[Dosimetric evaluation for three dimensional conformal, conventional, and traditional radiotherapy plans for patients with early nasopharyngeal carcinoma].

BACKGROUND & OBJECTIVE: Traditional external beam irradiation techniques for nasopharyngeal carcinoma have a lot of shortcomings, and improving external beam techniques have become an endeavor to enhance curative effectiveness. This study was designed to compare the dose distribution of three dimensional conformal radiotherapy (3D CRT) with traditional and conventional radiotherapy plans in the patients with early nasopharyngeal carcinoma using three dimensional treatment planning system.

METHODS: Twenty-two patients with early nasopharyngeal carcinoma were selected. Traditional, conventional, and 3D CRT plans were made for each of them and compared with respect to target coverage (V95), normal tissue sparing (D50, D33, and D5, etc), normal tissue complication probability (NTCP).

RESULTS: Dosimetric comparison indicated that the V95 of PTVnx60 and PTVnx50 for three different plans were 90.29% and 77.67% (traditional), 98.44% and 98.85% (conventional), 99.98% and 99.63% (3D CRT), respectively; and both conventional and 3D CRT had satisfied dose coverage of target volume especially in subclinical lesion region compared with traditional radiotherapy. With respect to normal tissue sparing, 3D CRT and conventional treatment plans could spare more brainstem, temporal lobe, optic chiasm, and pituitary than traditional plans; and 3D CRT could spare more parotid gland and temporomandibular joint than traditional and conventional treatments.

CONCLUSION: Considering the dose distribution of the three treatment plans, both conventional and 3D CRT had satisfied dose coverage of target volume especially in subclinical lesion region compared with traditional radiotherapy, and 3D CRT plans can spare more normal tissues such as parotid gland and temporomandibular joint etc, and decrease their NTCP while it get the same dose distribution in target volume as traditional and conventional plans do in the treatment of early nasopharyngeal carcinoma.