An open‐source software for monitoring intrafraction motion during external beam radiation therapy based on superimposition of contours of projected ROIs on cine‐MV images

Purpose To present an open‐source software (https://github.com/CHUSRadOncPhys/FluoMV) for monitoring intrafraction motion that is based on the visualization of superimposed contours of projected region‐of‐interests from DICOM RTSTRUCT files on cine‐MV images acquired and displayed in real‐time during radiation therapy delivery. Clinical use with prostate gold fiducial markers is presented. Methods Projections of regions of interest (ROI) in the reference frame of the electronic portal imaging device are computed offline for different gantry angles before the first treatment fraction. During treatment delivery, the contrast of portal images is automatically adjusted using a histogram equalization algorithm. The projections associated with the current gantry angle are then superimposed on the images in real time. This allows the therapist to evaluate if the imaged structures of interest remain within their respective contours during treatment delivery and to potentially interrupt the treatment if deemed necessary. The spatial accuracy of the method was evaluated by imaging a ball bearing phantom in a set‐up where the position of the projected ROI is highly sensitive to gantry angle errors. The visibility of fiducial markers during one fraction of seven different volumetric modulated arc therapy (VMAT) prostate treatments is characterized. Results The geometric validation showed a negligible systematic error μ