Optimization Of Key Workflows For Adaptive Radiotherapy

Changes of patient anatomy during radiotherapy may cause deviation of actual delivered dose within human body from the planned dose.Under-dose to target or over-dose to normal tissue will reduce the therapeutic ratio of radiotherapy.To achieve high precision radiotherapy,radiotherapy treatment plans should be adjusted in accordance with the measurement during the treatment process,namely implementing the adaptive radiotherapy(ART).The essential steps of ART include image acquisition,deformable image registration(DIR)and dose accumulation.Image acquisition is the prerequisite of ART;DIR is the basis of ART;Dose accumulation is the decision-making criterion in ART.To address the problems of extra dose induced by frequent imaging,lack of quality assurance(QA)tools and the uncertainty of replanning time points,this study optimized the key workflow of ART,including:(1)explore the integration scheme of imaging and treatment dose;(2)explore low-dose imaging protocols to reduce risks of concomitant dose;(3)establish QA framework for DIR algorithm based on virtual deformation to improve the accuracy of ART;(4)simulate dose accumulation on real patient data to offer a decision-making guidance for ART.This work validated the accuracy of MVCBCT imaging dose calculated by Eclipse TPS and simulated the imaging dose error caused by isocenter shift.An in-house ESAPI code was developed to automatically correct the error,making the integration of imaging and treatment dose more accurate.In addition,this work compared the imaging dose and image guidance precision of"Image Gently" protocol with standard kVCBCT protocols,as well we between the "High Quality" and "Low Dose" modes of Halcyon’s MVCBCT scanning system.It was found that the low-dose protocols of kVCBCT and MVCBCT could provide comparable image guidance precision as standard or high-dose protocols of kVCBCT and MVCBCT for pediatric patients,yet with a lower imaging dose.Low dose scanning protocols should be preferable in ART for pediatric patients.DIR is one of the core components of ART.This study quantitatively evaluated the spatial and HU accuracy of DIR algorithm based on virtual deformation,and systematically analyzed the impact of deformation magnitude and image modality on the accuracy of DIR algorithm,providing methodological support for QA and choice of DIR algorithm in clinical practice.Based on phase Ⅱ clinical trial of Halcyon,this study retrospectively simulated the variation of dose distribution caused by patient anatomy change during radiotherapy.The result suggested that dose accumulation could be beneficial for identifying over-dose to organs-at-risk and cold spots in tumor target,as induced by patient anatomy change.This work showed that the objective criterion for ART should be accumulated dose rather than empirical principles.