Browsing by Author "Loewen, Shaun"

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    A phase III, multicenter, randomized controlled trial of preoperative versus postoperative stereotactic radiosurgery for patients with surgically resectable brain metastases
    (2022-12-30) Das, Subhadip; Faruqi, Salman; Nordal, Robert; Starreveld, Yves; Kelly, John; Bowden, Gregory; Amanie, John; Fairchild, Alysa; Lim, Gerald; Loewen, Shaun; Rowe, Lindsay; Wallace, Carla; Ghosh, Sunita; Patel, Samir
    Abstract Background Postoperative stereotactic radiosurgery (SRS) is a standard management option for patients with resected brain metastases. Preoperative SRS may have certain advantages compared to postoperative SRS, including less uncertainty in delineation of the intact tumor compared to the postoperative resection cavity, reduced rate of leptomeningeal dissemination postoperatively, and a lower risk of radiation necrosis. The recently published ASCO-SNO-ASTRO consensus statement provides no recommendation for the preferred sequencing of radiotherapy and surgery for patients receiving both treatments for their brain metastases. Methods This multicenter, randomized controlled trial aims to recruit 88 patients with resectable brain metastases over an estimated three-year period. Patients with ten or fewer brain metastases with at least one resectable, fulfilling inclusion criteria will be randomized to postoperative SRS (standard arm) or preoperative SRS (investigational arm) in a 1:1 ratio. Randomization will be stratified by age (< 60 versus ≥60 years), histology (melanoma/renal cell carcinoma/sarcoma versus other), and number of metastases (one versus 2–10). In the standard arm, postoperative SRS will be delivered within 3 weeks of surgery, and all unresected metastases will receive primary SRS. In the investigational arm, enrolled patients will receive SRS of all brain metastases followed by surgery of resectable metastases within one week of SRS. In either arm, single fraction or hypofractionated SRS in three or five fractions is permitted. The primary endpoint is to assess local control at 12 months in both arms. Secondary endpoints include local control at other time points, regional/distant brain recurrence rates, leptomeningeal recurrence rates, overall survival, neurocognitive outcomes, and adverse radiation events including radiation necrosis rates in both arms. Discussion This trial addresses the unanswered question of the optimal sequencing of surgery and SRS in the management of patients with resectable brain metastases. No randomized data comparing preoperative and postoperative SRS for patients with brain metastases has been published to date. Trial registration Clinicaltrials.gov , NCT04474925; registered on July 17, 2020. Protocol version 1.0 (January 31, 2020). Sponsor: Alberta Health Services, Edmonton, Canada (Samir Patel, MD).
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    Development and Clinical Implementation of Applications for Guiding Linac-Based Stereotactic Radiosurgery Planning
    (2023-08) Mann, Thomas David; Thind, Kundan S.; Moazzen-Ahmadi, Nasser; Ploquin, Nicolas P.; Pierce, Greg David; Loewen, Shaun
    Stereotactic Radiosurgery (SRS) is a well-established treatment technique for brain lesions that uses a high dose of radiation delivered in a single fraction. Studies have shown improved cognitive outcomes with SRS for the treatment of brain metastases compared to whole brain radiation therapy. While effective, SRS planning is a complex and time-consuming process due to non-coplanar beam angles, multiple metastases, and proximity to organs-at-risk within the brain. Scripting can be used to automate complex planning processes and analyze patient data through a treatment planning system application programming interface. Applications developed using scripting can help inform planner decision-making and improve clinical efficiency. This thesis investigates the design and clinical implementation of two scripting applications developed to assist SRS planning at the Tom Baker Cancer Centre. The use of non-coplanar beam angles in SRS increases the risk of collision between the linac gantry and the patient or treatment table. We developed the Clearance Check application to predict possible collisions in radiation treatment plans using patient CT body contours and accurate models of the gantry and immobilization. The collision prediction algorithm uses oriented bounding boxes and binary tree hierarchies to improve algorithm efficiency. Algorithm accuracy was assessed using a calibration phantom and several simulated treatment positions. Initial results from clinical implementation are reported and a follow-up summary after five years of use is also included. Collision prediction, beam angle optimization and automated plan creation were combined to create the Stereotactic Optimized Automated Radiotherapy (SOAR) application. SOAR planning was compared to manual SRS planning and found to achieve similar plan quality with a significant increase in plan creation efficiency. SOAR was then benchmarked against the commercial SRS planning solution HyperArc. SOAR showed improved target conformity, better organ-at-risk sparing, and lower plan complexity. The SOAR application provides greater versatility in SRS planning, straightforward integration with the treatment planning system, and is not restricted to a specific immobilization device. Initial improvements in SRS planning efficiency using SOAR are reported. Overall, this thesis presents novel applications of scripting to improve the SRS planning process, enhancing clinical efficiency while maintaining plan quality.