Comparison Of Two Planning Of Intensity Modulated Radiation Therapy For Early Nasal NK/T Cell Lymphoma

Recently,with rapid developments of computer technology,medical imaging technology and biomedical engineering,the radiation therapy for tumors is constantly upgrading and developing.Radiotherapy techniques have evolved from traditional two-dimensional irradiation into new precision one.IMRT?intensity modulated radiation therapy?,originated from three-dimensional conformal radiotherapy,is deemed to an important milestone in tumor radiotherapy history.It can guarantee high conformal irradiation dose in target area,and can minimize dose in normal tissues,thus the tumor control rate has been greatly improved and less damage of normal tissues occurs.Nasal NK/T cell lymphoma is the most common NK/T cell lymphoma in China,about 30%of the total.Radiation therapy is an effective method for early nasal NK/T cell lymphoma.Conventional radiotherapy for nasal NK/T cell lymphoma is likely to result in inhomogeneous target dose,irregular low dose and high dose areas,and excessive irradiation of normal tissues.This project uses the retrospective study,puting forward a new improved IMRT planning other than the original 7-Fields old one,and tries to reduce the maximum and average dose on lens and optic nerves while remaining the dose on tumor for patients with early nasal NK/T cell lymphoma.As a result,it doesn't change the therapeutic effect of NK/T cell lymphoma of nasal cavity when alleviating the radiation damage of lens and optic nerve.Hence this improved planning can be applied to the clinic.Twenty eight patients were collected with early IE stage nasal natural killer/T-cell lymphoma in Jiangsu Province Cancer Hospital during 2014-2016,and all of them were treated with intensity-modulated radiotherapy.For each patient,an IMRT 7 fields planning and an improved IMRT planning with same fields were designed,denoted by PlanA and PlanB respectively.The latter one makes use of the small angle non-coplanar technology and fixed field technology with same gantry direction.The two plans have been optimized by the same objective function.Of two planning,the dose volume distribution of the target and normal tissue,the CI and HI of target and MU,as well as the pass rate of IMRT verification and the impact of setup offset error,are compared to make a dicision if the PlanB can be used in clinic.PlanB,comparing with those of PlanA,the maximum doses of the left and right lens decrease13.3%and 16.5%,P<0.05,and the average doses of the left and right lens decrease22.5%and 24.2%,P<0.05,the results have statistical significance.The maximum doses of the left and right optic nerves decrease 5.9%and 8.5%,and the average doses of the left and right optic nerves decrease18.6%and 19.0%,and the average doses of the left and right eyes decrease 23.5%and 14.7%,P<0.05,the results have statistical significance.But the maximum doses of the eye are almost the same,P>0.05,the results don't have statistical significance.The target doses(D_98%,D_50%,D_2%)and target HIs of the two plans,have minor differences,P>0.05,the results don't have statistical significance,but the CIs of target of PlanA are better than those of PlanB,P<0.05,the results have statistical significance.The results of the verification,using Gamma analysis,the standard of the analysis is 3mm/3%?distance error is 3mm,and dose error is 3%?,are both over 98%,P>0.05,the results don't have statistical significance.The impact of the setup error on the dose,by simulating the setup offset error?1mm and 2mm?,has a bigger impact on PlanB than that of PlanA for the lens.However,the maximum and average doses of the lens and optic nerves of PlanB are still less than those of PlanA.The impact to the target is smaller,of which the difference between PlanA and PlanB doesn't have statistical significance.With respect to the results above,the improved PlanB is superior to PlanA in protecting lens and optic nerves,which can be used as a reference for radiotherapy planning of nasal NK/T cell lymphoma.