Study On The Tumor Local Boost And Brachytherapy Combiend With External Beam Radiotherapy Dose Accumulation Method In Three Dimensional Radiotherapy For Cervical Cancer

Study one:Purpose:Combined therapy of external beam radiotherapy and brachytherapy is considered as the standard therapeutic means for the local advanced cervical cancer.With the three-dimensional intracavitary/interstitial brachytherapy（IC/IS BT）,the tumor tissue is well covered,and the dosage for organ at risks（OARs）can be reduced effectively.However,the technology involves great difficulty in the process of implementation,and there is strict requirement on the clinical application.To investigate the dosimetry differences in the treatment of locally advanced cervical cancer with IC/IS BT,intracavitary and intensity modulated radiotherapy（ICBT+IMRT）and simple IMRT.Method:16 patients with local advanced cervical cancer were included to study,which were treated by three-dimensional brachytherapy.All of them have accepted IMRT（45 Gy/25 times in total）.After the external beam radiotherapy is finished,they have accepted five times of three dimensional brachytherapy,with 6 Gy/time.On the basis of the original three-dimensional intracavitary/interstitial brachytherapy plan,ICBT+IMRT and only IMRT plan were designed respectively to study the dosimetry differences of target and different organs at risk for the three kinds of plan.By adopting the methods of graphical optimization（GO）and inversely optimization simulation anneal（IPSA）,the following requirements on the total equivalent dose in 2 Gy fractions（EQD2）for external beam radiotherapy and brachytherapy are fulfilled:HRCTV D₉₀≥85 Gy,IRCTV D₉₀≥60 Gy,bladder D_2cc<85 Gy,rectum,small intestine and sigmoid Colon D_2cc<75 Gy.The doses difference of three plans in terms of tumor target and organ at risk（OARs）is studied.Results:A total of 75 brachytherapy treatment plans were designed,including 25 IC/IS BT,25 ICBT+IMRT and 25 IMRT.There was little difference in target dose parameters between ICBT+IMRT and IC/IS BT plan（P>0.05）,lower doses for OARs.In the plan of simply IMRT,The doses of OARs in the Only IMRT plan were relatively large and the volume irradiated to more than 60 Gy(_uwas significantly higher.Conclusion:Theoretically,ICBT+IMRT is similar with IC/IS BT,and ICBT+IMRT is convenient to implement.The ICBT+IMRT technique not only provides better target coverage but also maintains lower dose to the OARs,which can be used as an alternative treatment for IC/IS BT.Although the target coverage of Only IMRT is better,the protection of OARs is poor,so it is not suitable for local boost therapy of advanced cervical cancer.Study two:Purpose:The accurate dosage accumulation of brachytherapy and external beam radiation therapy provides important guidance for the clinic treatment,which affects the survival rate of patients and the late side effects.In this study,the dose parameters direct addition and the deformable image registration（DIR）dose addition are performed at the dosage of brachytherapy and external beam radiotherapy for the patients with local advanced cervical cancer,and dosimetric comparisons were made between the two methods.Method:12 patients with local advanced cervical cancers are recruited,and after 23 times of volumetric modulated arc radiation therapy（VMAT）are performed,5times of three-dimensional intracavitary brachytherapy（ICBT）is performed,with 6Gy/time.The dose accumulation is conducted for the brachytherapy and external beam radiotherapy therapy through the deformable registration by using the software of MIM,and it is compared to the parameters direct addition.Results:The difference in the values of HRCTV D₉₀doesn’t show statistical significance（P>0.05）between DIR addition method and parameters direct addition method.Compared to the DIR addition,the parameter direct addition underestimates the values of OARs dose,and the difference shows statistical significance.Conclusion:The dose of organs at risk should be more strictly limited in the practical design of the plan.The DIR dose addition method provides guidance for the clinical treatment.