Radiotherapy Light Field Ghosting Elimination via Filter
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Solution Overview
Problem
The multi-leaf collimator (MLC) in radiotherapeutic apparatuses experiences 'ghosting' due to the reflective properties of its leaves, which creates spurious bright lines in the light field during alignment, making it difficult to accurately position patients and test collimator operation.
Innovation Solution
A filter with linear dark sections is placed in the path of the visible light beam, corresponding to the MLC leaves, to prevent light from falling on the leaves and eliminate ghost images, allowing the light source to be positioned similarly to the radiation source and enabling accurate alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the multi-leaf collimator leaves are positioned at a shallow angle to the light source, then the collimator can effectively shape the radiation beam, but the reflective surfaces of the leaves create ghosting in the light field
Solution Approach 1:
A filter is introduced as an intermediary element in the light path between the light source and the MLC leaves. This filter absorbs or blocks the light before it reaches the reflective leaf surfaces, preventing the creation of ghost images while allowing the MLC to maintain its radiation-shaping function unchanged
Solution Approach 2:
The harmful reflective property of the MLC leaves is effectively removed from the light field by placing the filter in the light path. The filter extracts or removes the problematic light reflections before they can create ghosting, while the MLC leaves continue to function normally for radiation beam shaping
2Object-affected harmful factors
If surface treatment is applied to reduce leaf reflectivity, then ghosting can be eliminated, but the complexity and cost of manufacturing increases
Solution Approach 1:
Instead of treating the entire MLC assembly as a single complex unit requiring surface modification, the solution segments the problem by introducing a separate, simpler filter component. This filter can be manufactured independently and integrated into the existing light path, avoiding the need to modify the complex MLC structure itself
Solution Approach 2:
The filter represents a simpler, more cost-effective solution compared to surface treating the MLC leaves. The filter can be a relatively inexpensive component that is easier to manufacture and replace than modifying the permanent MLC structure, reducing overall manufacturing complexity and cost
3Measurement precision
If the light source is positioned in the same optical location as the radiation source, then accurate alignment can be achieved, but the light beam directly strikes the MLC leaves causing ghosting
Solution Approach 1:
The filter serves as a mediator that allows the light source to be positioned at the same optical location as the radiation source for accurate alignment, while simultaneously preventing the harmful light reflections from reaching the MLC leaves. The filter is positioned in the light path to block reflections before they can create ghosting
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 effectively reduces ghosting by creating dark sections in the light field, ensuring precise patient positioning and collimator operation without the need for surface treatments, providing a cost-effective solution.
Implementation Method 1
a filter is disposed in the path of the visible light beam, having a plurality of linear dark sections corresponding to leaves of the collimator
Implementation Method 2
A mirror can deflect the path of the visible light to correspond to that of the radiation beam
Data Source
AI summary
A radiotherapeutic apparatus comprises a source of therapeutic radiation, a source of visible light arranged to cast a light field corresponding to the beam of radiation, and a multileaf collimator for shaping the beams, wherein a filter is disposed in the path of the visible light beam having a plurality of linear dark sections corresponding to leaves of the collimator. This prevents the incident light from falling on the leaves and removes the ghost images at source. By placing the filter in the head, the line can be very narrow and will be blurred into penumbra at the isocentre. This is therefore a very inexpensive yet effective method of reducing ghosting. A mirror can deflect the path of the visible light to correspond to that of the radiation beam, and the filter can be disposed anywhere in the beam path, such as prior to the mirror, subsequent to the mirror and prior to the collimator, or subsequent to the collimator. The filter thus creates dark sections in the light field corresponding to leaves (preferably all the leaves) of the collimator.