CONTENTS 17.1 Introduction 213 17.2 Anatomy 214 17.2.1 Anatomy of the Nasopharynx and its Surrounding Structures 214 17.2.2 Classification of Lymph Node Levels in the Neck 215 17.2.2.1 Retropharyngeal Lymph Nodes 218 17.2.2.2 Retrostyloid Space 221 17.2.2.3 Supraclavicular Lymph Nodes 221 17.3 Target Volume Selection and Delineation of the Primary Disease 221 17.3.1 Defining the Gross Tumor Volume of the Primary Disease 223 17.3.2 CTV of the Primary Disease 225 17.4 Target Volume Selection and Delineation in the Neck 226 17.4.1 Diagnosis of Cervical Lymph Adenopathy 226 17.4.2 Patterns of Cervical Lymph Node Metastases 226 17.4.2.1 Retropharyngeal Lymph Nodes 226 17.4.2.2 Level II Lymph Nodes 227 17.4.2.3 Level V Lymph Nodes 228 17.4.2.4 Level III and IV Lymph Nodes 228 17.4.2.5 Level I Lymph Nodes 228 17.4.2.6 Supraclavicular Lymph Nodes 228 17.4.2.7 “Skip” Metastasis of Lymph Nodes 229 17.4.2.8 Bilateral Cervical Node Involvement 229 17.4.3 Selecting Clinical Target Volumes in the Neck 229 17.4.3.1 Clinical Target Volumes in N0 Disease 230 17.4.3.2 Clinical Target Volumes in N+ Disease with Extracapsular Extension 230 17.5 Conclusions 231 References 231 17.1 Introduction Radiation therapy is the mainstay therapeutic modality for nasopharyngeal cancer (NPC), and high-dose radiation is required for curative treat- ment of the disease. Nasopharynx is in close proxim- ity to the critical structures such as brainstem and brain (temporal lobes), parotid glands, and spinal cord. Irradiating structures close to the nasophar- ynx may cause symptoms that substantially affect the quality of life of patients after treatment; precise radiation therapy for this malignancy has always been the focus of technology development. The implementation of intensity-modulated radi- ation therapy (IMRT) allows a significant improve- ment in the control of radiation dose distribution and is considered more advantageous for definitive ther- apy for nonmetastatic NPC. However, the utilization of IMRT in the treatment of NPC requires a different mindset when compared with conventional radio- therapy. One of the most important differences is the selective treatment of structures surrounding the pri- mary disease and neck nodes required with IMRT. Target volumes harbor gross and subclinical diseases that need to be accurately determined and delineated before the planning of IMRT can be initiated. There- fore, the utilization of IMRT in the treatment of NPC requires full understanding of the criteria of radio- logical diagnosis of the primary disease and cervical Jiade J. Lu, MD, MBA Department of Radiation Oncology, National University Can- cer Institute, National University Health System, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074, Republic of Singapore Vincent Grégoire, MD, PhD Radiation Oncology Department and Center for Molecu- lar Imaging and Experimental Radiotherapy, Université Catholique de Louvain, St-Luc University Hospital, 10 Avenue Hippocrate, 1200 Bruxelles, Belgium Shaojun Lin, MD Department of Radiation Oncology, Cancer Hospital of Fujian Medical University, 91, Fumalu Maluding Road, Fuzhou, Fujian 350014, PR China Selection and Delineation of Target Volumes 17 in Intensity-Modulated Radiation Therapy for Nasopharyngeal Cancer Jiade J. Lu, Vincent Grégoire, and Shaojun Lin