Study On The Feasibility And Safety Of Contouring Clinical Target Volume(CTV) In Reference To Image Visible Glands After Breast Conserving Surgery In Early Stage Breast Cancer

Objective:Breast cancer is one of the most common malignant tumors in women.Whole breast irradiation after breast conserving surgery is the standard treatment for early breast cancer.Because of the long survival time of early breast cancer,how to lay out a radiotherapy target area is particularly important.A number of studies have confirmed that most of the tumors are located:in high-density areas of the mammography(enriched glands).If it is feasible to contour the clinical target volume(CTV)of patients in reference to the image visible glands after breast-conserving surgery,the target volume will be effectively reduced,and the toxic side effects to surrounding normal tissues will be decreased.This study attempts to seek for the relationship between tumor location and visible glands by CT or MRI on the basis of the RTOG-recommended target volume criteria,and to explore the feasibility and safety of contouring the clinical target volume according to the image visible glands.Methods:1.Patient selection:Retrieval of patients diagnosed as breast malignancy by histopathology from January 2013 to May 2017 in the Third Affiliated Hospital of Kunming Medical University.The main enrolled patients were menopause women aged 50 years or older;they had preoperative CT and MRI;the maximum diameter of the tumor(CT,MRI)was less than or equal to 20 mm.Exclude factors that interfere with the locating of the tumor,including local resection,hormone therapy within 1 year,and non-breast tissue-derived malignancy.2.Image analysis:Take the images of the patients when diagnosed and invite two radiographers who worked more than 5 years to read the images independently,mark the tumor position and judge that the tumor is inside the gland(the tumor is completely located inside of the gland),on the edge of the gland(tumor partially inside the visible gland,partially beyond the glandular area),and outside the gland(the tumor is independent from the visible gland).3.Contour the target volume:(1)The visible gland is pre-set as CTV(gland),and the probability that the tumor is located inside,on the edge of,and outside the CTV(gland)is counted.(2)Screen the lesions that are beyond CTV(gland),spreading CTV1 evenly over CTV(gland)basis,allowing CTV1 to completely cover the tumor.Results:1.Patient characteristics:There were a total of 8018 patients diagnosed as breast malignant tumors by histopathology.The final qualified lesions were 451 with an age of between 50 and 91;346 lesions had breast MRI images and 302 lesions had CT images;single lesions accounted for 73%(n = 330),multiple lesions 27%(n =121);For the tumor T stage,T0,T1 ratio is 98%(n = 440);For N stage,N0-1 patients are 89%(n=399),for pathological types,78%of lesions(n=353)were invasive ductal carcinoma.2.Imaging characteristics:Of the 451 lesions,78.5%were located inside the glandular tissue,21.5%were located on the edge of the gland,and the tumor independent of the glandular region was 0.The related factors of tumors beyond the gland include:among them,26.36%of 243 single lesions were beyond the edge of the glands(n=87),and the proportion of multiple lesions located at the edge of the glands was 10%(n=10).There was a significant difference between the two studies(P<0.00001).The probability of trumor located at the edge of the gland in the central area was only 5.77%,and the probability of the junction area was 6.67%,which was significantly lower than that of other quadrants.Statistically,there was a significant difference(P=0.001).Tumors that are on the right breast,ER,and ER positive are also more likely to protrude beyond the edge of the gland.3.Radiotherapy target volume CTV(gland):Analysis of 302 cases with CT visible lesions showed that the number of CTV(gland)covered tumors was 76.5%(n=231),and CTV(gland)expanded 8mm covered 95.7%(n=289)tumors,a 9 mm external expansion can cover 97%(n=293)tumors,and a 12 mm external expansion will cover 99%(n=299)tumors.Conclusion:1.After breast conserving surgery,the target volume of whole breast radiotherapy contouring only the glands has the risk of potential recurrence.2.The target volume of whole breast irradiation combined with the actual clinical situation,with the CT visible gland external expansion of 8-12mm is more reasonable and safe(the frontier does not exceed the skin,and the posterior does not exceed the pectoralis major surface).