Abstract
The distal fall-off of the Bragg curve in proton therapy is influenced by beam energy spread. Real-time determination of beam energy and energy spread remains challenging because current quality assurance methods—such as water phantoms, multi-layer ionisation chambers (MLICs), and multi-layer Faraday cups—are invasive and unsuitable for continuous monitoring. Furthermore, existing approaches to estimating energy spread require a priori knowledge of a pristine monoenergetic beam, typically obtained through Monte Carlo simulations.The objective was to determine whether a quantitative relationship exists between distal slope, beam energy, and energy spread, and to assess whether these parameters can be measured in real time under clinical conditions. Polynomial relationships between beam energy, energy spread, and distal slope were derived for both water phantom measurements and a multi-layer Faraday cup–based instrument. These relationships were validated against simulated and measured beam data. The instrument was incorporated into a model of a clinical beam line, and its impact on beam characteristics was evaluated relative to a control configuration and to data from an independent beam line.
The polynomial models demonstrated a reproducible relationship between distal slope and both beam energy and energy spread. The instrument should enable determination of the energy and energy spread inherent in a beam within clinical tolerances of ±3% in cases where the beam energy is greater than 70 MeV but at the expense of beam quality and quantity.
The distal slope of the Bragg curve provides a basis for estimation of proton beam energy and energy spread. It is hoped that the proposed instrument might offer a potentially minimally-invasive alternative to current quality assurance techniques and may support continuous beam monitoring in clinical proton therapy however this method substantially reduces the transmission of the beam whilst substantially increasing the emittances.
| Date of Award | 2 Jun 2026 |
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| Original language | English |
| Supervisor | Konstantina Lambrinou (Main Supervisor) |