Preliminary Validation Of An Imrt Target Volume Delineation Protocol For Patients With Locally Advanced Gastric Cancer Receiving Preoperative Chemoradiation In Comparison With Preoperative Chemotherapy

Target volume delineation remains controversial in preoperative chemoradiation (CRT) for locally advanced gastric cancer. This study is to validate a proposal target volume delineating protocol for patients with locally advanced gastric cancer, in terms of postoperative pathological response, as well as reduction of positive rates for individual regional lymph node stations, compared with those treated with preoperative chemotherapy (ChT). 93 patients (aged 27-74 years, median 56 yrs) were treated from June, 2013 till Feb., 2019, in two treatment groups, including 47 patients in CRT group receiving XELOX chemo for 1 induction cycle plus 2 cycles with concurrent IMRT 45Gy/25f, and 46 patients in the ChT group receiving XELOX chemo for 3 cycles. There were 21 females and 72 males. The tumor locations were EGJ (Siewert type III) in 16 patients, proximal portion in 37pts, middle portion in 19 pts, dismal portion in 18 pts, and the entire stomach in 3 patients. Clinical stage before treatment was cT3N2-3, cT4aN+, or cT4bNany, and M0, suggesting TRUE locally advanced clinical stages. Clinical characters were comparable in both groups. The target volume delineating protocol mainly included moderate mucosal CTV expansion (3cm) in an emptying condition of stomach, and extended elective regional LN stations irradiation (including 16a2 LN as the lower border). The time interval between end of radiotherapy and surgery was 4 to 8 weeks. All of the 93 patients received D2 radical gastrectomy with comprehensive pathological examinations for further analyses. Addition of IMRT didn’t increase perioperative complications. Ten patients got pathological complete remission (pCR), 9 (19.1%) in the CRT group, and 1 (2.2%) in the ChT group (p=0.023). The rates of ypN0 were 61.7% (29/47) and 23.9% (11/46) in CRT and ChT groups (p<0.001), respectively. The other yp stages distribution was ypI (21.3%), ypII (44.7%), and ypIII (14.9%) in CRT group, and ypI (8.7%), ypII (41.3%), and ypIII (47.8%) in ChT group, respectively. Primary NCCN tumor regression grading (TRG) evaluation also favored the CRT group significantly (p=0.003), with Grade 0-1 in 21 patients in the CRT group, and 7 patients in the ChT group, respectively. 2 patients got R1 resection, both in the ChT group. Each of 1st to 12th regional lymph node station got obvious reduced positive rates, which were 33%, 30%, 54%, 35%, 15%, 24%, 39%, 13%, 22%, 13%, 9%, and 4%, in the ChT group, compared with 11%, 17%, 21%, 6%, 2%, 6%, 15%, 9%, 15%, 0%, 4%, and 0%, in the corresponding lymph node station in the CRT group, respectively. The preliminary pathological results after preoperative chemoradiation vs. preoperative chemotherapy were satisfying, suggested the feasibility of our proposal IMRT target volume delineating protocol for locally advanced gastric cancer. Survival benefits and detailed toxic effects comparisons need to be tested in further clinical trials.