Why subclinical involvement is prescribed the same high dose as gross tumor volume: A study on high-dose clinical target volume in intensity-modulated radiotherapy plan of nasopharyngeal carcinoma

BackgroundMost nasopharyngeal carcinoma (NPC) protocols define primary gross tumor volume (GTVnx) plus a range from 2 to 5 mm as the high-dose clinical target volume (hd-CTV). However, in China, hd-CTV is defined as GTVnx plus 0 mm. MethodsA total of 40 patients with newly diagnosed nonmetastatic NPC (T1-T4 ten cases each) treated with IMRT were consecutively enrolled. Real and virtual treatment plans were designed according to the definitions of hd-CTV recommended by China and Radiation Therapy Oncology Group (RTOG), respectively. ResultsThe hd-CTV in China was significantly smaller than that of RTOG. Exposure doses to 5 mm subclinical involvement and OARs as well as NTCP in the China treatment plan were significantly lower than those of RTOG. ConclusionIt could be recommended to divide the hd-CTV into GTV and subclinical target volume and to prescribe different doses for the GTV and subclinical involvement in the IMRT plan of NPC.