Detector response and dose calculation lateral to material interfaces for 6 MV photon beam
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-10-21 |
| Journal | Journal of Applied Clinical Medical Physics |
| Authors | Jonas Ringholz, Otto A. Sauer, Sonja Wegener |
| Institutions | Universitätsklinikum Wßrzburg |
| Analysis | Full AI Review Included |
Technical Documentation: MPCVD Diamond for High-Resolution Dosimetry in Inhomogeneous Media
Section titled âTechnical Documentation: MPCVD Diamond for High-Resolution Dosimetry in Inhomogeneous Mediaâ6CCVD Analysis of âDetector response and dose calculation lateral to material interfaces for 6 MV photon beamâ
This document analyzes the application of synthetic diamond detectors in high-precision medical physics dosimetry, specifically focusing on the challenges of dose calculation near material interfaces (inhomogeneities). The findings strongly validate the use of high-quality Single Crystal Diamond (SCD) for advanced radiotherapy quality assurance and research.
Executive Summary
Section titled âExecutive Summaryâ- Application Focus: Validation of dose calculation algorithms in highly inhomogeneous media (aluminum cylinder simulating bone in a water phantom) using a 6 MV photon beam.
- Detector Performance: The Synthetic Diamond (microDiamond, PTW 60019) and the PinPoint Ion Chamber demonstrated the most consistent and reliable dose response near the high-density interface.
- Key Achievement: The microDiamond showed a highly similar response to the ion chamber, with differences contained within 1% (10x10 cm² field) and 3% (2x2 cm² field) at 3 mm from the cylinder edge.
- Material Advantage: Diamondâs solid-state nature and small active volume minimize the volume averaging effect and energy dependence, making it ideal for steep dose gradients and non-equilibrium situations.
- Recommendation: The study recommends the use of at least two different detector types, specifically a combination of a solid-state detector (like microDiamond) and a small ionization chamber, for verifying dose calculations near interfaces.
- 6CCVD Value Proposition: 6CCVD specializes in providing the high-purity, custom-dimensioned SCD substrates necessary to manufacture next-generation, high-spatial-resolution diamond detectors for clinical and research applications.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper detailing the experimental setup and key results for the synthetic diamond detector.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Photon Beam Energy | 6 | MV | Elekta Synergy linac |
| Aluminum Cylinder Density | 2.8 | g/cmÂł | Simulating bone (Zeff similar to bone) |
| Measurement Depth | 7.5 | cm | Radial profiles in water phantom |
| Field Sizes Tested | 10x10 and 2x2 | cm² | Large field (exceeding) and small field (irradiating only cylinder) |
| Synthetic Diamond Radius (rd) | 1.1 | mm | Detector area according to recommended mounting direction |
| SCD Effective Measurement Point (reff) | 1.0 | mm | Axial orientation |
| SCD Signal Increase (10x10 cm² field) | 1.7 | % | At 3 mm distance from cylinder edge (x = 18 mm) |
| SCD vs. Ion Chamber Consistency (10x10 cm² field) | < 1 | % | Difference at x = 18 mm |
| SCD vs. Ion Chamber Consistency (2x2 cm² field) | < 3 | % | Difference at x = 18 mm |
| TPS Algorithm Deviation (Collapsed Cone) | Up to 3 | % | Difference from detector values at 3 mm from cylinder |
Key Methodologies
Section titled âKey MethodologiesâThe experiment focused on comparing detector responses and dose calculations in a highly controlled, inhomogeneous phantom setup.
- Phantom Construction: An aluminum cylinder (3 cm diameter, 3 cm height) was inserted axially into a PTW MP3-XS water phantom.
- Irradiation: The setup was irradiated with a 6 MV photon beam at 0° gantry angle, using two nominal field sizes (10x10 cm² and 2x2 cm²).
- Detector Deployment: Detectors, including the PTW microDiamond (SCD), were mounted consecutively in the phantom holder. Radial measurements were taken at a depth of 7.5 cm, starting as close to the lateral cylinder surface as detector dimensions allowed.
- SCD Operation: The microDiamond was used in axial orientation. No biasing voltage was applied, and the detector was pre-irradiated as per manufacturer recommendations.
- Film Dosimetry: EBT3 Gafchromic film strips were mounted between two halves of the aluminum cylinder to provide high-resolution dose profiles for comparison.
- Computational Validation: Measured profiles were compared against calculations from commercial Treatment Planning Systems (TPS) (Pinnacle, Eclipse) using algorithms like Collapsed Cone and Acuros XB, as well as EGSnrc Monte Carlo simulations.
- Data Analysis: Results were normalized to the signal obtained centrally in the 10x10 cm² water field without the cylinder present. Ratios of profiles (with cylinder / without cylinder) were calculated to isolate the effect of the inhomogeneity.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research confirms that Single Crystal Diamond (SCD) detectors are essential tools for accurate dosimetry in complex, high-gradient environments like those found near bone or metal implants. 6CCVD is uniquely positioned to supply the foundational MPCVD diamond materials required to replicate and advance this critical research.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the high spatial resolution and radiation hardness demonstrated by the microDiamond detector, Optical Grade Single Crystal Diamond (SCD) is the required material.
| 6CCVD Material | Recommended Specifications | Application Context |
|---|---|---|
| Optical Grade SCD | Thickness: 0.1 Âľm to 500 Âľm | Ideal for defining the precise, small active volume (detection layer) necessary to minimize volume averaging in steep dose gradients. |
| High-Purity SCD Substrates | Plates/Wafers up to 125 mm | Used as the base material for fabricating arrays or large-area detectors for comprehensive QA mapping. |
| Boron-Doped Diamond (BDD) | Custom Doping Levels | Applicable for extending research into BDD detectors, which can offer unique electrical properties for specialized radiation detection or electrochemical sensing applications. |
Customization Potential
Section titled âCustomization PotentialâThe study noted that detector outer dimensions are a major limitation, preventing measurements very close to the interface. 6CCVDâs customization capabilities directly address this challenge by enabling the fabrication of ultra-small, high-precision detectors.
| Research Requirement | 6CCVD Customization Service | Benefit to Researcher |
|---|---|---|
| Ultra-Small Active Area | Precision Laser Cutting & Shaping | Allows for the creation of custom-shaped SCD elements with lateral dimensions significantly smaller than 1 mm, enabling measurements closer to the material interface (e.g., < 0.6 mm). |
| Electrode Fabrication | In-House Custom Metalization | We offer deposition of Au, Pt, Pd, Ti, W, and Cu contacts, crucial for creating reliable electrode structures on the SCD surface for detector fabrication. |
| Surface Finish for Lithography | Ultra-Smooth Polishing (Ra < 1 nm) | Ensures the SCD surface is atomically smooth, which is critical for high-yield lithography and subsequent processing steps required to define the detector geometry. |
| Large-Scale Validation | PCD Wafers up to 125 mm | For developing large-area detector arrays or phantoms, 6CCVD provides Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, polished to Ra < 5 nm. |
Engineering Support
Section titled âEngineering SupportâThe authors recommend using a combination of a solid-state detector and a small ionization chamber, noting that the microDiamond and PinPoint chamber produced the most consistent results. 6CCVDâs in-house PhD team possesses deep expertise in material science and radiation physics, and can assist engineers and scientists in selecting the optimal diamond material specifications (purity, thickness, doping, and orientation) for similar Medical Dosimetry and Radiotherapy QA projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Background Dose calculation around inhomogeneities is challenging for many algorithms. A validation of dose distributions in these conditions is not straightforward, as detector response close to material interfaces is affected by the nonâequilibrium situation, the changing energy spectrum and the volume effect in a steep dose gradient. Purpose Detector response lateral to an inhomogeneity of high density was studied, mimicking the situation of bone surrounded by soft tissue. Methods Profiles obtained with different detectors (diodes, ion chamber, synthetic diamond) in water in the vicinity of an aluminum cylinder were compared. Dose deposition was also calculated with different commercial treatment planning systems and algorithms as well as using Monte Carlo simulations within and lateral to the cylinder and compared to measurements. Results Dose deposition in the vicinity of an inserted aluminum cylinder changes and is registered by the detectors to a different degree. The ion chamber shows the largest change irradiated with a 10Ă10 cm 2 at 3 mm distance from the cylinder surface (2.5%), followed by the synthetic diamond (1.7%), then the unshielded (1.4%) and finally the shielded diode (1.0%). Dose calculated by different commercial dose engines differed up to 3% at that point from the detector values (Collapsed Cone). Conclusions Dose calculation near inhomogeneities depends on the used algorithm, dose measurements in the same region differ depending on the detector type used. We recommend verification of dose calculation with second type of algorithm and measurements with at least two detector types.