Magnetic Resonance Imaging-Guided Single-Fraction Preoperative Radiotherapy for Early Stage Breast Cancer (The RICE Trial): Feasibility Study

Abstract Background: Over the past decade, the adoption of screening programs, digital mammography, and Magnetic Resonance Imaging (MRI) has increased early-stage breast cancer diagnosis rates. Mortality rates have decreased due to early detection, improved treatments, including personalized therapies. Accelerated partial breast irradiation (APBI) is emerging as a convenient and effective treatment for some patients, with studies exploring its preoperative use. Preoperative APBI, especially with MRI guidance, offers improved tumor targeting and reduced side effects. The RICE trial aims to assess the feasibility and efficacy of MRI-guided single-dose radiotherapy for early-stage breast cancer. Methods: The RICE study is a prospective, single-arm study evaluating single fraction pre-operative, accelerated partial breast irradiation treatment in patients with early-stage breast cancer using a Magnetic Resonance Imaging Linear Accelerator (MR Linac). Eligible patients enrolled in this study will have a core biopsy to confirm estrogen receptor positive, Her2 negative subtype. Radiotherapy planning will use a planning computed tomography co-registered with a magnetic resonance imaging (MRI) with the patient in either the supine or prone position. For the diagnostic workup, [18] Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography ([18]FDG PET/CT) and [18] Fluoroestradiol Positron Emission Tomography/Computed Tomography ([18]FES PET/CT) will be performed prior to treatment. Thirty patients will receive a single ablative RT dose of 21 Gy to the tumor. Pre- and post-treatment MRI scans will be acquired at baseline and 5 weeks post radiotherapy respectively. Breast-conserving surgery will be scheduled for 6 weeks after APBI treatment using the MR- Linac. The primary study endpoint is the successful administration of a single fraction of preoperative breast radiotherapy under the guidance of an MR-linac. Secondary endpoints include evaluating the utility of MRI, [18F] FDG PET/CT and [18F] FES PET/CT as a non-invasive method for assessing treatment response in patients undergoing single fraction preoperative accelerated partial breast irradiation. Conclusion: The RICE trial represents a significant step in breast cancer treatment, offering insights that could lead to treatment protocols with minimized radiotherapy and enhanced patient outcomes. Trial Registration: This trial is registered with the Australian New Zealand Clinical Trials Registry (ANZCTR). Registered 31st of May 2021. Registration number: ACTRN12621000659808 https://anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12621000659808