Dosimetric Characteristic of Intensity Modulated Radiotherapy(IMRT) in Nasopharyngeal Carcinoma

[Purpose] To investigate the dosimetric characteristic on target and surrounding organs in intensity modulated radiotherapy(IMRT) for nasopharyngeal carcinoma(NPC). [Methods] From June to October 2004,10 primary NPC cases were treated with IMRT using anterior 7 fields. The area of each field was from skull base to supraclavicular lymph node area. The prescribed dose was 2.18Gy in 32 fractions(f) for gross tumor volume1(GTV1); 2.03Gy in 32f for GTV2; 1.88Gy in 32f for clinical tumor volume 1(CTV1);1.80Gy in 28f for CTV2. Maximum dose, minimum dose, average dose of GTV, minimum dose of CTV, and maximum dose on spinal cord, brain stem, lens, and dose delivered to 50% the parotids were examined.[Results]Maxinum dose, minimum dose, average dose of GTV1 in 10 patients were 72.01Gy,68.65Gy,70.48Gy respectively; and those of GTV2 was 68.66Gy,65.50Gy,66.98Gy respectively. Minumum dose of GTV1 ang GTV2 was 60.10Gy and 51.18Gy respectively. Maximum dose of spinal cord, brain stem and lens was 44.7Gy,51.7Gy and 6.8Gy respectively.High or low dose to 50% of parotid gland was 44.39Gy and 39.36Gy respectively. [Conclusions] IMRT may yield enough and uniformity dose to every target volume, and toxicity to surrounding normal tissue is tolerable. A dose of 40Gy~45Gy delivered to half volum of parotid gland reveals protecting function for salivery gland.