The Optimization of IMTR Plan for NPC

Objective: To discuss the method of optimization of IMRT for NPC. Methods: Between April 2005 and September 2005, 24 patients underwent IMRT for NPC. IMRT plans were designed using Eclips treatment planning system. Appropriate dose constraints were specified and weight factors were given. Then three kinds of Doss Shaping Structures were delineated, and the plan was optimized until each structure got appropriate dose distribution. Results: Analysis of the 24 patients' dose-volume histograms (DVHs) showed that the average maximum, minimum, and mean dose delivered were 73.46 Gy, 67.86 Gy, and 70.65 Gy to the GTV1, and 68.83 Gy, 64.67 Gy, and 66.29 Gy to the GTV2. The average minimum dose deliverd were 60.95 Gy and 51.37 Gy to the CTV1 and CTV2. The average dose delivered to 1% of the spinal cord, brainstem ,and optic nerves were 38.10 Gy, 46.94 Gy, and 27.43 Gy, and 50% of the left and the right of the parotid gland were 36.03 Gy and 35.88 Gy. Con- clusion: Careful beam angle and beams number selection, and appropriate dose constraints could produce a high-quality plan. Usually contouring Dose Shaping Structures was helpful. IMRT provided excellent tumor target coverage and allowed the de- livery of a high dose to the target with significant sparing of the salivary glands and other nearby critical normal tissues.