Nested Ionization Chamber for Partial Volume Correction
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Solution Overview
Problem
Existing radiation therapy systems face challenges in accurately measuring and correcting for partial volume effects when using small radiation beams, as conventional ionization detectors are difficult to construct to avoid these errors while maintaining sensitivity.
Innovation Solution
A nested radiation detector system with two measurement volumes, where one is substantially surrounded by the other, allowing for detection and correction of partial volume effects by using readings from both detectors, and optionally including a third detector for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ionization chamber volume is made small to avoid partial volume effects, then measurement accuracy improves, but sensitivity deteriorates
Solution Approach 1:
The patent employs nested ionization chambers where a smaller inner chamber is positioned within a larger outer chamber. Both chambers share the same gas volume but have different collection electrode configurations. The inner chamber provides high spatial resolution for small beams, while the outer chamber maintains sufficient gas volume for sensitivity, thereby resolving the contradiction between small volume for accuracy and large volume for sensitivity.
2Quantity of substance
If the ionization chamber volume is made large to maintain sensitivity, then sensitivity improves, but partial volume effects worsen
Solution Approach 1:
The patent segments the measurement function into two distinct chambers: an inner chamber optimized for small beam measurements with reduced partial volume effects, and an outer chamber providing sufficient gas volume for sensitivity. By segmenting the detection volume and using both chambers in coordination, the system achieves both high sensitivity and accurate measurement of small radiation beams.
3Device complexity
If a single ionization chamber is used, then device complexity is low, but the ability to detect and correct partial volume effects deteriorates
Solution Approach 1:
The nested chamber configuration provides differential measurement capability where the inner and outer chambers respond differently to partial volume effects. By comparing signals from both chambers, the system can detect and mathematically correct for partial volume effects, transforming a potential source of error into a useful feedback mechanism for improving measurement accuracy.
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
Enables accurate measurement and correction of partial volume effects in narrow radiation beams, maintaining calibration and sensitivity without altering the energy spectrum of the radiation beam, and allowing for automatic correction of beam misalignment.
Implementation Method 1
The gas is ionized by the radiation passing through the chamber volume and the ions are collected on one collector electrode under the influence of a voltage applied across the electrodes.
Data Source
AI summary
Nested ionization chambers provide independent measurements of a radiation beam that does not fully irradiate the volume of one or both chambers. By mathematically combining these independent measurements, partial volume effects caused by a change in ionization detector calibrations when the full detector volume is not irradiated by the radiation beam, may be decreased, providing more accurate measurement of extremely small radiation beams.