A Dosimetric Comparison Of Intensity Modulated Radiotherapy And Volumetric Modulated Arc Therapy For Brain Gliomas

Objective:To investigate the dosimetric differences among fixed field dynamic intensity modulated radiotherapy(dlMRT) and volumetric modulated arc therapy (VMAT) used flattened or flattening filter free photon for brain gliomas that were located within the frontal lobe and temporal lobe. Evaluating the advantages and disadvantages in four plans provide a reliable objective evidence for the clinical selectoin of radiotherapy technologies.Methods:We retrospectively selected21patients that the tumors were located within the temporal lobe in11cases and frontal lobe in10,who had been recently treated for glioma radiotherapy in the First Affiliated Hospital of ZhengZhou University from2013to2014. The CT-Sim images of the patients were available on the3D-TPS. The contours of target volumes, normal tissue and critical organs were based on patients’pre-radiotherapy MRI images. For each patient,four treatment plans were generated, including a6X-dIMRT plan, a6FFF-dIMRT plan, a6X-VMAT plan, a6FFF-VMAT plan. Prescribe in plan is60Gy/30F.We compared dose distribution of CTV (Dmax, Dmin, Dmean),PTV(Dmax, Dmin, Dmean, dose conformity and heterogeneity index), Dmax、Dmean of organs at risk, normal tissue(Dmean、V20Gy, V10Gy and V5Gy) and MU between the four plans. Results:1. Target:Both dIMRT and VMAT used different radiation mode can meet the target requirements well. For frontal lobe tumor, the average of CTVDmax、Dmean, PTVDmax、 Dmean in dIMRT plan is higher than VMAT plan (P<0.05). VMAT plan is slightly better than the dIMRT plan in homogeneous degree (HI). For temporal lobe tumor, the average of PTVDmax、Dmean in dIMRT plan is higher than VMAT plan (P<0.05).6FFF-VMAT is relatively better than other plans in HI.2. Organs at risk(OARs):All four plans can protect OARs well.About frontal tumor.The average of Dmax at brain stem reduces from1711.94cGy-1838.13cGy in dIMRT plan to1174.82-1188.24cGy in VMAT plan(P<0.05),and the average of Dmean reduces from287.57cGy-296.29cGy to233.06cGy-237.40cGy. On protection of lens, the performance of FFF mode is superior to the FF mode.Compared with FF mode plan, FFF mode reduces the Dmax of ipsilateral lens by16%-21%,and the number about Dmean is18%-22%;With respect to contralateral lens,its Dmax reduces by10%-17%,and Dmean by11%-18%.For temporal lobe tumor,Dmax of pituitary、lens、and optic chiasma in dIMRT plan is lower than VMAT plan.And the Dmax of the contralateral temporal lobe is decreased by19%-20%in VMAT plan.3. Normal brain tissues:For frontal tumors,Dmean reduces significantly for FFF treatment (P=0.013). While the V20Gy and V10Gy are less for VMAT plans than for dIMRT plans (P<0.05). Temporal lobe tumors,there’s less Dmean and V10Gy for FFF treatment.On the other hand,V20Gy in VMAT plans less than other plans.4. MU:Frontal lobe tumors:Compared to6X-dIMRT,6X-VMAT reduced average MU from543.9to414.7, and Compared to6FFF-dIMRT,6FFF-VMAT reduced average MU by19%. Temporal lobe tumors:Compared to6X-dIMRT,6X-VMAT reduced average MU from562.7to450.0, and Compared to6FFF-dIMRT,6FFF-VMAT reduced average MU by20%.Conclusions:1. Different lobes of the brain glioma influence dose distribution characteristics for dIMRT and VMAT. 2. In the same circumstances, different radiation patterns affect the dose distribution of brain glioma.3. For frontal lobe and temporal lobe tumors,all dIMRT and VMAT used FFF or FF beams can be good to satify the requirement of clinic dosimetry in the target coverage, homogeneity and conformity.4. For the frontal gliomas, VMAT is better than dIMRT and FFF treatment is superior to the FF treatment in OARs.For temporal lobe tumors, dIMRT is better than VMAT and FFF beams is superior to the FF beams in O ARs.5. VMAT plan is lower than dIMRT for MU either used FFF beams or used conventional FF beams.