Application of computed tomography and magnetic resonance imaging fusion images for delineating gross tumor volume in three-dimensional conformal radiotherapy of nasopharyngeal carcinoma

Background: to evaluate computed tomography (ct) and magnec resonance imaging (mri) fusion images for delineang gross tumor volume (gtv) in three-dimensional conformal radiotherapy (3d-crt) of nasophanrygeal carcinoma (npc),and compare treatment outcomes between ct- and ct+mri-based targets. materials and methods: a total of 120 npc paents treated with 3d-crt were included,in which,60 each were treated with ct-based and 60 with ct+mri fusion targets. we explored the clinical applicaon of ct+mri fusion targets and compared the 1-,3-,and 5-year survival and relapse rates between both targets. results: the clinical characteriscs and treatment factors were well balanced. the differences in public volume using ct alone in the ct+mri (group a) and the ct arm (group b) were not significant (33.6±2.18 vs. 34.3±2.98,p > 0.05). the public volumes of gtv in the two arms were 49.48±2.46 cm3 and 33.6±2.18 cm3 respecvely (p < 0.05). ct+mr fusion images did not influence the one-,three-,and 5-year survival rates (100% vs. 98.3%,85.0% vs. 81.2%,and 73.3% vs. 68.3%,respecvely). the three- and 5-year out-of-field progression was reduced in the ct+mri arm. however,only the difference in 3-year out-of-field relapse rate was significant (3.3% vs. 13.3%; p < 0.05). the incidence of acute toxicies was similar between groups. conclusion: the variability in gtv delineaon in npc was ascribed to intermodality and not interobserver variability. ct+mr fusion images likely reduced the 3-year out-of-field relapse rate.