Application Of Dosimetry Analysis In Breast Cancer And Thymoma

Part I A comparative study on the dose distribution and setup error of two different position and immobilization techniques in breast cancer radiotherapyObjectiveTo compare the dose distribution and setup error of angled breast board position(ABB)versus plain breast board position(PBB)in breast cancer radiotherapy.Patients and Method:Twenty consecutive postoperative left breast cancer patients in our hospital were enrolled from March 2017 to January 2018.10 cases were randomly assigned into the ABB and PBB groups respectively.The target volume,heart and lung structures were defined on the CT images of the localized scan.The plan was designed using the field in field(FIF)technique to compare the dosimetric parameters of the PTV,lung,and heart treatments,and the setup errors for the two different positions.Results:The ipsilateral lung V20(ABB:11.2%± 3.4%,PBB:14.7%± 5.5%,p<0.05),and V30(ABB:9.8%± 1.5%,PBB:12.9%± 2.2%,p<0.05)were both statistically significant for the two different position and immobilization.Heart dose V25(ABB:1.9%± 0.2%,PBB:2.8%± 0.4%,p<0.05),V30(ABB:1.8%± 0.1%,PBB:2.7%士0.3%,p<0.05),and Dmean of heart(ABB:3.0±0.5Gy,PBB:5.3 ± 1.2Gy,p<0.05)were all statistically significant for the two different positions.The translational errors of ABB and PBB on LR,SI,and AP are(3.23 ± 2.63),(5.42±3.22),(4.58 ± 2.30)mm,and(2.35 ± 1.22),(2.17 ± 1.29),(2.27 ± 1.58)mm,respectively.The rotation errors of pitch(θ),yaw(Φ)and roll(Ψ)for ABB and PBB are(1.60 ±0.56),(3.40 ± 1.65),(2.50 ±1.72)deg,and(1.37 ± 0.43),(1.79 ± 0.71),(2.06 ±0.63)degee,respectively.Meanwhile,the in and out SI,anterior and posterior AP,yaw rotation error(Φ)were also statistically significant(p<0.05).Conclusion:There was no statistically significant difference in the tumor target between the two position and immobilization techniques.However,the ABB was better than the PBB in normal tissue sparing,but the setup accuracy of PBB is better than the ABB.PartⅡ To analysis dosimetric results of postoperative intensity modulated radiation therapy using single-energy or mixed-energy photons in invasive thymoma patientsObjectiveTo compare dosimetric results of postoperative intensity modulated radiation therapy(IMRT)using single-energy or mixed-energy photons in invasive thymoma patients.MethodsSimulation CT images were acquired and clinical target volume(CTV),planning target volume(PTV)and organs at risk(OARs)were defined.Three sets of fixed-field IMRT planning were generated using 6 MV,10 MV and mixed 6/10 MV photons for each case.Monitor Units(MUs)for each plan were recorded after optimization,and parameters of PTV such as conformity index(CI),homogeneity index(HI)and dose to OARs were evaluated on dose-volume histograms.ResultsNear-Maximal dose(D2%)received by PTV was better in mixed-energy IMRT as compared with 6 MV(t= 3.1,P<0.05).HI was better in mixed-energy than in 6MV(t=3.151,P<0.05).There were statistically significant differences in CI among three IMRT plans.MU was higher in 6 MV than in both 10MV and mixed-energy IMRT.The percentages of lung volumes receiving 5 Gy(V5),10 Gy(V10),20 Gy(V20),30 Gy(V30)and the mean lung dose(Dmean)were also significantly different in most plans.V30 and V40 of the heart were comparable between 6 MV and mixed energy plans but better than in 10 MV plans.ConclusionIf the reasonable choice of beam angles and number,and capability of energy selection according to beam directions,with combined advantages of low-and high energy photons,mixed IMRT plans can improve the quality of IMRT plans in General and has clinical potential for postoperative radiotherapy of invasive thymomas.