Study of angular dependence in Fiber Optic Dosimetry by Monte Carlo simulations

NAHUEL MARTINEZ; MARTIN SANTIAGO ; JOSÉ MASSA; YOHANA FERNANDEZ; PABLO MOLINA; SOLEDAD MACHELLO; WALTER R CRAVERO

La Habana

Congreso; LASNPA & WONP-NURT 2017; 2017

IAEA, IUPAP

Real-time dosimetry for radiotherapy with high spatial resolution is a growing research field. Development ofnew radiotherapy techniques, such as intensity-modulated radiation therapy, stereotactic radiosurgery, andhigh dose rate brachyterapy among others, require high performance dosimetrics techniques. Even thoughdifferent kinds of detection systems have been investigated to perform in-vivo dosimetry, most of them donot permit simultaneously spatial resolution, real-time dose assessment and intracavitary measurements.The so-called fiberoptic dosimetry (FOD) technique has shown to meet most of these requirements mostlyneeded in radiotherapy [1]. FOD is based on the use of a tiny piece of a scintillation crystal (1mm^3 aprox)attached to the end of an optical fiber [1]. The fiber collects the light emitted by the scintillator during irradi-ation (radioluminescence, RL) and a light detector at the other end of the optical fiber measures its intensity.FOD technique allows for in-vivo and real-time dose assessment, and due to the small size of the detector itnot only permit 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 areemployed as usual in this technique.In the present work, we study the angular response of a YVO_4:Eu^{3+} based FOD probe by using MonteCarlo simulations in order to explain the different attenuation process.Two geometrical configurations have been studied: 1mm diameter spherically shaped detector, and 2mmlength-1mm diameter cylindrical detector. Simulations have been achieved by using PENELOPE employingan hybrid virtual source model based on IAEA phase space data base. In both cases results have been comparedwith 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.Spasic, E., et al., 2011. Intracavitary in vivo dosimetry based on multichannel fibercoupled radioluminescenceand optically stimulated luminescence of Al2O3:C. In: IEEE Conference Publication. 2nd International Confer-ence on Advancements in Nuclear Instrumentation Measurement Methods and Their Applications (ANIMMA),pp. 1-6.N Martinez, et al., 2017. Characterization of YVO4:Eu3+ scintillator as detector for Fiber Optic Dosimetry.Radiation Measurements, in press.