Biomedical Engineering Reference
In-Depth Information
As a consequence of these and related considerations, neither the
radiation oncologist nor the physicist can dare to design or deliver a
radiation treatment without anticipating the biological consequences
for the patient of the physical deposition of dose.
M
ODELS
If one is to take the biological consequences for the patient of the
physical deposition of dose into account, then one must have a model
or models of the processes that lead from dose to damage. The
development of biophysical models is held in quite some suspicion,
and for very good reasons, I must say. But, the fact is that
every
radiation oncologist has a number of mental models in his or her
head when designing a plan of treatment
. It cannot be otherwise.
How can one decide on the dose to deliver if one does not have at
least a mental model of how tumor control and normal tissue damage
depend on dose? Or, how can one decide how much dose can be
tolerated by a particular volume of a critical normal tissue without
having a mental model of normal tissue tolerance as a function of
dose and volume?
1
Those who develop biophysical models attempt to capture, in a
mathematical recipe, that which is in the clinician's head and make
it explicit. Once it is explicit, a few things follow: the model can be
examined and discussed with colleagues; the model can be clinically
tested, leading one hopes to improvements in the model; and the
model can be implemented in a computer that can then allow the
planner, or the computer itself, to make use of it in designing a plan of
treatment.
Established experience
Radiation has been used in the treatment of cancer for over a century
- incredibly, the first treatment of a cancer with radiation came only a
1
The terms “organ” and “normal tissue” are both used in discussing
radiation damage to nonmalignant tissues. In the case of the former, one
usually has in mind an organized body part, such as the kidney, whose
damage is expressed in terms of an impairment of the organ's function(s).
In the latter case, one generally thinks of a tissue compartment, possibly
with a less clear function. For the most part, the terms are used
interchangeably, and I will generally use the term “normal tissue” for both
meanings.
