The current status of the delineation and determination of the targets and the radiation protocols for nasopharyngeal cancer with intensity-modulated radiotherapy

Abstract

IMRT has increased the local-regional control and decreased the complications from treating nasopharyngeal cancer (NPC). Therefore studying IMRT is important. CT and MRI are complementary, and their joint use is currently considered to be the optimal modality to delineate the extent of the primary spread of NPC. The key problem in delineation of the neck nodes is how to translate anatomic node regions into the CT boundaries. The consensus guideline which narrowed the gap among different cancer centers is recommended in delineating the boundary of the cervical lymph node regions. The definition of the NPC GTV is clear and almost the same among the main cancer centers in their IMRT planning protocols.The suggested biological dose to the GTV is close to or more than 80 Gy; the main differences are the definitions of the CTVs and their schemes for the prescribed dose, and also the dosage to the high cervical region is different among those centers. According to their long-term follow-up results, it is suggested that, besides adding 5~10 mm margins to the primary lesions, the immediate high-risk structures (including the entire nasopharyngeal cavity, retropharyngeal space, clivus, base of the skull, pterygoid plates and muscles, parapharyngeal space, the sphenoid and partial ethmoid sinuses, the posterior third of the maxillary sinuses and the nasal cavity) should also be included with a prescription of more than 60 Gy, and the bilateral Ib, II and Va node levels should be ranked as high-risk regions and differentially prescribed for treatment with no less than 60 Gy.According to the large-case reports on the traditional treatment of nasopharyngeal cancer (NPC) with the facial-cervical field as the main irradiation field, the 5-year locoregional controls were 81.7%~85%, and the 5-year overall survival was 59%~75%, but the complications induced by irradiation were relatively high [1][2][3][4] . Intensity-modulated radiotherapy (IMRT), which can not only improve the locoregional control, but also reduce the complication rates, is currently deemed as the optimal means to treat NPC. Experience from the University of California at San Francisco (UCSF) indicated that the 4-year local control was 98% with a 4-year survival of 88%. The accumulating complication rates above level III were 11.9% [5] . The Cancer Center of the Sun YatSen University in China recently reported a 3-year locoregional control of 93.2% and a 3-year overall survival of 85.1% [6] . Those results were superior to those treated with the traditional means. However when applying IMRT to the treatment of NPC, the displays of the extension of the primary lesions were not wholly in accordance with each other when using different image modali-