Biomedical Engineering Reference
In-Depth Information
12.
Q
UALIT Y
A
SSURANCE
This is a very short chapter, but it is nevertheless one of the most
important ones. Quality assurance is the process by which one
assures oneself that
what is done is that which was intended to be
done
. Quality assurance (QA) is the
sine qua non
of any practice, but
especially one in which people's lives and health are at stake.
In the matter of quality assurance, the process of radiation therapy is
no different from most forms of industrial production - for which
there are tried and true methods to achieve and maintain safety and
reliability. Safety must be built into the system from the beginning, in
the design and construction of all components of the system - as well
as in their maintenance and use.
A radiation therapy facility is complex, with very many parts and with
complex interactions between them. Faults can arise from a multitude
of causes and scenarios, many of which are probably not even known
to the user. It is absolutely impossible in practice to test all com-
binations and permutations of the input signals, so a targeted strategy
must be developed to monitor the most important functions and
failure modes. This process is termed
quality control
when it is
applied to the verification of input signal processing, and
quality
assurance
when the performance of the overall system is verified.
QA involves a very large number of checks that must be made at
various time intervals, typically: in real time (e.g., the ratio of
dosimeter responses); daily (e.g., absolute dose delivery, field size,
positioning aids); weekly; monthly; and annually.
Whole topics are written about QA, but in sum what has to be done is
very simple. One must:
1.
determine and document, in the case of a procedure, how one
plans to go about implementing it
or, in the case of
equipment or software, how it should function;
2.
decide how to test whether what is done or built is that which
was intended to be done or built;
3.
perform the tests
−
−
and, if unsatisfactory, do whatever is
necessary to fix the problem(s)
and then, re-test;
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