Feasibility study for dose calculation with a radiation treatment planning system using a fixed-size electron cone applicator for small electron fields

At a Glance

Metadata	Details
Publication Date	2025-08-14
Journal	PLoS ONE
Authors	Su Chul Han, Min Cheol Han, Jihun Kim, Heerim Nam, Jin Sung Kim
Institutions	Sungkyunkwan University, Yonsei University
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for High-Precision Electron Dosimetry

Executive Summary

This research validates a critical methodology for integrating specialized, fixed-size electron cone applicators into commercial Treatment Planning Systems (TPS) for small-field electron beam radiotherapy. The study relies heavily on the precision and stability of micro-diamond detectors for accurate dosimetric measurements, directly aligning with 6CCVD’s expertise in high-purity MPCVD diamond materials.

Application Validation: Confirmed the feasibility of calculating Monitor Units (MU) and dose distributions for small electron fields (2-5 cm) using an indirect scaling factor approach within a commercial TPS (RayStation eMC algorithm).
Dosimetric Accuracy: Achieved exceptional agreement, with the difference between indirect TPS calculations and direct measurements for the fixed-size electron cone applicator remaining within 1.0%.
Detector Performance: The use of a micro-diamond detector (PTW 60019) was essential for obtaining high-resolution beam profiles and PDD curves necessary for small-field dosimetry validation.
Gamma Index Success: High-confidence results were confirmed by gamma analysis, showing passing rates of >99% for beam profiles (2%/2 mm criteria) and 2D dose distributions (3%/3 mm criteria).
Material Requirement: The study underscores the necessity of high-quality, radiation-hard diamond material (Single Crystal Diamond, SCD) for fabricating reliable, high-spatial-resolution detectors required for modern small-field radiotherapy quality assurance (QA).
6CCVD Value: 6CCVD supplies the foundational SCD material and custom metalization services required to manufacture next-generation micro-diamond detectors and specialized collimation components.

Technical Specifications

The following hard data points were extracted from the research paper, focusing on the experimental parameters and performance metrics relevant to high-precision dosimetry.

Parameter	Value	Unit	Context
Electron Beam Energy	6	MeV	Used for all dosimetric measurements
Detector Type	Micro-Diamond Detector	PTW 60019	Used for PDD, beam profile, and OF measurements
Small Field Sizes (Diameter)	2, 3, 4, 5	cm	Fixed-size electron cone applicators
Reference Field Size	10 x 10	cm	Used for Output Factor (OF) calculation
Source-Surface Distance (SSD)	95, 100, 105	cm	Evaluated SSD-dependent dosimetric variations
MU Difference (Indirect TPS vs. Direct)	< 1.0	%	Fixed-size electron cone applicator MU calculation
Gamma Pass Rate (Beam Profiles)	> 99	%	2%/2 mm criteria
Gamma Pass Rate (Depth Dose)	> 95	%	1%/1 mm criteria
Gamma Pass Rate (2D Dose Dist.)	> 99	%	3%/3 mm criteria (Gafchromic film)
Dose Grid Resolution (TPS)	2	mm	Monte Carlo (eMC) algorithm setting
Particles per Unit Area (TPS)	1,000,000	cm^-3	Monte Carlo (eMC) algorithm setting

Key Methodologies

The experiment followed a two-step process to validate the indirect calculation method for specialized electron applicators, relying on high-fidelity measurements using the micro-diamond detector.

Dosimetric Data Acquisition (Step 1): Beam quality (R₅₀), Percentage Depth Dose (PDD) curves, beam profiles (cross- and in-plane), and Output Factors (OFs) were measured for both the standard Cerrobend cutout applicator and the fixed-size electron cone applicator.
Detector Use: Measurements were performed using a micro-diamond detector (PTW 60019) within a Beamscan 3D water phantom, ensuring high spatial resolution necessary for small-field characterization.
Profile Measurement Depths: Beam profiles were specifically measured at five critical depths: R₁₀₀, R₉₀, R₇₀, R₅₀, and 1/2 R₉₀, at a fixed SSD of 100 cm.
TPS Modeling: The standard Cerrobend cutout applicator was modeled in the RayStation TPS (v. 5.0) using the Monte Carlo (eMC V.3.2) algorithm, which is preferred over pencil beam algorithms for small electron fields and high-density materials.
Indirect MU Calculation (Step 2): The Monitor Unit (MU) for the fixed-size electron cone applicator (MU_{FC for TPS}) was calculated indirectly by scaling the TPS-calculated MU for the standard applicator (MU_{C from TPS}) using the measured relative output factor (OF_relative).
2D Dose Verification: Two-dimensional dose distributions were measured using Gafchromic EBT3 film at a depth of 14 mm in a slab phantom and compared against TPS calculations using gamma evaluation (3%/3 mm criteria).

6CCVD Solutions & Capabilities

This research confirms the critical role of high-performance diamond detectors in validating advanced radiotherapy techniques. 6CCVD is uniquely positioned to supply the core materials and custom fabrication services required to replicate and extend this research, particularly in developing next-generation micro-diamond detectors and specialized beam collimation components.

Applicable Materials & Components	6CCVD Capability & Value Proposition
Micro-Diamond Detector Fabrication	Optical Grade Single Crystal Diamond (SCD): The PTW 60019 detector relies on high-purity SCD. 6CCVD provides high-quality SCD plates (up to 500 µm thick) with extremely low nitrogen content, ensuring superior charge collection efficiency, minimal signal degradation, and exceptional radiation hardness for high-dose-per-pulse environments.
High-Precision Surface Finish	Ultra-Low Roughness Polishing: Achieving accurate dosimetry requires minimizing surface scatter. Our SCD material is polished to an industry-leading surface roughness of Ra < 1 nm, critical for precise detector geometry and reliable signal output in small fields.
Custom Detector Geometries	Custom Dimensions & Thickness: We offer SCD wafers in custom dimensions, essential for creating micro-detectors tailored to specific field sizes (e.g., 2 cm diameter fields). We can supply SCD substrates up to 500 µm thick and up to 10x10 mm in size.
Electrical Contacting	Advanced Metalization Services: Detector fabrication requires precise electrical contacts. 6CCVD offers in-house metalization capabilities, including Au, Pt, Pd, and Ti, allowing researchers to prototype and manufacture custom diamond detectors with optimized ohmic contacts for reliable signal extraction.
Specialized Applicator/Collimator Development	Polycrystalline Diamond (PCD) Plates: For future studies exploring diamond-based collimation (replacing Cerrobend or stainless steel cones), 6CCVD offers large-area PCD plates up to 125 mm in diameter and up to 500 µm thick, providing superior thermal management and mechanical stability compared to traditional materials.
Engineering Support	In-House PhD Expertise: 6CCVD’s engineering team, composed of PhD material scientists, can assist researchers in selecting the optimal diamond material (SCD vs. PCD vs. BDD) and specification for specialized electron beam dosimetry and high-energy physics applications.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Objective This study aims to evaluate the feasibility of radiation treatment planning using a commercial treatment planning system (TPS) for small fixed-size electron cone electron applicators not natively supported by the TPS. Methods Dosimetric characteristics, including beam profiles and output factors (OFs), were compared between a 6 MeV electron beam collimated by a small fixed-size electron cone applicator and a cerrobend cutout-based general applicator. Measurements were performed using a micro-diamond detector in a water phantom for field sizes of 2, 3, 4, and 5 cm. The monitor units (MUs) from the TPS were compared with direct measurements. To estimate the MU for the fixed-size electron cone applicator using the TPS, the relative OFs were defined as the ratio of the OFs for the fixed-size electron cone and general applicators. Dose distributions obtained from the TPS were validated against measurements using Gafchromic films, ensuring accuracy. Results Gamma analysis showed a passing rate >95% with 1%/1 mm criteria for depth dose comparisons and >99% with 2%/2 mm criteria for beam profiles. The general applicator’s OFs were consistently higher across all measured field sizes. The MU difference between the TPS and measurements was within 2.0%, while the difference between indirect TPS calculations and direct measurements for the fixed-size electron cone applicator remained within 1.0%. Dose distribution analysis showed >99% agreement (3%/3 mm) between the 2D dose distribution obtained using film in the fixed-size electron cone applicator and that calculated by the TPS of cerrobend cutout-based applicator. Conclusion The results demonstrate the feasibility of calculating monitor units and dose distributions for small fixed-size electron cone applicators using a commercial TPS combined with relative output factors. This approach offers a reliable method for dose calculation in specialized electron therapy applications.

Tech Support

Original Source

DOI: https://doi.org/10.1371/journal.pone.0324722

References

2006 - Review of electron beam therapy physics [Crossref]
2015 - Assessment of clinically relevant dose distributions in pelvic IOERT using Gafchromic EBT3 films [Crossref]
2015 - Characterization of a microDiamond detector in high-dose-per-pulse electron beams for intra operative radiation therapy [Crossref]
2018 - Evaluation of prototype of improved electron collimation system for Elekta linear accelerators [Crossref]
2015 - AAPM Medical Physics Practice Guideline 5.a.: Commissioning and QA of Treatment Planning Dose Calculations - Megavoltage Photon and Electron Beams [Crossref]
2015 - Comparison between small radiation therapy electron beams collimated by Cerrobend and tubular applicators [Crossref]
2009 - Recommendations for clinical electron beam dosimetry: supplement to the recommendations of Task Group 25 [Crossref]
2020 - Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG-55 [Crossref]
2014 - Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71 [Crossref]
2013 - Radiotherapy electron beams collimated by small tubular applicators: characterization by silicon and diamond diodes [Crossref]