Clinical Research On The Delineation Of High-risk Clinical Target Volume By Volumetric Expansion Of8mm From The Gross Tumor Volume During Intensity-modulated Radiotherapy Of Patients With Nasopharyngeal Carcinoma

Background and ObjectiveThe current practice in the delineation of the clinical target volumes (CTV)during the intensity-modulated radiotherapy (IMRT) of patients with nasopharyngealcarcinoma (NPC) is largely based on the experiences of the two-dimensionalradiotherapy. In most cancer center, the CTV is generally sub-divided into twodifferent volumes according to the tumor invasion probabilities. The volume whichhas a high risk of tumor involvement is referred to as the high-risk CTV (CTV1), andoften includes the gross tumor volume (GTV) plus5to10mm margins and the wholenasopharyngeal mucosa plus5mm sub-mucosal tissues (volumetric and anatomicexpansion); Whereas the volume which has a relatively low risk of tumor invasion isreferred to as the low-risk CTV (CTV2), and the CTV-2is usually encompassed theCTV1plus the structures with low to moderate risk of tumor involvement (theanatomic expansion). Up till now, there is no consensus regarding the delineation ofthe CTV in the treatment of patients with NPC. This research was designed toinvestigate the short term results and the toxicities of volumetric expansion alonefrom GTV by8mm to form the CTV1in the IMRT of patients with nasopharyngealcarcinoma.MethodsBetween October2010to July2011,37patients with newly diagnosed NPCwere treated with IMRT according to this protocol. The GTVnx was defined as theprimary tumor and involved retropharyngeal nodes as determined by imaging, clinical,and endoscopic findings, and the GTVnd was defined as the involved neck nodes asshown in the imaging and clinical palpation. The CTV1included GTVnx with8mmmargin; CTV2included the5mm of the posterior nasal cavity and maxillary sinussubmucosal, inferior one third of the sphenoid sinus, retropharyngeal lymph nodes(up to the hyoid bone appeared), the pterygopalatine fossa, musculus pterygoideusmedialis and part of musculus pterygoideus lateralis, petrous apex, cavernous sinus,and foramen of cranial base. Neck nodes level â…¡, â…¢, â…¤a were also included in the CTV2. The planning target volumes were created by expanding the correspondingvolumes (GTV, CTV1, and CTV2) by5mm to account for setup uncertainty, andthese volumes were named PTV70, PTV60, and PTV54. The prescription dose was70Gy to the PTV70,60Gy to the PTV70, and54Gy to the PTV54in30fractions.Patients with stage â…¢o r â…£ diseases also received cisplatin-based chemotherapy.ResultsA total of37patients with stages I through IVb NPC were enrolled according tothe2008Fuzhou staging (Stage â…  of3cases, â…¡ of4cases, â…¢ of10cases, IV of20cases). In28of the37patients, the CTV1constructed from the volumetric expansionof8mm from GTV can completely cover the entire nasopharyngeal mucosa andsub-mucosal tissues with5mm margin, whereas in9patients, the CTV1missed somepart of the nasopharyngeal mucosa or the sub-mucosal tissues. The median follow-uptime was13months, and the1-year recurrence free survival (RFS), distant metastasisfree survival (DMFS), disease free survival (DFS), and overall survival rates were95.2%,94.7%,95.2%, and97.1%, respectively. No grade4acute toxicities wereobserved. There was one patient (2.7%) with local recurrence, one patient (2.7%)with bone metastasis, and one patient interrupt radiotherapy due to the oropharyngealmucositis and died7months later.ConclusionsIn IMRT of patients with nasopharyngeal carcinoma, the volumetric expansionby8mm alone from GTV to form the CTV1can reduce the high risk CTV andprovide a favorable outcome with acceptable toxicities.