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Comparison of setup error using different reference images: a phantom and lung cancer patients study
Bo Jiang1, Jianrong Dai, Ye Zhang
1Department of Radiation Oncology, Cancer Institute (Hospital), Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing, China. jiangbo122@126.com
Summary
For lung cancer patients, average 4D CT (AVG-CT) images provide more accurate patient setup localization than free-breathing CT (FB-CT) when using kilovoltage cone-beam CT. AVG-CT is recommended for improved accuracy in radiation therapy targeting.
Area of Science:
- Medical Imaging
- Radiation Oncology
- Image-Guided Therapy
Background:
- Accurate patient setup is crucial for effective radiation therapy, especially for lung cancer patients where respiratory motion can displace the tumor.
- Kilovoltage cone-beam computed tomography (CBCT) is widely used for image-guided radiation therapy (IGRT).
- Comparing different reference image types for CBCT-based patient setup is essential for optimizing accuracy.
Purpose of the Study:
- To compare setup errors derived from CBCT using free-breathing CT (FB-CT) versus average 4D CT (AVG-CT) as reference images.
- To investigate the correlation between translational setup error differences and gross tumor volume (GTV) motion in lung cancer patients.
- To determine the preferred reference image for accurate patient positioning in lung cancer radiotherapy.
Main Methods:
- Utilized a respiratory phantom and 14 lung cancer patients for image acquisition.
- Acquired 3D helical CT and 4D CT, generating AVG-CT from 4D CT data.
- Performed image registration between CBCT and both FB-CT and AVG-CT to determine translational and rotational setup errors.
Main Results:
- AVG-CT proved more accurate than FB-CT in phantom studies.
- Patient translational setup errors were significantly larger with FB-CT than AVG-CT in LR, SI, and AP directions (p < 0.05).
- Significant differences in rotational setup errors were observed between FB-CT and AVG-CT in LR and AP directions (p < 0.05).
- A strong correlation was found between translational setup error differences and GTV centroid movement, particularly in the SI direction (r=0.902, p < 0.001).
Conclusions:
- Respiratory motion significantly impacts on-line target positioning for lung cancer patients.
- AVG-CT provides distinct and more reliable reference information compared to FB-CT.
- The discrepancies between FB-CT and AVG-CT increase with GTV motion, supporting AVG-CT as the preferred reference image for patient setup.
