Objective.There is an increasing interest in calculating and measuring linear energy transfer (LET) spectra in particle therapy in order to assess their impact in biological terms. As such, the accuracy of the particle fluence energy spectra becomes paramount. This study focuses on quantifying energy depositions of distinct proton, helium, carbon, and oxygen ion beams using a silicon pixel detector developed at CERN to determine LET spectra in silicon.Approach.While detection systems have been investigated in this pursuit, the scarcity of detectors capable of providing per-ion data with high spatial and temporal resolution remains an issue. This gap is where silicon pixel detector technology steps in, enabling online tracking of single-ion energy deposition. The used detector consisted of a 300μm thick silicon sensor operated in partial depletion.Main results.During post-processing, artifacts in the acquired signals were identified and methods for their corrections were developed. Subsequently, a correlation between measured and Monte Carlo-based simulated energy deposition distributions was performed, relying on a two-step recalibration approach based on linear and saturating exponential models. Despite the observed saturation effects, deviations were confined below 7% across the entire investigated range of track-averaged LET values in silicon from 0.77 keVμm-1to 93.16 keVμm-1.Significance.Simulated and measured mean energy depositions were found to be aligned within 7%, after applying artifact corrections. This extends the range of accessible LET spectra in silicon to clinically relevant values and validates the accuracy and reliability of the measurements. These findings pave the way towards LET-based dosimetry through an approach to translate these measurements to LET spectra in water. This will be addressed in a future study, extending functionality of treatment planning systems into clinical routine, with the potential of providing ion-beam therapy of utmost precision to cancer patients.

ADVACAM Department of Research and Development U Pergamenky 12 17000 Prague Czech Republic

Clinical Cooperation Unit Translational Radiation Oncology National Center for Tumor Diseases 69120 Heidelberg Germany

Currently at Faculty of Mechanical Engineering Leibniz University of Hannover

Department of Medical Physics in Radiation Oncology German Cancer Research Center Neuenheimer Feld 280 69120 Heidelberg Germany

Department of Radiation Oncology Heidelberg University Hospital Im Neuenheimer Feld 450 69120 Heidelberg Germany

Faculty of Physics and Astronomy Heidelberg University Im Neuenheimer Feld 226 69120 Heidelberg Germany

Heidelberg Institute for Radiation Oncology Im Neuenheimer Feld 280 69120 Heidelberg Germany

Heidelberg Ion Beam Therapy Center Department of Radiation Oncology Heidelberg University Hospital Im Neuenheimer Feld 450 69120 Heidelberg Germany

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