Date of Graduation
8-2015
Document Type
Thesis (MS)
Program Affiliation
Medical Physics
Degree Name
Masters of Science (MS)
Advisor/Committee Chair
David Followill, Ph.D.
Committee Member
Laurence Court, Ph.D.
Committee Member
Michele Guindani, Ph.D.
Committee Member
Falk Poenisch, Ph.D.
Committee Member
Paige Taylor, M.S.
Abstract
As proton therapy increases in popularity, so does the need for effective quality assurance. Proton therapy institutions participating in NCI funded clinical trials rely heavily on the credentialing and auditing services of IROC-H and therefore the process must be well understood. The purpose of this project is to understand the uncertainties in proton therapy treatment planning for the IROC-H proton phantom QA program due to variations in CT technique and proton energy. It was hypothesized that variations in CT technique and proton energy will alter the delivered dose distributions of typical proton treatments by reducing the percent of passing pixels by 10% using a gamma analysis criteria of ±3%/5mm as measured using a heterogeneous proton QA phantom. A CT phantom used by IROC-H during therapy site visits was scanned using three CT techniques (80, 120, 140kV) with a CT scanner used for proton therapy simulations and irradiated with a passively scattered beam at three energies (140, 200, 250 MeV) to measure, respectively, HU and Relative Linear Stopping Power (RLSP) in order to create HU to RLSP calibration curves for comparison with reference curves as defined by this study. The phantom has proton equivalent materials with a wide variety of HU and RLSPs to allow for the creation of a calibration curve for common tissue equivalent materials. Treatment plans were created for an anthropomorphic proton lung phantom using the various CT technique/ beam energy calibration curves to determine the differences in the dose distributions by performing a gamma analysis. The 3D gamma analysis resulted in a pass rate of 100% for all plans and the 2D gamma analysis resulted in a pass rate above 99%. This result implied the varying treatment plans did not substantially affect the outcome of the dose comparison and therefore rejects the stated hypothesis and further work is needed to investigate the uncertainty present in this QA process.
Keywords
proton therapy, quality assurance, clinical trials, IROC, CT calibration, phantom, proton, calibration