Ridge Filter Design for Single-Layer PBS Dose Distribution
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Solution Overview
Problem
Current methods for designing ridge filters for proton beam scanning in radiation therapy are complex and lack a simple, reliable, and reproducible approach to optimize energy degrading units for depositing predefined doses across a treatment volume, particularly for ultra-high dose deposition rates, which prolongs treatment time and complicates the production of accurate filters.
Innovation Solution
A method for designing a ridge filter that involves dividing the treatment volume into subvolumes and cells, attributing beam weights to each cell, and configuring energy degrading units with subunits of specific lengths and areas to achieve uniform dose distribution across a single painting layer, using energy degrading units in the form of orifices or pins arranged along the beam axes, and potentially combining different materials to optimize compactness and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple painting layers are used in PBS to deposit doses into different depth zones, then dose distribution accuracy is improved, but treatment time increases significantly
Solution Approach 1:
The treatment volume is segmented into multiple depth zones along the beam propagation direction, with each zone corresponding to a specific painting layer. The ridge filter is accordingly segmented into multiple energy degrading units, each responsible for depositing dose into a specific depth zone. This segmentation allows the system to achieve accurate dose distribution while reducing treatment time by enabling simultaneous multi-zone treatment through single-layer PBS.
2Loss of time
If complex ridge filter designs are used to optimize energy degrading units for single-layer PBS, then treatment time is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The ridge filter employs energy degrading units with locally optimized properties, where each unit is specifically designed to degrade beam energy to a target value suitable for its corresponding depth zone. This local quality approach allows each unit to be independently optimized, simplifying the overall manufacturing process while maintaining the precision needed for accurate dose deposition in single-layer PBS.
3Measurement precision
If traditional multi-layer PBS approach is used, then dose distribution accuracy is maintained, but productivity decreases due to prolonged treatment time
Solution Approach 1:
The ridge filter is pre-configured with multiple energy degrading units positioned at specific locations to automatically degrade beam energy to appropriate levels for different depth zones as the beam passes through. This preliminary action of pre-positioning the energy degradation function in the ridge filter eliminates the need for sequential layer-by-layer treatment, enabling simultaneous multi-zone dose deposition through single-layer PBS and thereby improving productivity while maintaining dose distribution accuracy.
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 approach allows for efficient, accurate, and reproducible deposition of specific doses across the treatment volume, reducing treatment time and improving the production feasibility of ridge filters, especially for FLASH irradiation at ultra-high dose rates, by enabling the entire treatment volume to be covered with a single paint layer.
Implementation Method 1
Each energy degrading unit (11.i) is configured for degrading an energy of a beam (100.i) of charged particles
Implementation Method 2
charged particle beams, in particular protons deposit most of their energy close to the end of their beam path, forming a so-called Bragg peak
Implementation Method 3
Pencil beam scanning (PBS) is a technique consisting of steering a beam of charged particles along corresponding beam axes (Xi) towards individual spots of a mesh of spots (Sij) defining a target volume
Implementation Method 4
at least a first degrading subunit (11.11) of a first energy degrading unit (11.1) is made of a first material different from a second material of a second degrading subunit (11.12) of the first or of a second energy degrading unit (11.2). The first material having a value of the subunit water equivalent thickness per unit length (Wu) which is different from the second material
Data Source
AI summary
The present invention concerns a method for designing a ridge filter for a charged particle accelerator, for depositing with beams of accelerated particles (100.i) specific doses (Dij) into specific locations within a treatment volume (V) of tissue comprising tumoral cells (3t) by single layer pencil beam scanning (PBS), according to a predefined treatment plan (TP), the method comprising the following steps,Defining an array of spots (Si) defining the bases of cylindrical subvolumes (Vi) defining the treatment volume (V); the subvolumes (Vi) are divided into N cells (Cij).The ridge filter is designed comprising the same number of energy degrading units (11.i) as there are spots (Si). Each energy degrading unit (11.i) is formed by N cylindrical degrading subunits (11.ij) of lengths (Lij) and area (Aij).The lengths (Lij) of each degrading subunit (11.ij) are calculated as Lij=Wij/Wu, and Wij=W0−dij, whereinWij is the desired subunit water equivalent thickness (Wij),Wu is the subunit water equivalent thickness per unit length (Wu),W0 is the maximum beam range anddij is the desired position of the Bragg peak along the irradiation axis (X).The area (Aij) of each degrading subunit (11.ij) is obtained by determining the area boundary (Aij) of the integral at the numerator satisfying the following Equation (1).ωij∑ jωij=∫∫AijF(y,z)·dy·dz∫∫AbiF(y,z)·dy·dz,wherein(1)ωij/Σjωij is the normalized beam weight,F(y,z) is the fluence of the beam,Abi is the base area (Abi) of the degrading unit (11.i).