Design and dosimetric characterization of a transportable proton minibeam collimation system
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-12-17 |
| Journal | Frontiers in Oncology |
| Authors | Mabroor Ahmed, Elke Beyreuther, Sebastian Gantz, Felix Horst, Juergen Meyer |
| Institutions | Klinikum rechts der Isar, Technical University of Munich |
| Citations | 1 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Proton Minibeam Dosimetry
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Proton Minibeam DosimetryâExecutive Summary
Section titled âExecutive SummaryâThis research successfully characterized a transportable mechanical collimation system for Proton Minibeam Radiation Therapy (pMBRT), validating the use of diamond detectors for high-resolution online dosimetry.
- Core Achievement: Demonstrated a transportable pMBRT setup achieving a Peak-to-Valley Dose Ratio (PVDR) of 10 (150MeV) and 14 (50.5MeV) in a 5mm PMMA phantom depth.
- High-Resolution Dosimetry: A synthetic Single Crystal Diamond (SCD) microDiamond detector (active volume 1”m thick) was successfully utilized for online dosimetry, offering a crucial alternative to time-intensive film methods.
- Material Requirement: The study highlights the critical need for ultra-thin, high-purity Single Crystal Diamond (SCD) materials to achieve the necessary spatial resolution (beam width 250”m, ctc 1000”m).
- Key Challenge Identified: Significant discrepancies (up to 21%) were observed between microDiamond and film readings in the peak dose region, necessitating position-specific correction factorsâa challenge directly related to the detector material and geometry.
- 6CCVD Value Proposition: 6CCVD is uniquely positioned to supply the high-purity SCD wafers required for next-generation microDiamond detectors and offers custom Polycrystalline Diamond (PCD) or thick SCD substrates as radiation-hard alternatives for collimator fabrication.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Minibeam Width | 250 | ”m | Mechanical collimation goal |
| Target Center-to-Center (ctc) Distance | 1000 | ”m | Mechanical collimation goal |
| Achieved PVDR (Dresden) | 10 | Ratio | 150MeV beam, 5mm depth |
| Achieved PVDR (Seattle) | 14 | Ratio | 50.5MeV beam, 5mm depth |
| Achieved FWHM (Dresden) | 265 | ”m | Measured with EBT3 film |
| Achieved FWHM (Seattle) | 320 | ”m | Measured with EBT3 film |
| Proton Beam Energy (Dresden) | 150 | MeV | University Proton Therapy Dresden |
| Proton Beam Energy (Seattle) | 50.5 | MeV | University of Washington Medical Center |
| MicroDiamond Active Volume Thickness | 1 | ”m | SCD detector (PTW 60019) |
| Collimator Material | Brass | N/A | Pre-collimator (3cm thick), Minibeam Collimator (5cm thick) |
| Collimator Distance (Air Gap) | 10 | mm | Between collimator exit and PMMA phantom |
| Proton Loss Rate | 99.5 | % | Initial protons lost during selection process |
Key Methodologies
Section titled âKey MethodologiesâThe experimental setup and characterization relied on a combination of Monte Carlo simulation and physical dosimetry at two distinct proton facilities.
- Simulation & Optimization: Monte Carlo simulations were performed using the Geant4 toolkit (TOPAS) to optimize system parameters (pre-collimator slit opening, PMMA block thickness, collimator distance) to maximize PVDR while maintaining an acceptable valley dose rate.
- Collimator Design: The system utilized a two-stage mechanical collimation setup: a 3cm thick brass pre-collimator (4mm slit opening) followed by a 5cm thick brass minibeam collimator (11 slits, 250”m width, 1mm ctc).
- Beam Homogenization: A Polymethylmethacrylate (PMMA) block (4cm for 150MeV, 0.5cm for 50.5MeV) was placed between the collimators to ensure uniform proton distribution at the minibeam collimator surface.
- Dosimetry Protocol: Dose profiles were measured at a fixed depth of 5mm in a PMMA phantom using two methods:
- Film Dosimetry: Gafchromic EBT3 films (high spatial resolution, 48-hour stabilization time).
- Online Dosimetry: MicroDiamond detector (synthetic SCD Schottky diode) operated in edge-on mode for high spatial resolution, read out by an electrometer.
- Alignment and Precision: Components were mounted on rotational and linear translation stages (micrometer scale precision) to achieve angular alignment accuracy down to 0.02° and translational precision of 1mm.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful implementation of high-resolution proton minibeam dosimetry relies directly on the quality and precision of Single Crystal Diamond (SCD) materials. 6CCVD is an industry leader in supplying custom MPCVD diamond solutions necessary to replicate, refine, and advance this research.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Solution | Key Specification Match |
|---|---|---|
| High-Resolution Dosimetry | Optical Grade SCD Wafers | SCD is the base material for microDiamond detectors. We offer high-purity, low-defect SCD plates up to 500”m thick, ideal for fabricating next-generation detectors requiring superior charge collection efficiency. |
| Ultra-Thin Active Volume | Custom SCD Films | The paper used a 1”m active layer. 6CCVD specializes in ultra-thin SCD films, offering thicknesses from 0.1”m to 500”m, enabling detectors with even higher spatial resolution and reduced volume effects. |
| Radiation-Hard Collimation | Thick SCD or PCD Substrates | While brass was used, diamond offers superior radiation hardness and thermal conductivity. 6CCVD can supply thick SCD or PCD substrates (up to 10mm) for collimators, ensuring long-term stability in high-flux environments. |
| Custom Detector Fabrication | Boron-Doped Diamond (BDD) | For custom detector designs (e.g., p-n junctions or ohmic contacts), 6CCVD provides BDD material, allowing for tailored conductivity and doping profiles. |
Customization Potential for pMBRT Systems
Section titled âCustomization Potential for pMBRT SystemsâTo address the precision and material requirements of advanced pMBRT systems, 6CCVD offers comprehensive engineering and fabrication services:
- Custom Dimensions: We provide SCD and PCD plates/wafers up to 125mm in diameter, allowing researchers to design large-area collimators or detector arrays.
- Precision Processing: We offer high-precision laser cutting and etching services to create custom slit geometries (e.g., 250”m width, 1000”m ctc) in diamond substrates, potentially offering sharper beam edges than brass.
- Surface Finish: For optimal detector performance and minimal scattering, 6CCVD guarantees ultra-smooth polishing: Ra < 1nm for SCD and Ra < 5nm for inch-size PCD.
- Metalization Services: We offer in-house metalization (Au, Pt, Pd, Ti, W, Cu) crucial for fabricating Schottky diodes or creating precise contact pads on custom diamond detectors, addressing the need for robust electrical interfaces mentioned in the paper.
Engineering Support
Section titled âEngineering SupportâThe observed discrepancies in microDiamond peak dose measurements (up to 21% deviation) highlight the complexity of position-specific correction factors in high-gradient fields. 6CCVDâs in-house PhD team, specializing in diamond material science and radiation physics, can assist researchers in:
- Material Selection: Optimizing SCD purity and thickness to minimize differential response effects in high-gradient dose fields.
- Detector Geometry: Consulting on optimal detector design (e.g., active volume dimensions, edge-on orientation) for similar Proton Minibeam Dosimetry projects.
- Custom Fabrication: Ensuring that custom SCD wafers meet the stringent requirements for spatial resolution (e.g., 0.1”m thickness) necessary for future microbeam research.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).
View Original Abstract
Background Proton Minibeam Radiation Therapy has shown to widen the therapeutic window compared to conventional radiation treatment in pre-clinical studies. The underlying biological mechanisms, however, require more research. Purpose The purpose of this study was to develop and characterize a mechanical collimation setup capable of producing 250”m wide proton minibeams with a center-to-center distance of 1000”m. Methods To find the optimal arrangement Monte Carlo simulations were employed using the Geant4 toolkit TOPAS to maximize key parameters such as the peak-to-valley dose ratio (PVDR) and the valley dose rate. The experimental characterization of the optimized setup was carried out with film dosimetry at the University Proton Therapy beamline in Dresden and the proton beamline of the University of Washington Medical Center in Seattle with 150MeV and 50.5MeV, respectively. A microDiamond detector (PTW, Freiburg, Germany) was utilized at both beamlines for online proton minibeam dosimetry. Results A PVDR of 10 was achieved in Dresden and a PVDR of 14 in Seattle. Dosimetry measurements were carried out with EBT3 films at a depth of 5mm in a polymethylmethacrylate (PMMA) phantom. When comparing film dosimetry with the microDiamond, excellent agreement was observed in the valleys. However, the peak dose showed a discrepancy of approximately 10% in the 150MeV beam and 20% in the 50.5MeV beam between film and microDiamond. Discussion The characteristics of the minibeams generated with our system compares well with those of other collimated minibeams despite being smaller. The deviations of microDiamond measurements from film readings might be subject to the diamond detector responding differently in the peak and valley regions. Applying previously reported correction factors aligns the dose profile measured by the microDiamond with the profile acquired with EBT3 films in Dresden. Conclusion The novel proton minibeam system can be operated independently of specific beamlines. It can be transported easily and hence used for inter-institutional comparative studies. The quality of the minibeams allows us to perform in vitro and in vivo experiments in the future. The microDiamond was demonstrated to have great potential for online dosimetry for proton minibeams, yet requires more research to explain the observed discrepancies.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 1912 - Roentgentiefentherapie mit metallnetzschutz
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