The Anatomical Volume Target Of Rabbit VX2 Brain Tumor Model In Precise Radiotherapy Evaluation With CT Perfusion

Subjective: To evaluate the gross target volume (GTV)and the clinically delineated target volume (CTV) with CT perfusion imaging contrasting to the conventional pathological examination in rabbit VX2 brain tumor model. Materials and methods: Rabbit VX2 brain tumor models were established by an intracranial inoculation,and following a conventional CT scanning, then were administered with a contrast agent (Omnipaque) by an intravenous injection with a rate of 5ml/S and dose of 1.5ml/kg via rabbit hindlimb vein, a dynamic scanning were simultaneously performed by using a Philip 64-slice CT scanner with the parameters involving the same slice of dynamic collection, tube voltage of 80kV, tube current of 100mA, matrix 512x512, FOV9.6CM acquisition slice thickness of 2.5mm, scan speed 1S/cycle, scan time 70S and a total of 560 images.The dynamic images were reconstructed and processed with a cerebral perfusion CT software package of the PERFUSION to acquire the perfusion images, and the cerebral blood flow and volume in regions of interest images were measured and analysed quantitatively. The perfusion parameter values in tumor center and margin and normal brain tissue were calculated in regions of interest of tumor selected in pseudo-color maps.According to the laser marks at the same slice location given by CT laser positioning with the Sametip System of mobile bed, the scalp was incised, the skull was drilled, and a piece of tag with 3～5mm of width and 1mm of thickness was vertically inserted into brain tissue, then the marked slice was scanned for in vivo validation. After that, the animals were sacrificed within 2 hours, the brain tissues were anatomized and examined in pathology.The tumor sizes displayed in images of CECT, BF and BV were measured and contrasted to that observed in pathology/ histology. The microscopic tumor extent of invasion was observed under microscope to define which image can really reflect the grossly visible tumor and the clinically delineated gross tumor boundary.Results: CECT showed that the mean long and short diameters (GTVCECTlong/short) were 6.93±4.28mm and 3.17±1.93mm respectively; CT perfusion parameters of BF map showed that the mean GTVCECTlong/short were 10.18±3.00mm and 5.57±1.65mm respectively; BV maps showed that the mean GTVCECTlong/short were 11.16±3.01mm and5.83±1.54mm respectively; the mean GTVCECTlong/short observed in the gross pathological sections were 7.98±2.11mm and 4.40±1.19mm respectively; The microscopic tumor-invasive distances of long and short diameters were 4.86±2.36mm and 3.24±1.57mm respectively; The amounts of long and short diameters and their microscopic tumor-invasive distances (CTVlong/short) were 12.87±3.74mm,7.64±2.05mm respectively.The differences between the tumor sizes derived from CECT, BF, BV, gross pathology and histology are statistically significant( for long diameter, P = 0.000;for short diameter, P=0.000). The differences beteen the tumor sizes of different individuals statistically significant( for long diameter, P=0.000;for short diameter, P=0.000). The fractions of the long diameters of GTVCECT,GTVBF and GTVBV to that of the pathological GTV were 81±46% (95%CI,60-103%),134±48%(95%CI,112-156%) , and 145±38%(95%CI,128-163%) respectively; The fractions of the short diameters of GTVCECT, GTVBF and GTVBV to that of the pathological GTV were 71±44% (95% CI,50-91%), 132±44% (95% CI,111-152%) and 135±29% (95%CI.121-148%) respectively; The fractions of long and short diameters of GTVBF to that of the CTVlong/short were 84±30% (95%CI,70-98%) and 77±28% (95%CI,64-90%).Conclusions: The rabbit brain tumor model established by using a intracerebral inoculation with VX2 tumor cells is stable and could simulate the feature of intracranial growth and the appearance of characters of primary glioma, and would be applicable for the experimental studies of CT perfusion imaging and precision radiotherapy planning in brain tumors.CT perfusion imaging may provide a more accurate biological informations about microvascular proliferation and neovascularization in brain tumor, which may be useful to guide the definition of precision radiotherapy planning.BV image could be better for defining of tumor size. In-vivo validation of on-line at same slice could provide a new basis for precision radiotherapy. CT perfusion imaging is also feasible for defining of precision radiotherapy planning in glioma.