Comparative Research Of IGRT Rectification Between In Room CT And EPID Of Tumor In Head And Neck

Background and objective : With the renewal of radiotherapy equipment and technological progress,guided by the image system, precision radiotherapy era has come, setup error will also become one of the important factors that influence tumor radiation therapy effect. In this research, we used two kinds of image-guided technology which were called In Room CT and EPID to adjust IGRT in the position of the registration for the tumor in head and neck, to measure and analyze its position error and evaluate In Room CT value in radiotherapy for its position correction function.Methods: Randomly selected 20 patients who underwent IMRT for head and neck tumor in our hospital, all used a head pillow(type B or C) + neck shoulder mask to fix,every week took a group of samples of EPID side position piece before the radiotherapy, and then scan in room CT,took manual registration respectively for EPID images and radiotherapy planning system in the reconstruction of the DRR images utilizing bony marker, took software automatic fusion for in room CT image and the planning CT images first then adopt manual fine tuning, the registration obtained respectively two groups in the X axis(left and right), Y axis(head foot direction), the Z axis(before and after) three line pendulum position error data. In order to correct the error of the Room CT In group, the position of the positive lateral film was received and the DRR image was registered with the EPID image, then a set of position error data were obtained. The mean and standard deviation of the three sets of data were calculated.Results1.Before radiotherapy,all patients(B type and C type head rest + neck shoulder mask fixed) EPID, in room registration of CT group in the X axis error is(0.070 +0.120) /(0.068 + 0.138) cm, and the Y axis error(0.032 + 0.158) /(0.011 0.193 +) cm,Z axis error(0.141 + 0.152) /(0.043 + 0.195) cm, two kinds of image guidance tools before radiotherapy in X, Y axis direction of registration of setup error value is similar(P > 0.05), and the Z axis direction in room registration setup error has statistical significance(P < 0.05);2.In the test group who used head pillow(type B or C) + neck shoulder mask to fix,the positioning error data of EPID and Room CT registration X, Y axis direction(P >0.05), Z axis direction(P < 0.05) have statistical significance. In the fixed group of C head and head and neck shoulder mask, there was no significant statistical significance in the registration of In, Y and Z axis direction(P > 0.05) of EPID and Room CT X. B pillow + head and neck shoulder mask group, C pillow + head and neck shoulder mask fixed group between the two groups of EPID registration phase comparison, Room CT In registration, the X, Y, Z axis direction of the swing error was not statistically significant3. Before radiotherapy EPID group registration, in room CT correction after radiotherapy EPID group registration on the X axis error respectively(0.070 + 0.120) /(+ 0.020 0.096) cm, Y axis respectively(0.032 + 0.158) /(-0.031 + 0.093) cm, the error of Z axis respectively(0.141 + 0.152) /(0.049 + 0.078) cm, by before and after two group comparison, apply the in room CT modified pendulum position error in Y and Z axis has statistical significance(P < 0.05).4. In Head and neck neoplasms IGRT, in the the group of X, y and Z axis direction in the EPID registration CTV-PTV expansion distance MPTV are 0.26 cm, 0.19 cm,0.46cm; in room registration of CT group MPTV are 0.27 cm, 0.16 cm,0.24cm; used in room CT will set bit error correction, MPTV respectively is 0.12 cm, 0.14 cm, 0.18 cm.Conclusion:In Room CT and EPID system are the effective tools for image guidance in head and neck tumor IGRT. With Room CT In registration as the standard, through position correction the patient’s position error can be reduced, and the MPTV will be reduced to 2 mm. And Room CT In images can be intuitive analysis of the target area of radiation and the three-dimensional direction of the crisis in the direction of the crisis, to avoid the EPID positive side of the image due to overlap with the impact of the introduction of errors. Therefore, it is recommended to take Room CT In body, in the head and neck tumor IGRT, to complete the high precision, involving high-risk organ protection of radiotherapy, Room CT In should be given priority to use.