Measurement Of The Distance Of The Micro-Cancer Foci On The Side Of The Gross Tumor In Pathological Specimens After Neoadjuvant Radiotherapy And Chemotherapy For Locally Advanced Rectal Cancer

Objective:Based on surgical pathological specimens of patients with locally advanced rectal cancer after neoadjuvant radiotherapy and chemotherapy,the object of this essay is to measure the distance of the micro foci lateral to the gross tumor,and hence to provide reference value to form the clinical target volume(CTV)for high dose boost radiotherapy to rectal cancer.Materials and Methodology:119 patients who underwent total mesenteric resection(TME)after neoadjuvant radiotherapy and chemotherapy in Hunan Cancer Hospital from 2013 to 2020 were collected.Measure the shortest distance between the farthest small cancer foci on the side and the edge of the general tumor.According to the "in vivo-in vitro" tumor shrinkage factor R1 and the "pathological specimen processing shrinkage factor" R2 obtained from the previous research of our research group,the measured distance value is corrected to be the in vivo extension distance(MEin vivo).Results:Among the 119 patients,71(60%)patients with gross tumors which could be observed with pathological specimens,and 19 cases(16%)were able to observe small tumors on the side,and the total number of small tumors is 42.According to the data obtained from previous studies of the research group,the average value of the "in vivo-in vitro" shrinkage factor(R1)is 0.913,and the average value of the pathological specimen shrinkage factor(R2)is 0.803.After correction by the two shrinkage factors,the farthest distance of the lateral small cancer foci was 8.525 mm,and the closest distance was 0.682 mm.After calculation,the average distance is 2.7 mm,and the median distance is 2.4 mm.19 cases of micro-cancer foci on the side of the general tumor are within 4.433 mm of 94.7% from the general tumor.Meanwhile 94.4% of the small cancer foci on the side of the tumor in all 71 patients were within 3.41 mm.Conclusion:Based on the micro foci distance from the lateral edge of GTV after neoadjuvant radiotherapy and chemotherapy,when the radiotherapy target area GTV expands into CTV,the recommended lateral expansion is 3.4-4.4mm.