MR-Based Electron Density Map Correction for Radiotherapy Dose Accuracy
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Solution Overview
Problem
Magnetic resonance-only radiotherapy planning faces challenges in determining electron density maps required for dosage calculation, as magnetic resonance image data lacks a clear physical relationship with electron density, leading to errors in bone and air region identification, which can affect radiation dose distribution accuracy.
Innovation Solution
A method is developed to calculate a first electron density map from magnetic resonance image data, followed by a second electron density map with reduced values for bone regions, allowing for comparison of radiation dose distributions based on these maps to assess the accuracy of electron density allocation and decide on the validity of MR-only RT planning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If magnetic resonance image data is used for radiotherapy planning, then soft tissue contrast is improved, but electron density determination accuracy deteriorates
Solution Approach 1:
The patent introduces an intermediary process: a first electron density map is calculated from MR image data, then a second electron density map is generated by reducing electron density values in bone regions of the first map. This second map serves as a corrected intermediary that compensates for the overestimation error in bone regions, enabling accurate dose calculation while maintaining the soft tissue contrast advantage of MR imaging
Solution Approach 2:
The patent applies parameter changes by modifying the electron density values in bone regions. Specifically, electron density values in bone regions are reduced from the first map to create the second map, based on the principle that MR-based electron density estimation overestimates bone electron density. This parameter adjustment corrects the measurement error while preserving soft tissue characterization
2Measurement precision
If electron density values in bone regions are reduced, then dose calculation accuracy is improved, but electron density map reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by first calculating the first electron density map from MR image data, then identifying bone regions and reducing their electron density values before performing dose calculations. This preliminary correction of electron density values in bone regions ensures that subsequent dose calculations are accurate while maintaining overall map reliability through the systematic correction approach
Solution Approach 2:
The patent implements feedback by comparing dose calculations performed with the original first electron density map versus the corrected second electron density map. The difference in dose values, particularly in regions near bone structures, provides feedback on the magnitude of correction applied, allowing verification that the electron density reduction improves dose accuracy without creating new errors
3Measurement precision
If CT image data is used for radiotherapy planning, then electron density accuracy is improved, but soft tissue contrast deteriorates
Solution Approach 1:
The patent merges the advantages of both MR and CT imaging by using MR image data for soft tissue contrast and target organ identification, while applying a correction algorithm that combines MR data with known characteristics of bone electron density to generate a corrected electron density map. This merging approach eliminates the need for separate CT scans while achieving both soft tissue contrast and electron density accuracy
4Loss of time
If MR-only radiotherapy planning is implemented, then patient scan time is reduced, but dosimetric accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating the first electron density map from MR image data and then applying the bone region correction to generate the second electron density map before dose calculation. This preliminary processing ensures that dosimetric accuracy is maintained while implementing MR-only planning, thereby reducing patient scan time by eliminating the need for separate CT scans
Solution Approach 2:
The patent applies parameter changes by modifying electron density values in bone regions of the MR-based electron density map. This parameter correction compensates for the inherent limitation of MR imaging in accurately representing bone electron density, thereby maintaining dosimetric accuracy while using MR-only planning and reducing overall scan time
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 quality control mechanism for radiotherapy planning using only magnetic resonance image data, enabling reliable dosage calculations and reducing the need for additional imaging modalities by identifying deviations in dose distributions, thus ensuring accurate radiation therapy planning.
Implementation Method 1
nuclear spins of specific atoms, excited in a resonant manner by these radio-frequency pulses
Implementation Method 2
Radio-frequency pulses (excitation pulses) are emitted by a radio-frequency antenna unit by suitable antenna devices
Implementation Method 3
gradient pulses are activated by a gradient coil arrangement
Implementation Method 4
When the nuclear spins relax, radio-frequency signals, known as magnetic resonance signals, are emitted which are received by suitable radio-frequency antennae
Data Source
AI summary
In a quality control method and computer for planning radiotherapy of patient, magnetic resonance (MR) image data, acquired from a planning volume of a patient, are provided to a computer and are used in the computer to generate a first electron density map of the planning volume. A second electron density map is generated using the first electron density map, wherein a value of electron density for a bone region in the planning volume is reduced compared to the first electron density map. First and second radiation dose distributions in the planning volume are respectively determined from the radiotherapy plan and the first electron density map, and the radiotherapy plan and the second electron density map. These distributions are compared in order to generate output information.