SPOT SCANNING PROTON BEAMS CHARACTERIZATION VIA PLASTIC SCINTILLATOR DETECTOR
by
Saad Bin Saeed Ahmed

A Thesis Submitted to the Faculty of The Charles E. Schmidt College of Science in Partial Fulfillment of the Requirements for the Degree of Master of Science

Florida Atlantic University
Boca Raton, FL
March 2026

ABSTRACT
Author:	Saad Bin Saeed Ahmed
Title:	Spot Scanning Proton Beams Characterization Via Plastic Scintillator Detector
Institution:	Florida Atlantic University
Thesis Advisor:	Dr. Wazir Muhammad
Degree:	Master of Science
Year:	2026

Spot scanning proton therapy offers superior dose conformality but introduces complex dosimetric challenges requiring high-resolution, real-time quality assurance instrumentation beyond the capability of conventional ionization chambers. This thesis presents a comprehensive characterisation of spot scanning proton beams using Blue Physics plastic scintillation detector (PSD) at 100 MeV and 200 MeV on a Varian ProBeam system, benchmarked against a PTW Bragg Peak Chamber reference and a validated TOPAS Monte Carlo simulation. The PSD demonstrated sub-millimeter spatial agreement with Monte Carlo predictions in longitudinal depth-dose profiles and resolved lateral spot profiles at Bragg peak depth with sub-percent sigma values, including the reproduction of the beam’s intrinsic X-Y asymmetry. Ionization quenching suppressed the raw PSD signal by up to 44% at the Bragg peak; however, a Birks’ law correction formalism employing TOPAS-scored dose-averaged linear energy transfer maps fully recovered the true Peak-to-Plateau Ratio at both energies, confirmed by three-way concordance between the corrected PSD, the Bragg Peak Chamber, and the Monte Carlo ground truth. These findings establish the PSD as a clinically meaningful advancement over conventional ionization chamber dosimetry in the pencil beam scanning environment, with a clear roadmap identified for extension across the full therapeutic energy spectrum.