Date of Graduation
8-2014
Document Type
Thesis (MS)
Program Affiliation
Medical Physics
Degree Name
Masters of Science (MS)
Advisor/Committee Chair
Laurence E Court, Ph.D.
Committee Member
Beth Beadle, M.D., Ph.D.
Committee Member
Peter Balter, Ph.D.
Committee Member
Pai-Chun Chi, Ph.D.
Committee Member
Francesco Stingo, Ph.D.
Abstract
There are numerous benefits to treating patients in the upright position such as better patient comfort and increased total lung volume with reduced lung motion. The purpose of this study was to investigate the feasibility of implementing upright treatments for lung and H&N cancers. Several clinical aspects were examined, including radiation shielding for various fixed beams, collision avoidance, retrospective treatment planning, and an end-to-end test with an anthropomorphic lung phantom.
Results from the shielding study indicated that the primary barrier required an additional 10-26 cm of shielding while the secondary barrier in the beam path required an additional 2-12 cm for the fixed-beam scenarios. Due to the conservative assumptions in the workloads and the NCRP computational methods, it was determined that additional shielding for a pre-existing treatment vault was not likely. However, physical measurements are required to ensure that regulatory limits are not exceeded. The collision software safely predicted all collisions for three tested cases. The differences between the computed results and the actual measurements were between 0.2-4.1 cm, which was compensated by the uncertainties incorporated into the results. The actual measured collisions were never in the area of the maps that was designated as safe. The treatment planning study resulted in clinically acceptable upright plans for five lung and five H&N patient cases. The upright lung plans produced acceptable and comparable results to those in the original plans. The dose coverage and normal tissue doses were less optimal in the upright H&N plans. However, with proper planning techniques, similar quality as the original plans is likely achievable. For the end-to-end test, the treatment plan passed the IMRT QA criteria of 0.95-1.05 for point dose and obtained a gamma index of 89.25%. Dosimetry verification demonstrated good agreement between the treatment plan doses and the delivered doses and obtained a point-dose dose difference of 2% and gamma analysis index of 100%, which were within the acceptability of IROC Houston criteria. The results of this research confirmed the feasibility of upright treatments for lung and H&N cancers and can aid the institution in future clinical studies with actual subjects.