Commissioning of a precision preclinical 200 kV x‐ray irradiator based on modular adaptations
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-03-26 |
| Journal | Medical Physics |
| Authors | Lorenz Wolf, Peter Kuess, Sabine Leitner, Dietmar Georg, Barbara Knäusl |
| Institutions | Fachhochschule Wiener Neustadt, Medical University of Vienna |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details the modular adaptation and commissioning of an industrial 200 kV X-ray unit to create a high-precision preclinical irradiation platform, serving as a cost-effective reference system for particle therapy studies.
- Core Modification: An industrial kilovoltage X-ray unit was adapted with a horizontal beam line and a custom dual brass collimation system, offering variable apertures from 5 mm to 30 mm.
- Modular Components: Dedicated 3D-printed modular components, including a multimodal mouse bedding unit, a small field dosimetry phantom (SFDP), and a tissue-equivalent QA phantom, were developed to ensure reproducible positioning and streamlined workflow.
- TPS Integration: A commercial Treatment Planning System (TPS), µ-RayStation 8B, was successfully commissioned using acquired beam data (PDDs, LDPs) and a GPU-based Monte Carlo dose engine.
- Dosimetric Accuracy: The resulting beam model was validated with high accuracy, showing a maximum relative dose deviation of 1.7% across various depths and apertures, well within the estimated total uncertainty range (2.4-4.7%).
- Preclinical Performance: In silico planning for a 5 mm mouse brain target achieved excellent coverage, demonstrated by a Homogeneity Index (HI) of (9.9 ± 0.7)%.
- Verification Success: Subject-specific QA measurements confirmed the system’s reliability, achieving a median gamma passing rate of 100% (using a strict 1%/1 mm acceptance criterion).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| X-ray Unit | YXLON Maxishot | - | Industrial kilovoltage system |
| Tube Voltage / Current | 200 / 20 | kV / mA | Operating conditions |
| Target Material / Angle | Tungsten / 20° | - | Source configuration |
| Filtration | 3 mm Be, 3 mm Al, 0.5 mm Cu | - | Inherent and added filtration |
| Half-Value Layer (HVL) | 1.13 (Calculated); 1.09 ± 0.03 (Measured) | mm Cu | Beam quality |
| Source-to-Surface Distance (SSD) | 331 | mm | Reference geometry |
| Source-to-Axis Distance (SAD) | 341 | mm | TPS reference point (10 mm depth) |
| Secondary Collimator Apertures | 5, 7, 8, 10, 15, 20, 25, 30 | mm | Available field sizes |
| Reference Dose Rate | 1.722 ± 0.002 | Gy min-1 | Measured at 10 mm depth (for 0.9 to 10 Gy total dose) |
| Minimum Dose Increment | 0.03 | Gy | Corresponds to 1 s timer increment |
| Penumbra (5 mm aperture, 20 mm depth) | 0.6 | mm | 80%-20% dose fall-off |
| Beam Model Validation Deviation | -1.5 to 1.7 | % | Relative dose agreement (TPS vs. measurement) |
| Total Standard Uncertainty (1-sigma) | 2.4-4.7 | % | Combined uncertainty budget (field size dependent) |
| QA Gamma Passing Rate (Median) | 100 | % | 1%/1 mm criterion |
| Mouse Bedding Material | ABS | - | 3D-printed (FDM technique) |
| QA Phantom Material | Solid Water HE | - | Water-equivalent material |
Key Methodologies
Section titled “Key Methodologies”- Hardware Modification: An industrial X-ray unit was physically adapted to provide a horizontal beam line, mimicking the geometry of a particle therapy beam line for comparative radiobiology studies.
- Collimation System Design: A dual brass collimation system (fixed Primary Collimator, interchangeable Secondary Collimators) was designed and manufactured to achieve precise small-field irradiation (5 mm to 30 mm diameters).
- Modular Component Manufacturing: Mouse bedding units (compatible with CT, MR, PET, and irradiation), a Small Field Dosimetry Phantom (SFDP), and a mouse-mimicking QA phantom were 3D-printed using ABS and Solid Water HE.
- Dosimetry Chain Establishment: Air kerma calibration of a Farmer chamber was converted to dose-to-water using IAEA TRS-398 recommendations, cross-calibrating a microDiamond (mD) detector for small-field measurements.
- Beam Data Acquisition: Percentage Depth Dose (PDD) curves were measured using the mD detector in the SFDP. Lateral Dose Profiles (LDPs) were acquired using Gafchromic EBT3 films, calibrated up to 10.0 Gy.
- TPS Commissioning: The X-ray spectrum (calculated via SpekPy), PDDs, and relative LDPs were input into the µ-RayStation 8B Monte Carlo dose engine (0.2 mm grid resolution).
- In Silico Validation: Treatment plans for 5, 8, and 30 mm apertures were calculated on a virtual RW3 phantom and validated against mD measurements at five depths (1 mm to 50 mm).
- Subject-Specific QA: Treatment plans for 10 µCT-scanned mice (1.0 Gy prescription, 5 mm aperture) were verified by recalculating the dose on a virtual QA phantom. Verification utilized both mD point dose measurements and 2D dose distribution analysis via EBT3 films, assessed using a 1%/1 mm gamma criterion.
Commercial Applications
Section titled “Commercial Applications”The developed modular adaptations and validated workflow contribute significantly to the following fields:
- Preclinical Radiation Research: Provides a high-precision, standardized X-ray reference platform essential for comparative radiobiological studies, particularly those involving Relative Biological Effectiveness (RBE) determination in particle therapy.
- Cost-Effective System Upgrades: Offers a validated, open-source framework (CAD files provided) for upgrading existing industrial kilovoltage X-ray units, making high-precision preclinical irradiation accessible without purchasing expensive dedicated commercial irradiators.
- Small Animal Imaging and Irradiation Workflow: The modular mouse bedding unit ensures consistent animal positioning across multiple modalities (CT, MR, PET, and irradiation), streamlining complex in vivo experimental protocols.
- Dosimetry Standardization: The developed SFDP and QA phantoms facilitate standardized, reproducible small-field dosimetry and quality assurance, addressing challenges inherent in kilovoltage beam measurements.
- Treatment Planning Software Validation: Demonstrates a robust methodology for commissioning and validating commercial TPS (µ-RayStation) for complex, small-field kilovoltage photon beams used in preclinical settings.
View Original Abstract
Abstract Background Preclinical research in radiation oncology encompasses a range of methodologies, including in vitro cell studies and in vivo small animal experiments, as well as in silico studies to evaluate radiation‐induced side effects and tumor responses. Purpose This study addresses the need for high‐precision x‐ray irradiation solutions as reference for preclinical research. Modifications of an industrial kilovoltage x‐ray unit, along with the commissioning of a commercial treatment planning system (TPS), aimed to enable reliable irradiation of small animals in a horizontal beam geometry. All advancements enhancing the irradiation framework are made available, offering cost‐effective upgrades for existing systems. Methods An industrial kilovoltage x‐ray unit was equipped with a dual collimation system, featuring a fixed primary and variable secondary collimators with aperture diameters of 5 to 30 mm. Additional modular adaptations were designed and manufactured, including a multimodal mouse bedding unit, a dedicated dosimetry phantom and a quality assurance (QA) phantom. Output factors, percentage depth dose curves and lateral dose profiles were acquired to generate a beam model in the ‐RayStation 8B (RaySearch Laboratories, Stockholm, Sweden), using a diamond detector and radiochromic films. Treatment plans for 10 mice were created, evaluated via dose‐volume metrics and the homogeneity index and subsequently dosimetrically compared to QA measurements through a gamma analysis with a 1%/ acceptance criterion. Results The resulting beam model was validated within a maximum dose deviation of 1.7%. Aperture diameters close to potential target diameters were found to be effective for achieving sufficient target coverage in silico, as demonstrated for a 5 mm target with a homogeneity index of (9.9 0.7)%. Dedicated QA measurements revealed a maximum dose deviation of 1.9% from the TPS and a median gamma passing rate of 100%, confirming the suitability of the proposed solution. Conclusions Cost‐effective adaptations for an kilovoltage x‐ray irradiation framework were designed, manufactured and commissioned, and contribute to the accessibility of preclinical irradiation research. These components are integrated into a comprehensive preclinical particle beam platform.