3778 - Clinical Implantation of Adaptive Radiation Treatment using MR-guided Linac for Salvage Radiation Treatment of Gynecological Malignancies
Presenter(s)
A. AlQaderi1,2, E. Kong3, L. Chin4, E. Barnes5, H. Su6, M. Nielsen3, D. Erler7, and E. W. Leung2; 1University of Toronto, Toronto, ON, Canada, 2Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 3Odette Cancer Centre, Toronto, ON, Canada, 4University of Toronto - Sunnybrook Odette Cancer Centre, Toronto, ON, Canada, 5Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 6Odette Cancer Centre, toronto, ON, Canada, 7Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada
Purpose/Objective(s): Online adaptive radiotherapy with MRI integration may improve target localization in gynecologic malignancies allowing for smaller planning margins and reduced toxicity. We report our initial institutional experience in treating recurrent gynecologic cancers with salvage radiation therapy using a magnetic resonance imaging–guided linear accelerator (MRL).
Materials/Methods: Patients with gynecologic malignancies requiring salvage radiation were selected for MRL treatment based on prior radiation, extent of tumor, and brachytherapy eligibility. Patients were enrolled on an IRB-approved protocol. Treatments were planned with step-and-shoot intensity-modulated radiation therapy (IMRT) and delivered on a 1.5T MRL. All patients received 5 fractions. A 5-mm margin was added to the gross tumor volume (GTV) to create the planning target volume (PTV).
Daily online adaptation using adapt-to-shape (ATS) was done for every patient which allows adjustment of target and normal structure contours prior to plan adaptation. If required, adapt- to-position (ATP) will be applied following a verification scan. Recorded workflow parameters included treatment duration, need for ATP, isocenter shift magnitudes, and number of beams.Results: Sixteen patients received salvage treatment using MRL. Median age was 70.5 years (55-95). Fifty percent (n=8) of patients had primary uterine adenocarcinoma and the rest had cervical (n=3), vaginal (n=2), colorectal (n=2), and ovarian (n=1) primaries. Prescribed dose ranged from 25–35 Gy in 5 fractions using an 11-16 beam arrangement. Salvage treatment was delivered as stand-alone therapy (n=14) or as a boost after external beam radiation (n=2). Fifteen of 16 patients were treated to the vagina and 1 to the cervix and uterus. Average total appointment time was 59 minutes, including an average contouring time of 16 minutes. Average beam-on time was 7 minutes and 20 seconds. All patients completed the prescribed course. Of 80 delivered fractions, ATP was used in 11 fractions. On average, the isocenter shift was 0.02cm (left-right), 0.01cm (superior-inferior), and 0.1cm (anterior-posterior).
Conclusion: Salvage radiation therapy on a 1.5T MR-Linac is clinically feasible for selected patients with recurrent gynecologic cancers, as demonstrated by treatment completion and reported workflow times. Additional follow-up and reporting of clinical outcomes are needed to support efficacy and safety conclusions in larger cohorts.