10 General Aspects of Head and Neck Brachytherapy

General Aspects of Head and Neck Brachytherapy

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 30/01/2019

systems (TPS) during the 1990´s allowed to generate and deliver more conformal treatment plans in anatomical areas where HN BT was more technically demanding and hazardous such as the oropharynx. The widespread availability of 3DCRT prompted a decrease in the use of HN BT in traditional locations such as base of the tongue, tonsil, soft palate, etc. As a result, former active HN BT schools disappeared or were reduced to a minimum and more importantly, the number of HN BT experts gradually decreased, leaving HN BT teaching at risk. However, the decline inHNBT during the late 90´s has been halted to some extent with the implementation of the brachytherapy 3D TPS and the replacement of the former LDR technology by modern stepping source PDR or HDR equipment. In spite of this, HN BT is today an endangered species and needs to find its place in the world of multidisciplinary oncology. Awareness of strengths and weaknesses is essential. Return to the old days of performing HN BT procedures based solely on clinical grounds with limited imaging workup is no longer possible. Modern HN BT should adopt the quality standards required by other state-of-the-art radiation oncology specialities. Optimal case selection is mandatory and requires accurate determination of the gross extension of the tumor through comprehensive clinico-radiological workup in cases primarily managed with brachytherapy alone or combined with EBRT. In those cases treated in combination with surgery, optimal case selection requires complete surgicopathological information. Finally, HN BT lacks the necessary standards in CTV definition, dose prescription and OAR constraints that are mandatory in modern brachytherapy. It must be recognized, however, that the heterogeneity and complexity of HN BT in terms of distinct anatomical scenarios, diverse implantation and brachytherapy techniques surely represent an obstacle towards the required uniformity. However, further progress in HN BT requires the development of a common methodology similar to that already implemented by different groups of experts in other brachytherapy specialities (i.e, gynaecological or breast brachytherapy).

of the desired location. Buttons at the entry and exit points are required in most locations to avoid catheter displacement.

4.1.2. Oropharynx Anatomical Description

The oropharynx follows the oral cavity, extending from the plane of the hard palate to the hyoid bone (Figure 3). The oropharynx includes the faucial arch (soft palate, uvula, tonsils and anterior and posterior pillars of the tonsils), the base of tongue, and the pharyngeal walls [4]. Accessibility Many oropharyngeal locations are implantable. The degree of technical expertise ranges fromhigh to very high. Oropharyngeal locations are usually accessed through the posterior submental route close to the mandibular angle in a way similar to the oral cavity sites although the degree of maneuverability is limited. Buttons at the entry and exit points are required inmost locations to avoid catheter displacement. Neck locations usually refer to the implantation of lymph node metastases from head and neck sites present in the nodal groups Ib to V. Neck lymph node metastases fromother sites draining into the neck such as the skin of the head and face are usually included within this disease category. The vascular and neural networks of the neck can be seen in figure 4. Accessibility Nowadays most neck implants are performed after surgical resection, and therefore, there are no anatomical limitations to the placement of brachytherapy catheters into the surgical bed. Catheters are usually placed along the neck structures using single- leader tubes but can also be placed across the neck structures using button-ended tubes. Lesions adjacent tomajor vessels carry the risk of vascular damage. This can occur during implantation or at removal (procedural damage) ormonths to years after the implant (late radiation damage). Procedural vascular damage should always be kept in mind when dealing with posterior and lateral lesions located close to the carotid artery and its branches, especially the lingual arteries. In closed-cavity implants (i.e, intact tumors or postoperative implants) anatomical references or palpation may help to determine the location of the carotid artery. Doppler US can be sometimes used. In open-cavity implants (i.e, intraoperatively placed catheters), the vessels are visible and direct damage is unlikely. In these cases, placement of catheters directly over the vessels must be avoided to minimize the risk of mechanical trauma resulting fromprolonged catheter stay. Although the risk of procedural vascular damage is low (1-2%)[5], implants close to large vascular structures must be placed and removed with a surgical teamon-call. Airway protection with a temporary tracheostomy may be necessary. 4.1.3. Neck Anatomical Description 4.2. Special Anatomical Hazards 4.2.1. Vascular Damage

4. TOPOGRAPHY OF THE MAIN BRACHYTHERAPY SITES

4.1. Implantability 4.1.1. Oral Cavity Anatomical Description

The oral cavity begins at the lips (vermilion border) and ends at a virtual plane defined by the soft palate, the anterior pillar of the tonsil, and the posterior limit of the mobile tongue (Figure 2). The oral cavity includes the posterior part of the lips and the commissure, the floor of mouth, the mobile tongue, the buccal mucosa, and the alveolar ridges [4]. Accessibility The vast majority of tumors of the oral cavity are implantable. The degree of technical expertise required ranges from low tomoderate. Lip locations are implanted through the adjacent normal mucosa or skin with entry and exit points lateral to the lesion. Oral cavity locations are usually implanted through the submental route with entry points in the submental skin and exit points at the surface