ßÉßɱ¬ÁÏ

Topic

Decision-support strategies to improve radiotherapy outcomes in prostate and gynecological cancer treatment planning

Department of Physics and Astronomy

Date & location

• Wednesday, July 23, 2025
• 9:00 A.M.
• Clearihue Building, Room B021

Examining Committee

Supervisory Committee

• Dr. Manuel Rodriguez Vega, Department of Physics and Astronomy, ßÉßɱ¬ÁÏ
  (Co-Supervisor)
• Dr. Magdalena Bazalova-Carter, Department of Physics and Astronomy, UVic (Co-Supervisor)
• Dr. Isabelle Gagné, Department of Physics and Astronomy, UVic (Member)
• Dr. Ibrahim Numanagić, Department of Computer Science, UVic (Outside Member)

External Examiner

• Dr. Hervé Choi, Department of Surgery, University of British Columbia

Chair of Oral Examination

• Dr. David Berg, Department of Chemistry, UVic

Abstract

Effective radiotherapy treatment depends on delivering a sufficient dose to the tumour to kill all cancer cells while minimizing radiation exposure to surrounding healthy tissues and nearby sensitive structures known as organs at risk (OARs). Achieving this balance is particularly important in prostate and gynecological cancers where critical structures are located in close proximity to the target. This thesis investigates decision-support strategies that aim to improve the robustness, precision, and overall quality of radiotherapy treatment plans. The research focuses on two clinically distinct applications of radiotherapy involving low-dose rate (LDR) prostate brachytherapy and external beam radiation therapy (EBRT) for gynecological cancers.

In the LDR prostate brachytherapy component, an in-house dose engine was used to simulate seed placement uncertainties associated with procedural variability during implantation. Based on these simulations, the software calculated the probabilities of achieving pre-implant dosimetric constraints, including the planning target volume (PTV) receiving 150% of the prescription dose (PTV V150%) and global coverage metrics. These probabilities were then used to determine threshold values predictive of achieving one of the post-implant objectives, prostate D90%, defined as the dose received by 90% of the prostate volume. The resulting thresholds provided a quantitative framework for assessing plan robustness and guiding data-informed adjustments prior to treatment.

In the EBRT component, the dose gradient optimization performance of the Normal Tissue Objective (NTO) and Concentric Ring Structures (CRS) was systematically evaluated in gynecological cancer treatment plans. Both methods achieved clinical constraints for target coverage and OAR sparing. The NTO demonstrated consistent and reliable performance, while CRS provided enhanced flexibility in shaping the dose gradient in anatomically complex scenarios. These findings contribute to treatment planning by informing the selection of optimization strategies based on case complexity and clinical priorities.

These findings contribute to the development of robust, data-informed planning strategies tailored to the clinical and anatomical challenges of prostate and gynecological cancer radiotherapy treatment. By guiding adjustments to planned seed placement in LDR brachytherapy and informing dose gradient optimization in EBRT planning, they address the critical need to balance effective tumour coverage with the protection of OARs, ultimately improving plan quality and supporting more consistent patient care.