Conceptualization of electronic dose to water for dosimetry in external beam radiotherapy

Abstract

This study conceptualizes electronic dose to water, which is the radiation energy imparted to a unit mass of water by electronic interactions. The new dosimetry framework excludes nuclear interactions and consequently associated corrections and uncertainties from conventional dosimetry. Based on the international code of practice for dosimetry in radiotherapy, the procedures to determine electronic doses were formulated for high-energy photon, electron, proton, and ion beams. Nitrogen-based water-equivalent gas (WEG) mixtures were designed for use in gas-sealed ionization chambers for proton and ion beams. The proposed procedures were tested in a thought experiment and demonstrated compatibility with conventional absorbed dose for photon and electron beams and improved accuracy for proton and ion beams. The dosimetric uncertainty will be reduced from \SI{1.4}{\%} to \SI{1.3}{\%} for proton beams and from \SI{2.4}{\%} to \SI{1.9}{\%} for ion beams. With WEG ionization chambers, it will be further reduced to \SI{0.7}{\%} for proton beams and \SI{1.0}{\%} for ion beams. The new dose concept, electronic dose to water, can be readily used in radiotherapy practice and it will be medically more relevant than absorbed dose.