Purpose: Application of MOSFET detectors in photon beam dose measurements in vivo in radiotherapy. Materials and methods: Before measuring doses in vivo the following parameters such as: the dosimeter response to dose absorption, temperature, gantry angles and field side changes were determined using 6MV and 15MV photon beams. All measurements were made in a phantom to investigate the MOSFET accuracy, in electron equilibrium with a 0.6 cm 3 Farmer ionization chamber. Results: MOSFET parameters

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... re presented in graphs. The conformity between the planned dose and the dose measured in vivo within ±5% was observed in 86% of patients treated with 6MV photon beams and 91% patients treated with 15MV, respectively (SD=3.5%). Conclusions: MOSFET detectors are a useful tool for verifying the planned dose in external photon radiotherapy.