Dynamic PTV Margin Adjustment for Adaptive Radiation Therapy
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Solution Overview
Problem
Current external beam radiation therapy (EBRT) systems fail to accurately account for intrafraction and interfraction motion of tumors, leading to incomplete dose coverage and increased damage to surrounding normal tissue due to static margins and inadequate adjustment for tumor shrinkage during radiation therapy.
Innovation Solution
A therapy system that updates treatment plans based on pre-fraction imaging and tracking data to dynamically adjust the size and shape of the internal target, using body surface tracking to improve correspondence between external and internal target motion, enabling more precise delivery gating and reduced normal tissue exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If static margins are added around the target to ensure complete dose coverage, then target coverage is improved, but damage to surrounding normal tissue increases
Solution Approach 1:
The patent implements dynamic PTV margins that are adjusted in real-time based on actual target motion measured during treatment delivery. Instead of using fixed static margins, the system continuously updates the PTV boundary to match the actual tumor position, allowing margins to shrink when the target is well-positioned and expand only when motion requires it. This dynamic adaptation resolves the contradiction by providing coverage only when necessary.
Solution Approach 2:
The system incorporates real-time feedback from surface tracking devices and internal imaging systems to monitor target position during treatment. This feedback loop allows the delivery control system to adjust beam delivery parameters and PTV margins dynamically based on actual target location, ensuring complete coverage when the target moves into the margin zone while minimizing exposure when the target remains centrally positioned.
2Reliability
If large static margins are used to account for tumor motion, then incomplete dose coverage is prevented, but the effectiveness of treatment is reduced due to increased normal tissue exposure
Solution Approach 1:
The system dynamically adjusts PTV margins during treatment delivery based on real-time target position feedback. When the target remains within the central region, margins are effectively reduced or eliminated, maximizing treatment effectiveness. When motion pushes the target toward the margin boundary, the system automatically expands margins to maintain complete coverage, thus resolving the contradiction between coverage completeness and treatment effectiveness.
Solution Approach 2:
The patent changes the PTV margin parameter from a fixed static value to a dynamic value that varies continuously during treatment based on target position. This parameter change allows the system to optimize the balance between coverage and effectiveness in real-time, using smaller margins when appropriate and larger margins only when motion requires it.
3Device complexity
If pre-procedural planning data is used for the entire treatment course, then planning complexity is reduced, but accuracy of target motion prediction deteriorates due to tumor shrinkage and pattern changes
Solution Approach 1:
The system performs preliminary adaptive re-planning at scheduled intervals during treatment (e.g., mid-course adaptations). Before these adaptation points, the original pre-procedural plan is used to maintain simplicity. At the adaptation points, updated planning data is acquired to account for tumor shrinkage and pattern changes, then this updated plan is used for the remaining fractions. This approach balances planning complexity with accuracy by updating only when necessary.
Solution Approach 2:
The patent implements periodic adaptive re-planning at scheduled intervals during the treatment course rather than continuously. This periodic update approach maintains planning simplicity for most of the treatment while periodically refreshing the motion prediction models to account for tumor changes, resolving the contradiction between complexity and accuracy.
4Device complexity
If body surface tracking is used to predict internal target motion, then cost and implementation complexity are reduced, but prediction accuracy is insufficient without accurate correspondence data
Solution Approach 1:
The patent uses internal anatomical structures visible on planning images as intermediaries to establish the correspondence between external surface motion and internal target motion. These internal structures serve as a bridge, allowing the system to learn the transformation relationship between surface tracking data and target position without requiring direct internal imaging during treatment. This intermediary approach maintains simplicity while improving prediction accuracy.
Solution Approach 2:
The system creates a computational model (copy) of the target and surrounding anatomy from pre-procedural imaging data. This digital copy includes the learned correspondence relationships between surface and internal structures. During treatment, surface tracking data is transformed through this copied model to predict actual target position, maintaining simplicity while improving accuracy through the pre-established correspondence model.
Data Source
AI summary
A therapy system and method treats an internal target of a patient (16). A treatment plan (36) is received to treat the internal target. The treatment plan (36) includes a plurality of treatment fractions including correspondences (38) between the internal target and an external body surface based on a pre-procedural planning image (14) and pre-procedural tracking data (20). Before selected treatment fractions of the plurality of treatment fractions, a pre-fraction planning image (50) of the target is received, tracking data (20, 52) of the external body surface of the patient (16) is received, and the correspondences (38) between the internal target and the external body surface are updated based on the received pre-fraction planning image (50) and the received tracking data (20, 52). Therapy is delivered to the patient (16) in accordance with the treatment plan (36) and using the updated correspondences (38).