Semester of Graduation

Fall 2018

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

Purpose: This work investigated the delivery accuracy of high-dose lung and spine stereotactic treatments delivered with the Elekta Infinity and Versa HD platforms. The accuracy of these platforms will be used for consideration in implementing a spine stereotactic radiosurgery (SSRS) program at Mary Bird Perkins Cancer Center.

Methods: A geometric phantom was used to perform Winston-Lutz type tests that assessed the relevant degrees of freedom (gantry, collimator, and couch) of the delivery system. A lung stereotactic body radiation therapy (SBRT) and spine SRS treatment plan were generated for use in end-to-end testing. Delivery accuracy was tested using a novel diode array design, which achieved a spatial resolution of 1 mm along a single axis. On board imaging aided in setup of the diode array to the desired position before commencing treatment delivery. The delivered dose distribution and calculated planar dose distributions were compared and analyzed. Several metrics were analyzed from the overlaid profiles, including: percent difference between calculated and measured field centers, and comparison of spatial shifts of the 75% and 60% isodose levels. Percent difference between a calculated and measured point dose quantified discrepancies for the approximate region of the spinal cord. Calculated dose profiles and shifts at the 60 and 75% isodose levels indicated distortions in the profiles.

Results: All machines demonstrated an MV Isocenter radius for gantry and treatment table rotation less than 0.70 mm as limited by the Elekta customer acceptance protocol. For SSRS plans, percent difference of the point representing the spinal cord produced results that were consistently higher as a result of a higher dose delivery than calculated. All lung SBRT and SSRS deliveries were capable of achieving an average of 1-mm accuracy. Moreover, profiles showed that the measured profile fell within the planned profile, suggesting a systematic distortion in the profiles.

Conclusion: Based on the findings of this project, the Elekta Infinity and Versa HD delivery systems were adequate for lung SBRT treatments but require further exploration for the commencement of spine SRS treatments at Mary Bird Perkins Cancer Center.

Date

7-31-2018

Committee Chair

Fontenot, Jonas

DOI

10.31390/gradschool_theses.4780

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