Modulated Arc Therapy Arc Splitting Using Geometric Freedom
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Solution Overview
Problem
Existing methods for identifying optimal partial/split-arcs in modulated arc therapy (MAT) are time-consuming and lack a principled basis for removing unnecessary arc segments, leading to increased treatment time and dose to critical structures.
Innovation Solution
A method involving a geometric freedom (GF) metric is computed for each control point (CP) of the arc segment, identifying contiguous groups with low GF values as candidate segments for removal, and redistributing the dose using GF values to estimate the impact of their removal, allowing for quick assessment without iterative optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single arc is used for complex cases requiring significant beam modulation, then the gantry rotation speed must be reduced and dose rate reduced, but this increases treatment time and requires more monitor units
Solution Approach 1:
The patent divides the treatment arc into multiple discrete arc segments, each optimized for specific beam modulation requirements. This segmentation allows the system to achieve complex dose distributions without requiring the gantry to slow down continuously, as each segment can be delivered at optimal speed and dose rate independently.
Solution Approach 2:
The patent implements dynamic adjustment of gantry rotation speed and dose rate across different arc segments. By making the delivery parameters dynamic rather than uniform, the system can maintain high speed where beam modulation is minimal while slowing down only where necessary for complex modulation, thereby reducing overall treatment time while preserving dose quality.
2Adaptability or versatility
If multiple arcs are used to provide necessary degrees of freedom for beam modulation, then the flexibility is improved, but the total treatment time and required monitor units increase
Solution Approach 1:
The patent segments the treatment into multiple arc segments, each with optimized modulation parameters. This allows the system to achieve the necessary beam modulation flexibility within a single arc by carefully dividing it into segments, avoiding the need for multiple complete arcs and thereby reducing treatment time.
Solution Approach 2:
The patent applies different optimization criteria to different arc segments based on local anatomical and dosimetric requirements. Each segment can be tailored with appropriate beam modulation, energy levels, and delivery speeds, achieving high adaptability without requiring excessive total arc coverage.
3Manufacturing precision
If the gantry rotates through angles where radiation produces little or no beneficial effect, then the arc coverage is complete, but the dose to critical structures increases and total monitor units increase
Solution Approach 1:
The patent identifies and extracts (removes) arc segments where the geometric freedom metric indicates minimal therapeutic benefit and potential harm to critical structures. By taking out these non-beneficial segments from the treatment arc, the system reduces unnecessary dose to healthy tissue and critical organs while maintaining effective treatment coverage.
Solution Approach 2:
The patent changes the delivery parameters (gantry angle range, dose rate, beam energy) based on the geometric freedom metric for each arc segment. In segments with low geometric freedom where radiation produces little beneficial effect, the system reduces or eliminates beam delivery, thereby minimizing dose to critical structures while maintaining treatment efficacy in high-value segments.
4Manufacturing precision
If existing methods apply global search technique to detect avoidable arc-segments, then the optimal segments can be identified, but the computational time is highly time consuming
Solution Approach 1:
The patent performs preliminary calculation of the geometric freedom metric for each control point before final arc segment optimization. This preliminary assessment provides a quick indicator of which segments are likely to be beneficial or harmful, allowing the system to focus detailed optimization only on relevant segments and avoid exhaustive global search of all possible segment combinations.
Solution Approach 2:
The patent changes the optimization approach from exhaustive global search to a metric-guided selective optimization method. By introducing the geometric freedom metric as a filtering parameter, the system can quickly identify promising arc segments for removal or modification without performing computationally intensive global search, thereby achieving good optimization results with reduced computational time.
Data Source
AI summary
A non-transitory computer readable medium (26) stores instructions executable by at least one electronic processor (20) to perform a method (100, 200) of identifying possible arc segments for removal in a modulated arc therapy plan. The method includes: iteratively optimizing a modulated arc therapy plan for an initial arc segment; and computing a geometric freedom (GF) metric for each control point (CP) of the initial arc segment.