Radiotherapy Beam Calibration via 180-Degree Rotation Midpoint Alignment
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Solution Overview
Problem
Current methods for calibrating linear accelerators in radiotherapy systems are inaccurate and prone to mechanical errors due to backlash and eye-aligned alignment, which can lead to incorrect beam positioning and increased damage to healthy tissue.
Innovation Solution
A method involving a beam measurement device coupled to the radiation head, where the radiation head is rotated 180° to determine the beam center twice, allowing the device to be aligned with the midpoint of the displacement, ensuring precise alignment without mechanical variations and backlash issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single ion chamber is scanned through the beam using mechanical movement and eye alignment, then the beam position can be measured, but the measurement precision deteriorates due to backlash and alignment errors of approximately 2 mm
Solution Approach 1:
The patent replaces the mechanical scanning system with an optical alignment system. A laser is projected through the crosshair reticle to define the beam axis, and the ion chamber is positioned along this optical reference. This substitution eliminates mechanical backlash and improves alignment precision from approximately 2 mm to sub-millimeter accuracy, directly resolving the technical contradiction between measurement precision and reliability.
2Measurement precision
If the beam measurement device is positioned relative to the beam using conventional methods, then the beam center can be located, but the alignment consistency deteriorates when the radiation head is rotated
Solution Approach 1:
The patent introduces a laser as an intermediary element that creates a stable optical reference line passing through the crosshair reticle and the beam axis. This laser reference serves as a mediator between the crosshair alignment and the beam measurement device positioning. When the radiation head rotates, the laser can be re-aligned with the rotated crosshair, ensuring the beam measurement device remains correctly positioned relative to the new beam axis, thus maintaining alignment consistency across different head positions.
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 method provides a more accurate and repeatable calibration of the radiation beam, reducing errors and ensuring consistent setup, thereby minimizing damage to healthy tissue and improving the effectiveness of radiotherapy.
Implementation Method 1
an ion chamber array (such as that described by U.S. Pat. No. 6,125,335) can be used to provide a detecting device with a wide cross-sectional area
Data Source
AI summary
The present invention provides a method of calibrating a radiotherapy apparatus, in which a beam measurement device is accurately located with respect to the radiation beam center. The method comprises acquiring the center of the radiation beam at two angles of rotation, separated by 180°, and aligning a beam measurement device with the midpoint of the respective centers.