10/19/2022
By Lee Goddard

The Kennedy College of Sciences, Department of Physics and Applied Physics, invites you to attend a Ph.D. dissertation defense by Lee Goddard on "Prostate Stereotactic Body Radiation Therapy: Development, Commissioning, Testing and Clinical Implementation of a Real Time Motion-Adapted Approach."

Date: Nov. 2, 2022
Time: 1 p.m.
Location: Via Zoom. Those interested in attending should contact Lee_Goddard@student.uml.edu

Title: Prostate Stereotactic Body Radiation Therapy: Development, Commissioning, Testing and Clinical Implementation of a Real Time Motion-Adapted Approach

Committee Chair:
Wolfgang A. Tomé, Ph.D., Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell, Director of Medical Physics, Institute for Onco-Physics at the Albert Einstein College of Medicine

Committee Members:

  • Wilfred Ngwa, Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell, Associate Professor of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins
  • Erno Sajo, Ph.D., Professor, Director - Medical Physics, Department of Physics and Applied Physics, University of Massachusetts Lowell

Abstract:
Stereotactic body radiation therapy is a highly accurate and precise treatment technique that utilizes high doses of radiation to target various cancers, including prostate cancer. Achievable radiation dose distributions are compared for advanced photon and proton-based delivery techniques. It was found that whilst similar treatment plans could be generated when range and HU uncertainties were neglected, when accounting for these uncertainties during robust optimization, photon techniques outperform proton techniques in terms of achievable target conformity and high dose sparing of nearby organs at risk (OARs). As expected, integral dose and low dose sparing was improved with proton techniques.

Commissioning of state-of-the-art motion compensation delivery technology and helical fan beam kV-CT imaging technology was performed for a ring gantry photon radiation therapy delivery device. Large improvements in delivered dose distribution were measured with a range of phantoms and motion types. Testing methods and QA procedures including imaging quality metrics, imaging dose parameters, dose deposition accuracy, target detection coincidence, and target position detection accuracy are described to provide guidance for new users of the system.

Image quality metrics (IQMs) were evaluated to assess the capabilities of the newly available kV-CT. IQMs were evaluated and compared to a kVCT simulator and linear accelerator-based cone beam CTs (CBCT). Helical fan beam kVCT was found to allow for daily image guidance for localization and setup verification with comparable performance to existing kV-CBCT systems. Improved image quality was found over the MVCT imaging system previous iterations of the device were limited to, this has the potential to reduce patient setup time, improve setup accuracy and greatly improve manual and automated adaptive monitoring and planning.

A large component of the target margins utilized in prostate SBRT is due to the potential motion of the target. Motion compensation and gating techniques were investigated utilizing five patient plans and four different motion types. When target motion was not accounted for large shifts in planned vs. delivered isodose distributions were found, however, when motion compensation, or gated techniques were applied, much smaller differences between planned and delivered isodose distributions were found. With these techniques a 2 mm PTV margin was found to be sufficient to ensure adequate CTV coverage. Minimizing target margins reduces the volume of nearby OARs receiving high doses of radiation, potentially improving patient toxicity outcomes.