remains representative of the patient.
Delivery of treatment
There is many a slip 'twixt cup and lip. The flawless transfer of
consistent data between prescription, treatment plan and actual
treatment is critical and is a common source of problems. When I
