Dosimetric Study Of Volumetric-modulated Arc Radiotherapy、Intensity-modulated Radiotherapy Compared With3-dimensional Conformal Radiotherapy For Locally Advanced Non-small Cell Lung Cancer

OBJECTIVE：To compare the difference of dose distribution in planning targetvolume and organ at risk (OAR) between Volumetric-modulated Arc Radiotherapy(VMAT)、 intensity-modulated radiotherapy (IMRT) and conventionalthree-dimensional conformal radiotherapy(3D-CRT) in the radiotherapy of locallyadvanced non-small cell lung cancer(NSCLC).METHODS: Twenty-seven patients with locally advanced (stage III) NSCLC wereincluded. The next steps were CT scan, targets and organs at risk (OARs) contour.VMAT plan, IMRT plan and3D-CRT plan were performed for each patient respectivelywith the prescribed dose60Gy. Homogeneity index (HI), conformity index (CI),maximum dose of planning target volume (PTVDmax), minimum dose of PTV(PTVDmin), mean dose of PTV (PTVDmean) and irradiated volume of OARs werecalculated and the results were compared.RESULTS: The Dmax of spinal cord, CI and HI of IMRT and VAMT plans weresuperior to3D-CRT plans, the differences were statistically significant (P<0.05).Although IMRT and VAMT plans reduced the V20and Dmean of lung, V40, V45andDmean of heart compared with3D-CRT plans, but there was no significant difference(P>0.05). Compared with3D-CRT plans, the IMRT and VAMT plans increased the V5of lung. That is an increased low dose volume of irradiated normal lung. The differencewas significant (P<0.05). Meanwhile, there was no statistically difference between VAMT plans and IMRT plans in V5, V20and mean dose of lung, V40, V45, V60, andthe mean dose of heart, Dmax of spinal cord, PTVDmax, PTVDmean, PTVDmin, CIand HI.For central locally advanced NSCLC, The Dmax of spinal cord, CI and HI inIMRT and VAMT plans were better than those in3D-CRT plans, the difference wassignificant (P <0.05). Compared to3D-CRT plans, IMRT and VMAT plans reduced theV20and Dmean of lung, V40, V45and Dmean of heart, which also increased V5oflung, but there was no significant difference (P>0.05). For peripheral locally advancedNSCLC, PTVDmax of VMAT plans increased compared with3D-CRT plans, thedifference was statistically significant (P <0.05). There was no significant differencebetween the rest indexes (P>0.05).Comparisons of IMRT, VMAT, and3D-CRT plans from three physicists as follows:The CI of IMRT and VAMT plans from physicist A were superior to3D-CRT plans, butV5of the lung of3D-CRT plans were superior to IMRT and VAMT plans, the differencewas significant (P <0.05). No statistical difference was considered in the rest indexes(P>0.05). The CI and HI of IMRT and VAMT plans from physicist B were superior to3D-CRT plans, the difference was statistically significant (P<0.05). There was nosignificant difference between the rest indexes (P>0.05). The HI of IMRT and VAMTplans from physicist C were superior to3D-CRT plans, the difference was statisticallysignificant (P <0.05). The difference between the rest indexes demonstrated nosignificant (P>0.05).CONCLUSIONS: For locally advanced NSCLC, IMRT and VMAT have similardosimetric advantages compare to3D-CRT, which improve the CI and HI of the plans.IMRT and VMAT demonstrate a superior protection of OARs, which means a potentialto improve the therapeutic ratio in dose escalation and/or comprehensive treatment.Apply to central and peripheral locally advanced NSCLC, IMRT and VAMT havegreater advantage in decreasing the irradiate dose of OARs in the former one. IMRT andVMAT demonstrate dosimetric advantage in some selective patients, so it is veryimportant to choose the appropriate case. Greater sample size and more rigorous experimental methods are required to dismiss the dosimetric differences caused by theexperience and different planning priorities of the physicists.