Intensity-modulated radiotherapy in nasopharyngeal carcinoma: dosimetric advantage over conventional plans and feasibility of dose escalation

Abstract

Purpose: To compare intensity-modulated radiotherapy (IMRT) with two-dimensional RT (2D-RT) and three-dimensional conformal radiotherapy (3D-CRT) treatment plans in different stages of nasopharyngeal carcinoma and to explore the feasibility of dose escalation in locally advanced disease.

Materials and methods: Three patients with different stages (T1N0M0, T2bN2M0 with retrostyloid extension, and T4N2M0) were selected, and 2D-RT, 3D-CRT, and IMRT treatment plans (66 Gy) were made for each of them and compared with respect to target coverage, normal tissue sparing, and tumor control probability/normal tissue complication probability values. In the Stage T2b and T4 patients, the IMRT 66-Gy plan was combined with a 3D-CRT 14-Gy boost plan using a 3-mm micromultileaf collimator, and the dose-volume histograms of the summed plans were compared with their corresponding 66-Gy 2D-RT plans.

Results: In the dosimetric comparison of 2D-RT, 3D-CRT, and IMRT treatment plans, the T1N0M0 patient had better sparing of the parotid glands and temporomandibular joints with IMRT (dose to 50% parotid volume, 57 Gy, 50 Gy, and 31 Gy, respectively). In the T2bN2M0 patient, the dose to 95% volume of the planning target volume improved from 57.5 Gy in 2D-RT to 64.8 Gy in 3D-CRT and 68 Gy in IMRT. In the T4N2M0 patient, improvement in both target coverage and brainstem/temporal lobe sparing was seen with IMRT planning. In the dose-escalation study for locally advanced disease, IMRT 66 Gy plus 14 Gy 3D-CRT boost achieved an improvement in the therapeutic ratio by delivering a higher dose to the target while keeping the normal organs below the maximal tolerance dose.

Conclusions: IMRT is useful in treating all stages of nonmetastatic nasopharyngeal carcinoma because of its dosimetric advantages. In early-stage disease, it provides better parotid gland sparing. In locally advanced disease, IMRT offers better tumor coverage and normal organ sparing and allows room for dose escalation.