Ionization Chamber Reference Detector for Radiation Field QA
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Solution Overview
Problem
Current methods for quality assurance of radiation therapy apparatuses face challenges in measuring small radiation fields due to limitations in placing reference detectors, leading to instability and inefficiency, especially when dealing with fluctuations in beam intensity and size variations.
Innovation Solution
A method and device utilizing an ionization chamber as a reference detector positioned to intercept the entire radiation beam, combined with field detectors and a control unit to compute dose ratios, ensuring accurate beam profiles and depth/dose curves, particularly suitable for small fields by using detectors with low attenuation and high sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference detector is placed in the corner of the radiation field to correct for beam intensity fluctuations, then measurement accuracy is improved, but there is not enough space to place the reference detector inside small fields
Solution Approach 1:
The patent introduces a transmission ionization chamber as an intermediary device that passes through the radiation beam from the irradiation side to the non-irradiation side. This mediator enables reference measurements without occupying space within the radiation field, resolving the contradiction between needing reference detection and having limited space in small fields.
Solution Approach 2:
Instead of placing the reference detector laterally within the radiation field (2D plane), the patent moves it to a different spatial dimension by passing it through the beam path from one side to the other. This dimensional change allows reference detection without competing for lateral space in small fields.
2Reliability
If a reference detector is positioned outside the field to avoid disturbing measurements, then measurement interference is reduced, but the signal becomes very weak leading to high noise
Solution Approach 1:
The transmission ionization chamber acts as an intermediary that traverses the radiation beam, allowing the reference detector to be positioned outside the field while still intercepting sufficient radiation signal. This mediator approach maintains both low interference and adequate signal strength.
3Measurement precision
If the reference detector is repositioned at the edge of the field for each different field size, then measurement accuracy for different field sizes is improved, but time is lost due to repeated repositioning and entering the treatment room
Solution Approach 1:
The transmission ionization chamber is designed as a universal reference detector that can measure reference signals for multiple field sizes without repositioning. It passes through the radiation beam at a fixed location, enabling it to function for various field configurations, thus eliminating repeated repositioning and time loss.
4Device complexity
If a reference detector is traversed by only a fraction of the radiation beam, then device complexity is reduced, but it becomes necessary to reposition the reference detector as beam size changes
Solution Approach 1:
The transmission ionization chamber serves as a mediator that fully traverses the radiation beam path. This configuration maintains relatively simple device structure while achieving high adaptability to different beam sizes, as the chamber passes through the entire beam regardless of its dimensions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides reliable, time-efficient quality assurance for both small and large radiation fields, reducing noise and position sensitivity, and ensuring machine-independent measurements.
Implementation Method 1
providing an ionization chamber detector as reference detector for measuring a signal indicative of the dose of said radiation field
Data Source
Figure 1
AI summary
The invention relates to a method for quality assurance of a radiation field (30) emitted by a radiation therapy apparatus (10), comprising the steps of: (i) providing an ionization chamber (40) detector as reference detector for measuring the dose of the radiation field (30) at the exit of the radiation head (20), said ionization chamber (40) having a size and being positioned for being traversed by said radiation beam (30), said ionization chamber (40) having an attenuation equivalent to less than 1 mm Al; (ii) providing one or more field detectors (50); moving the field detector (50) across the radiation field (30) and measuring simultaneously the dose from the field detector (50) and from the ionization chamber (40); (iii) computing the ratio of the dose from the field detector (50) to the dose of the ionization chamber (40). The invention also relates to a device for performing the method.