Accuracy and efficiency of image-guided radiation therapy (IGRT) for preoperative partial breast radiosurgery.

Objective: To analyze and evaluate accuracy and efficiency of IGRT process for preoperative partial breast radiosurgery. Methods: Patients were initially setup with skin marks and 5 steps were performed: (1) Initial orthogonal 2D kV images, (2) pre-treatment 3D CBCT images, (3) verification orthogonal 2D kV images, (4) treatment including mid-treatment 2D kV images (for the final 15 patients only), and (5) post-treatment orthogonal 2D kV or 3D CBCT images. Patient position was corrected at each step to align the biopsy clip and to verify surrounding soft tissue positioning. Results: The mean combined vector magnitude shifts and standard deviations at the 5 imaging steps were (1) 0.96 +/- 0.69, (2) 0.33 +/- 0.40, (3) 0.05 +/- 0.12, (4) 0.15 +/- 0.17, and (5) 0.27 +/- 0.24 in cm. The mean total IGRT time was 40.2 +/- 13.2 minutes. Each step was shortened by 2 to 5 minutes with improvements implemented. Overall, improvements in the IGRT process reduced the mean total IGRT time by approximately 20 minutes. Clip visibility was improved by implementing oblique orthogonal images. Conclusion: Multiple imaging steps confirmed accurate patient positioning. Appropriate planning and imaging strategies improved the effectiveness and efficiency of the IGRT process for preoperative partial breast radiosurgery.