Abstract: Objective The aim of this study was to investigate whether it is safe and reliable to reduce the size of radiotherapy field under the guidance of PET/CT in stage Ⅰ~Ⅱ diffuse large B-cell lymphoma(DLBCL)in the era of immunochemotherapy.Methods Fifty-seven patients with the stage Ⅰ~Ⅱ DLBCL who had CR/PR and PET/CT examination records after chemoradiotherapy in our hospital were selected and divided into two groups of CTV expansion at the upper and lower limits of the target area for comparison.The first research purposes compared their rates of overall survival and progression-free survival.The secondary research purposes compared survival rate without distant metastasis,recurrence pattern and side effects of radiotherapy.Results Median follow-up was 31.1 months;The 5-year overall survival rate,progression-free survival rate,and no distant metastasis survival rate for the CTV≤4.74 cm and CTV＞4.74 cm groups in the upper limit of the radiation field were 96.3% and 77.1%(P=0.135),96.3% and 59.5%(P=0.013),96.3% and 69.3%(P=0.038),respectively;Narrowing the upper limit of the target area in the CR group could extend PFS and DMFS(P=0.023).Multi-factor analysis showed that the upper limit of the target area ≤4.74 cm was an independent protective factor of PFS(P=0.039).Among them,side effects related to long-term radiotherapy of grade 2 or higher occurred in the CTV ＞4.74 cm group(P=0.026).Conclusion For CR or PR evaluation after chemotherapy,it is feasible to reduce the upper bound of the target area of early DLBCL to CTV ≤ 4.74 cm(INRT ≤ 5 cm)and reduce the lower bound to CTV ≤8.5 cm(INRT ≤8 cm).While ensuring the benefits of long-term survival,it can also reduce the incidence of long-term radiotherapy side effects and does not increase local recurrence and distant metastasis.

Key words: Diffuse large B-cell lymphoma, Radiation field, Radiotherapy