Medical Physics Plastic Scintillators as InVivo Dosimeters Angular

Medical Physics Plastic Scintillators as In-Vivo Dosimeters: Angular Dependence of Response Ethan Avila Ruiz, MSc 1, Thalat Monajemi, Ph. D 1, 2 1 Department of Physics and Atmospheric Science, Dalhousie University 2 Department of Radiation Oncology, Dalhousie University 2021 -03 -12 1

Plastic scintillation dosimetry (PSD) Medical Physics • Benefits of PSDs • Similar density to water • Less corrections • High temporal resolution • Linear response with dose 2

Scintillator with spectrometer setup Medical Physics • 1 cm scintillator • 40’ optical fiber • Exemplar plus spectrometer Scintillation detector: components Jacket SC SF-3 HF Placeholder PMMA core of fiber-optic cable SC SF-78 3

Validate spectral invariability of system signal Medical Physics • Well-characterized signal components in arbitrary dose measurements 4

Determination of scintillation signal Total signal: -Spectrometer signal Medical Physics Scintillation: - Proportional to dose - Acquired by subtracting Cerenkov: - Highest intensity at 45 o - Obtained from stem measurement 5

Spectral variability with angle Inline Medical Physics Crossline 6

Spectral variability of stem signal Inline Medical Physics Crossline 7

Relative dose affected by variability Inline Medical Physics Crossline 8

Effect is reduced with depth Inline Medical Physics Crossline 9

Summary Medical Physics • Surface dosimetry requires a cautious approach • Subtraction correction does not account for Cerenkov in scintillator • Spectral correction more robust under all measurement conditions 10