The Metrology Comparison And Clinical Research Between Imrt And VMAT Of Thoracic Esophageal Carcinoma

Objective: As one of common malignancies, esophageal cancer occurs frequently with a high death rate in our country which is at the forefront leading cause of cancer death according to many surveys.[1] The surgical operation is the first treatment way for the patients with esophagus cancer and radiation therapy is one of main, effective and safe treatment[2].It is very difficult to make radiation plan satisfied the clinical treatment due to the very special position of esophagus which is surrendered by heart,lungs and spinal cord and other OARs with low tolerance dose. In recent years, with the development of computer technology and the application of new physical algorithm which improved the computing speed and optimization speed fast and IMRT is widely used in clinical practice especially the new type of intensity-modulated technology-VMAT which gradually developed in China, which provides new ideas for radiation therapy of esophagus cancer. So we compared and analysis the difference between these two treatments IMRT and VMAT to find the features in terms of metrology to provide some future reference and practices.Method: analysis the clinical data of 15 esophagus patients who is squamous cancer diagnosed by pathology collected in our hospital from January 2013 to October2014. And then divide these case into two groups stage IIa period(5 cases) and stage III period(10 cases). Adapt thermoplastic body mask or head and shoulder mask to fix the position and use CT(Philips Brilliance Big Bore CT) to collect images and the target and organs at risk were delineated by the radiologist and radiation therapist. As to each image of patient, use Oncentra® treatment planning system(version 4.3.0410) to design IMRT &VMAT plans for every patient. PTV prescription dose is 60 Gy divided 30times(6weeks). Evaluating the tumor target volume(GTV) and other dose distribution of various parameters and endangered organ such as total lungs,heart and spinal cord illuminated dose analysis and comparisons of MU and the time of effective treatments then verify the two groups of treatment plan relative dose gamma pass rate. The two difference of the two groups were compared with the paired T test.Results: two groups of plan GTV dosimetry parameter has the difference. In two sets of plans, GTV Dmax, D2, D98 all have differences respectively, P = 0.008, P = 0.040,P = 0.002, the GTV D50 have no difference(P = 0.525), compared with IMRT plan,the dose of VMAT plans more even which can handle the GTV dose hot point better.There are differences between the two sets of plans of PTV dose distribution, VMAT planning groups Dmax, D2, D98, CI, HI were better than IMRT planning groups P value respectively, P = 0.003, P = 0.0015, P = 0.0036, P = 0.001, P = 0.001, PTV D50 no difference(P = 0.890).Compared with the two sets of plans in both lungs tolerance difference, in which the whole lung V5 worse in IMRT of VMAT(P < 0.001), V20, V30 is better than that of IMRT, obvious difference(P < 0.001), the mean dose of V10, lung(MLD) there were no significant differences(P = 0.190, P = 0.190). Compared with IMRT, VMAT can significantly reduce the illuminated the dose of the heart, V30, V40 obvious difference(P = 0.002, P < 0.001). VMAT plans are better than IMRT plans by reducing the radiation dose of spinal cord.there are obvious difference(P = 0.001).Other indicators: to the total number of machine unit: VMAT plans to significantly lower than that of IMRT plans, were 578.47±116.11 MU, 649.75±58.94 MU(t = 2.644,P = 0.019). Effective treatment time significantly shortened, 510.73 ± 91.84 S, 91.84±67.41 S significant difference(t = 15.406, P < 0.001). Gamma pass of VMAT plan lower than that of IMRT plan, 93.69 ±1.64%, respectively, 96.33±1.53%(t = 6.08, P <0.001), but it can meet the needs of the clinical use(> 90%).Conclusions: compared with IMRT, VMAT can improve the target dose distributions under the circumstances that protect the OARs better and shorten the treatment time, make the target distribution more reasonable, lower the illumination which shorten the treatment time greatly making patients feel more comfortable and all these pleasant results is helpful for IGRT.VMAT is a good choice for Radiation therapy ofesophageal carcinoma.