A pressure based respiratory motion management system with biofeedback for MR-based radiotherapy

Purpose: Motion must be accounted for with focal treatments such as liver directed stereotactic body radiotherapy otherwise there is a risk of marginal miss and/or increased toxicity to surrounding structure. There have been many proposed methods for motion management including respiratory gating, inhibition and tracking. The purpose of this study is to evaluate a pressure-based respiratory motion management system with biofeedback to the patient for MR-guided radiotherapy treatments. Methods: A respiratory motion management belt was modified in house to provide visual biofeedback of subject respiratory trace using pressure readings from an air bladder. Three groups participated in the study: Group I included two investigators who were imaged twice, with imaging sessions separated by one week, while wearing the motion management belt. Group II included four healthy volunteers, imaged using the belt for CINE and anatomical imaging. Group III included two cancer patients with liver lesions imaged while wearing the device, imaged pre-radiotherapy treatment, and post-treatment. During image acquisition, a display showed participants their respiratory traces and guidelines to indicate the desired respiratory amplitude. Results: The average peak-to-peak motion of the liver dome was decreased from 30.557.83 mm to 5.580.85 mm for free-breathing and utilizing a small window guiding box with visual guidance CINE image sets respectively in the investigator study. Volunteers and cancer patients were able to consistently manage their breath traces, including sequential breath holds, over the course of 30-60 min imaging sessions. Conclusions: The proposed motion management belt with visual biofeedback design is able to provide greatly reduced respiratory motion of the liver, and repeatable breath hold in MR simulation. The components used in the device also allow it to be in place during all steps of the radiotherapy planning process, including MR anatomical imaging, CT simulation, and treatment delivery due to the absence of high z or metallic material.