4D CT Image Verification for Respiratory Gated Radiation Therapy
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Solution Overview
Problem
Respiratory gated radiation therapy faces challenges in adapting to current breathing patterns of patients, leading to variability in the correlation between external surrogate signals and internal tumor positions, resulting in potential errors during treatment.
Innovation Solution
A method involving 4D computed tomography (CT) image acquisition, fluoroscopic imaging, and digitally reconstructed radiographs (DRRs) to assess similarity matrices, determine optimal time point synchronization, and adjust treatment beam activation based on these synchronizations, using techniques like Hidden Markov Models and Auto-Regressive models to ensure accurate tumor targeting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If respiratory gating is used to treat tumor only at prescribed position, then radiation dose delivery precision is improved, but adaptability to current breathing patterns deteriorates
Solution Approach 1:
The system continuously monitors the surrogate signal during treatment and compares it with the pre-acquired 4D CT images and fluoroscopic images to determine the current breathing phase. Based on this real-time feedback, the radiation beam is dynamically gated to deliver radiation only when the tumor is in the prescribed position, thus adapting to the patient's current breathing patterns while maintaining dose delivery precision.
Solution Approach 2:
The gating system dynamically adjusts the radiation beam delivery based on the patient's real-time breathing motion. By acquiring 4D CT images that capture the tumor position throughout the breathing cycle and using fluoroscopic verification, the system adapts the treatment delivery to the patient's actual breathing patterns, making the static gating approach dynamic and responsive.
2Ease of operation
If external surrogate signals are used to detect tumor motion, then non-invasiveness is improved, but measurement precision of tumor position deteriorates
Solution Approach 1:
The system uses an external surrogate signal (such as a marker on the abdomen or chest) as an intermediary to indirectly measure tumor position. This external marker is non-invasive and easy to apply, but its correlation with actual tumor position may vary. The system addresses this by acquiring 4D CT images and fluoroscopic images to establish and verify the relationship between the external surrogate and internal tumor position, thereby improving measurement precision while maintaining non-invasiveness.
3Manufacturing precision
If 4D CT images and fluoroscopic images are acquired and synchronized, then tumor targeting accuracy is improved, but device complexity increases
Solution Approach 1:
The system creates digitally reconstructed radiographs (DRRs) from the 4D CT images as copies of the expected tumor position at different breathing phases. These DRRs are then compared with actual fluoroscopic images to verify tumor position and determine the current breathing phase. This copying approach simplifies the verification process by avoiding the need for complex real-time 3D imaging during treatment, thus improving tumor targeting accuracy while managing device complexity.
Data Source
AI summary
A method for four-dimensional (4D) image verification in respiratory gated radiation therapy, includes: acquiring 4D computed tomography (CT) images, each of the 4D CT images representing a breathing phase of a patient and tagged with a corresponding time point of a first surrogate signal; acquiring fluoroscopic images of the patient under free breathing, each of the fluoroscopic images tagged with a corresponding time point of a second surrogate signal; generating digitally reconstructed radiographs (DRRs) for each breathing phase represented by the 4D CT images; generating a similarity matrix to assess a degree of resemblance in a region of interest between the DRRs and the fluoroscopic images; computing a compounded similarity matrix by averaging values of the similarity matrix across different time points of the breathing phase during a breathing period of the patient; determining an optimal time point synchronization between the DRRs and the fluoroscopic images by using the compounded similarity matrix; and acquiring a third surrogate signal and turning a treatment beam on or off according to the optimal time point synchronization.