Static small radiation fields and detectors for relative small field dosimetry in external beam radiotherapy
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-26 |
| Journal | Doklady BGUIR |
| Authors | V. S. Piskunou, Đ. Đ. ТаŃŃŃин |
| Institutions | N.N. Alexandrov National Cancer Centre, State Healthcare Institution âRegional Clinical Oncological Dispensaryâ |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Small Field Dosimetry
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Small Field DosimetryâSource Paper: Piskunou V.S., Tarutin I.G. Static small radiation fields and detectors for relative small field dosimetry in external beam radiotherapy. Doklady BGUIR. 2021; 19(5): 94-101.
Executive Summary
Section titled âExecutive SummaryâThis documentation analyzes the requirements for relative small field dosimetry in advanced External Beam Radiotherapy (EBRT) techniques (e.g., SRS, SBRT, IMRT), highlighting the critical role of MPCVD diamond detectors.
- Application Focus: Accurate relative dosimetry in small static photon fields, typically <4 x 4 cm, where traditional ionization chambers fail due to volume averaging.
- Physical Challenges: Dosimetry uncertainty is driven by the loss of Lateral Charged Particle Equilibrium (LCPE), source occlusion effects, and the detectorâs volume averaging effect relative to the small field size.
- Detector Recommendation: The analysis identifies diamond detectors, liquid ionization chambers, and silicon diodes as the most suitable solid-state options for fields <2 x 2 cm.
- Diamond Advantage: Diamond detectors are highly recommended due to their near water/tissue equivalence, high spatial resolution, and suitability for high dose gradient regions (stereotactic radiosurgery).
- Material Requirement: Successful implementation requires high-purity Single Crystal Diamond (SCD) with precisely controlled active volumes and stable metal contacts (e.g., gold), capabilities offered by 6CCVD.
- 6CCVD Value Proposition: We provide custom-dimensioned SCD wafers and plates, tailored thickness (down to 0.1 Âľm), and internal metalization services (Au, Pt, Ti) necessary to manufacture optimized, high-performance diamond dosimeters.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points and requirements were extracted from the analysis regarding small field characteristics and detector geometry.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Small Field Definition (Minimum) | <2 x 2 | cm | Critical for Stereotactic Radiotherapy (SRS) |
| Small Field Definition (General) | 2 x 2 - 4 x 4 | cm | General small field dosimetry |
| Classic IC Volume | 0.3 - 0.6 | cmÂł | Too large; unsuitable for small fields |
| Micro IC Volume Range | 0.002 - 0.01 | cmÂł | Suitable for fields <2 x 2 cm |
| Silicon Diode Volume (Typical) | <0.2 | mmÂł | High resolution, low volume averaging |
| Liquid IC Voltage Requirement | 800 - 1000 | V | High voltage needed for operation |
| Radiochromic Film Resolution | 0.1 - 0.2 | mm | Limited by densitometer scanning resolution |
| Diamond Detector Suitability | Suitable | N/A | Recommended for fields <2 x 2 cm and 2 x 2 cm - 4 x 4 cm |
Key Methodologies
Section titled âKey MethodologiesâThe research paper employed a comprehensive analytical review methodology to evaluate the suitability of various detectors for relative small field dosimetry.
- Definition of Small Field Conditions: Established the three physical conditions under which an external photon beam is designated as a small field:
- Loss of Lateral Charged Particle Equilibrium (LCPE).
- Partial source occlusion by collimating devices.
- Detector size being comparable to or larger than the radiation field size (leading to volume averaging).
- Analysis of Dosimetric Errors: Investigated the impact of these conditions on clinical dosimetry, specifically focusing on the effects of volume averaging, fluence perturbation, and detector positioning uncertainty.
- Review of Existing Detectors: Conducted an extensive review of detectors suitable for relative small field dosimetry, including liquid ionization chambers, silicon diodes, organic scintillators, and diamond detectors.
- Evaluation Criteria: Analyzed detector performance based on critical requirements:
- Spatial resolution (small active volume).
- Dependence on beam direction and energy.
- Dependence on absorbed dose rate (dose-per-pulse).
- Water/tissue equivalence.
- Categorization and Recommendation: Categorized detectors based on their suitability for fields <2 x 2 cm and 2 x 2 cm - 4 x 4 cm, concluding that solid-state detectors (especially diamond) are necessary for the smallest fields.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research confirms that diamond detectors are essential for accurate relative dosimetry in modern radiotherapy, particularly in high-gradient, small-field applications like SRS. 6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials required to meet these stringent technical demands.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, high-purity, electronic-grade diamond is mandatory for optimal signal-to-noise ratio and stability.
- Primary Material: Optical Grade Single Crystal Diamond (SCD). SCD offers superior charge carrier mobility and purity, minimizing noise and maximizing sensitivity, which is crucial for accurate measurements in small fields where signal strength is limited.
- Alternative (If Doping is Required): Boron-Doped Diamond (BDD). While the paper focuses on undoped diamond, BDD can be engineered for specific conductivity requirements, potentially simplifying electrode design or enhancing stability under certain operating conditions.
Customization Potential
Section titled âCustomization PotentialâThe paper emphasizes that the detectorâs active volume size must be precisely known and minimized to overcome the volume averaging effect (Fig. 3). 6CCVDâs custom manufacturing capabilities directly address this need.
| Requirement from Paper | 6CCVD Customization Capability | Technical Benefit for Dosimetry |
|---|---|---|
| Precise Active Volume Control | Custom SCD thickness from 0.1 Âľm up to 500 Âľm. | Allows engineers to define the exact sensitive depth, minimizing volume averaging in fields <2 x 2 cm. |
| Custom Detector Geometry | Plates/wafers up to 125 mm, with in-house laser cutting. | Enables the creation of highly specialized, small-footprint detector geometries required for complex MLC-defined fields. |
| Stable Electrical Contacts | Internal Metalization Services (Au, Pt, Pd, Ti, W, Cu). | Fabrication of thin, uniform metal contacts (e.g., gold contacts mentioned in the paper) directly onto the SCD surface, ensuring stable polarization and reliable signal collection. |
| Surface Quality | Polishing to Ra < 1 nm (SCD). | Ensures optimal surface preparation for subsequent metalization and device integration, reducing surface defects that could contribute to noise or instability. |
Engineering Support
Section titled âEngineering SupportâThe challenges identified in the paperâsuch as pre-irradiation stabilization, dose rate dependence correction, and optimization of active volume geometryârequire deep material science expertise.
- Material Selection for High-Gradient Fields: 6CCVDâs in-house PhD team specializes in optimizing diamond material properties (purity, defect density, crystal orientation) to minimize polarization effects and dose rate dependence, critical for Stereotactic Radiosurgery (SRS) projects.
- Geometry Optimization: We assist clients in defining the ideal SCD thickness and lateral dimensions to achieve the necessary spatial resolution while maintaining sufficient signal output for relative dose measurements.
- Global Supply Chain: We offer reliable global shipping (DDU default, DDP available) to ensure researchers and clinical engineers receive their custom diamond materials promptly, regardless of location.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The aim of this work is to analyze existing detectors for the relative dosimetry of small radiation fields in external beam radiation therapy and the requirements for them, consider the problems in carrying out dosimetry of small radiation fields, determine the physical conditions under which an external photon beam can be designated as a small field. In modern radiation therapy, there is an increase in the use of small static fields, which is facilitated by the general availability of standard and optional multileaf collimators and new generation treatment machines of various designs. There is growing interest in the use of such radiation techniques as stereotactic radiosurgery, stereotactic body radiotherapy, intensity modulated radiotherapy, which are widely used small fields. This has increased the uncertainties in clinical dosimetry, especially for small fields. Accurate dosimetry of small fields is important when commissioning linear accelerators and is a difficult task, especially for very small fields used in stereotactic radiotherapy. In the course of the work, a study of topical problems in the dosimetry of small radiation fields in external beam radiation therapy has been carried out. The physical conditions under which the external photon beam can be designated as a small field are considered. A review and analysis of existing detectors for the relative dosimetry of small radiation fields, as well as an analysis of the requirements for the character. The analysis revealed that liquid ionization chambers, silicon diodes, diamond detectors, organic scintillators, radiochromic films, thermoluminescent dosimeters and optically stimulated luminescence detectors are considered suitable for relative dosimetry of small photon fields and are recommended for use in clinics where radiotherapy is performed.