Ion Radiotherapy Beam Direction Planning Using WEPL Robustness

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Solution Overview

Problem

Existing ion-based radiotherapy treatment plans face challenges in ensuring robustness due to uncertainties from patient anatomy variations, tissue inhomogeneity, and setup errors, which affect the Bragg peak positions and dose distribution.

Innovation Solution

A method for evaluating the robustness of treatment plans by calculating and displaying the accumulated path length, particularly Water Equivalent Path Length (WEPL), to select beam directions that minimize variations and ensure uniform tissue traversal, using Monte Carlo dose engines for data.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If beam directions are selected to maximize dose to target, then dose coverage of treatment volume is improved, but dose to surrounding tissue increases

Engineering Contradiction:

Improvedose coverageVSAvoiddose to surrounding tissue

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The treatment volume is divided into multiple portions, and the accumulated path length is evaluated for each portion individually. This segmentation allows for precise evaluation of dose distribution across different regions, enabling optimization of beam directions to maximize target coverage while minimizing dose to surrounding tissues.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The accumulated path length is calculated before final treatment plan implementation. This preliminary evaluation of path length variations allows the planning system to predict and avoid beam directions that would result in excessive dose to surrounding tissues, thereby preventing harmful effects before treatment begins.

Inventive Principle:

Principle #10Preliminary action

2Manufacturing precision

If Bragg peak positions are precisely controlled, then dose distribution accuracy is improved, but sensitivity to setup errors increases

Engineering Contradiction:

Improvedose distribution accuracyVSAvoidrobustness to setup errors

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The system calculates accumulated path length for multiple portions of the treatment volume and uses this information to evaluate and adjust beam directions. This feedback mechanism allows the plan to be optimized for robustness, where beam directions are selected not only for precise Bragg peak positioning but also for minimizing sensitivity to potential setup errors and tissue variations.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The evaluation of accumulated path length provides information about how dose distribution changes with different beam directions and tissue conditions. By analyzing path length variations, the system can adjust treatment parameters to achieve an optimal balance between dose distribution accuracy and robustness to setup uncertainties.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If beam directions are selected to minimize path length variations, then robustness to patient movement is improved, but dose coverage of treatment volume may be reduced

Engineering Contradiction:

ImproverobustnessVSAvoiddose coverage

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The accumulated path length calculation serves multiple functions: it evaluates robustness to patient movement, assesses dose distribution accuracy, and guides beam direction selection. By using this single metric for multiple evaluation purposes, the system can balance competing requirements of robustness and dose coverage in the treatment planning process.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enhances the robustness of ion-based radiotherapy plans by identifying beam directions that maintain dose consistency despite patient movement or tissue changes, thereby improving treatment delivery accuracy.

Implementation Method 1

using Monte Carlo dose engines for data

Methodology Applied

Scientific EffectMonte Carlo simulation:

Implementation Method 2

obtaining information related to accumulated path length of tissue traversed by ions when they reach the portion

Methodology Applied

Scientific EffectIon traversal through tissue:

Implementation Method 3

The WEPL is defined as the distance that is equivalent to that measured in water, taking into account the densities of the tissues traversed by the ion and the variation of stopping power ratio between water and the traversed media. It is usually calculated as the product of the distance in the considered materials times the density times the water to medium stopping power ratio.

Methodology Applied

Scientific EffectWater Equivalent Path Length calculation:

Implementation Method 4

In ion-based radiotherapy each ion will emit most of its energy towards the end of its path, creating what is known as the Bragg peak

Methodology Applied

Scientific EffectBragg peak:

Data Source

PatentUS12544591B2System, computer program product and method for ion-based radiotherapy treatment planning

Publication Date: 2026.02.10 RAYSEARCH LAB

AI summary

Accumulated path length for ions that reach a particular area of a patient is used in dose planning as an indicator of plan robustness. Also, the magnitude of the variations of the accumulated path lengths is determined for a number of beam directions, allowing beam directions to be selected for maximum robustness in treatment planning.