Compare the registration results with different registration methods in cone beam CT guided radiotherapy for nasopharyngeal carcinoma

Abstract

Objective To compare the results of three different registration methods in the kilovolt CBCT guided IMRT for nasopharyngeal cancer (NPC).Methods Total 560 CBCT images of 24 NPC patients who received kilovolt CBCT guided IMRT were analyzed off line.Three registration methods were used for alignment between CBCT and planning CT,including translational and rotational errors for bone and grey (BoneT + R,GreyT+ R),only translational errors for grey (GreyT).The registration results were analyzed by mean paired t-test respectively.Results With method BoneT+R,the translational errors on x,y and z axes were (-0.11 ± 1.35) mm,(0.40 ± 2.09) mm and (0.95 ± 1.56) mm and the rotational errors were 1.06° ±0.67°,0.01° ± 1.28° and 0.92° ± 1.00° respectively.With GreyT+R,the translational errors on x,y and z axes were (-0.02 ± 1.06) mm,(0.68 ± 1.92) mm and (0.81 ± 1.46) mm and the rotational errors were 0.85° ±0.61°,-0.05° ± 1.32° and 0.91° ±0.72° respectively.With GreyT,the translational errors on x,y and z axes were (0.58 ± 1.02),(0.52 ± 1.89) and (0.44 ± 1.43) mm.The results of compared mean t-test for different registration methods groups have significant difference (P =0.00-0.01) except for the rotational errors on y and z axes between BoneT+R and GreyT+R (P =0.05,0.62).Conclusions There have different alignment errors when different registration methods used for NPC kilovolt CBCT guided radiotherapy.If there have correct methods for rotation errors,GreyT+R registration method may be a better choice.In opposite,GreyT+R registration method would be used firstly to verify whether the rotational error ＞ 2°or 3°.If the rotational error ＞ 2°or 3°,the patient should be re-setup.If not,according to these alignment results,the GreyT method,manual method would be used to compensate the translational errors. Key words: Nasopharyngeal neoplasms/radiotherapy; Tomography, X-ray computed, conebeam ; Image registration