To Study The Feasibility Of Volumetric Modulated Arc Radiotherapy (Rapidarc) Combined Active Breathing Control In The Radiotherapy Of Hepatocellular Carcinoma

Background and Objective:Hepatocellular carcinoma is one of the most common malignancies worldwide, lots of patients was diagnosed at intermediate-advanced stage for the lack of high sensitive screening means. Comprehensive treatment approaches should be applied for patients with advanced hepatocellular carcinoma, radiotherapy which is an important treatment approach for hepatocellular carcinoma play essential role. The radiation included liver injury (RILD) is the major limitation for the application of radiotherapy in treatment of HCC. The liver position and shape are affected by respiratory motion, the precise simulation for hepatocellular carcinoma is very necessary. Active breathing control (ABC) has been proven to be an effective approach to spare more normal liver tissue ensuring the accurate position of target volume. With the development of equipment, volumetric modulated arc radiotherapy (VMAT) has been applied in clinical therapy, it holds the features of shorted treatment time, less monitor unit and better dose delivery than conventional intensity modulated radiotherapy (IMRT). The character of short treatment time makes it become possible to combine volumetric modulated arc radiotherapy with active breathing control in radiotherapy of hepatocellular carcinoma. The present research aims to study the feasibility of volumetric modulated arc radiotherapy (the production of VARIAN company is RapidArc) combined ABC in the Radiotherapy of hepatocellular carcinoma comparing of three dimensional radiotherapy(3D-CRT), IMRT and RapidArc plans in free breathing(FB), end inspiration hold(EIH) and end expiration hold(EEH).Methods:12Hepatocellular carcinoma patients after TACE treatment were selected. Three series simulation CT scanning were completed in FB, EIH and EEH associated with ABC device-active breathing coordinator. The gross tumor volumes (GTVs) and organs at risk(OARs) were manually contoured on different CT images, planning target volumes (PTVs) were obtained from GTVs applying different margins.3D-CRT, IMRT, RapidArc plans were designed for PTVs respectively,4-7planar fields were used in3D-CRT and5planar fields in IMRT plans, three planar135°Arcs in RapidArc plans, the optimization parameters were identical in IMRT and RapidArc. All plans were evaluated by the prescription dose of50Gy (2Gy/fraction×25fractions). The volumes of liver, normal liver (liver subtract PTV), GTV and PTV were compared. Conformity index (CI), homogeneity index (HI), monitor unit, the maximum/minimum dose of PTV; the mean dose, V5, V10, V20, V30, V4o of normal liver and the maximum dose, the dose of5cm3volume of stomach and duodenum were compared among3D-CRT, IMRT and RapidArc plans overall (the same plan type in different breath conditions was consider as the same one). To compare the differences of the evaluation indexes above among RapidArc plans in three breath status.Results:(1)12patients underwent the CT simulation associated with ABC successfully and breath holding times were all over30s in EIH and EEH.(2)There were no significant difference among the volume of liver, normal liver and GTV under different breath conditions; the PTV of FB was larger than of EEH and EIH, the difference between FB and EEH, FB and EIH were significant (P<0.05).(3) The CI and HI in three type plans overall was RapidArc>IMRT>3D-CRT (P<0.05); the mean dose, V20, V30, V40of normal liver were3D-CRT>RapidArc>IMRT, and all the difference were significant (P<0.05); there were no significant difference in the V5, V10of normal liver and the maximum dose, D5cm3of stomach and duodenum among three type plans overall.(4)The CI、HI was similar in differenr RapidArc plans under three breath conditions were no significant (P>0.05); The mean dose, V10of normal liver were FB>EEH>EIH,and V20, V30, V40were FB>EEH and EIH, there was no stably variation regular between EEH and EIH:the difference of all the indexes above were significant in RapidArc plans between FB and EEH, FB and EIH,except for V40. The D5cm3of duodenum was EIH>FB>EEH (P<0.05). The monitor unit of IMRT was more than RapidArc and3D-CRT significantly, and the treatment time of RapidArc was equal to3D-CRT which was less than IMRT remarkably.Conclusions:The RapidArc applying three135°arcs combined ABC in radiotherapy of hepatocellular carcinoma could achieve better dose delivery than IMRT with fewer monitor units and shorter delivery time which were equal or shorter than3D-CRT treatment time, and could spare more normal liver tissue ensuring the precise position of target volume.