Biomedical Engineering Reference
In-Depth Information
upgrading part of their radiation oncology installation to proton therapy. Several
proposals have been put forward to achieve such a size and cost reduction, and we
will discuss a selection of these in this report.
Introducing new accelerator concepts to the medical community is especially
difficult due to the stringent requirements on an accelerator used for treatments of
human patients. Above all, the beam obtained from the accelerator must meet all
specifications set forth by the clinical treatment plans, without any exceptions. This
not only refers to beam energy, but also to beam shape and delivery options (spot
scanning, passive scattering, etc.). If the time structure significantly deviates form
current standards, one needs to be assured that the biological effects are not altered.
This will require a number of additional test experiments, both in-vitro and in-vivo,
before a system otherwise meeting the basic requirements of energy and intensity
can be fully certified for medical use.
Additionally one typically requires a system availability of more than 95%
to avoid extended interruptions of patient treatments due to technical failures.
Considering that the actual accelerator is only a small part of a complex chain
between ion source and patient, it may be necessary to call for an up-time of
the actual accelerator of 98% or more. As a back-up solution one may consider
setting up agreements with other particle therapy centers in the same geographical
region to transfer patients when technical problems endanger the completion of an
already started treatment course. Alternatively one may consider using more than
one accelerator per facility [
2
] and allowing all beam lines to be served by all
accelerators, or even to duplicate installations of a facility to achieve maximum
accessibility to treatment for patients already enrolled. Continued, possibly in-
beam, quality assurance will need to be developed for new systems, and a fail safe
operation needs to be achieved through complex control systems adapted to the
specific acceleration scheme. Background radiation from the acceleration column
in terms of physical dose and particle spectrum must be understood and be bound
by the ALARA (As Low As Reasonably Achievable) concept.
Considering the stringent requirements on performance and quality assurance
placed on medical installations as well as the long lead time to introduce new
technology and to obtain approval by the relevant authorities in different countries, a
logical approach obviously is to start from proven standard technology and modify it
such that it can meet new requirements with a minimum of deviations from standard
approved systems.
30.2
Reducing the facility footprint
The following paragraphs will show various examples from simple modifications
of facility lay-out to using proven modifications to the two widely used standard
accelerator schemes, cyclotrons and synchrotrons, to achieve a smaller foot print,
thereby making the technology of hadron therapy available to more clinics. Most
of the development ongoing at this time is focusing on protons only, even though
