Dosimetric Analysis Of Treatment Plans Of Left-sided Early-stage Breast Cancer Treated With Three-dimensional Conformal Radiotherapy And Field-in-field Intensity Modulated Radiotherapy

Objective:By analyzing the radiation dose and volume of left anterior descending coronary artery(LAD)under different adjuvant radiotherapy techniques after breast conserving surgery for early stage left-sided breast cancer,a new method to reduce the radiation dose and volume of lad is to be found.The best radiotherapy technique and method for early stage breast cancer after breast conserving surgery to reduce the radiation dose and volume of Lad and the risk of cardiovascular disease caused by radiotherapy is to be found.Methods:The clinical data of 41 female patients with early stage left-sided breast cancer(2010 AJCC staging standard:T1N0M0 IA)after breast conserving surgery treated in our department from January 2012 to June 2017 were retrospectively analyzed.19 cases of primary tumors were located in medial quadrant 22 cases of primary tumors were located in lateral quadrant.15 were treated with three-dimensional conformal radiotherapy(3D-CRT),6 field tangent field isocentric irradiation is designed for the affected side mammary gland,the x-line energy is 6 MV,total dose of the breast:PTV:5040 CGy/28 f,180 CGy/f,5f/week,according to the maximum depth of the local tumor bed,the electronic linear push of 6-18 Mev-E is used,total dose:1000CGy/5f,200CGy/f,5f/week.And the other 26 cases are treated with field-in-field intensity modulated radiation therapy(FIF-IMRT).PTV as target region,using the conventional tangent field as the direction of incidence of the main field,according to the equal dose weight of the internal and external tangent field,the high dose regions with different levels were selected in order to set up the sub-fields in the internal and external tangent field,and the dose optimization was carried out form satisfactory sub-fields.External irradiation of 6MV X-ray under accelerator is performed,total dose of the breast:5040 CGy/28 f,180 CGy/f,5f/week,tumor bed area synchronous push to 60 Gy.Both plans set a maximum dose of no more than 110% in PTV and a minimum dose of no less than 95% of prescription dose.The differences of LAD and and heart in dose volume histogram(DVH)were compared between the two schemes.Independent sample t-test,correlation analysis and multiple linear regression analysis were used to process the data,to compare the difference of radiation dose and volume of LAD between 3D-CRT and FIF-IMRT plan,and to analyze the related factors affecting the dose and volume of LAD exposure.Results:(1):The mean dose and maximum dose of LAD in 3D-CRT treatment plan was higher than that of IMRT,and the difference was statistically significant(p <0.05);The average V5 of LAD in IMRT plan was higher than 3D-CRT,the difference was statistically significant(p < 0.05);The average V10 of IMRT LAD was greater than that of 3D-CRT,but the difference was not statistically significant(P = 0.143).The mean values of V20,V30,V40 and V50 in the 3D-CRT plan were greater than IMRT(p <0.05).The LAD Dmean of the lateral quadrant tumor was larger than that of the medial quadrant,and the LAD Dmax、V5、V10、V20、V30、V40、V50 of the medial quadrant tumor was higher than that of the lateral quadrant,but the difference was not statistically significant(p > 0.05).(2)LAD Dmean was positively correlated with PTV and CTV volume(P < 0.05),and the correlation coefficients were 0.313 and 0.311 respectively.There was no significant correlation between Dmax,V5-V50 and target area,LAD,and heart volume(P > 0.05).There was significant correlation between LAD Dmax and cardiac Dmax、Dmean(P < 0.01),and the correlation coefficients were 0.926 and 0.612 respectively.There was also a significant correlation between LAD Dmean and cardiac Dmax、Dmean(P < 0.01),and the correlation coefficients were 0.607 and0.874 respectively.(3):The influential factors of LAD Dmean are the techniques and PTV volume,the influence of techniques is larger than PTV volume to LAD Dmean.Conclusion:In early stage breast cancer after breast conserving surgery with postoperative adjuvant radiotherapy,IMRT can reduce the dose of LAD and V20、V30、V40、V50 of LAD,but increase the V5 of LAD,compared with 3D-CRT technique.There is no significant difference between the two techniques in V10 of LAD.The primary tumor quadrant had no significant effect on LAD dose parameters.There was a linear correlation between the volume of PTV and the mean dose of LAD.