Abstract:

Objective To study the target delineation method of normal spinal cord tissue after implanta⁃tion of 125I radioactive particles. Methods The CT images of chest and abdomen of 5 healthy people were selected.The slice thickness was 0.5 cm，and the 3D treatment planning system was used. At the 12th thoracic vertebrae，the cylindrical tumors with the diameter of 4 cm，3 cm high（group A），5 cm in diameter and 4 cm in height（group B），6 cm in diameter and 5 cm in height（Group C）and 1.0 cm in length，width and height（Group D），5 cm in length，5 cm in width and 5 cm in height（Group E），and 6 cm in length，6 cm in width and 6 cm inheight（Group F）and 1.0 cm in length，width and height were respectively depicted at the 12th thoracic vertebraeThe tumor is a triangular pyramid. According to the rule of sparse in the middle and dense in the periphery，theprescription dose was 135 Gy，and the preoperative plan was carried out. Then the target areas of normal spinalcord tissue were delineated as -1.0，-0.5，0，0.5，1.0，1.5，2，2.5，3.0 cm，respectively. The mean，Max andD2cc of GTV were calculated. Results The particles used the dose of D2cc and the maximum point increases with thesize of the tumor. In group A，B，C，D，E and F，the length of the target area which was delineated normal spinalcord tissue，was not related to the maximum dose received by the spinal cord. With the increase of the length of thetarget area of normal spinal cord tissue，the average dose received by the spinal cord decreased gradually. In groupA，B，C，D，E and F，when the target area of normal spinal cord tissue was less than the GTV layer，the D2ccdecreased with the reduction of the target area of normal spinal cord tissue，greater than or equal to the GTV layerIn face time，D2cc did not change with the increase of target length in normal spinal cord，and was not related totumor shape and size. There was a significant difference in the length of spinal cord sketch between the tumor targetlevel and the tumor target level（P < 0.05）. Conclusion When the target area of normal spinal cord tissue afterimplantation of 125I radioactive particles was longer than or equal to the GTV level ，the amount of spinal cordtissue received has nothing to do with tumor size and tumor shape. It is recommended that the target length of normalspinal cord tissue after implantation of 125I radioactive particles be the visible level of all tumor targets.【Key words】target delineation； spinal cord； 125I particle； the 3D treatment planning system

Key words: target delineation, spinal cord, 125I particle, the 3D treatment planning system