The Study Of Volumetric Modulated Arc Therapy And Inte Nsity Modulated Radiotherapy For Newly Diagnosed Nasop Haryngeal Carcinoma On The Protection Of Thyroid

Background and Objective: Nasopharyngeal carcinoma(NPC)is one of the most common malignant tumor in our country,its biological characteristics and anatomical characteristics determine the radiotherapy is the main means of treatment.In recent years,With the development of radiation technology,Conformal intensity modulated radiotherapy(IMRT)received gradually replaced the past conventional radiotherapy(CRT)and three-dimensional conformal radiation therapy(3D-CRT)of nasopharyngeal carcinoma radiotherapy become the preferred method.But the emergence of volumetric modulated arc therapy(VMAT)was able to more accurate control and detection of radiation dose distribution of the target area and normal tissue,it primary nasopharyngeal carcinoma(NPC)in improving stove control at the same time can reduce the crisis surrounding organs by the irradiation dose and volume.This research through the intensity modulated radiation therapy(IMRT)accept volume and conformal intensity modulated radiation therapy of two groups of patients with nasopharyngeal carcinoma(NPC)treated first and thyroid tumor targets illuminated dose volume were compared(Including to limit thyroid dose and obtain thyroid DVH).To evaluate two groups of patient’s dose distribution of PGTV,PGTVnd and PTV,dose and volume of the thyroid gland,the accelerator’s MU,and the differences of the average treatment time,etc,it will be better to compare the difference of thyroid gland protection effect to volumetric modulated arc therapy(VMAT)and intensity modulated radiotherapy(IMRT)for newly diagnosed nasopharyngeal carcinoma.Materials and Methods: Since January 2014 to December 2015,30 patients wit h newly diagnosed nasopharyngeal carcinoma(no other thyroid disease),confir med by microscopic examination of the nasopharyngeal pathology of squamous cell carcinoma,were selected from anhui provincial hospital affiliated tumor ra diotherapy.The patients without distant metastasis were clinical discussed and d ecided to accept early radiotherapy of nasopharyngeal carcinoma(According to the 2008 nasopharyngeal carcinoma(NPC)staging criteria for phase II ~ IVa),did not have pituitary and thyroid disorders before radiotherapy(normal thyroid function,imaging showed no abnormal thyroid patients,pituitary without spac e-occupying lesions before treatment,and not combined with other endocrine dis eases),without the history of head and neck surgery.Regular physical examinati on,X-ray,ultrasound,and oral pretreatment were chested before chemotherapy.Every patient signed the informed consent and completed before and after ind uction chemotherapy of nasopharyngeal magnetic resonance image acquisition a nd neck.The treatment planning system(TPS)was adopted to design therapy pla ns,and the radiation dose parameters of thyroid gland were remeasured.Patients were respectively treated with VMAT(15 cases)and IMRT(15 cases),in whic h planning gross tumor volume(PGTV)and the positive neck lymph nodes(P GTVnd)was delivered to 66~71.94 Gy.Planning target volume(PTV)was deli vered to 60~66 Gy in PTV1 and 54~58.24 Gy in PTV2,with intentionally do se constraints(pituitary<54 Gy;thyroid gland: V40<80%,V50≤60% and mean thyroid dose(MTD)<50 Gy).Dosimetric comparisons between VMAT and IMRT were analyzed to evaluate coverage,homogeneity and conformity of PGTV,PTV and thyroid gland.Average monitor units(MU)and average treatmentdelivery ti me were also compared.Results: PGTV,PGTVnd,PTV1,PTV2 dose of VMAT and IMRT could well meet the requirements of clinical dose distribution.VMAT compared with IMR T treatment PGTV,PGTVnd,PTV1,PTV2,The Dmax、Dmeanand V95%tvalue wer e no statistically significant difference,but the Dmin of PTV1,PTV2 in IMRT was higher(P < 0.05).The HI value of PTV1 and PTV2 in VMAT and IMR T treatment plan was smaller,more close to 1(P < 0.05).The CI value is clo ser to 1 and the difference was statistically significant(P < 0.05).That means PTV dose in VMAT was uniformity and conformal better.Both VMAT and IM RT could have similar PGTV,PGTVnd and PTV coverage and meet clinical n eeds.However,for PTV and thyroid gland protection,VMAT plans got better resu lts,particularly on homogeneity and conformity.Moreover,VMAT provided fewer monitor units and shorter delivery time than IMRT,and better for clinical appl ication.Conclusion: For newly diagnosed nasopharyngeal carcinoma,VMAT is able to deliver good dose coverage of PGTV and PTV and achieves better thyroid gla nd protection.It had obvious advantages in the conservation of thyroid functio n and shorten the average treatment time,etc.VMAT radiotherapy could be us ed as initial treatment of choice for nasopharyngeal carcinoma(NPC).