Animal Studies For The Target Delineation Of Liver Cancer

Radiation has been changed from conventional radiotherapy to accurate radiotherapy as the development of radiotherapy technique and concept. Accurate radiotherapy demands the technique provides high dose ray to tumor target region according to the shape of tumor in order to kill tumor cell, at the same time normal tissue should be protected to reduce radiation injury. According to this management concept, three dimensional conformal radiotherapy (3DCRT) began to be used into clinic from 1990's, which can provide high dose area conforming to the shape of tumor. Target delineation is very important in the progress of 3DCRT. The target consists of gross tumor volume(GTV),clinical target volume(CTV) and planning target volume(PTV). All of these are difficult to be delineated in clinical practice.CT scan is the main method to pick-up imaging information of the tumor. In the progress of CT enhancement scanning, the imaging between venous phase and arterial phase exist slight difference. However, which phase can provide clearer tumor imaging information should be further studied.CTV contains the area of subclinical cancer, which also has arguments. As there is not effective technique to definite the exact area of subclinical tumor, it is one of the most difficult job for the doctor to delineate CTV. Because it is hard to obtain the pathological dissect after delineating the target volume, we don't know if CTV that we have delineated is right or wrong. Animal experiment can solve such tough problem.More and more scholar began to think highly of the importance of liver cancer radiotherapy in recent 10 years. After experiencing whole-liver irradiation,local irradiation,moving strip irradiation and hyperfractionation irradiation, 3DCRT has been accepted by more and more medical institution. In the progress of 3DCRT of liver cancer, exact target delineation is the base of radiotherapy, and the delineation of CTV and GTV is the key point of target delineation.Objective:1,To make animal models of liver cancer and observe the differences in tumor size among arterial phase,venous phase of CT image and gross anatomy. Then determine which phase is more similar as the real size of liver tumor in the process of simulation using CT image that before target area definition and GTV determination.2,To examine the subclinical microscopic tumor extention of rabbit liver model with VX2 tumor in order to define the clinical target volume(CTV) according to the degree of microscopic extention for radiotherapy of hepatic cancer.Part 1 Animal Studies about the Choice of CT Phase in the Delineation of GTV for Liver Cancer Radiotherapy Target DelineationMaterials and Methods:1,Model building: Prepare rabbit liver tumor model with VX2 tumor. Frigorific VX2 cell suspension was resuscited and cultured in RPMI1640 culture fluid. Then inoculated it under the skin of posterior limb to make the tumor grow and passage. The tumor was taken out and cut into fragments with the size of 2.5～3.5mm3 when it was as large as 1.5～2.5cm3. 16 New Zealand white rabbits 4-month old and 2.3～2.7 kg by weight were prepared then transplanted the VX2 tumor fragments into their livers by surgical intervention. After 3 weeks later, these animal models were used to empirical study.2,Observe by CT image: The animal models were undergone plant CT scan and enhancement CT scan. Low-density tumor image could be seen according to plant CT scan. Arterial phase images and venous phase images were collected at the time of 15s and 41a after injecting contrast media of Uitravist 370. High-density ring shaped tumor image could be seen according to the arterial phases and low-density sharply marginated tumor image could be seen according to the venous phases. One of the certain CT slice was chosen as the slice of interest then measured the size of liver tumor both arterial phase and venous phase and compared if there is statistical significance between them.3,Comparison between CT image and gross anatomy: After CT enhancement scanning, moved the scanning bed to the location at the slice of interest and then used the laser to locate on the surface of the animal model. Punctured two needles into the liver according to the laser location and collected CT images, the slice which there were two needles image was the right slice of interest. Sacrificed the rabbit and dissect the liver with the two needles, cut the liver into two parts from the plane that the two needles located and got the identical anatomical slice with CT, measured the real size of tumor with measuring scale.Results:1,Modeling of rabbit liver tumor model with VX2 cell: 16 rabbit liver tumor model were made, and 15 of them were transplanted successfully, the rate of tumor growth is 93.8%.2,Results of enhancement CT scan: The mean tumor size of arterial phase, venous phase and gross appearance were 14.59±3.14mm,12.93±3.18mm and 16.21±3.78mm, respectively. No statistical difference between arterial phase and gross appearance (P>0. 05), but it was significantly different between venous phase and gross appearance (P<0. 05).Conclusion:Arterial phase is better than venous phase to determine the GTV of liver tumor,and arterial phase is more similar as the real size of liver tumor in the process of simulation using CT image that before target area definition and GTV determination.Part 2 Animal Studies about the Proper Distance from GTV to CTV in the Liver Cancer Radiotherapy Target Delineation Materials and Methods:1,Comparison between CT image and pathological section: Specimen both tumor and normal liver tissue was fixed into formalin, embedded into paraffin and colored with hematoxylin and eosin stain, observed and measured the range of subclinical cancer under light microscope, ensured the distance of subclinical cancer, tried to find out the relationship between subclinical cancer and gross tumor volume.2,Identified the proper margin from GTV to CTV in target delineation of liver cancer radiotherapy.Results:1,There was no tumor cell infiltrated outside the amicula in 3 of 15 pathological sections, the left 12 pathological sections were observed tumor cell infiltration, which the furthest infiltration distance was 8.1mm, and the median distance was 2.8mm, 95% range of subclinical cancer was 7.75mm.2,The correlation test between the range of subclinical cancer and tumor size showed that there was correlation (p=0.037,R=0.473) but no linear correlation(p=0.075) between them.Conclusion:1,When the diameter of liver tumor is less than 22mm, the margin from GTV to CTV is 7.75mm can contain 95% subclinical cancer.2,The margin from GTV to CTV is positive correlation with GTV, but it is not linear correlation, there are other influencing factors except GTV.