Dosimetric Research Of Volumetric Modulated Arc Therapy For Cervical Carcinoma

Objective:Cervical carcimona is one of the most common female malignant tumors,and the incidence and mortality rate is second which is only below breast cancer in female malignant tumors in the worldwide.There are about more than 110000 new cervical carcinoma patients and 20000-30000 cervical carcinoma patients die each year in our country.Early symptoms of cervical cancer is not obvious so that about 66.7% of the patients have to be in middle or advanced stages when confirmed.So the diagnosis and treatment of middle and advanced cervical cancer have become the most important women’s health problem in the worldwide.In recent years, Intensity Modulated Radiotherapy(IMRT)has been widely used in the treatment of cervical cancer with the development of radiotherapy technology.IMRT is different from the conventional radiotherapy technology and it uses reverse intensity modulated technology so IMRT can ensure maximum dose of tumor at the same time reduce the dose of normal tissue around the tumor.But as a result of IMRT for a long time, it has increased the impact of uncertain factors in the process of treatment.Volumetric modulated arc therapy(VMAT) develops on the basis of image guided radiotherapy and has been used in clinical.Existing research reports at home and abroad points out that VMAT required fewer MU and shorten the treatment time significantly compared with IMRT,besides,VMAT achieves equal or better dose distribution to the target and organs at risk sparing.We aim to assess the feasibility and the potential advantages of VMAT for cervical carcinoma by comparing the dosimetric difference between VMAT and IMRT.Methods:Ten patients of middle and advanced cervical carcinoma were enrolled in this study.Before the treatment,all the CT scan images were transmitted to the treatment planning system by local area network and we sketch the GTV、CTV、PTV and the small intestine、rectum、bladder、ilium、femoral heads、cauda equina. ssIMRT and VMAT plans were generated for these patients by using the pinnacle9.2 treatment planning system.The dose of GTV is 60 Gy and PTV is 50 Gy.Dose volume histograms are adopted for the statistics of D2、D98、Dmean,conformal index(CI),homogeneity index(HI) of GTV and PTV,dose volumetric parameters of normal tissues,the small intestine 、 rectum 、 bladder 、 ilium 、 femoral heads 、cauda equina,total accelerator output monitor units and total treatment time. It provides theoretical basis for planning target volume by analyzing the setup errors distribution law with P less than 0.05.Statistical analysis was performed using an SPSS statistical package(Version18.0).Results:(1)All the VMAT and IMRT plans can satisfy the clinical dosimetry requirements.The mean dose of the GTV for the VMAT plan is higher than the 7IMRT plan,and have statistical significant differences(P=0.007).The D2、D98、CI、HI of the GTV for both plans have no significant differences(P>0.05),The D2、D98、Dmean、CI、HI of the PTV for the two plans have no significant differences(P>0.05).(2)VMAT has a better sparing effect on the V40、V46、 Dmean of the rectum((P<0.05)and the two plans have no significant differences on the V10、V20、V30 of the rectum(P>0.05).VMAT has a worse sparing effect on the V10、V20、 Dmean of the ilium(P<0.05) but has a better sparing effect on the V50(P<0.05).And the effect of other sparing on the small intestine、bladder 、femoral heads and cauda equina is similar between VMAT and IMRT.(3)The mean monitor units of VMAT(785.7)is fewer by 35.68% in comparison with IMRT(1221.6),the treatment time of VMAT(4min)is shorten by 60% in comparison with IMRT(10min).Conclusions:VMAT achieves equal or better in dose distribution to the target compared with IMRT and the mean dose of the GTV for the VMAT plan is higher than the IMRT.VMAT and IMRT are similar in organs at risk sparing. VMAT needs fewer monitor units and less time so it reduces the uncertain factors during the treatment and the discomfortableness of the patient.It improves the efficiency of the machine and has the potential to improve the curative effect.VMAT can be used as an effective and safe radiotherapy technology in the treatment of cervical carcinoma.