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Special Report Rafael Martinez-Monge, MD Patrick S. Fernandes, MD Nilendu Gupta, PhD Reinhard Gahbauer, MD Cross-sectional Nodal Atlas: A Tool for the Definition of Clinical Target Volumes in Three-dimensional Radiation Therapy Planning1 Virtual three-dimensional clinical target volume definition requires the identification of areas suspected of containing microscopic disease (frequently related to nodal stations) on a set of computed tomographic (CT) images, rather than the traditional approach based on anatomic landmarks. This atlas displays the clinically relevant nodal stations and their correlation with normal lymphatic pathways on a set of CT images. When radiation is used with curative intent, the radiation volume usually encompasses the detectable tumor and the anatomic areas thought to be at risk for metastatic spread. The International Commission on Radiation Units and Measurements Report No. 50 (1) defines gross tumor volume (GTV) as the gross palpable or visible or demonstrable extent and location of the malignant growth. The same report defines clinical target volume (CTV) as a volume that contains a demonstrable GTV and/or is considered to contain (only) microscopic, subclinical extensions at a certain probability level. In clinical practice, the determination of the extent of the CTV is based on the knowledge of the patterns of spread for each specific disease presentation. Additional reliable information can be obtained from patterns-of-failure analysis and necropsy series. For most tumors, the CTV will encompass one or more nodal stations, usually near the primary lesion. Traditionally, the location and boundaries of these nodal stations have been established in reference to anatomic landmarks during the standard simulation setup. Therefore, the radiation oncologist has been specifically trained to determine the bound- aries of the different nodal stations on standard two-dimensional radiographs, especially in the anteroposterior and posteroanterior views. With the advent of three-dimensional (3D) virtual clinical target definition, the radiation oncologist faces the challenge of defining the CTV on cross-sectional CT or magnetic resonance images. Unfamiliarity with this new technique can make correlations with the known spatial references difficult to establish. The present nodal atlas is intended to assist radiation oncologists who will use new 3D virtual clinical target definition and treatment planning programs. CLASSIFICATION AND NOMENCLATURE The anatomic patterns of lymphatic drainage for different organs to their first echelon (or efferent) nodal stations were taken from Rouviere’s Anatomy of the Human Lymphatic System (2) and confirmed with other lymphatic anatomy textbooks (3,4). The main and accessory lymphatic routes for different organs that are relevant in radiation oncology are summa- rized in Tables 1–8, with an explanation of the abbreviations appearing in the Key Box. When different subsites within an organ had unique drainage patterns, these were individualized in the Tables as well. The classification of and nomenclature for the different nodal areas usually followed the guidelines of Rouviere’s system (2). In the classification of the mediastinal nodes, the widely used American Joint Committee on Cancer classification Index terms: Computed tomography (CT), three-dimensional, 99.12917, 99.92 Lymphatic system, 99.12917, 99.92 Special reports Treatment planning, 99.92 Radiology 1999; 211:815–828 Abbreviations: CTV 5 clinical target volume GTV 5 gross tumor volume 3D 5 three-dimensional 1 From the Division of Radiation Oncol- ogy, the Arthur G. James Cancer Hospital, Ohio State University, 300 W Tenth Ave, Columbus, OH 43210. Received July 15, 1998; revision requested August 27; revision received October 16; ac- cepted November 23. Address re- print requests to R.M. r RSNA, 1999 Author contributions: Guarantor of integrity of entire study, R.M., R.G.; study design, R.M.; defini- tion of intellectual content, R.M.; lit- erature research, R.M., P.S.F.; data acquisition and analysis, R.M., N.G.; manuscript preparation, R.M.; manu- script review, R.G. 815 was chosen instead (5). The nodal areas represented are listed in the Key Box. When clinically relevant, some nodal sta- tions were further divided into sub- groups, which are noted as lowercase letters after the abbreviation codes pro- vided in the Tables and the Figures. The nonparenthesized lowercase letters indi- cate differentiated subgroups, usually in the direction of the zz8 axis. Parenthe- sized letters indicate subgroup subdivi- sion, usually in the direction of the xx8 axis (shown only for inguinal and exter- nal iliac nodes). LOCALIZATION OF NODAL STATIONS The different nodal stations were out- lined and labeled on five different sets of consecutive and equidistant CT images (head and neck, thorax, abdomen, male pelvis, and female pelvis) (Figs 1–6). We elected to use CT images because they are the customary image support in most 3D virtual clinical target definition pro- grams. The nodal stations on the cross- sectional images were localized by ex- Key Box for Abbreviations in Tables and Figures Abbreviation Nodal Group Abbreviation Nodal Group APWN Aortopulmonary window nodes PFL Pyriform fossa lymphatics ATL Anterior tongue lymphatics PG&N Parotid gland and nodes AxN Axillary nodes PHN Hilar nodes BTL Base tongue lymphatics PL Parametrial lymphatic plexus CIN Common iliac nodes PLN Prelaryngeal nodes CN Celiac axis nodes PPL Periprostatic lymphatic plexus CPN Cervical pretracheal nodes PRL Perirectal lymphatic plexus DN Diaphragmatic nodes PSL Paranasal sinuses lymphatics EIN GL External iliac nodes Glottic lymphatics PsRN Superior posterior pharyngeal wall lymphatics and retro- pharyngeal nodes HMN High mediastinal nodes PiL Inferior posterior pharyngeal wall lymphatics HN Hepatic nodes PTrN Mediastinal pretracheal nodes HPL Hard palate lymphatic plexus PVgL Paravaginal lymphatic plexus IGL Infraglottic lymphatics PVL Perivesical lymphatic plexus IIN Internal iliac nodes PVsN Prevascular nodes IJN Internal jugular nodes RAN Retroaortic nodes IMN Internal mammary nodes RCP Right cervical paratracheal nodes IN Superficial inguinal nodes, deep inguinal RRH Right hilum renal nodes nodes RLP Right lower paratracheal nodes IPN Internal pudendal nodes RPN Right paraaortic nodes IRN Inferior rectal nodes RUP Right upper paratracheal nodes JVN Juxtavertebral nodes SAN Spinal accessory nodes LCP Left cervical paratracheal nodes ScIN Supraclavicular nodes LGN Left gastric nodes SCN Subcarinal nodes LPN Left paraaortic nodes SGL Supraglottic lymphatic plexus LRH Left renal hilum nodes SMaN Submandibular nodes LUP Left upper paratracheal nodes SMeN Submental nodes MN Mastoid nodes SMN Superior mesenteric nodes NL Nasopharyngeal lymphatic plexus SN Sacral nodes PAN Preaortic nodes SPL Soft palate lymphatics PAuN Preauricular nodes SplN Splenic nodes PCL Postcricoid lymphatic plexus SRN Superior rectal nodes PecN Pectoral nodes SVL Seminal vesicles lymphatic plexus PEN Paraesophageal nodes TL Tonsil lymphatic plexus TABLE 1 Head and Neck Lymphatic System (I) Anatomic Site First Echelon Nodal Group Subgroup Category Abbreviation Lacrimal gland Preauricular nodes Main PAuN Parotid nodes Main PG&N Submandibular nodes Main SMaN Eyelids, conjunctiva Preauricular nodes Main PAuN Parotid nodes Main PG&N Submandibular nodes Main SMaN Pinna Preauricular nodes Main PAuN Parotid nodes Main PG&N Mastoid nodes Main MN Internal jugular nodes Upper Main IJNu External auditory canal Parotid nodes Main PG&N Internal jugular nodes Upper Main IJNu Middle ear Preauricular nodes Main PAuN Retropharyngeal nodes Main PsRN Internal jugular nodes Upper Main IJNu External nose Submandibular nodes Main SMaN Nasal cavity Retropharyngeal nodes Main PsRN Internal jugular nodes Upper Main IJNu Paranasal sinuses Retropharyngeal nodes Main PsRN Internal jugular nodes Upper Main IJNu Lip, upper Submandibular nodes Main SMaN Submental nodes Accessory SMeN Preauricular nodes Accessory PAuN Lip, lower Submandibular nodes Main SMaN Submental nodes Main SMeN Cheek, cutaneous Submandibular nodes Main SMaN Submental nodes Main SMeN Parotid nodes Main PG&N Buccal mucosa Submandibular nodes Main SMaN Tongue, apex Submental nodes Main SMeN Internal jugular nodes Upper, middle Main IJNu, m Tongue, lateral and posterior Submandibular nodes Main SMaN Internal jugular nodes Upper Main IJNu 816 x Radiology x June 1999 Martinez-Monge et al Figure 1. CT images depict head and neck nodal stations at levels hn01 through hn09 on the topogram in Figure 7. Volume 211 x Number 3 Cross-sectional Nodal Atlas for Definition of Clinical Target Volumes x 817 trapolating information from cross- sectional anatomy atlases (6), lymphatic atlases (3), and vascular atlases (4). To allow easy correlation, the five sets of CT images were connected with a recogniz- able bone structure on a topogram (Fig 7). REPRESENTATION OF THE ANATOMY OF THE LYMPHATIC SYSTEM IN THE NODAL ATLAS The initial lymphatic system is composed of capillary lymphatics, which originate in the intima of the tissue and are im- mersed in the ground substance of the tissue space. These capillaries anastomose in networks to form the peripheral lym- phatic plexuses. These plexuses are only represented in the atlas for certain organs that are frequently irradiated while intact (prostate, rectum, some head and neck subsites, etc) to facilitate the recognition of the organ or site and its spatial relation- ship with the surrounding nodal stations. The lymphatic plexuses drain to the first echelon lymph nodal stations through precollecting and collecting ducts. Sometimes, there are intercalating lymph nodes in the path of the collecting ducts. In general, no intermediate paths between the organ of interest and the first echelon nodal station have been repre- sented in the atlas to avoid unnecessary complexity. However, some clinically rel- evant intercalating nodes have been rep- resented (superior and inferior rectal nodes and internal pudendal nodes). The first nodal station reached by the lymphatic drainage of a given organ is called the first echelon nodal group. The first echelon lymph nodes connect to each other through postlymphonodal col- lecting ducts and finally drain to more central efferent lymph nodes or directly into the venous system through the main lymphatic trunks, depending on ana- tomic location. As a rule, the first echelon nodal stations for all the different organs of the head and neck, thorax, abdomen, and pelvis are represented. These are listed in the Tables 1–8. One exception to this rule has been the case of the small bowel and most of the large bowel. Due to the TABLE 2 Head and Neck Lymphatic System (II) Anatomic Site First Echelon Nodal Group Subgroup Category Abbreviation Floor of mouth Submental nodes Main SMeN Submandibular nodes Main SMaN Internal jugular nodes Upper, middle Main IJNu, m Lower gum Submandibular nodes Main SMaN Submental nodes Main SMeN Internal jugular nodes Upper, middle Main IJNu, m Upper gum Submandibular nodes Main SMaN Retropharyngeal nodes Main PsRN Hard palate, soft Internal jugular nodes Upper Main IJNu palate inferior Submandibular nodes Accessory SMaN Retropharyngeal nodes Accessory PsRN Soft palate, superior Retropharyngeal nodes Main PsRN Internal jugular nodes Upper Main IJNu Tonsil Internal jugular nodes Upper Main IJNu Nasopharynx Retropharyngeal nodes Main PsRN Internal jugular nodes Upper Main IJNu Spinal accessory nodes Main SAN Pyriform fossa Internal jugular nodes Upper, middle Main IJNu, m Posterior cricoid Internal jugular nodes Upper, middle Main IJNu, m Posterior pharyngeal Retropharyngeal nodes Main PsRN wall, superior Internal jugular nodes Upper Main IJNu Posterior pharyngeal wall, inferior Internal jugular nodes Middle Main IJNm Supraglottic larynx Internal jugular nodes Upper, middle Main IJNu, m Infraglottic larynx Internal jugular nodes Middle, lower Main IJNm, l Cervical pretracheal nodes Cervical Main CPN Prelaryngeal nodes Main PLN Trachea Cervical pretracheal nodes Cervical Main CPN Cervical paratracheal nodes Cervical Main LCP, RCP Prelaryngeal nodes Accessory PLN Thyroid Cervical pretracheal nodes Cervical Main CPN Cervical paratracheal nodes Cervical Main LCP, RCP Internal jugular nodes Upper, middle, lower Main IJNu, m, l Retropharyngeal nodes Accessory PsRN Parotid gland Parotid nodes Main PG&N Submandibular nodes Main SMaN Submandibular gland Submandibular nodes Main SMaN Internal jugular nodes Upper Main IJNu Sublingual gland Submandibular nodes Main SMaN Internal jugular nodes Upper Main IJNu 818 x Radiology x June 1999 Martinez-Monge et al Figure 2. CT images depict head and neck nodal stations at the levels hn10 through hn18 on the topogram in Figure 7. Volume 211 x Number 3 Cross-sectional Nodal Atlas for Definition of Clinical Target Volumes x 819 anatomic mobility of these organs, the efferent pre- and paraaortic nodal groups (fixed structures with reproducible loca- tion), rather than the first echelon nodal groups (juxtaintestinal and paracolic), are represented in the atlas. Patterns of anomalous nodal spread, such as retro- grade spread, are not shown in this atlas. ERRORS IN LOCALIZATION OF NODAL STATIONS Lymphography is the technique of choice to visualize nodal groups. However, its decline in the field of diagnostic radiol- ogy has led to the decline of its use as a tool for radiation therapy planning, and it has been virtually abandoned for both purposes. However, currently used stan- dard radiation ports still follow the bound- aries determined during the lympho- graphic era. During standard simulation, the different nodal stations are not actu- ally seen on the simulation radiographs; therefore, a margin of normal tissue is taken around the CTV to allow for any localization uncertainties. Three-dimen- sional virtual clinical target definition, like standard simulation, lacks visualiza- tion of nodal stations. However, because localization errors on cross-sectional im- ages are minimized (as are the associated increases in CTV uncertainty and size of the planning taget volume), this problem is not as great. During 3D virtual clinical target definition, only a few of the nodal stations represented in the atlas are vis- ible on a CT image. So, the exact location of a given station in an individual is difficult to determine. Furthermore, the internal structure of the lymphatic sys- tem (different normal variants among subjects) precludes any categorical state- ment (2–4). Therefore, we chose to out- line wide areas rather than discrete loca- tions for each nodal station to account for the differences in normal anatomic TABLE 3 Thoracic Lymphatic System Anatomic Site First Echelon Nodal Group Subgroup Category Abbreviation Lung; RUL antero- medial Right paratracheal nodes Upper, lower Main RUP, RLP Lung; RUL postero- lateral, RML, RLL superior Right paratracheal nodes Right hilar nodes Subcarinal nodes Upper, lower Main Main Main RUP, RLP PHNr SCN Lung; RLL inferior Right hilar nodes Main PHNr Subcarinal nodes Main SCN Lung; LUL superior Left upper paratracheal nodes Main LUP Prevascular nodes Main PVsN Aortopulmonary window nodes Main APWN Lung; LUL inferior, LLL superior, LLL middle Left upper paratracheal nodes Prevascular nodes Aortopulmonary window nodes Left hilar nodes Subcarinal nodes Main Main Main Main Main LUP PVsN APWN PHNl SCN Lung, LLL inferior Left hilar nodes Main PHNl Subcarinal nodes Main SCN Costal pleura, Supraclavicular nodes Main SclN superior Internal jugular nodes Lower Main IJNl Costal pleura, Juxtavertebral nodes Any level Main JVNs, m, i middle Internal mammary nodes Any level Main IMNs, m, i Costal pleura, Axillary nodes Main AxN inferior Juxtavertebral nodes Any level Main JVNs, , m, i Internal mammary nodes Any level Main IMNs, m, i Right diaphragm, Diaphragmatic nodes Right lateral Main DNlat subperitoneal Retroaortic nodes Suprarenal, thoracic Main RANsr, t Left diaphragm, Paraesophageal nodes Inferior Main PENi subperitoneal Retroaortic nodes Suprarenal, thoracic Main RANsr, t Right and left dia- phragm, sub- pleural Diaphragmatic nodes Paraesophageal nodes Retroaortic nodes Anterior, lateral Inferior Suprarenal Main Main Main DNa, lat PENi RANsr Breast Axillary nodes Main AxN Internal mammary nodes Any level Main IMNs, m, i Supraclavicular nodes Accessory SclN Pectoral nodes Accessory PecN 820 x Radiology x June 1999 Martinez-Monge et al Figure 3. CT images depict the nodal stations in the thorax (th). Volume 211 x Number 3 Cross-sectional Nodal Atlas for Definition of Clinical Target Volumes x 821 TABLE 4 Gastrointestinal Lymphatic System (I) Anatomic Site First Echelon Nodal Group Subgroup Category Abbreviation Gastric cardia Left gastric nodes Juxtacardiac Main LGNc Gastric lesser cur- Left gastric nodes Gastropancreatic Main LGNlc vature Lesser curvature Main LGNlc Gastric antrum Hepatic nodes Right gastroepiploic Main HNrg and pylorus Infrapyloric Main HNp Suprapyloric Main HNp Greater omentum Hepatic nodes Right gastroepiploic Main HNrg Infrapyloric Main HNp Suprapyloric Main HNp Gastric greater curvature Splenic nodes Suprapancreatic Main SplNs Duodenum Hepatic nodes Infrapyloric Main HNp Retropyloric Main HNp Pancreaticoduodenal Main HNpd Superior mesenteric nodes Postpancreaticoduodenal Main SMN Pancreas Hepatic nodes Infrapyloric, suprapyloric Main HNp Pancreaticoduodenal Main HNpd Hepatic artery Main HNha Splenic nodes Suprapancreatic Main SplNs Splenic hilum Main SplNh Left gastric nodes Gastropancreatic Main LGNlc Superior mesenteric nodes Root of mesentery Main SMN Middle colic Main SMN Postpancreaticoduodenal Main SMN Right paraaortic nodes Superior Main RPNs Left paraaortic nodes Superior Main LPNs Spleen Splenic nodes Splenic hilum Main SplNh Liver Hepatic nodes Gallbladder, hepatic artery Main HNha Celiac axis nodes Main CN Left gastric nodes Lesser curvature Main LGNlc Diaphragmatic nodes Anterior, lateral Main DNa, lat Paraesophageal nodes Inferior Main PENi Renal hilum nodes Main RRH, LRH Gallbladder and Hepatic nodes Gallbladder Main HNha cystic duct Foramen of Winslow Main HNha Hepatic duct Hepatic nodes Foramen of Winslow Main HNha Common bile duct Hepatic nodes Foramen of Winslow Main HNha Postpancreaticoduodenal Main HNpd TABLE 5 Gastrointestinal Lymphatic System (II) Anatomic Site Efferent Nodal Group* Subgroup Category Abbreviation Jejunum, ileum Superior mesenteric nodes Main SMN Cecum and appendix Superior mesenteric nodes Main SMN Ascending colon Superior mesenteric nodes Main SMN Transverse colon, right Superior mesenteric nodes Main SMN Transverse colon, left Superior mesenteric nodes Main SMN Descending colon Left paraaortic nodes Any level Main LPNsr, s, m, i, LRH Superior mesenteric nodes Main SMN Sigmoid colon Preaortic nodes Inferior mesenteric Main PANs, m Left paraaortic nodes Superior, middle Main LPNs, m Rectum Preaortic nodes Inferior mesenteric Main PANs, m Internal iliac nodes Accessory IIN Sacral nodes Accessory SN * In the small and large intestine, the first echelon nodal group is represented by the juxtaintestinal (small-bowel) or paracolic (large-bowel) nodes located in the mesenteric border of the organ. Because of the mobility of these organs, the efferent nodal groups (fixed structures with reproducible location), rather than the first echelon nodal groups, are represented in the atlas. 822 x Radiology x June 1999 Martinez-Monge et al variability and nodal interconnection. An- other difficult problem is the mobility of the nodal stations located proximally in the limbs (inguinal, axilla). The location of these nodal groups will vary greatly, depending on simulation positioning. The cross-s