Technical note: Angular dependence in fiber optic dosimetry using YVO₄ :Eu³.

Area of Science:

• Medical Physics
• Radiation Detection and Measurement

Background:

• Fiber optic dosimetry (FOD) offers real-time, high spatial resolution dose assessment for intracavitary applications.
• Assessing the angular response of FOD probes is critical for their clinical viability.

Purpose of the Study:

• To characterize the angular response of a YVO4:Eu3+ scintillator-based FOD probe.
• To evaluate the probe's performance under a 6 MV photon beam from a linear accelerator (LINAC).

Main Methods:

• Irradiation of FOD probes within a plastic phantom using a 6 MV LINAC at various azimuthal angles.
• Measurement of scintillation output with a photomultiplier tube, with and without an optical filter.
• Comparison with PENELOPE Monte Carlo simulations to interpret experimental data.

Main Results:

• The unfiltered FOD probe exhibited maximum signal at rear incidence (0°) and minimum at frontal incidence (180°), with a 37% signal ratio.
• The filtered probe showed a plateau from 15° to 115°, with maximum signal at 60° and minimum at 180° (16% ratio).
• Experimental findings on angular symmetry contrasted with Monte Carlo simulation predictions.

Conclusions:

• Photoluminescence induced by Cherenkov light contributes to the angular dependence of FOD probes.
• Radiation attenuation and partial light collection by the optical fiber cause asymmetrical responses.
• Minimizing angular dependence is essential for optimizing FODs in clinical settings.