Research On Precision Radiotherapy For Breast Cancer

Part one The impact of different simulation localization modalities on target volume delineation of radiotherapy for breast cancerObjectiveFirst,the purpose of this study was to evaluate the impact of magnetic resonance(MR)and computed tomography(CT)simulation on definition of tumor bed and whole breast in patients without the aid of surgical clips.Second,we aimed to quantify consistency of MR-and CT-based target volume delineation for breast-conserving radiotherapy.MethodFrom August 2018 to March 2019,a total of twenty patients with T1-2N0M0 breast cancer in Peking Union Medical College Hospital were included in this study.All the patients had been treated by breast conserving surgery without placement of surgical clips,and prepared to receive radiotherapy.CT-and MR-simulator images were required in the same day for each patient,and the images were uploaded to the Varian Eclipse treatment planning system.Three radiation oncologists independently assigned cavity visualization score(CVS),and delineated the tumor bed(N=20)and whole breast(N=14)clinical target volume(CTVWB)based on CT then MR images.Interobserver variability was assessed by volumes,generalized conformity index(CIgen)and center of mass distance(dCOM).Differences in mean or median values for parameters between two simulation modalities were tested by paired sample t-test or Wilcoxon singed rank test.One-way analysis of variance or Kruskal-wallis test were used to compare mean or median values among three observers.ResultThe median age of included patients was 48 years old.First,mean volumes of tumor bed derived from MR were 22%,27%and 21%smaller than those based on CT images for each observer.However,there was no significant difference between CT-and MR-based CTVWB.Second,for tumor bed,mean CIgen was significantly superior and dCOM was smaller for MR when compared to CT(CIgen:0.59 vs 0.52,P=0.008;dCOM:1.30 cm vs 1.39 cm,P=0.095);for CTVWB,the mean CIgen and dCOM did not differ significantly.Third,mean CVS was 3.23±1.34 and 2.43±0.92 for MR and CT images(P=0.035).In the subgroup with a CT-based CVS?3,the mean dCOM was larger obtained from CT than those from the MR images(1.35cm vs 1.19 cm,P=0.048).Last,there was a positive correlation between CVS and CIgen for both modalities(CT:r=0.699,P=0.001;MR:r=0.895,P<0.001).CVS was negatively associated with dCOM for MR simulation.ConclusionIn the present study,when compared to CT,MR-simulation were able to improve the visualization of postoperative tumor bed changes.In addition,MR-simulation yielded a more precise definition of tumor bed,and improved the consistency of tumor bed contouring in patients without surgical clips.Part two The dosimetry study on different radiotherapy techniques of breast cancerObjectiveAim to compare dosimetric characteristics between intensity modulated radiation therapy(IMRT)technique and volumetric intensity modulated arc therapy(VMAT)technique for whole breast irradiation with simultaneous integrated boost.MethodTen patients with left-sided breast cancer who treated by breast conserving surgery followed by radiotherapy were included in this study.All patients had undergone computed tomography(CT)and magnetic resonance(MR)simulation according to the criteria shown in Part one.Target volume of tumor bed and whole breast(PTVTB and PTVWB),and organs at risk(OAR)including the left and right lungs,the contralateral breast,the heart,and the left anterior descending coronary artery(LAD)were contoured by a radiation oncologist based on CT.And thereafter the delineations were modified according MR images.Two treatment plans(IMRT and VMAT)were generated by Varian Eclipse treatment planning system for each patient.The prescription doses of 50Gy in 25 fractions and 60Gy in 25 fractions were planned to the PTVWB and PTV TB,respectively.Dose volume histograms were performed to analyze target coverage and doses to OAR.In addition,the conformal index(CI)and homogeneity index(HI)were used to evaluate the plan quality.Differences in mean or median values for parameters between two planning techniques were tested by paired sample t-test or Wilcoxon singed rank test.A two-sided P<0.05 indicated statistical significance.ResultBoth IMRT and VMAT plans were able to meet the PTVTB and PTVWB dose prescription of V95%?57Gy and 47.5Gy,respectively.The dose coverage(V100%)was superior with VMAT plans as compared to IMRT plans,but no significant difference was detected(PTVWB:98.08%vs 97.30%,P=0.162,PTVTB:97.36 vs 96.95%,P=0.349).When compared to IMRT,with VMAT technique the HI of PTVTB and PTVWB was significantly lower(both P<0.001),which lead to a better dose homogeneity.VMAT reduced average maximum dose and average near-maximum-dose(D2%)to PTVTB and PTVWB.VMAT achieved significantly higher dose conformity with a higher CI as compared with IMRT(PTVWB:0.82 vs 0.75,P=0.004;PTVTB:0.88 vs 0.77,P<0.001).In terms of OARs,significant decrease in low dose volume(V5)of ipsilateral lung,the heart and the LAD was achieved with IMRT plan when compared with VMAT technique.The mean dose of the contralateral breast and the heart of IMRT plan were lower than those of VMAT.In addition,IMRT technique decreased the mean dose of the ipsilateral lung and the average volume of the ipsilateral lung receiving 20Gy(V20)as compared to VMAT(P<0.01).With VMAT technique,the reduction of high dose volume(V30)to the heart and LAD was obvious when compared with IMRT.Moreover,the mean dose,the maximum dose,V10 and V20 of the LAD was significantly higher in IMRT than those of VMAT plan(all P<0.05).ConclusionIn the present study,for planning for left-side breast irradiation with simultaneous integrated boost,VMAT technique had advantage in improving the dose homogeneity and conformity,as well as reducing maximum dose of PTV.In addition,VMAT technique were able to reduce high do volumes to LAD.However,when compared to VMAT technique,IMRT technique can reduced dose irradiation to normal tissues,as well as achieved similar dose coverage and reasonable target homogeneity.