[Intensity modulated radiotherapy for local-regional advanced nasopharyngeal carcinoma]

Local-regional uncontrolled is an important reason of treatment failure for advanced nasopharyngeal carcinoma (NPC) after radiotherapy. Local-regional control rate increased with dose to tumor target volumes. Because of the complex anatomy features, dose escalation using conventional two-dimensional radiotherapy planning is limited by the tolerance of adjacent critical organs. In order to enhance doses to target volumes and local-regional control rates, this study explored application of intensity modulated radiation therapy (IMRT) in local-regional advanced NPC.

Sixty patients with naive primary NPC, 49 in stage III, and 11 in stage IVa, received IMRT alone with an inverse planning system (CORVUS 3.0, Peacock plan). Treatment was delivered with the Multi-leaf Intensity Modulating Collimator (MIMiC) using a slice-by-slice arc rotation approach. The prescription dose was 68 Gy to nasopharynx gross tumor volume (GTVnx), 60-64 Gy to positive neck lymph nodes (GTVnd), 60 Gy to clinical target volume I (Target I), and 54 Gy to clinical target volume II (Target II), delivered by 30 fractions. Acute normal tissue effects were graded according to RTOG/EORTC radiation morbidity scoring criteria. Local control rate, regional control rate, distant metastasis-free rate, and overall survival rate were calculated using Kaplan-Meier method.

Analysis of dose-volume histograms (DVH) showed that the average mean dose delivered were 71.21 Gy to GTVnx, 65.85 Gy to GTVnd(L), 66.26 Gy to GTVnd(R), 67.59 Gy to Target I, and 61.42 Gy to Target II. The mean fractional dosage delivered were 2.37 Gy to GTVnx, 2.20 Gy to GTVnd(L), and 2.21 Gy to GTVnd(R). The average volumes of all target volumes covered by 95% isodose were more than 99%, and the average volume of GTVnx covered by 105% isodose was 43.87%; 5% of brainstem volume, and 1cc of spinal cord volume received average dosage were 46.96 Gy, and 39.99 Gy; 33% of volume of bilateral parotids, and T-M Joints received average dose was less than 38 Gy. There was no Grade 4 acute toxicity in all patients, and incidences of acute grade 3 toxicity of skin, mucous membrane, and salivary glands were 1.7%, 15.0%, and 1.7%, respectively. With the median follow-up of 15.5 months (6-37 months), no patient failed at the primary site, 2 patients relapsed at neck, 7 patients developed distant metastases, 9 patients died. The 3-year local control rate, regional control rate, and distant metastasis-free rate were 96.67%, 94.06%, and 84.98% respectively, 3-year overall survival rate was 74.97%.

IMRT could escalate the total dose and fractional dosage to target volumes, and decrease the irradiation dose of surrounding critical organs. The acute toxicities were slight and tolerable. The local-regional control rates were satisfied. Distant metastasis is the main cause of failure.