Radiation Dosimetry of Proton Beams

Abstract

This chapter aims to review the currently practiced radiation dosimetry principles and procedures for passively scattered and magnetically scanned proton pencil beam spots (PPBS). Usefulness and limitations of various dose measuring devices, like ion chambers, films, solid-state detectors, gel, and plastic and liquid scintillators that are used in proton dosimetry are reviewed. Absolute or reference dosimetry procedures using calorimeter, ion chambers and Faraday cup are described. Relative dosimetry techniques for beam data collection are presented. Monitor unit calculation procedure for patient treatment fields for passively scattered fields using simple dosimetry factors is discussed. The detector size effects in the measurement of PPBS profiles and integral depth-dose are described. The importance of the contribution of low-dose envelopes present in PPBS profiles to 3-D dose distribution is discussed, and possible ways to measure and account for them in the modeling of PPBS in the treatment planning system are outlined. The feasibility of 3-D dosimetry using gel and liquid scintillators is discussed. Our experience at the Proton Therapy Center in Houston with the dosimetry of passively scattered and discrete spot-scanned proton beams including dose verification of patient treatment fields with intensity-modulated proton therapy is presented.