arXiv subjects

Stephan Brons

Publications and source records attributed to Stephan Brons.

6 recordsLinked to original sources

arXiv2025

Clinical beam test of inter- and intra-fraction relative range monitoring in carbon ion radiotherapy

Interaction Vertex Imaging (IVI) is used for range monitoring (RM) in carbon ion radiotherapy. The purpose of RM is to measure the Bragg peak (BP) position for each contributing beam, and detect any changes. Currently, there is no consensus on a clinical RM method, the use of which would improve the safety and consistency of treatment. The prototype filtered IVI (fIVI) Range Monitoring System is the first system to apply large-area and high-rate-capable silicon detectors to IVI. Two layers of these detectors track prompt secondary fragments for use in RM. This device monitored 16 cm and 32 cm diameter cylindrical plastic phantoms irradiated by clinical carbon ion beams at the Heidelberg Ion Beam Therapy Center. Approximately 20 different BP depths were delivered to each phantom, with a minimum depth difference of 0.8 mm and a maximum depth difference of 51.9 mm and 82.5 mm respectively. For large BP range differences, the relationship between the true depth difference and that measured by fIVI is quadratic, although for small differences, the deviation from a linear relationship with a slope of 1 is negligible. RM performance is strongly dependent on the number of tracked particles, particularly in the clinically-relevant regime. Significant performance differences exist between the two phantoms, with millimetric precision at clinical doses being achieved only for the 16 cm phantom. The performance achieved by the prototype fIVI Range Monitoring System is consistent with previous investigations of IVI, despite measuring at more challenging shallow BP positions. Further significant improvements are possible through increasing the sensitive area of the tracking system beyond the prototype, which will both allow an improvement in precision for the most intense points of a scanned treatment plan and expand the number of points for which millimetric precision may be achieved.

physics.med-ph↗

arXiv2025

Hybrid Compton-PET Imaging for ion-range verification:A Preclinical Study for Proton-, Helium-, and Carbon-Therapy at HIT

Enhanced-accuracy ion-range verification in real time shall enable a significant step forward in the use of therapeutic ion beams. Positron-emission tomography (PET) and prompt-gamma imaging (PGI) are two of the most promising and researched methodologies, both of them with their own advantages and challenges. Thus far, both of them have been explored for ion-range verification in an independent way. However, the simultaneous combination of PET and PGI within the same imaging framework may open-up the possibility to exploit more efficiently all radiative emissions excited in the tissue by the ion beam. Here we report on the first pre-clinical implementation of an hybrid PET-PGI imaging system, hereby exploring its performance over several ion-beam species (H, He and C), energies (55 MeV to 275 MeV) and intensities (10$^7$-10$^9$ ions/spot), which are representative of clinical conditions. The measurements were carried out using the pencil-beam scanning technique at the synchrotron accelerator of the Heavy Ion Therapy centre in Heidelberg utilizing an array of four Compton cameras in a twofold front-to-front configuration. The results demonstrate that the hybrid PET-PGI technique can be well suited for relatively low energies (55-155 MeV) and beams of protons. On the other hand, for heavier beams of helium and carbon ions at higher energies (155-275 MeV), range monitoring becomes more challenging owing to large backgrounds from additional nuclear processes. The experimental results are well understood on the basis of realistic Monte Carlo (MC) calculations, which show a satisfactory agreement with the measured data. This work can guide further upgrades of the hybrid PET-PGI system towards a clinical implementation of this innovative technique.

physics.med-ph↗

arXiv2024

First experimental test of a coded-mask gamma camera for proton therapy monitoring

Objective. The objective of the presented study was to evaluate the feasibility of a coded-mask (CM) gamma camera for real-time range verification in proton therapy, addressing the need for a precise and efficient method of treatment monitoring. Approach. A CM gamma camera prototype was tested in clinical conditions. The setup incorporated a scintillator-based detection system and a structured tungsten collimator. The experiment consisted of the irradiation of PMMA phantom with proton beams of energies ranging from 70.51 to 108.15 MeV. Experimental data were benchmarked against Monte Carlo simulations. The distal falloff position was determined for both experimental data and simulations. Main results. The tested CM camera achieved a statistical precision of distal falloff position determination of 1.7 mm for $10^8$ protons, which is consistent with simulation predictions, despite hardware limitations such as non-functional detector pixels. Simulations indicated that a fully operational setup would further improve the performance of the detector. The system demonstrated rate capability sufficient for clinical proton beam intensities and maintained performance without significant dead time. Significance. This study validates the potential of the CM gamma camera for real-time proton therapy monitoring. The technology promises to enhance treatment accuracy and patient safety, offering a competitive alternative to existing approaches such as single-slit and multi-slit systems.

physics.med-ph↗

arXiv2022

A Beam Monitor for Ion Beam Therapy based on HV-CMOS Pixel Detectors

Particle therapy is a well established clinical treatment of tumors. More than one hundred particle therapy centers are in operation world wide. The advantage of using hadrons like protons or carbon ions as particles for tumor irradiation is the distinct peak in the depth dependent energy deposition, which can be exploited to accurately deposit dose in the tumor cells. To guarantee this, high accuracy of monitoring and control of the particle beam is of utmost importance. Before the particle beam enters the patient, it traverses a monitoring system which has to give fast feedback to the beam control system on position and dose rate of the beam while minimally interacting with the beam. The multi-wire chambers mostly used as beam position monitor have their limitations when fast response time is required (drift time). Future developments like MRI-guided ion beam therapy pose additional challenges for the beam monitoring system like tolerance of magnetic fields and acoustic noise (vibrations). Solid-state detectors promise to overcome these limitations and the higher resolution they offer can create additional benefits. This article presents the evaluation of an HV-CMOS detector for beam monitoring, provides results from feasibility studies in a therapeutic beam and summarizes the concepts towards the final large-scale assembly and readout system.

physics.med-ph↗

arXiv2021

Does FLASH deplete Oxygen? Experimental Evaluation for Photons, Protons and Carbon Ions

Purpose: To investigate experimentally, if FLASH irradiation depletes oxygen within water for different radiation types such as photons, protons and carbon ions. Methods: This study presents measurements of the oxygen consumption in sealed, 3D printed water phantoms during irradiation with X-rays, protons and carbon ions at varying dose rates up to 340 Gy/s. The oxygen measurement was performed using an optical sensor allowing for non-invasive measurements. Results: Oxygen consumption in water only depends on dose, dose rate and linear energy transfer (LET) of the irradiation. The total amount of oxygen depleted per 10 Gy was found to be 0.04 - 0.18 % atm for 225 kV photons, 0.04 - 0.25 % atm for 224 MeV protons and 0.09 - 0.17 % atm for carbon ions. consumption depends on dose rate by an inverse power law and saturates for higher dose rates because of self-interactions of radicals. Higher dose rates yield lower oxygen consumption. No total depletion of oxygen was found for clinical doses. Conclusions: FLASH irradiation does consume oxygen, but not enough to deplete all the oxygen present. For higher dose rates, less oxygen was consumed than at standard radiotherapy dose rates. No total depletion was found for any of the analyzed radiation types for 10 Gy dose delivery using FLASH.

physics.med-ph↗

arXiv2013

Absorbed Dose in Ion Beams: Comparison of Ionisation and Fluence-based Measurements

A direct comparison measurement of fluorescent nuclear track detectors (FNTDs) and a thimble ionisation chamber is presented. Irradiations were performed using monoenergetic protons (142.66 MeV, 3*10^6 1/cm2) and carbon ions (270.55 MeV/u, 3*10^6 1/cm2). It was found that absorbed dose to water values as determined by fluence measurements using FNTDs are, in case of protons, in good agreement (2.4 %) with ionization chamber measurements, if slower protons and Helium secondaries were accounted for by an effective stopping power. For carbon, however, a significant discrepancy of 4.5 % was seen, which could not be explained by fragmentation, uncertainties or experimental design. The results rather suggest a W-value of 32.10 eV +/- 2.6 %. Additionally, the abundance of secondary protons expected from Monte-Carlo transport simulation was not observed.

physics.med-ph↗