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A Self-Calibrating Optical System to Improve Patient Positioning During Breast Radiotherapy

D Nazareth

D Nazareth1*, C Merrow2, H Malhotra3, K Hoffmann4, (1) Roswell Park Cancer Institute, Buffalo, NY, (2) ,Buffalo, NY, (3) Roswell Park Cancer Institute, East Amherst, NY, (4) Neurosurgery at SUNY at Buffalo, Buffalo, NY

SU-E-J-53 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Breast radiotherapy, particularly electronic compensation, may involve large dose gradients and difficult patient positioning problems. We have developed a simple self-calibrating optical image-guided system, which assists in accurately and reproducibly positioning the patient, by displaying her real-time optical image from a single camera superimposed on a perspective projection of her 3D CT data. Our method requires only a standard high-zoom digital camera capable of live-view mode, set up in the treatment suite at a fixed orientation and position (rotation, R and translation, T).

Methods: A 10-sphere calibration jig was constructed and CT imaged to provide a 3D model. The camera R and T were determined by taking a photograph of the jig and optimizing an objective function, which compares the true image points to points calculated with a given candidate R and T geometry. Using this geometric information, 3D CT patient data, viewed from the camera perspective, is plotted using a Matlab routine. This image data is superimposed onto the real-time patient image, acquired by the camera, and displayed using standard live-view software. This enables the therapists to view both the current and desired positions of the patient, and guide her into assuming the correct position. The method was evaluated using an in-house developed breast phantom, mounted on a supporting platform, which could be tilted at various angles to simulate treatment-like geometries.

Results: Our system allowed us to align the breast phantom, with an accuracy of about 0.5 cm and 5°. Better resolution could be possible with a camera with higher-zoom capabilities.

Conclusion: We have developed a system to superimpose a perspective projection of a CT image on a patient real-time optical image. Such a system has the potential to improve patient setup accuracy during breast radiotherapy, and could possibly be used for other disease sites as well.

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