en Radiation Biology Radiation Biology تحقيق بديع Original Research <div style="text-align: justify;">Background: To evaluate computed tomography (CT) and magnetic resonance imaging (MRI) fusion images for delineating 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 patients 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 application of CT+MRI fusion targets and compared the 1-, 3-, and 5-year survival and relapse rates between both targets. Results: The clinical characteristics 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&plusmn;2.18 vs. 34.3&plusmn;2.98, P > 0.05). The public volumes of GTV in the two arms were 49.48&plusmn;2.46 cm³ and 33.6&plusmn;2.18 cm³ respectively (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%, respectively). 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 toxicities was similar between groups. Conclusion: The variability in GTV delineation in NPC was ascribed to intermodality and not interobserver variability. CT+MR fusion images likely reduced the 3-year out-of-field relapse rate.<br> &nbsp;<br> <br> &nbsp;</div> Nasophanrygeal carcinoma, image fusion, three-dimensional conformal radiation therapy. 251 257 http://ijrr.com/browse.php?a_code=A-10-1-673&slc_lang=en&sid=1 H. Chen 7900319475328460015474 7900319475328460015474 No Department of Medical Oncology, the Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China H. Huang haixinhuangcn@163.com 7900319475328460015475 7900319475328460015475 Yes Department of Medical Oncology, the Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China G. Li 7900319475328460015476 7900319475328460015476 No Department of Medical Oncology, the Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China D. Huang 7900319475328460015477 7900319475328460015477 No Department of Medical Oncology, the Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China S. Huang 7900319475328460015478 7900319475328460015478 No Department of Medical Oncology, the Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China Z. Wang 7900319475328460015479 7900319475328460015479 No Department of Medical Oncology, the Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou 545005, China