Study On Accurate Evaluation Of Internal And External Radiation Therapy Dose For Cervical Cancer

Background:Cervical cancer is one of the most common malignant tumors in females.At present,the best way to treat cervical cancer recommended by the National Comprehensive Cancer Network（NCCN）guidelines（2020 edition）is the combination of external radiation therapy and three-dimensional intracavitary brachytherapy,which can make the tumor target area completely lethal dose,and reduce the dose to organs at risk.Since the afterloading radiotherapy system is a newly installed domestic equipment,the current quality control method is cumbersome and there is no uniform standard,and it is necessary to carry out detailed quality control to provide data reference for the accuracy of subsequent dose superposition and the formulation of a reasonable radiotherapy process.Because of the large difference in patient position between the two radiotherapy modes（external radiotherapy:supine position,afterloading intracavitary radiotherapy:lithotomy）.When performing postloading intracavitary radiotherapy,the packing of the applicator and other packing materials will also cause differences in the positions of the patient’s tumor target area and organs at risk.This makes it impossible to accurately assess the radiation dose and volume of the tumor target area and organs at risk after combined radiotherapy,which is not conducive for clinicians to evaluate the local control rate of cervical cancer and the toxicity side effects of the organs at risk.Study one:Objective To explore the main errors of the three-dimensional post-installation intracavity radiotherapy system for cervical cancer,provide a stable and accurate quality control method,ensure that the errors of the equipment and the planning system are within the standard range,and provide stable and accurate data reference for subsequent work.Methods The standard phantom was used to detect the reconstruction error of TPS images;the DVH parameters were used to compare the dosimetric difference between the manual reconstruction and the automatic reconstruction of the applicator channel in the TPS;the source appearance activity of the after-loading therapy machine was measured by the well-type ionization chamber and the film measurement method,The accuracy of the source in place and the accuracy of the source retreat are verified.Results The appearance activity of the radioactive source of the after-loading treatment machine,the accuracy of the source in place and abdication,the image reconstruction error in the planning system,and the automatic reconstruction error of the applicator were all within the allowable accuracy and met the clinical treatment requirements.The radioactive source activity error of the afterloading therapy machine is 0.43%,the average deviation of the source placement accuracy and the abdication accuracy is less than 1 mm,and the image reconstruction error in the treatment planning system is less than 1 mm.The applicator channel is automatically reconstructed and manually reconstructed.There was no significant difference in the dose parameters between the two groups（P>0.05）.The after-installation machine and its planning system meet the requirements of clinical treatment.Conclusion The verification method introduced in Study One is simple and accurate,and has certain reference significance for the acceptance and routine quality control of after-loading equipment and its planning system,which can ensure the stable and accurate dose during after-loading treatment,and is helpful for clinicians and physicists to be familiar with after-loading.The main source of radiotherapy errors can provide data reference for formulating rationalized and personalized radiotherapy procedures.Study two:Objective To analyse the difference in the cumulative doses of cervical cancer internal and external radiation between different dose stacking methods,evaluate the accuracy of the direct stacking method,and provide a reference for clinical application.Methods A retrospective analysis of the radiotherapy plans of 10 patients with cervical cancer who received internal and external radiation therapy was performed.With the help of the deformation registration method in the MIM software,the fractional internal radiation dose and external radiation dose of each patient were superimposed and compared with the direct superposition method.Results When superimposing the fractional internal radiation radiotherapy dose,it is found that the average values of the tumor target area D_90%,bladder D_2cc,and rectum D_2cc obtained by the direct superposition method are 6.54 Gy,1.66 Gy,4.05 Gy higher than the results of the deformation registration method,and there are significant differences（t=-4.129、-3.236、-4.168;P<0.05）.When the internal and external radiation doses are superimposed,it is found that the average values of the tumor target area D_90%,the bladder D_2cc,and the rectum D_2cc obtained by the direct superposition method are 5.35Gy,0.78 Gy,and 6.72 Gy higher than the results of the deformation registration method,and tumor target area D_90%and rectum D_2cc are significant differences（t=-3.090、-4.321;P<0.05）,bladder D_2cc is not significant differences（P>0.05）.Conclusion The direct stacking method assesses the high dose of normal tissues,and the conditions can be relaxed appropriately in actual work.The deformation registration method in MIM software can relatively accurately reflect the cumulative dose of cervical cancer internal and external radiation and provide a certain reference basis for clinicians and physicists in hospitals that are not equipped with deformation registration software.