Study On MVCT Image Registration Method And Setup Errors In Helical Tomotherapy

Helical tomotherapy is the most advanced intensity-modulated radiotherapy system,which can transmit uniform and conformal dose to the tumor target area and protect the organs at risk.The homogenous MVCT image guidance system carried by the Helical tomotherapy system can correct the patient’s position to ensure the accuracy of radiotherapy.However,the accuracy of MVCT image-guided radiotherapy is affected by image acquisition pitch,registration method,and registration range.There are few research reports about how much influence these factors have on the positioning accuracy.Therefore,this subject aims to study the factors that influence the MVCT image-guided accuracy and the influence of different immbolization techniques on positioning accuracy.By combining simulation phantoms and patient experiments,three factors that affect the positioning accuracy of helical tomotherapy:image acquisition pitch(Coarse,Normal and Fine),image registration method(Bone Technique,Bone and Tissue Technique and Full Image Technique)and registration range(Independent target registration and overall registration)are studied separately.The influence of immbolization technique on the setup errors of neck tumors in radiotherapy was studied using the recommended method in previous research.The positioning accuracy is evaluated by parameters such as translation error(Δx,Δy,Δz),vector error(Δ),target coverage(CR)and volume similarity index(DSC).The statistical method used non-parametric paired test,and P<0.05 indicated that the difference was statistically significant.Regarding to the effect of different image acquisition pitches and registration methods on the registration accuracy,the results show that when the image acquisition distances are Fine,Normal and Coarse,the vector errors of the different registration methods Bone Technique,Bone and Tissue Technique,and Full Image Technique are(0.76±0.4,0.76±0.4,0.73±0.46)mm,(0.79±0.5,0.71 ±0.38,0.69±0.36)mm and(1.20±0.52,1.35±0.6,1.42±0.68)mm.When the scanning pitch is Normal and the Bone and Tissue Technique method is used,the registration accuracy is good and the efficiency is high.Regarding to the influence of different image registration ranges on the positioning accuracy of MVCT image-guided multi-target areas,the results show that There was no significant difference in the CR,DSC and geometric center deviation between the two target regions when registered with all targets(p>0.05).When only registered with one target region,the DSC and geometric center deviation of this target were significantly better than the other one(p<0.05).For single target,the CR,DSC,and geometric center deviation obtained by registered with this target region are significantly better than that registered with all targets,registered with the other side target area obtained the worst results(p<0.05).Regarding to the influence of immobilization methods on the accuracy of tomotherapy,the results show that the setup errors of the immobilization methods are significantly different in the three translation directions and cross-sectional rotation directions.The margin of the foam group are smaller than those of the vacuum group.In the foam group,the errors in the LR,SI,and AP directions were(-0.64± 1.55,0.38±1.82,1.77±2.54)mm respectively,and the margin was(3.708,4.289,4.692)mm,The errors in the LR,SI,and AP directions of the vacuum group were:(-0.20±2.02,0.94±2.71,2.58±2.62)mm respectively,and the margin was(4.181,5.245,5.603)mm.In conclusion,we recommend the Normal scanning pitch and the Bone and Tissue Technique for registration,which can get high registration accuracy and improve efficiency.The image guidance range for multiple metastases should include all target regions or registrated independently.For tomotherapy of the neck tumor,the recommended immobilization method is the foam group to improve the accuracy of radiotherapy,which can reduce the MPTV.