Dosimetric Study Of Two Radiotherapy Techniques And Incidental Irradiation Dose To The Internal Mammary Region After Modified Radical Mastectomy Of Breast Cancer

Objective:Breast cancer is one of the most common malignant tumors in women.With the development of CT,MRI and other imaging techniques,the radiotherapy technique of breast cancer is becoming more and more perfect.Due to the influence of chest wall anatomical structure and side effects of radiotherapy,the choice of radiotherapy technique is controversial.How to improve the accuracy of radiotherapy,reduce radiation damage,and choose the most appropriate individualized radiotherapy techniques and schemes for patients is the focus of attention of tumor radiotherapy workers at present.Whether intramammary lymph node irradiation can improve the survival of breast cancer patients after radical mastectomy is also a controversial issue.Our study analyzed the clinical data and radiotherapy data of 77 patients with breast cancer after modified radical mastectomy with chest wall and regional lymph node radiotherapy,compared the dosimetry data of three dimensional conformal radiation therapy?3D-CRT?and volumetric modulated arc therapy?VMAT?radiotherapy technology,to explore a better individualized clinical radiotherapy scheme.Methods:Radiotherapy data and clinical data of 77 patients after modified radical mastectomy were analyzed retrospectively,according to different radiotherapy techniques,they were divided into two groups:3D-CRT and VMAT.The prescriptive dose of clinical target was the 95%CTV met50Gy.The dose volume histogram?DVH?analysis was used to evaluate the dose parameters of CTV,Including conformity index?CI?and homogeneity index?HI?,V_95%,V_100%,V_110%.To compare the difference of the ipsilateral lung mean dose,V₅,V₁₀,V₂₀,V₃₀,V₄₀;the mean dose,V₅,V₁₀,V₂₀,V₃₀,V₄₀0 in the left breast cancer patients,and the contralateral breast mean dose.Delineated the internal mammary lymph node?IMN?drainage area in the two original radiotherapy plans,to analyze and compare the differences in the mean dose(IMN Dmean_and the dose of 95%the volume irradiated(IMN D_95%)of the internal mammary lymph node drainage area which were actually accepted.The statistical software of SPSS version 20.0 was used for data processing.The measurement data is expressed as mean±standard?x±s?,the comparison between the two groups of plans was used t-test,and rank sum test was used for heterogeneity of variance or abnormal distribution.Correlation analysis was performed by multiple linear regression analysis.P<0.05,indicating statistical significance.Results:1.There was no significant difference in clinicopathological features between the 3D-CRT group and the VMAT group,the clinical radiotherapy datas of the two groups were comparable.There was a positive correlation between CI and the anterior and posterior thoracic diameter(D_AP)?0.218,P=0.028?.There was a negative correlation between HI and weight,body surface area?BSA?,BMI,thoracic transverse diameter?D_T??-0.225,P=0.024;-0.194,P=0.045;-0.252,P=0.013;-0.222,P=0.026?.There was a negative correlation between IMN Dmean and thoracic ratio?-0.302,P=0.004?;IMN D_95%and positive correlation with D_AP?0.200,P=0.041?.2.Dosimetric comparison of CTV:The CI of CTV in the the VMAT group was better than that in 3D-CRT group,the difference is statistically significant?P=0.030?.The V_100%had fewer high dose regions in the VMAT group,the difference was statistically significant?P=0.036?.There was no significant difference in the HI?V_95%?V_100%between the two groups?P>0.05?.3.Dosimetric comparison of OAR:In the ipsilateral lung dose,the mean dose,V₅ and V₁₀ in the VMAT group was lower than that in the 3D-CRT group,the difference is statistically significant?P<0.05?.There was no significant difference in the V₂₀,V₃₀,V₄₀ between the two groups?P>0.05?.In patients with left breast cancer,the VMAT group had higher V₅ in than the3D-CRT group,the difference is statistically significant?P=0.028?.There was no significant difference in the heart mean dose,V₁₀,V₂₀,V₃₀,V₄₀ between the two groups?P>0.05?.4.Dosimetric comparison of contralateral breast and IMN:In the contralateral breast dose,the 3D-CRT group was superior to the VMAT group,difference had statistical significance?P=0.001?.The IMN Dmean was higher in the VMAT group,difference had statistical significance?P=0.048?.There was no significant difference in the IMN D_95%between the two groups?P>0.05?.Conclusions:1.CI,HI,IMN Dmean,IMN D_95%was correlated with the anatomical features of the patients.When choosing radiotherapy scheme,it is necessary to refer to the clinical characteristics of the patients and realize individualized and accurate radiotherapy.2.The VMAT was superior to the 3D-CRT in CI of CTV.The V_100%had fewer high dose regions in the VMAT group,and both of two technology in HI,V_95%,V_100%,V_110%can meet the dosimetric requirements of chest wall and regional lymph node radiotherapy after radical mastectomy of breast cancer.3.The VMAT technique can effectively reduce the average dose and the dose in the low dose area of the ipsilateral lung.The 3D-CRT technology reduces the dose in the low-dose area of the heart.4.The mean dose of the contralateral breast in 3D-CRT and VMAT techniques were higher than the dose limit,and the VMAT technique was higher.Some patients with IMN Dmean can reach the treatment dose.