Requirements to be met by transmission type ionization chambers in medical linear accelerators

Modern radiotherapy with linear accelerators claims to be superior to conventional techniques because of the enlarged spectrum of possible radiation qualitites, such as different electron and photon energies. Especially in comparison with the telecobalt equipment it is doubtable whether commercial medical linear accelerators can ensure the radiation field parameters such as energy, symmetry, field flattening, dosimetry, etc. In this context the suitable segmentation of the internal monitor chamber is of importance. The constancy of the parameters is evaluated on the basis of the ICRU recommendation, which sets a target volume dose deviation of ±5%. Different monitor systems are compared from the medical-physical point of view. (orig./HP)