LINAC Beam Alignment via Bending Magnet Current Modulation

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Solution Overview

Problem

Mechanical rotations in medical linear accelerators (LINACs) lead to inaccuracies in radiation beam delivery due to gantry translation errors, resulting in high doses of radiation being delivered outside the tumor, causing adverse side effects.

Innovation Solution

The LINAC modulates beam alignment by adjusting the current to bending magnets at each gantry position, using radiation transmission images to ensure the beam center aligns with a marker, thereby compensating for mechanical errors and maintaining beam accuracy across different gantry angles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the gantry rotates to different angles to deliver radiation beams from multiple directions, then the treatment coverage and effectiveness are improved, but mechanical translation errors cause the beam center to deviate from the tumor location

Engineering Contradiction:

Improvebeam alignment accuracyVSAvoidgantry rotation mechanical precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The system uses radiation transmission images (EPID images) to detect the actual position of the beam center relative to the tumor marker at each gantry angle. This feedback information is used to calculate corrective actions that compensate for mechanical errors, ensuring accurate beam delivery despite gantry translation issues

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system dynamically adjusts beam parameters (such as bending magnet currents) based on the detected gantry angle and measured beam position deviations. By changing these parameters in real-time, the system compensates for mechanical errors and maintains accurate beam-tumor alignment throughout the rotation cycle

Inventive Principle:

Principle #35Parameter changes

2Strength

If the gantry is designed with robust mechanical structures to maintain stability, then mechanical strength is improved, but the gantry still translates under its own weight during rotation

Engineering Contradiction:

Improvegantry structural strengthVSAvoidbeam delivery accuracy

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

Instead of relying solely on mechanical precision to maintain beam accuracy, the system substitutes mechanical solutions with electromagnetic control. Bending magnets are used to dynamically adjust the beam direction and compensate for gantry translation, replacing the need for perfectly precise mechanical rotation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If radiation beams are delivered from multiple gantry angles to cover the entire tumor, then treatment effectiveness is improved, but beam misalignment causes high doses to be delivered outside the tumor

Engineering Contradiction:

Improvetreatment effectivenessVSAvoidunwanted radiation exposure

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The system continuously monitors beam position using radiation transmission images at each gantry angle. This feedback allows real-time detection and correction of beam misalignment, ensuring that high-dose radiation is delivered precisely to the tumor while minimizing exposure to surrounding healthy tissues

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs beam alignment verification and correction at each gantry angle before delivering the therapeutic radiation dose. By ensuring proper alignment in advance, the system prevents misdirected radiation exposure while maintaining effective tumor treatment

Inventive Principle:

Principle #10Preliminary action

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 improves the precision of radiation delivery by ensuring the radiation beam center remains aligned with the tumor at all gantry angles, reducing unwanted radiation exposure and adverse side effects.

Implementation Method 1

The method may include, if the center of the radiation field of the adjusted radiation beam is determined to be at the center of the shadow of the radiation opaque marker, using the LINAC to store the adjusted beam alignment parameter as an optimal beam alignment parameter for the first gantry angle. The method may include, using the adjusted beam alignment parameter stored as the optimal beam alignment parameter for the first gantry angle to adjust the current supplied by the LINAC to the one or more bending magnets when the gantry of the LINAC rotates to the first gantry angle.

Methodology Applied

Scientific EffectLorentz force: Lorentz Force

Data Source

PatentUS11617902B2Modulated radiation beam alignment for medical linear accelerator

Publication Date: 2023.04.04 AKTINA CORP

AI summary

Systems and methods for delivering a radiation beam using a linear accelerator (LINAC). Optimal beam alignment parameters may be determined and stored for each of N gantry angles. The beam alignment parameters may adjust a current supplied to one or more bending magnets of the LINAC and, thus, change an angle and direction of the radiation beam. An optimum beam alignment parameter for a gantry angle may be determined by adjusting the beam alignment parameter until a center of a radiation field of the radiation beam in a radiation transmission image is at a center of shadow of a radiation opaque marker, which may be placed at a radiation isocenter. The beam alignment parameters stored for the N gantry angles may be used to adjust the beam steering current as the gantry is rotated through any arbitrary gantry angle.