Our studies focus on dedicated dosimetry systems based on the Gallium Nitride (GaN) probe for Quality Assurance and patient safety in radiotherapy, brachytherapy and interventional radiology. The small size GaN transducer in the probe has high radioluminescence (RL) yield and rapid RL signal response for real time measurements. Preliminary prototypes of dedicated systems were tested in clinical conditions for external beam radiotherapy, brachytherapy and interventional radiology. The obtained pre-clinical results appear favorable and encouraging: in radiotherapy, GaN RL response has not significant dependence on the main influence parameters, excepted for the field size. In brachytherapy, using an instrumented phantom with integration of GaN probes allows real time verification of planned treatments. In interventional radiology, skin dose measurements using GaN probe based dosimeters show consistent results with those from a reference dosimeter.