| Background and purposeMagnetic resonance imaging(MRI) can well distinguish soft tissue,but its usage in radiotherapy for brain tumors was limited by image distortion and lack of electron density for dosage calculation. The registration of MRI with computed tomography(CT) could resolve this problem.With the development of imaging and medical image fusion technology, the concept of biological intensity-modulated and biological target volume(BTV) emerged. The functional imaging technology, such as PET, PET-CT, SPECT, MRS, etc., can obtain the information of tumor biological characteristics. This study was to compare and analyze CTVs difference betweenCTVs of CT/MRI image fusion and CT image, and investigated the influence of peritumor edema on target delineation of intracanial tumors’ precise radiotherapy, and studied the influence of PET-CT image registration on the definition of BTV.Materials and methods1. From November 2013 to April 2014, 60 cases with intracranial tumors scanned by CT and MRI were collected from the department of radiation oncology in the First Affiliated Hospital of Zhengzhou University in the same period. All images were transmitted to VARIAN treatment planning system and CT images were fused into CT/MRI images, 60 patients received MRI scanning before radiotherapy, and then 65 pairs of clinical tumor volume(CTVCT and CTVCT/MRI)were delineated both on CT and CT/MRI. Finally we compared CTV difference between two groups,and analyzed the influence of peritumoral edema on target volume delineation of intracranial tumors’ precise radiotherapy. 2. From November 2013 to October 2014, 3 cases with tumors who also received PET/CT scanning were collected from the department of radiation oncology in the First Affiliated Hospital of Zhengzhou University in the same period. Including 1 case for non-small cell lung cancer, 1 patient of non-Hodgkin’s lymphoma, 1 case for cancer of bone metastasis. All PET/CT images were transmitted to VARIAN treatment planning system and fused into PET-CT images. 3 patients underwent PET/CT scanning before radiotherapy. In the first and eighth day, GTVCT and GTVPET-CT based on CT alone images and PET-CT fused images were defined by four experienced radiation oncologists, respectively. This procedure was repeated 10 times every day. Finally, intra-groups difference and inter-groups difference were compared,and the influence of PET-CT image fusion on the definition of biological target volume definition was further analyzed. 3. SPSS 17.0 software package was used to perform all statistical analysis. Wilcoxon matched-pairs signed-ranks test was performed to compare the volume difference on 65 pairs of intracranial tumors’ CTVs. Kruskal-Wallis ranks test was adopted to compare the difference among the four groups. Bonferroni method wasused to compare the differecnce between each two groups. T test was used to compare the volume difference of GTVs defined by the four doctors in the first day and the eight day. One-way ANOVA was used to compare the volume difference among the four groups and LSD-t test was used to compare BTV difference between each two groups. P≦0.05 was considered as statistically significant.Results1. The average volume of CTVCT in 65 pairs from 60 cases was(99.45±84.08) cm3 and the average volume of CTVCT/MRI was(83.38±72.11)cm3. Among the 65 control groups, 15 cases of CTVCT were lower than CTVCT/MRI and 50 cases of CTVCT were higher than CTVCT/MRI. In most cases, CTVs delineated on CT/MRI images were smaller than those delineated on CT images and the difference was statistically significant(n=65, Z=-3.885, P<0.001). 2. According to the degree of peritumoral edema, we selectly chose 50 cases with CTVCT > CTVCT/MRI. The overall distribution of CTVCT and CTVCT/MRI difference is not all the same among different edema group before and after image fusion( χ2=16.311, P=0.001). The Bonferroni method results showed there were significant differences between none edema group, light edema group and severe edema group, respectively(P=0.000, P=0.005). 3. The radiation oncologists defined GTVs at different time before and after PET-CT image fusion, respectively. The results indicated a statistically significant difference on volume differences of GTVCT that were defined by some doctors based on the CT alone at the first day and the eight day(P<0.05). However, there wasn’t a significant difference on volume differences of GTVPET-CT that were defined by almost all doctors based on PET-CT image fusion at different time(P>0.05). One-way ANOVA results showed the volume differences of GTVCT were significantly different in the four groups(F=66.529, P=0.000; F=18.762, P=0.000; F=6.681, P=0.000), while the volume differences of GTVPET-CT weren’t significantly different in the four groups(F=2.638, P=0.056;F=2.243, P=0.090;F=1.346, P=0.266). It revealed no difference on GTVPET-CT defined by the four doctors. LSD-t test revealed great difference onGTVCT based on CT alone defined by the most of doctors groups(P<0.05). GTVsPET-CT delineated by the four doctors after the PET-CT image fusion compared to GTVsCT based on CT alone, Coefficient of variation(CV) was significantly reduced.Conclusion1. The technology of CT/MRI image registration can improve the accuracy of target delineation for intracranial neoplasms. The improving accuracy of intracranial neoplasms’ target volume by CT/MRI image fusion is more suitable for radiotherapy planning. 2. Peritumoral edema has significant influence on the target delineation of intracranial tumors. The greater the peritumoral edema, the lower the accuracy of target delineation. 3. PET-CT image fusion can improve the accuracy of the target delineation and reduce the variation of inter-observers and intra-observers. |
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