MC study of size effects and angular response of fiberoptic scintillator detectors for radiation therapy

Y. FERNANDEZ; J MASSA; N MARTINEZ; P MOLINA; M SANTIAGO; J MARCAZZÓ

Cordoba

Congreso; International Symposium on Radiation Physics; 2018

International Radiation Physics Society

Improvements in radiotherapy techniques such as intensity-modulated radiation therapy, stereotactic radiosurgery and high dose rate brachytherapy among Others, demands research of real time dosimetry with high spatial resolution to assess doses precisely in real time. Different kinds of detection systems have been investigated so far to perform in-vivo dosimetry, but most of them do not permit simultaneously spatial Resolution, real-time dose assessment and intracavitary measurements.Fiberoptic dosimetry (FOD) is a technique that has shown to fill most of these requirements mostly needed in radiotherapy. FOD is based on the use of a small scintillator (1mm^3 aprox) attached to the end of an optical fiber [1]. Light emitted by the scintillator is collected by the optical fiber during irradiation (radioluminescence, RL). Light detector at the other end of the optical fiber measures light intensity.FOD allows in-vivo and real-time dose assessment, and due to the small size of the detector it not only permits accurate measurements in regions of high dose gradients but also intracavitary measurements [2].Martinez et al. [3] observed angular dependency of the scintillating signal when cylindrical detectors based on YVO4:Eu3+ are employed as usual in this Technique.In the present work, we study the angular response of different FOD probes based on tissue-equivalent materials and inorganic materials with high Zeff by using Monte Carlo simulations in order to explain the different energy absorption processes.Two sizes of cylindrical detectors were studied: 2mm length-1mm diameter and 1mm length-1mm diameter. Simulations have been achieved by using PENELOPE employing 2x2cm2 square field size. In cases where experimental data are available, results have been compared with experimental measurements.[1] Justus, B.L. et al., 2004. Gated fiber-optic-coupled detector for in vivo real-time radiation dosimetry. Appl. Opt. 43, 1663-1668.[2] Kertzscher G. and Beddar S, 2017. Inorganic scintillation detectors based on Eu-activated phosphors for 192 Ir brachytherapy. Phys. Med. Biol. 62, 5046?5075.[3] N Martinez, et al., 2017. Characterization of YVO4:Eu3+ scintillator as detector for Fiber Optic Dosimetry. Radiation Measurements, in press.