Research Of Equivalent Uniform Dose Based On Organ At Risk Partition Constraint In Radiation Therapy For Abdominal Tumor

Objective:To assess the benefits of Equivalent Uniform Dose Optimization based on Organ At Risk Partition Constraint in Volumetric-Modulated Arc Therapy for abdominal tumor.Method:20 cases having clinical proved VMAT treatment plans with dose-volume constraints were randomly selected among patients with Rectal Cancer and Cervical Cancer(A).Based on the A-plans,depending on the position of PTV and small intestine,bladder and rectum will endanger the OAR’s partition and according to the difference of the sensitivity of the hot spot to EUD optimization by given different specific-tissue parameter(a values)(B).According to the characteristics of the greater of a values is more sensitive to the hot spot,the dose of PTV area overlaps with the OAR relatively higher than other regions,hot spots appear probability is bigger,take lager a values to EUD optimization.The section apart from the overlaping portions with the small intestine,bladder and the rectum intersecting is low,the a value of 8,5 and 9;in the same way,the rest of the regions away from PTV was taken the a value of 6.7,2.3 and 8.3.Then,based on the A-plan,the Equivalent Uniform Dose optimization is carried out for the overall constraints of the organs at risk(C).And the a value of the femoral head of the two plan was 4.The B-plans,A-plans and C-plan were compared in terms of dosimetry and biology as well as analyze the date by SPSS 22.Result:The condition of PTV almost the same in A-plan,B-plan and C-plan.Compared with A-plan,The dose parameters of OAR having received partition were improved in various degree.For the patient of rectal cancer,The mean dose of the small intestine and the bladder decreased 2.5Gy and 3Gy respectively;NTCP decreased 40% and 13% separately;For the patient of cervical cancer,The mean dose of the small intestine,bladder and the rectum decreased 2.2Gy,1.1Gy and 1,9c Gy respectively;NTCP of the small intestine decreased 40% and the others increased 1%.Compared with C-plan,The dose parameters of OAR having received partition were improved in various degree.For the patient of rectal cancer,The mean dose of the small intestine and the bladder decreased 0.2Gy and 2Gy respectively;NTCP of bladder decreased 7% and the small intestine increased 5% separately;For the patient of cervical cancer,The mean dose of the small intestine,bladder and the rectum decreased 1.4Gy,2Gy and 0.8c Gy respectively;NTCP of the bladder decreased 4% and the others increased 10% and 8% separately.Conclusion:EUD optimization based on OAR partition constraint in VMAT for abdominal tumor could keep the PTV from influence and decreased remarkable both the dose and the NTCP of some organ at risk having received partition,it has meaning to improve the quality of the plan.