http://hdl.handle.net/1957/19606 2013-05-18T14:44:20Z http://hdl.handle.net/1957/21286 Estimation of the setup accuracy of a surface image-guided stereotactic positioning system Meng, Lu Zheng Purpose: Stereotactic radiation therapy and stereotactic radiosurgery deliver radiation precisely to tumors, using special equipment to position and demobilize patients. The VisionRT system, with its component AlignRT, is a non-invasive stereotactic positioning and tracking system that uses cameras to capture infra-red images of patients, and process these images, to obtain precise shifts in patient location. This thesis evaluates the accuracy of the AlignRT system accuracy while setting up and tracking patients. Methods: This thesis investigates the setup accuracy of the AlignRT system based on the CT contour of an anthropomorphic phantom exported to the AlignRT from treatment planning systems, and compared results to those provided by the X-ray image-based positioning system ExacTrac. Measurements utilize a modified Winston-Lutz technique to derive the deviation of the planned isocenter relative to the radiation isocenter. A phantom embedded with a 16 mm metallic sphere and a Winston-Luts pointer were used as the positioning objects. A Varian electronic portal imaging device were utilized to obtain images. A Vidar scanner and RIT113v5.2 software were used to process images obtained in Winston-Lutz tests. Based on the equations derived for Winston-Lutz tests, shifts of the planned isocenter relative to the radiation isocenter were calculated, which were then used to judge the positioning the objects. Both positioning and tracking modes of AlignRT were tested. AlignRT, ExacTrac, and Winston-Lutz test measurements were all performed on the same Varian Novalis Tx system. Results: The results indicated that the AlignRT gave a positioning error of more than 1 mm based on CT contours and at small couch angles, which was larger than the clinical tolerance of 1mm for stereotactic radiation therapy. The positioning error would be less if the AlignRT system could be recalibrated with the same isocenter as the X-ray system or utilize its own initial image instead of CT contour. At larger couch angles, the positioning errors were larger than 1 mm even after recalibration. A further investigation and collaboration with the manufacture would be required to obtain desired accuracy. Graduation date: 2011 2011-05-11T00:00:00Z http://hdl.handle.net/1957/19594 Comparison of secondary neutron dose from 10 MV intensity modulated radiation therapy and volume modulated arc therapy Catchpole, Mary Elizabeth Photoneutron contamination produced during high-energy, external beam radiotherapy can contribute to total patient dose. This aspect of unwanted dose is not currently evaluated for patients undergoing radiation therapy. While multiple studies have examined the neutron dose from beams with energies above 10 MeV, research assessing neutron dose from a 10 MV beams is sparse. Additionally, no studies have assessed the neutron dose from volume modulated arc therapy (VMAT) or compared to that of intensity modulated radiation therapy (IMRT). A series of physical measurements were performed using neutron bubble dosimeters to determine neutron dose per Gy photon dose for field sizes 0x0 cm², 5x5 cm², and 10x10 cm² on a Varian Trilogy linac operating at 10 MV. These measurements were compared to photoneutron production simulated with a simplified model of the linac head using MCNP5. The simulations predicted within 6% of the measured dose for the 5x5 field and within 3% for the 10x10 field, however over predicted over 600% for the closed field. This indicates that the simplified model is not appropriate for small field neutron dose calculations but may be a good starting point for more complete models. Additional measurements were collected for clinically representative IMRT and VMAT plans designed to treat the same prostate tumor. Total neutron dose was higher 14.6% for the IMRT plan, which was less than expected based on the total delivered monitoring units and may be related to different average field sizes for the two treatments. This under-prediction of neutron dose suggests that neutron dose estimates should be independently assessed for the different modalities. Graduation date: 2011 2010-12-21T00:00:00Z