CT Number Organ And Homogeneous Assigned Methods-based Radiation Treatment Planning Of Pelvic Cavity Tumors

ObjectiveTo study the effect of CT changes on dose calculation,the CT values of human tissue were sampled and then divided into different interval.And to find a method to solve the missing information of magnetic resonance image(MRI).MethodsImaging data were analyzed from thirty patients in three different regions:head and neck(n =10),thorax(n = 10)and pelvic cavity(n = 10)by treatment planning system(Varian Eclipse version 10.0).The average CT number,standard deviation and 95%confidence interval were obtained by the Eclipse treatment planning system.Build a virtual phantom(Size:30 cm x 30 cm x 30 cm;SSD= 100 cm;Irradiation field:10 cmx 10 cm;Effective measuring points:underwater 5cm)in Varian Eclipse treatment planning system,and the prescribed dose is 100cGy,calculated by the machine output at different CT number.The CT number dose curve was drawn to study the effect of CT number on dose calculation.15 IMRT were Intensity-modulated radiation therapy(IMRT).Eclipse ver 10.0 was used for all delineations,registrations,and dose calculations.The different structures were assigned CT numbers were assigned to different structures to form a synthetic CT image.CT numbers of target and organs at risk(OAR)were assigned according to sampled CT number.Others organs were assigned a uniform CT value of 20HU which is an average number of multiple organs.At the same time,this paper studies the human tissue CT image is only divided into water + bone,CT value assignment(this method becomes homogeneous assigned method).Dosimetric differences and dose homogeneity were compared under the same dose and field conditions.ResultsThrough dividing the CT number by interval method and verifying in dose calculation,the different CT number interval can reflect the different human tissue or organ.The effect of CT number variation between-100HU and 100HU on dose calculation is within 2%.Under the same treatment plan,there is little deviation between synthetic CT image and original CT image.The Dmax,Dmean,Dmean,D98%,D95%,D5%,D2%of PTV are all below 1.61%,Dose percentage and volume percentage of OAR are below 1.86%.ConclusionsIt's feasible to combine CT number divide and MRI to perform MR-alone in pelvis tumor treatment plan.