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Purpose:To effective calculate the overlap volume histogram(OVH)descriptor,and improve the retrieval performance of intensity modulated radiation therapy(IMRT)plan.Methods:A method based on morphology for OVH descriptor calculation is proposed,and a novel similarity measurement is employed for the IMRT plan retrieval.First,the minimum distance and the maximum distance between the target and organs at risk are calculated as the start point and the end point for contraction/expansion operation,and a suitable step of contraction/expansion operation is determined according to the minimum distance and the maximum distance.Then,dilation/erosion morphology operator is employed to compute the OVH descriptor.Finally,the performance of IMRT plan retrieval is evaluated,where the area between OVH descriptors is taken as the similarity measurement,and 3D reconstruction of all cases are also performed for visual comparison.Results:28 nasopharyngeal carcinoma(NPC)cases are employed for the evaluation.The resulted OVH descriptors can be calculated effectively with the proposed method,and they are able to match well the 3D geometrical features of the target and OARs.The IMRT plan retrieval results also match well the visual similarity of their 3D geometrical features,the increasing of the area between OVH descriptors leads to the decreasing of visual similarity.Conclusions:The proposed method can be used effectively for OVH descriptor calculation,and be used to retrieval the IMRT similar cases effectively.