Implantable real-time dosimetric probe using GaN as scintillation material

This paper presents an implantable real-time dosimetric probe using near-tissue-equivalent GaN as a scintillator and an optical fiber for radioluminescence (RL) collection and transmission. Heavily-doped GaN was preferred because of enhanced light output with dominant near-band-edge UV emission and minimized yellow luminescence (YL) contribution. For encapsulating the small-volume GaN bulk at the end of the coupled fiber, a polymer cladding fiber was chosen and a core cavity was formed by a chemical-etching and tip-cleavage process. For testing the realized dosimetric probe, a probe-readout system was designed with UV-narrow-band selection and photodetection. Real-time measurements showed detected radiation pulses with fluctuations, but integrating the detected pulses exhibited a dose response curve steadily increasing, with less than 2% reproducibility errors between runs for a dose of more than 50 cGy. The GaN and fiber contributions to the averaged output signal were evaluated by different field size measurements. The fiber contribution was significant because of its much larger irradiated volume compared to that of GaN in the probe. On the other hand, the GaN contribution per volume was much larger than the fiber: 186 times for 6 MV photons and 89 times for 18 MV photons. The probe was also irradiated by receiving a 18 MeV 300 Gy electron beam dose. The GaN contribution was unchanged, while the fiber contribution was increased by 20%. This further demonstrates the need to subtract the fiber contribution for accurate measurements.