| Objective:1, Through the construction of rabbit VX2 nasopharyngeal transplanted tumor animal model, provide basic research condition and image pathological evidence for the human nasopharyngeal carcinoma target volume delineation;2,In this study, respectively based on the volume of pathology and target volume delineation of MRI as the standard to determine the optimal threshold of SUV for 18F-FDG PET/CT in the delineation of naopharyngeal tumor target volume;3, respectively as the pathological specimens and MRI target volume delineation standard, to make the accuracy of the comparative study of CT, MRI and 18F-FDG PET/CT three imaging to determine the nasopharyngeal tumor GTV, in order to provide certain imaging examination guidance and advice of target volume delineation for the clinical nasopharyngeal carcinoma radiotherapy. Methods:1, The establishment of rabbit VX2 nasopharyngeal transplanted tumor model: Firstly, preparing VX2 tumor tissue suspension(106~108 cells/m L), and then through the CT location guide punctures the nasopharynx to establish rabbit VX2 nasopharyngeal tumor animal model by tissue suspension inoculation method. Then periodically observing modeled rabbits by CT, when CT found the nasopharyngeal neoplasm, show that the model was successful. 2, To determine the best SUV threshold for 18F-FDG PET/CT delineation nasopharyngeal tumor GTV and compare the accuracy of delineating the nasopharyngeal tumors GTV for CT, MRI, 18F-FDG PET/CT three kinds of imaging data: when models were determined success each rabbit wascanned by enhanced CT, MRI, 18F-FDG PET/CT within 72 hours after one week. Then, rabbits were killed immediately for pathological a n a t o m y a f t e r t h e e n d o f a l l i m a g i n g, a n d m e a s u r e d r a b b i t nasopharyngeal tumor volume by using water-immersion method and sent specimens to the inspection. Finally, according to different imaging data delineated rabbit nasopharyngeal tumor GTV, and respectively based on the volume of pathology and target volume delineation of MRI as the standard, by comparing the results of 18F-FDG PET/CT data delineating nasopharyngeal tumor GTV for the best SUV threshold, and with this SUV threshold conditions comparativelyanalyzed the accuracy of CT, MRI, 18F-FDG and PET/CT three kinds of imaging data delineating the nasopharyngeal tumors GTV. Results: 1, By tissue suspension inoculattion building rabbit VX2 nasopharyngeal tumor, the modeling success rate was about 63.64%(7/11), and the number of subsequently actual experimental model is five. 2,Through the anatomy of rabbit VX2 nasopharyngeal tumor found that the growth characteristics of nasopharyngeal tumor was very similar with human nasopharyngeal squamous cell carcinoma, rapid tumor growth, invasion and growth to adjacent organs, early cervical lymph node metastasis, may occurring late pulmonary metastasis. 3,GTV comparison :①As GTVP standard: Under the condition of SUV4.0,SUV40%and SUV45%, the target volume delineation of GTVPET/CT compared with GTVP, there were no statistically significant difference between the three(P>0.05). In these three conditions, target volume delineation of PET/CT are basically the same size with tumor pathology volume. GTVMRI, GTVCT and GTVP were compared, the differences were statistically significant(P<0.05), both are larger than GTVP. ②As GTVMRT standard: Under the conditions of SUV3.5 and SUV35%,the target volume delineation of GTVPET/CT compared with GTVMRI, the difference was not statistically significant(P>0.05).It can be considered in these two conditions, the target volume of PET/CT to determine were basic agree with MRI. Compared GTVMRI with GTVCT, there was no statistically significant difference(P>0.05), can be considered by using the CT data nasopharyngeal tumor target volume delineation is consistent with MRI(P>0.05). 4, Wmax comparison :①As WP standard: PET/CT with SUV3.5,SUV4.0, SUV 40%, SUV 45%, SUV 50%, the maximum diameter of target volume delineation of comparison WPET/CT with WP, the difference was not statistically significant(P>0.05); These suggest that PET/CT under these SUV threshold condition delineated the maximum transverse were similar with pathological specimens. WMRI, WCT and WP were compared respectively, the differences were statistically significant(P>0.05), the first two are wide than the latter, indicating there were differences between the maximum transverse diameter of MRI, CT of target delineation and the pathological specimens, and wider than pathological specimen width, are not well reflect the true maximum diameter of tumor. ②Taking WMRI as standard: PET/CT with SUV2.5, SUV3.0, SUV3.5, SUV30%, SUV35%, SUV40%, SUV45%,the maximum diameter of target volume delineation of comparison WPET/CT with WMRI, the difference was not statistically significant(P>0.05); These suggest that under the SUV threshold condition the maximum transverse of PET/CT target delineation is almost the same size with MRI. Comparison of WCT and WMRI, the difference was not statistically significant(P>0.05), described in the target delineation of maximum diameter, CT and MRI are consistent. 5, Lmax comparison :①As LP standard: PET/CT with SUV3.0, SUV30%, SUV35%, SUV40%,the longest diameter of target volume delineation of comparison LPET/CT with LP, the difference was not statistically significant(P>0.05); Visiblely in these SUV threshold conditions PET/CT to delineate the longest diameter and pathological specimens were relatively close. LMRI, LCT and LP were compared respectively, the differences were not statistically significant(P>0.05), so that the two tumor volume delineation of the longest diameter consistent with pathological specimens. ②Taking LMRI as standard: PET/CT with SUV3.0, SUV25%, SUV30%, SUV35%, SUV40%,the longest diameter of target volume delineation of comparison LPET/CT with LMRI, the difference was not statistically significant(P>0.05); In these SUV threshold conditions PET/CT and MRI for the longest diameter of target delineation is almost the same; a comparison between LCT and LMRI, the difference was statistically significant(P<0.05), so that the target volume delineation of the longest diameter, CT and MRI are different, CT for target volume delineation of the longest diameter is longer than MRI. 6, The best SUV value determined: Comprehensive consideration of the tumor volume, maximum diameter and longest diameter, based on the volume of pathology as the standard, 40% SUVmax is considered as the best SUV value for PET/CT in determining target volume delineation; and target volume delineation of MRI as the standard,35% SUVmax is considered as the best SUV value for PET/CT in determining target volume delineation.7, ①Taking the pathological samples as the target volume delineation standard: The optimal SUV40% threshold conditions, PET/CT data of target volume in GTV, Wmax, Lmax were compared with pathological specimens, there were no significant differences(P>0.05), suggesting that PET/CT delineation target volume is very close to the true size of pathology. Respectively using MRI, CT data to delineate of GTV and Wmax were compared with the tumor pathological specimens, the differences were statistically significant(P<0.05), were compared with pathological specimens is too large; while LMRI, LCT and LP were compared, the differences were not statistically significant(P>0.05). Tip respectively with MRI, CT to delineate target volume, in addition to the longest diameter and pathological specimens are basically the same, the target volume and the maximum diameter compared with pathological specimens were statistically significant, is larger than pathological specimens. ② Taking the MRI data as the standard of target volume delineation: the optimal SUV35% threshold conditions, PET/CT data of delineation target in GTV, Wmax, Lmax respectively compared with MRI, there were no significant differences(P>0.05), suggesting that PET/CT and MRI target delineation are almost the same. CT data of target delineation for GTV and Wmax were compared with MRI, there were no significant differences in P>0.05); LCT compared with LMRI, the difference was statistically significant(P<0.05), LCT is longer than Lmax; Prompted by CT data delineating the target volume, in the target volume and the maximum diameter are basically same as MRI, but CT target volume delineation of the longest diameter was different with MRI,was too long for MRI. Conclusion: 1,This study believes that tissue suspension inoculation method to construct animal model of rabbit VX2 nasopharyngeal transplanted tumor is simple and easy to operate, high successful rate.2,Pathology confirmed that rabbit VX2 nasopharyngeal tumor animal model is the ideal animal model of human nasopharyngeal poorly differentiated squamous cell carcinoma in experimental study. 3, By SUV4.0 and SUV40%, SUV45% threshold conditions of GTVPET/CT are close to the tumor true pathology volume, in contrast to SUV40% threshold can better reflect the real tumor volume, 40% SUVmax was the best SUV value of target volume delineation for PET/CT with the pathological volume as the standard; By SUV3.5 and SUV35% threshold conditions of GTVPET/CT were similar to target volume delineation of MRI, in contrast to SUV35% threshold can reflect GTVMRI best, 35% SUVmax is the best SUV value of target volume delineation for PET/CT with GTVMRI as the standard.4,①With the pathological specimens as standard: CT, MRI data for target delineation can’t reflect the real situation of tumor pathology well. PET/CT with SUV40% threshold of target delineation compared with CT, MRI has higher accuracy, can accurately reflect the true volume of tumor pathology; ② Taking GTVMRI as the standard: The CT data of target delineation can not be completely consistent with MRI, the longest diameter are difference. PET/CT with the SUV35% threshold of target volume delineation were very close with MRI, the accuracy is higher than CT, can accurately reflect the target volume delineation of MRI.③No matter what the standard, compared with MRI, CT, PET/CT delineating target volume is more close to the pathology true volume; compared with CT, PET/CT can better reflect the target volume delineation of MRI. 5, The application of PET/CT in the delineation of target volume in nasopharyngeal carcinoma, more conducive to the implementation of precise radiotherapy for nasopharyngeal carcinoma. |
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