By Michael Lavelle
The Kennedy College of Science, Department of Physics, invites you to attend a master's thesis defense by Michael Lavelle entitled “MRI Guided Surface Brachytherapy: Feasibility and Directions for Clinical Implementation.”
MS Candidate: Michael Lavelle
Date: Friday, March 24, 2023
Time: 1 to 2:30 p.m.
Location: This will be a virtual defense via Zoom. Those interested in attending should contact MS candidate Michael_lavelle@student.uml.edu at least 24 hours prior to the defense to request access to the meeting.
Title: MRI Guided Surface Brachytherapy: Feasibility and Directions for Clinical Implementation
- Committee Chair Ivan Buzurovic, Ph.D., M.Sc. Assistant Professor & Faculty Medical Physicist, Radiation Oncology, Harvard Medical School
- Erno Sajo, Ph.D., M.Sc., Professor, Director of Medical Physics, Physics & Applied Physics, UMass Lowell
- Romy Guthier, Ph.D., M.Sc., Associate Professor, Physics, UMass Lowell
In this study, a comparison of surface brachytherapy treatment planning using CT-based and MR-based imaging was performed to determine whether magnetic resonance can be used as the sole modality for surface brachytherapy treatment planning. A phantom of solid water-equivalent was 3D printed to fit a Freiberg Flap applicator of 31 catheters, and images were taken using both a pointwise encoding time reduction with radial acquisition (PETRA) MR sequence optimized for catheter visualization and a helical CT scan to generate treatment plans. Additionally, three patients undergoing surface brachytherapy with bilateral Dupuytren’s Contracture/Palmar fascial fibromatosis were imaged using this PETRA sequence and a helical CT scan. Catheter digitization and dwell position activation were performed in the treatment planning software using both modalities. A point-by-point comparison of the dwell positions was performed by exporting the Cartesian coordinates of each set of catheters and performing a rigid registration. The average Euclidean distances between pairs of corresponding dwell positions were calculated to demonstrate whether the MR-based plan is clinically acceptable. Treatment plans were produced using the PETRA sequence from both phantom and patients. Euclidean distances between dwell positions were on average 0.68mm, 1.15mm, 1.22mm, and 1.69mm for phantom and patients respectively. The sub-millimeter accuracy of the catheter displacements for the phantom demonstrated that the digitization was clinically acceptable, and accurate treatment plans can be produced using only MR. By creating faithful representations of CT-based catheter digitizations using MR-based imaging, it has been demonstrated that it is possible to produce clinically acceptable treatment plans in surface brachytherapy using MR. With the increased soft tissue contrast afforded by MR, there is a potential for greater visualization of subcutaneous treatment sites, which can result in a more accurate visualization of tumor depth than the 3mm assumed by CT-based planning and therefore better patient outcomes.