Optimal electron and combined electron and photon therapy in the phase space of complication-free cure

The possibility of using intensity-modulated high-energy electrons beams al one or in combination with photon beams to treat tumours located at depths from 5 cm to 25 cm has been investigated. A radiobiologically based optimiz ation algorithm using the probability of complication-free tumour control h as been used to calculate the optimal dose distributions. Two different tar get volumes have been used; one advanced cervical cancer with locally invol ved lymph nodes and one astrocytoma in the upper brain hemisphere. Treatmen ts with only electron beams and also combinations between electron and phot on beams have been investigated. The dependence of the expected treatment o utcome on the beam energy and directions was investigated, and to some exte nt on the number of beam portals. It is shown that the beam direction inter vals resulting in a high expected treatment outcome increase with increasin g electron energy and also with some electron-photon combinations. For an e ccentrically placed, not too deeply situated tumour surrounded by sensitive normal tissue it is shown that the expected treatment outcome can be impro ved by using electron beams in combination with photon beams compared with using two photon beams, and using two electron beams results in almost as h igh an expected treatment outcome. The possibility of improving the dose co nformity from electron beams by adding photon fields parallel or orthogonal to the electron beams is demonstrated.