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The two dominant radiotherapy methods are either simplified in terms of beamgeneration and handling, which compromises the energy deposition curve intissues (photon therapy), or require extensive accelerator facilities andcomplex beam delivery systems to provide a favorable shape of the energydeposition curve (hadron therapy). The advantages of both of these methods,such as the low cost of the apparatus, ease of beam generation, and a suitableshape of the energy deposition curve in tissues, can potentially be achieved byusing a very high-energy electron beam (beam energy in the order of a fewhundreds of MeV) focused on the area of the tumor lesion. However, focusing ofthe beam is usually done with the use of quadrupole magnets which makes thebeam delivery system complex and challenging from the engineering point ofview. In this thesis, the feasibility of an alternative solution is explored,where focusing is performed by a bent silicon crystal with an appropriate shapeof its exit face. Such a crystal lens can be a very light object (mass in theorder of grams), allowing for much simpler beam delivery systems ofradiotherapy facilities. As a result of this feasibility study, a simulation ofa bent silicon crystal with profiled exit was prepared in Geant4. The outcomeobtained from the simulation proved the focusing ability of such profiledcrystal. However, the focusing strength of the crystal is not strong enough.Technical requirements needed to enable an improvement in focusing efficiencywere identified and understood. Moreover, alternative solutions providingstronger focusing while using profiled crystals were proposed.

Focusing of high energy electron beam using crystal lenses for applications in radiotherapy