Osorio, J; Dreindl, R; Grevillot, L; Letellier, V; Kuess, P; Carlino, A; Elia, A; Stock, M; Vatnitsky, S; Palmans, H (2021) Beam monitor calibration of a synchrotron-based scanned light-ion beam delivery system. Zeitschrift fur Medizinische Physik, 31 (2). pp. 154-165.

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Abstract

Purpose: This paper presents the implementation and comparison of two independent methods of beam monitor calibration in terms of number of particles for scanned proton and carbon ion beams.

Methods: In the first method, called the single-layer method, dose-area-product to water (DAPw) is derived from the absorbed dose to water determined using a Roos-type plane-parallel ionization chamber in single-energy scanned beams. This is considered the reference method for the beam monitor calibration in the clinically relevant proton and carbon energy ranges. In the second method, called the single-spot method, DAPw of a single central spot is determined using a Bragg-peak (BP) type large-area plane-parallel ionization chamber. Emphasis is given to the detailed characterization of the ionization chambers used for the beam monitor calibration. For both methods a detailed uncertainty budget on the DAPw determination is provided as well as on the derivation of the number of particles. Results: Both calibration methods agreed on average within 1.1% for protons and within 2.6% for carbon ions. The uncertainty on DAPw using single-layer beams is 2.1% for protons and 3.1% for carbon ions with major contributions from the available values of kQ and the average spot spacing in both lateral directions. The uncertainty using the single-spot method is 2.2% for protons and 3.2% for carbon ions with major contributions from the available values of kQ and the non-uniformity of the BP chamber response, which can lead to a correction of up-to 3.2%. For the number of particles, an additional dominant uncertainty component for the mean stopping power per incident proton (or the CEMA) needs to be added.

Conclusion: The agreement between both methods enhances confidence in the beam monitor calibration and the estimated uncertainty. The single-layer method can be used as a reference and the single-spot method is an alternative that, when more accumulated knowledge and data on the method becomes available, can be used as a redundant dose monitor calibration method. This work, together with the overview of information from the literature provided here, is a first step towards comprehensive information on the single-spot method.

Item Type:	Article
Keywords:	Light ion beam therapy, Beam monitor calibration, Dose area product, Commissioning, Protons, Carbon ions
Subjects:	Ionising Radiation > Dosimetry
Divisions:	Medical, Marine & Nuclear
Identification number/DOI:	10.1016/j.zemedi.2020.06.005
Last Modified:	05 May 2023 13:33
URI:	https://eprintspublications.npl.co.uk/id/eprint/9388