Source of Support: None, Conflict of Interest: None
The potential advantages of the MICROTRON as an electron accelerator for radiation therapy can be summarized as follows: 1. Dual photon energies can easily be obtained. 2. A favourable range of electron energies are available. 3. The beam current - and thus also the output - is high. 4. The electron energy spectrum is extremely narrow - thus offering: a. optimization of electron and photon beam properties b. a separate room with a stationary accelerator and a favourable gantry design c. electron transport through vacuum tubes to more than one irradiation facility. Medical microtrons have been in use since more than 10 years and a continuous improvement of design and energy range has taken place. The reasons for requesting higher energies are illustrated by means of treatment plans. The optimal photon energy for various treatment techniques will be discussed as well as the importance of the design of the target, the beam flattening filters, scattering foils and the collimator. Recent developments of a multileaf collimator will be presented as well as the expected advantages of such a system for some clinical applications. The layout of some special microtron therapy departments will be presented as well as performance data, reliability and maintenance requirements as experienced on some of the installations. A fairly detailed study of the neutron flux measured at some therapy installations will also be presented. The level of fast and thermal neutrons and their possible clinical significance will be discussed. In conclusion a process of improving the properties of external beam equipment - amongst them the medical microtrons - is still going on and this will hopefully further improve the survival and reduce the complication rate for patients treated with such modalities.