11 Lip and buccal mucosa

Lip and buccal mucosa

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 10/05/2019

Source: http://elementsofmorphology.nih.gov/anatomy-oral.shtml and https://headandneckcancerguide.org/adults/introduction-to-head-and-neck-cancer/oral-cancers/buccal-cancer/anatomy

8. TECHNIQUE

posterior third of the buccal mucosa (without involvement of the intermaxillary commissure), a combination of external-beam radiation and brachytherapy boost is indicated [9]. If there is deep involvement of the gingivobuccal sulcus, brachytherapy is contraindicated as in floor of mouth carcinoma, because of the unacceptable risk of osteoradionecrosis to the mandible [8-9-18]. For the posterior third of the buccal mucosa, the closest area to the retromolar trigone, the indication for implant alone must be discussed case by case as it may be technically difficult to cover completely that area with interstitial implants [19]. Brachytherapy is followed, as for other oral-cavity carcinomas, by a cervical node dissection in selected cases. It can be performed the next week after the treatment of the primary tumour, due to the shortness of the brachytherapy duration. The clinical target volume for lip includes all visible and palpable tumour extensions with a safety margin of at least 5 mm in all directions. Because there is nomovement of interstitial implanted sources when adequately fixedwith templates or pieces of nasogastric tubes, the PTV corresponds to the CTV. The target volume for buccal mucosa is defined by intraoral examination completed by a bidigital palpation of the tumour; with one finger in the mouth and the other on the skin of the cheek. The projection of the gross tumour volume (GTV) should be drawn and the clinical target volume (CTV) mapped out on the surface of the skin. The CTV comprises the GTV plus a safety margin of 10 mm at the anterior and posterior parts of the tumour (GTV) and 5-10 mm at its upper and lower limits, in relation to the mandible and upper maxilla. If brachytherapy is used as a boost, the initial tumour volume must be marked with metallic clips, or projection onto the skin should be drawn. CT-scan or preferablyMRI can contribute to defining the tumour volume and consequently the target volume more accurately. MRI is used at the time of diagnosis but also after the plastic tubes are implanted to check the quality of the implant and to adjust the position of the radioactive sources, according to the target delineation. 7. TUMOUR AND TARGET VOLUME

8.1 Technique for lip carcinoma Brachytherapy has been classically performed with hypodermic needles, classic nylon tubes, silk threads, small vascular catheters, guide gutters, or a combination of these techniques in the same patient [20] (Fig 1,2). No LDR wires are available in Europe nowadays, and PDR or HDR 192Iridium stepping sources are used, through rigid needles or plastic tubes.The implant procedure follows the same guidelines used with LDR-BT. The implant can be performed under local or regional (mental nerve) anaesthesia and sedation, if needed. 8.1.1 Rigid needles technique Parallel metallic rigid closed hollow needles are inserted to cover the whole volume of the target. It is better to start with the posterior needle at the transition of the vermillion and the wet mucosa and measure adequate spacing to the anterior needle to cover the CTV. They can be arrayed in equilateral triangular templates of 10-12 mm side [4] (Fig. 3). In some cases, needles can be placed outside the tissue to provide coverage of protruding lesions. In these cases, bolus material is placed between the lesion and the external needles to improve dosimetry (Fig. 4). The rigid steel and template system is fixed with screws which avoids collapse of the sources due to the elasticity of the soft tissues, and allows for an optimal dose homogeneity. Templates with predrilled holes in a triangular configuration and with spacing of 10 to 12 mm should be available. 8.1.2 Plastic tubes technique This requires the use of open point hollow needles to be replaced by the plastic tubes with buttons on the extremes. They are more flexible, allowing a better adaptation to round surfaces (Fig 5). However it is more difficult to keep good parallelism between tubes over the whole length of the treated volume. Plastic tubes are therefore indicated for larger masses, or when the lateral commissure or cheek is involved. The treatment has sometimes to be delayed as long as necessary for regression of the post brachytherapy trauma and oedema. 8.1.3 Mould technique Some series with small number of patients have used moulds made with resin or acrylic material and embedded plastic tubes