Review articleSelection and delineation of lymph node target volumes in head and neck conformal radiotherapy. Proposal for standardizing terminology and procedure based on the surgical experience
Introduction
The use of more precise ways to deliver the dose to the target volumes and protect the normal tissues at risk (e.g. intensity-modulated radiation therapy, conformal radiotherapy) obviously requires a proper knowledge of the volumes to be irradiated for any particular disease site, and an accurate delineation of these volumes on a three-dimensional (3D) basis. This requirement has always existed, but was greatly over simplified in 2D planning in the sense that one dimension was evidently missing or greatly over simplified. For instance, in head and neck tumors irradiated as still suggested in all major textbooks by two opposed lateral fields, there was no need to define the tumor or lymph nodes extension in the mediolateral direction. In some ways, conformal radiotherapy thus requires that the radiation oncologist approaches this issue with the spirit of a surgeon planning and performing his operation. The surgical field would be replaced by computed tomography (CT) scan (or magnetic resonance imaging (MRI)) images and the scalpel by a mouse or an electronic pencil. Without any doubt, this represents a new challenge for the radiation oncologist community. Such a procedure requires a precise knowledge of CT scan- or MRI-based anatomy, as well as microscopic extension of the tumors and/or nodes in the fatty tissues, along the aponeurotic fascia and muscles, or around the blood vessels and nerves. In this respect, the use of guidelines for the selection of the volumes to be irradiated, as well as standardized rules for delineation of these volumes based of modern imaging modalities should be promoted for every disease sites. Such guidelines and rules would contribute to reducing differences in treatment planning from patient to patient and make comparison of clinical series or conduction of multicenter trials much more accurate.
In this framework, the objective of the present review is to propose guidelines for the selection and definition of target volumes in the neck of patients with head and neck squamous cell carcinomas. Such guidelines are based on standardized neck dissection terminology adopted by head and neck surgeons. First, the terminology adopted by head and neck surgeons for the lymph node levels and for node dissection are presented. Then, information on metastatic nodal extension of major tumor sites are reviewed, from which guidelines for target volume extension are proposed. Lastly, following the surgical terminology, tentative rules are proposed for the delineation of the neck node levels based on modern imaging modalities.
Section snippets
Classification of neck node levels and dissection terminology
The head and neck region has a rich network of lymphatic vessels draining from the base of skull through the jugular nodes, the spinal accessory nodes and the transverse cervical nodes down to the venous jugulo-subclavian confluent or the thoracic duct on the left side and the lymphatic duct on the right side [44], [62]. A comprehensive anatomical description of this network has been performed by Rouvière more than 50 years ago [44]. The whole lymphatic system of the neck is contained in the
Cervical lymph nodes
The metastatic spread of head and neck tumors into cervical lymph nodes is rather consistent and follows predictable pathways at least in the neck which has not been violated by previous surgery or radiotherapy. Bataini and Lindberg reviewed the clinical pattern of metastatic neck involvement in patients with head and neck squamous cell carcinomas of the larynx, hypopharynx, oropharynx and oral cavity treated between 1948 and 1978 [3], [28]. For nasopharyngeal tumors, data from a more recent
Guidelines for the selection of the target volumes in the neck
The data presented in the previous section indicated that metastatic lymph node involvement of primary squamous cell carcinomas of the oral cavity, pharynx and larynx typically followed a predictive pattern. Both data on clinical and pathological neck node distribution, and on neck recurrence after selective dissection procedures, supported the concept that not all the neck node levels should be treated as part of the initial management strategy of head and neck primaries of squamous cell
Guidelines for the delineation of the target volumes in the neck
As already discussed in Section 2, the Committee for Head and Neck Surgery and Oncology of the American Academy for Otolaryngology – Head and Neck Surgery has recommended the use of a common terminology and procedures for the surgical treatment of the neck [41]. We propose to use similar recommendations for the treatment of the neck by radiotherapy.
Radical neck irradiation would become the reference procedure where levels I–V are included in the target volume along with the internal jugular
Conclusions
The increasing use of 3D treatment planning in head and neck radiation oncology has created an urgent need for new guidelines for the selection and delineation of the neck node areas to be included in the CTV. Surgical literature has provided us with valuable information on the extent of pathological nodal involvement in the neck as a function of the primary tumor site. In addition, a few clinical series have also reported information on radiological nodal involvement in those areas not
Acknowledgements
The authors wish to thank Dr J. Kaanders and Professor P. Scalliet for critical reading and constructive suggestions during the preparation of the manuscript.
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