The Effect Of MR Perfusion Weighted Imaging On The Precision Of Target Area Of IMRT In Nasopharyngeal Carcinoma

Objective:To investigate the effect of MR-PWI on radiotherapy accuracy of nasopharyngeal carcinoma(NPC),we compared the CT,MR,and MR-PWI imaging in the target area and dose of associated organs at risk of intensity modulated radiotherapy in nasopharyngeal carcinoma.Methods:A total of 20 cases of newly diagnosed nasopharyngeal carcinoma admitted to the Department of Oncology Radiology at the Affiliated Hospital of Qingdao University from March 2017 to July 2017 were collected.CT,MR,and MR-PWI images were taken and the images were transmitted to TPS system for CT and MRI fusion,CT and MR-PWI fusion.We used the TPS system for the design of the injection field and the calculation of the dose distribution to obtain the absolute volume of GTV-t,GTV-n by referring to ICRU-50,ICRU-62 report outlines of nasopharyngeal primary tumor gross tumor target area(GTV-t)and cervical lymph node metastasis target area(GTV-n).The mean dose and the maximum dose of associated organs at risk: brainstem,spinal cord,left and right parotid glands,left and right temporomandibular joints,mouth,throat,thyroid were determined.SPSS 22.0 statistical software was used for statistical analysis.The measurement data of each group were described by mean±standard deviation(x±s).The difference in volume and dose between different groups was analyzed by paired t test.P<0.05 was statistically significant.Results:The volume of GTV-t in MR,CT,and MR-PWI groups was(33.79±13.85)cm3,(54.97±28.50)cm3,and(31.41±13.14)cm3 respectively.The volume of target volume delineated by CT groups was larger than those by MR and MR-PWI.The statistical difference between MR group and CT group was significant(P<0.05).The difference between the MR-PWI group and the CT group was statistically significant(P<0.05).There was no significant difference between MR group and MR-PWI group(P>0.05).Because the neck was not perfused,the volumes of GTV-n delineated by the MR and CT groups were(37.56 ± 32.13)cm3 and(57.81 ±50.40)cm3 respectively.The volume of thetarget volume delineated by MR groups was smaller than that of the CT group,and the statistical difference between the two groups was significant(P<0.05).The maximum brainstem dose in the MR,CT,and MR-PWI groups was(4310.12±326.55)cGy,(4341.26±342.53)cGy,and(4094.14±298.35)cGy respectively,with statistical differences between the MR-PWI group and the CT group(P<0.05),while there was no statistically significant between MR group and CT group,also between MR group and MR-PWI group(P>0.05).The mean dose of brainstem was not significantly different among different groups.The maximum doses and the mean doses of spinal cord,left and right parotid glands,left and right temporomandibular joints,oral cavity,larynx,and thyroid gland were not significantly different among different groups.Conclusion:MR imaging is more accurate than CT.And MR-PWI,as an auxiliary imaging method can be be used as a reference for target area delineation,which is helpful to improve the accuracy of intensity modulated radiotherapy for nasopharyngeal carcinoma.