2832 - The Benefit of Repeat Magnetic Resonance Imaging before Each Fraction for Gynecological Brachytherapy
Presenter(s)
M. T. Roozeboom1, S. Rajan1, O. A. Alegi1, M. O. Evbuomwan1, A. R. Way1, U. A. Uzomah1, J. S. Zeng2, E. S. Rickles1, W. Sun1, and Q. Adams3; 1Department of Radiation Oncology, University of Iowa Health Care, Iowa City, IA, 2Department of Biology, University of Iowa, Iowa City, IA, 3Department of Radiation Oncology, Levine Cancer Institute, Atrium Health, Charlotte, NC
Purpose/Objective(s): The use of Magnetic Resonance Imaging (MRI) based treatment planning is the standard of care for locally advanced cervical cancer, and the most commonly involves a single MRI performed before the first fraction of brachytherapy. What remains unclear is whether repeat MRI before each subsequent fraction adds value by identifying tumor treatment responses, thus allowing for a more adaptive approach to brachytherapy planning. This study evaluates the potential benefit of identifying tumor volume changes on repeat MRI obtained before each brachytherapy fraction.
Materials/Methods: In this IRB-approved single-institution study, we included patients who received treatment for locally advanced cervical cancer using the precision radiation medicine company brachytherapy applicator at the University of Iowa Health Care between January 2020 and June 2024. We conducted a retrospective chart review and performed statistical analysis using descriptive statistics and a linear mixed-effects model in R (version 4.4.2).
Results: There was data collected for 94 patients who underwent high-dose rate brachytherapy during the data collection time period with a median age at diagnosis of 52 years old (range, 25-84 years). Disease stage ranged from FIGO IA to IVB, with majority of patients having cervical cancer FIGO stage IIIC (49.8%), and FIGO stage IV (14.8%). The most common brachytherapy prescription was 30 Gy in 5 fractions (63%). MRI was obtained at every treatment fraction for 90% of patients. Overall mean high-risk clinical target volumes (HR-CTV) were as follows: fraction 1: 44 cm³ (SD = 34, n = 91), fraction 2: 44 cm³ (SD = 28, n = 87), fraction 3: 40 cm³ (SD = 25, n = 86), fraction 4: 42 cm³ (SD = 26, n = 81), and fraction 5: 45.1 cm³ (SD = 26.7, n = 57). A linear mixed-effects model was applied to account for substantial inter-patient and baseline differences in HR-CTV. A significant decline in HR-CTV was observed in treatment fractions 3-5 compared to the first fraction (-11.7%, -8.5%, -12.9%, all p <0.05).
Conclusion: The statistically significant changes in HR-CTV observed in this study suggest that repeat MRI before each fraction of brachytherapy has the potential to identify substantial tumor responses throughout a brachytherapy course which could allow for clinically beneficial changes in brachytherapy volumetric planning.