Dissertation Abstract

Video-Based Patient Positioning for External Beam Radiation Therapy.

The goal of this work was to develop a video camera based patient positioning technique for external beam radiation therapy. The video camera system was developed to measure 3D patient location using a video camera system and data from computed tomography (CT) scanning. This work had two objectives: (1) develop a photogrammetric video camera calibration technique to calibrate video cameras to the native coordinate system of the radiation therapy linear accelerator; and (2) develop a technique to determine the three dimensional patient positioning error on the treatment table for daily radiation therapy treatments.

This work developed a new method to calibrate video cameras to the machine coordinate system of a linear accelerator. A novel calibration phantom was used that was designed for both video and X-ray imaging systems. An electric portal imaging device was used to locate the calibration phantom with respect the machine coordinate system. This technique was tested using extensive simulations to determine its ability to accurately determine the correct calibration. Patient positioning errors were measured using a new surface matching technique. Surface Patch Correlation (SPC) was developed to align a surface model of the patient to the position of the patient seen in the video images.

The SPC technique was tested on both a phantom and clinically. Clinical tests included four patients treated for prostate cancer. Portal imaging was used to determine the absolute patient positioning error. The results of measurements using the SPC technique were compared to the portal imaging results to determine if SPC could reduce patient positioning errors. Positioning experiments with the head phantom showed the SPC technique was able to measure positioning with an error of less than 1mm. The clinical experiments showed that in the pelvis, the SPC technique had difficulty matching the surface along the patients' cranial-caudal direction while showing better results in the lateral and anterior-posterior directions.

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