Radiotherapy Couch Sag Compensation for Accurate IGRT Positioning
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Solution Overview
Problem
In image-guided radiotherapy (IGRT), the radiotherapy couch tends to sag due to the weight of the object and the extended position during CT scans, leading to positional errors that affect the accuracy of treatment delivery.
Innovation Solution
A method and system that utilize a two-modality apparatus with image acquisition and registration modules to determine the couch sag at different positions, using standard data to estimate the sag difference and align the target portion with the isocenter of the modality units, ensuring precise positioning of the object for accurate radiotherapy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the couch extends longer from the support position into the bore of the CT gantry to enable IGRT, then the imaging and treatment capability is improved, but the couch sags or deflects along the longitudinal direction causing positional error
Solution Approach 1:
The system performs preliminary measurement of couch sag at the CT position before treatment, uses standard data to estimate the sag difference, and calculates the compensation amount in advance. This preliminary action allows the system to pre-determine the positional error and prepare the compensation strategy, ensuring accurate target positioning during treatment without physically adjusting the couch structure.
Solution Approach 2:
Instead of mechanically reinforcing the couch to prevent sag (which would increase complexity), the system substitutes a computational approach: measuring sag at CT position, using standard data to estimate sag at RT position, and calculating digital compensation. This replaces potential mechanical solutions with an information-processing solution that maintains couch design simplicity while achieving positioning accuracy.
2Reliability
If the couch is reinforced to reduce sag, then the positional stability is improved, but the device complexity increases
Solution Approach 1:
The patent replaces potential mechanical reinforcement solutions with a measurement and calculation-based approach. By measuring couch sag at the CT position and using standard data to estimate sag at the RT position, the system achieves positional stability through information processing rather than structural modification, thereby maintaining couch design simplicity.
Solution Approach 2:
The system uses the couch itself as the measurement object - by placing markers on the couch and imaging the couch structure at the CT position, the system self-diagnoses the sag amount. This self-service approach eliminates the need for external complex measurement equipment or structural modifications to the couch.
3Productivity
If image registration is performed without couch sag compensation, then the processing speed is maintained, but the registration accuracy deteriorates due to positional error
Solution Approach 1:
The system performs preliminary measurement of couch sag at the CT position and preliminary estimation of the sag difference using standard data before the actual treatment registration. This preliminary action separates the time-consuming measurement and calculation steps from the critical treatment registration step, allowing accurate compensation to be applied without delaying the treatment workflow.
Solution Approach 2:
The system introduces standard data as an intermediary element that bridges the measurement at CT position and the estimation at RT position. These standard data (pre-measured sag characteristics) act as a mediator that enables accurate sag estimation without requiring direct measurement at the treatment position, thus maintaining processing efficiency while improving registration accuracy.
Data Source
AI summary
A method and system for using in a two-modality apparatus. The two-modality apparatus comprises a couch with a table top, a first modality unit and a second modality unit. A second image of a target portion of an object when the table top is at a second working position of the second modality unit may be acquired. A second sag of the table top at a second measurement point of the table top according to the second image may be determined based on the image. A difference between a first sag of the table top at a first measurement point of the table top and the second sag may be estimated based on the second sag and standard data. The standard data provides a relationship relating to a sag of the table top positioned between the first modality unit and second modality unit.