ICDA-5

Experimental and Monte Carlo characterization of linear energy transfer and lineal energy in proton therapy beams

Jun 8, 2026, 12:00 PM

15m

Auditorium 115

Oral Presentation Micro- and nanodosimetry Micro- and nanodosimetry

Speaker

Maria Luz Olaguibe (Department of Oncology, Laboratory of Experimental Radiotherapy, Leuven, Belgium. Belgian Nuclear Research Center (SCK CEN), Mol, Belgium)

Description

Background
Dose-weighted linear energy transfer (LETd) is widely used in relative biological effectiveness (RBE) modeling; however, as an averaged quantity, it does not fully describe microscopic energy deposition patterns responsible for biological damage. Microdosimetry overcomes this limitation by describing energy deposition through probability distributions, with dose-weighted lineal energy (yD) as an analogous, though not strictly equivalent quantity to LETd. Dedicated detectors, such as silicon-based MicroPlus, can be used to measure yD and evaluate LETd. This study aimed to assess yD measured with Microplus and to compare against simulated LETd from the Monte Carlo code, OpenTOPAS.

Methods
Measurements were performed with the Microplus at the Danish Centre for Particle Therapy (DCPT) using a spread-out Bragg peak (SOBP, 84.463–149.824 MeV) and a 160 MeV monoenergetic proton beam. LETd and yD were evaluated at the beam entrance, middle of SOBP, at 75% and 95% of the maximum dose, and at the beam entrance. Treatment plans and irradiation geometry were simulated in OpenTOPAS and compared with experimental results. The MiniPix-Timepix and thermoluminescent detectors were also used, but their results are not presented in this work.

Results
Experimental yD spectra showed good agreement with simulations, especially at distal positions. However, yD values showed uncertainties up to 50% due to limited event statistics. From simulations at the entrance and plateau regions, detector voxel size and δ-electron contributions affected spectral shapes and mean values, with reduced influence toward the distal edge. Rare high-energy deposition events above the proton edge were attributed to secondary particle production.

Conclusions
Microplus showed good results for in-field microdosimetric spectral measurements when comparing with simulations, while accurate estimation of averaged quantities requires increased statistics. LETd and yD differ mainly at entrance and plateau regions and converge near the distal edge. Contributions from nuclear fragments should be considered when estimating biological effectiveness.