Evaluation Of Multi-fraction Dose Accumulation With Deformable Registration Algorithm In Brachytherapy

Studies have proved that there is a significant correlation between the volume and dose of exposure to organs at risk in radiotherapy and the incidence of complications,and the correct assessment of the exposure to organs at risk is of great significance for precise radiotherapy.In three-dimensional brachytherapy,the total radiation dose is usually the addition of 3-5 fractions of doses.Compared with external radiation,the fractional dose is large（usually 6-8Gy/time）,and the organ movement is different between the fractions.Large,large differences in planned dose distribution among subdivisions.The cumulative dose assessment method recommended by GEC-ESTRO,which is currently widely used,does not take into account factors such as organ movement and volume changes,and has certain limitations.Therefore,the use of a suitable cumulative dose assessment method is of great significance to accurately assess the cumulative dose between fractions.A large number of literature reports that the image deformation registration is to transform two images collected under different imaging devices at different time periods through a certain spatial transformation so that the corresponding points reach the same spatial and anatomical positions.It can be seen from the definition that the deformation registration algorithm is a suitable method for evaluating the cumulative dose of three-dimensional brachytherapy.The deformation registration algorithm takes into account the influencing factors such as the deformation of the organs at risk,position changes and uneven dose distribution during radiotherapy,which can more truly reflect the patient’s total exposure dose and reduce the target caused by overestimation of the cumulative dose.Insufficient dose in the area or underestimation of the occurrence of organ-threatening complications caused by the cumulative dose.Hybrid deformation algorithm is a deformation algorithm that combines image pixel information with feature information.The MORFEUS deformation algorithm is a non-rigid deformation registration algorithm based on the finite element model.This article first uses DSC as an evaluation index to evaluate the deformation accuracy of the two deformation algorithms.Using 70 cases of cervical cancer three-dimensional afterloading treatment,the bladder and rectum were selected as the deformation area of interest,and the volume of the area of interest was controlled.They were divided into a 40-case volume control group and a 30-case volume uncontrolled group.The results show that for the bladder of the volume control group,the DSC using the hybrid deformation algorithm is between 0.95 and 1,and the similarity coefficient using the MORFEUS deformation algorithm is between 0.94 and 1.The deformation under the two deformation algorithms has higher deformation.accuracy.For the bladder of the uncontrolled volume group,when the mixed deformation algorithm is used,when the volume ratio is greater than 1.5,the DSC value has been significantly reduced,and the deformation accuracy is significantly reduced.Similar results can also be observed using the MORFEUS deformation algorithm.When the volume ratio is greater than 1.3,the DSC value has also been significantly reduced,and the deformation accuracy is significantly reduced.The results of the rectum are not as obvious as the bladder.It can be seen that the control of the volume can effectively reduce the uncertainty caused by the deformation volume,but there is no statistical difference between the two deformation algorithms（P=0.34）.On this basis,this paper uses the hybrid deformation algorithm and the MORFEUS deformation algorithm to calculate the deformation doses D_0.1cc,D_1cc,and D_2cc,respectively,and compare them with the deformation dose superposition of the estimation method recommended by GEC-ESTRO.The study found.The total exposure dose calculated under the estimation method recommended by GEC-ESTRO is not as accurate as the superimposed total dose calculated using the two deformation algorithms,but the difference between the two algorithms is not obvious.Moreover,it is found that the deformation volume can affect the calculation result of the deformation cumulative dose,and reasonable control of the volume of the deformation profile not only helps to improve the accuracy of the deformation.In addition,the evaluation result of the total deformation dose is more stable.It is recommended to pay attention to the volume control of the bladder and rectum during the afterloading treatment.