One-Dimensional Strip Detector for MLC Position Monitoring
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Solution Overview
Problem
Current radiation therapy quality assurance methods are inadequate for real-time monitoring of multi-leaf collimator performance during treatment, particularly in stereotactic treatments, due to limitations in spatial resolution, repeatability, and sensitivity to anatomical changes, leading to potential errors in dose delivery.
Innovation Solution
A one-dimensional strip detector system with a planar array of electrically conductive strips and a bias electrode, which measures the position of multi-leaf collimator leaves and determines the fluence distribution, allowing for real-time comparison with planned positions and gantry angles, and calculates the delivered dose distribution using a processor and dose calculation engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-treatment quality assurance with phantom-based detectors is used, then calculation errors and systematic LINAC errors can be revealed, but it cannot detect lack of LINAC repeatability, positioning errors, and anatomical changes, and adds additional steps reducing workflow efficiency
Solution Approach 1:
The patent performs quality assurance measurements as a preliminary action during the treatment setup phase, before actual treatment delivery. The transmission detector array is positioned and measurements are taken while the patient is on the treatment couch, allowing detection of positioning errors and anatomical changes before irradiation begins, thus ensuring reliability without adding separate QA steps to the workflow
Solution Approach 2:
The patent introduces a transmission detector array as an intermediary device positioned between the LINAC and the patient. This mediator captures fluence information during treatment delivery, enabling continuous monitoring of MLC position and dose distribution without interfering with the treatment workflow, thus improving both reliability and productivity
2Productivity
If stereotactic treatments are used to deliver overall treatment dose in one or few fractions, then workflow efficiency is increased and inter-fractional anatomy changes are reduced, but the risk of severe consequences from dose errors is amplified
Solution Approach 1:
The patent implements real-time feedback by continuously monitoring the fluence distribution during treatment delivery using the transmission detector array. The measured fluence is compared against the planned fluence, and any deviations in MLC position or dose distribution are detected immediately, allowing for corrective actions before the treatment is completed. This feedback mechanism ensures high reliability in stereotactic treatments while maintaining workflow efficiency
Solution Approach 2:
The patent replaces traditional mechanical pre-treatment QA procedures with an electronic detection system. The transmission detector array with electronic readout provides instantaneous measurement and feedback, substituting the mechanical phantom-based QA approach with an electronic system that operates during treatment delivery, thus maintaining productivity while enhancing reliability
3Measurement precision
If a two-dimensional array with parallel readout is used for transmission detection, then spatial resolution and measurement accuracy are improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent segments the detection task by using a one-dimensional array of strip assemblies that are oriented parallel to the MLC leaves. Each strip assembly measures fluence at a specific location, and the collective measurements from all strips provide sufficient information for quality assurance. This segmentation approach achieves the necessary measurement precision while avoiding the complexity of a full two-dimensional array with parallel readout for each pixel
Solution Approach 2:
The patent transitions from a two-dimensional detection problem to a one-dimensional solution by orienting the strip assemblies parallel to the MLC leaves. The strips are arranged in one dimension perpendicular to the leaf motion, and by measuring fluence along this one-dimensional array, the system captures the essential variations in dose distribution without requiring a full two-dimensional detector array, thus reducing complexity while maintaining measurement precision
4Speed
If active sensors are used for quality assurance, then instantaneous signal readout and tracking of dynamical changes are enabled, but the device complexity and cost are higher compared to passive sensors
Solution Approach 1:
The patent uses a transmission detector array that serves multiple functions: it measures fluence distribution, monitors MLC position in real-time, and provides instantaneous feedback during treatment delivery. The same active sensor system performs all these quality assurance functions simultaneously, making the additional complexity worthwhile by enabling comprehensive real-time monitoring that improves both speed and reliability without requiring separate passive and active systems
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 solution provides an efficient and reliable method for online measurement of radiation dose distribution, enabling real-time adaptation and ensuring accurate dose delivery by determining the position of MLC leaves and fluence, thus reducing the risk of errors and improving treatment efficacy.
Implementation Method 1
A beam model is provided, and a fluence-reconstructing engine determines a fluence from the position of the pairs of leaves and the beam model
Implementation Method 2
An electrometer measures a current produced by the ionization chamber
Data Source
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AI summary
A sensing device for a radiation therapy apparatus, the apparatus comprising an accelerator and a beam-shaping device the beam shaping device being a multi-leaf collimator (MLC) (2) having a plurality of pairs of leaves, and a rotatable gantry, the sensing device comprising: • a transmission electronic detector (1) comprising an array of ionization chambers. The ionization chambers are defined by a bias electrode (11a, 11b, 34,42) on the one hand and by a planar array of conductive strips (40) or strip assemblies (30) on the other hand. The strips or strip assemblies are associated to the leaf pairs of the MLC. The strips are the collecting electrodes of the ionization chambers. Each strip assembly or in the case of one particular embodiment, each strip, yields two currents which allow to determine the position of the leaves of a leaf pair associated with the strip or strip assembly, • a gantry sensor configured to determine at least one position associated with a gantry angle; and • a processor, adapted to determine the position of at least one pair of leaves of the MLC using the currents i1 and i2 obtained from the collecting electrode strips.