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. Magnetic Resonance Imaging-Guided Single Fraction Pre-operative Radiotherapy for Early-Stage Breast Cancer (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 for 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 and Her² negative subtype. Radiotherapy planning will use a planning computed tomography (CT) co-registered with a magnetic resonance imaging (MRI) with the patient in either the supine or prone position. For the diagnostic workup, [18F] Fluorodeoxyglucose Positron Emission Tomography/CT ([18F] FDG PET/CT) and [18] Fluoroestradiol Positron Emission Tomography/CT ([18F] 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. 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