| Objective: Radiotherapy as an effective means for tumor treatment is increasingly widespread. In fact, many kinds of tumors can be cured. However, local recurrence is still problems. The reason is the lack of timeliness and more accuracy evaluation mechanism. At present, we depend on the conventional images (ultrasound, X-ray, CT, MRI, etc.) to evaluate the response of the treatment. But such images only provide the changes of volume. These are very blind and too late. With the help of the functional imaging, we obtain the images which show the metabolic activity of the tumor cells. These images provide more information for guiding the continued treatment plans and boosting the radiation dose. The research in evaluating the response of the tumor treatment using PET technology is rare. There are many problems in the application of PET. Comparing the conventional methods, the advantage of the PET is hardly confirmed. In this experiment, we use 18F-FDG-PET and CT to evaluate the response of the rabbit VX2 tumor model which undergoing the treatment ofγ-knife. With the help of statistical method, we analyze the change of SUVmax and volume in different periods, in order to demonstrate 18F-FDG-PET can discovery the difference earlier than CT among 25Gy group, 35Gy group and 0Gy group in the evaluation of the effect ofγ-knife radiotherapy.Method: 1 cells revitalization and establish VX2 tumor-bearing rabbits; 2 establish VX2 tumor test rabbit models, divided 18 rabbits into 25Gy, 35Gy, 0Gy group( 6 rabbits per group ); 3 beforeγ-knife radiotherapy, obtain all the rabbits'CT images and compute the volume through the software; 4 beforeγ-knife radiotherapy, obtain all the rabbits'PET images and compute the SUVmax by the software; 5γ-knife radiotherapy, 50% isodose curve contains target region; 6 2 days afterγ-knife radiotherapy, obtain all the rabbits'CT images and compute the volume through the software; 7 2 days afterγ-knife radiotherapy, obtain all the rabbits'PET images and compute the SUVmax through the software; 8 7 days afterγ-knife radiotherapy, obtain all the rabbits'CT images and compute the volume through the software; 9 statistical analysis using SPSS13.0 software.Result:1 Before treatment and after treatment two days,three dose groups evaluation of radiotherapy response by PET1.1. After Mann-Whitney test, the changes among 3 groups all had significant differences. 25 Gy and 35 Gy group, 25Gy group and 0 Gy group, 35 Gy and 0 Gy group (Z=-2.562 , P=0.010; Z=-2.882, P=0.004; Z=-2.882, P=0.004, respectively).1.2 25Gy group: mean of SUVmax changes is -1.1767±0.4360; 35Gy: mean of SUVmax changes is -1.1767±0.6249; 0Gy group: mean of SUVmax changes is -1.1767±0.1945.2 Before treatment and after treatment two days,three dose groups evaluation of radiotherapy response by CT2.1. After Mann-Whitney test, the changes among 3 groups all had no significant differences. 25 Gy and 35 Gy group, 25Gy group and 0 Gy group, 35 Gy and 0 Gy group (Z=-0.645 , P=0.519; Z=-0.987 , P=0.324;Z=-0.881 , P=0.418, respectively).2.2 25Gy group: mean of volume changes is -0.0133±0.0327cm3; 35Gy: mean of volume changes is -0.0250±0.0442cm3; 0Gy group: mean of volume changes is -0.0117±0.0133cm3.3 Before treatment and after treatment 7 days,three dose groups evaluation of radiotherapy response by CT3.1 After Mann-Whitney test, the changes among 3 groups all had significant differences. 25 Gy and 35 Gy group, 25Gy group and 0 Gy group, 35 Gy and 0 Gy group (Z=-2.402, P=0.016 ; Z=-2.882, P=0.004 ; Z=-2.882, P=0.004, respectively).3.2 25Gy group: mean of volume changes is -0.2483±0.1499cm3; 35Gy: mean of volume changes is -1.0317±0.5732cm3; 0Gy group: mean of volume changes is 1.0417±0.6969cm3.4 After treatment 2 days and 7 days,three dose groups evaluation of radiotherapy response by CT.After Mann-Whitney test, the changes among 3 groups all had significant differences. 25 Gy and 35 Gy group, 25Gy group and 0 Gy group, 35 Gy and 0 Gy group (Z=-2.242, P=0.025 ; Z=-2.882, P=0.004 ; Z=-2.882, P=0.004 respectively).Conclusion: Before treatment and after treatment 2 days,25Gy group mean of SUVmax decreases 38.53%, 35Gy group mean of SUVmax decreases 57.36%, 0Gy group mean of SUVmax increases 5.00%. Before treatment and after treatment 7 days,25Gy group mean of volume decreases 7.03%, 35Gy group mean of volume decreases 25.22%, 0Gy group mean of SUVmax increases 29.32%.All above demonstrate that before treatment and after treatment two days, the 18F-FDG-PET detected changes among 3 groups. But CT cannot detect these changes until 7 days after treatment. 18F-FDG-PET provide an accurate evaluation of efficacy earlier than CT.
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