Objective： Conventional external beam irradiation techniques for nasopharyngeal carcinoma have limitations, and improving external beam irradiation techniques is needed to enhance the curative rate. This study was designed to cvaluate the difference in dose distribution of three dimensional conformal radiotherapy （3D CRT） and conventional treatment plan in early untreated nasopharyngeal carcinoma using a three dimensional treatment planning system. Methods： Twenty-two patients with early untreated nasopharyngeal carcinoma were selected. Conventional and 3D CRT plans were made for each of them and compared with respect to target volume coverage （V95）,normal tissue sparing （D50, D33 and D5, etc）, normal tissue complication probability （NTCP）. Results： The average volumetric dose comparison indicated that the V95 of PTVnx70 were 98.22% and 99.99% （P=0.06）, and PTVnd60, 98.41% and 99.63% （P=1.00）, PTV,x60, 98.44% and 99.98% （P=0.03）, PTVnx50, 98.85% and 99.63% （P=0.02） in conventional and 3DCRT treatment plans respectively. With respect to normal tissue sparing, the average D50 of unilateral parotid glands were 51.91 Gy and 64.30 Gy （P=0.00） respectively, and the unilateral temporomandibular joints, 49.98 Gy and 64.47 Gy （P=0.00）, the Dlcc of spinal cords, 44.98 Gy and 48.09 Gy （P=0.00） in 3D CRT and conventional plans. Conclusion： Though only a little bit better dose coverage of target volume in subclinical lesion region was reached in 3D CRT plans, it spared more normal tissues e.g. parotid glands and temporomandibular joints etc and decreased their NTCP while it got the similar dose distribution in target volumes as conventional plans did for these early nasopharyngeal carcinoma cases.
