Comparative Dosimetric Study of Three Radiotherapy Strategy for Nasopharyngeal Carcinoma

Objective: To compare the dosimetric advantages and disadvantages of 2-dimensional radiotherapy(2DRT),2-dimensional radiotherapy plus 3-dimensional conformal radiotherapy boost(2DRT+3D Boost) and intensity modulated radiotherapy(IMRT) plans for patients with newly diagnosed primary nasopharyngeal carcinoma(NPC).Methods: 40 patients were enrolled.The scanning CT images were transmitted to Treatment Planning System(TPS),where painting the volumes of tumors and organ at risks(OARs).Three plans,that is,2DRT,2DRT+3D Boost and IMRT,were designed for each patient simultaneously with the same prescription dose.Then the dose distributions of tumor volume and organ at risks were analyzed with TPS.Results: For the IMRT/2DRT/2DRT+3DBoost plans: The Dmean,D95,V95 of nasopharyngeal tumor volume(PTVnx) were,respctively,77.3Gy/70.2Gy/70.4Gy,70.2Gy/66.0Gy/66.8Gy,98.2%/89.7%/92.9%;The Dmean,D95,V95 of clinical tumor volume(PTV1) were 72.5Gy/68.8Gy/68.7Gy,61.0Gy/61.0Gy/ 62.3Gy;97.1%/97.2%/98.8%;The Dmax of len,optical nerve,optical chiasma,Pituitary,were 8.40Gy/5.24Gy/5.90Gy,44.8Gy/43.3Gy/43.3Gy,47.6Gy/42.6Gy/42.7Gy,48.4Gy/48.3Gy/48.8 Gy,respctively.The dose to 33 percent temporal mandibula joint,to 1cm3 spinal cord(D1cc),to 3 percent of brain stem volume(D3),to 50 percent of parotid gland volume(D50) were 48.8Gy/ 68.1Gy/65.0Gy,42.9Gy/42.8Gy/45.8Gy,52.3Gy/53.1Gy/57.0Gy,30.6Gy/64.3Gy/60.7Gy.Conclusion: All three treatment plannings could provide quite good dose distributions,of which IMRT could provide not only best dose distributions to the tumor target with higher dose but well-protection to the surrounding organs,especially parotid gland and temporal mandibula joint.