Simple SummaryThe combination treatment of organ-preserving tumor resection and brachytherapy in children with bladder/prostate and perianal rhabdomyosarcoma can reduce therapy-associated side effects while maintaining excellent oncological outcome. This highly individualized hybrid treatment concept poses specific challenges for all clinicians involved in the local treatment. The aim of this study was to determine whether the use of an intraoperative MRI can improve the clinical workflow. These findings may have a positive impact on the treatment quality and patient safety of children with bladder/prostate and perianal RMS.AbstractIn children with bladder/prostate (BP) and perianal rhabdomyosarcoma (RMS), we use a hybrid treatment concept for those suitable, combining organ-preserving tumor resection and high-dose rate brachytherapy (HDR-BT). This treatment concept has been shown to improve outcomes. However, it is associated with specific challenges for the clinicians. The exact position of the tubes for BT is a prerequisite for precise radiotherapy. It can finally be determined only with an MRI or CT scan. We evaluated the use of an intraoperative MRI (iMRI) to control the position of the BT tubes and for radiotherapy planning in all patients with BP and perianal RMS who received the above-mentioned combination therapy in our department since January 2021. iMRI was used in 12 children. All tubes were clearly localized. No adverse events occurred. In all 12 children, radiotherapy could be started on time. In a historical cohort without iMRI, this was not possible in 3 out of 20 children. The use of iMRI in children with BP and perianal RMS improved patient safety and treatment quality. This technology has proven to be successful for the patient population we have defined and has become a standard procedure in our institution.