14 Nasopharynx Cancer

Nasopharynx Cancer

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THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 10/09/2019

in current times, given its advantages in radiation protection and dosimetry. For ICBT, the thickness of the clinical target volume (CTV) should not exceed 10mm. Consequently, only superficial tumours without involvement of the parapharyngeal space or underlying bone are eligible. ISBT by endoscopic guidance can potentially allow for treatment of parapharyngeal extension. Tumours extending into the anterior nasal cavity or oropharynx, or closely adhere to the major carotid vessels would not be candidates for brachytherapy. Potential indications for brachytherapy may therefore include (1) upfront dose-escalation of T1 and T2 disease after EBRT alone, when concurrent chemotherapy is contraindicated, or even after CCRT, (2) boosting minimal residual local disease in an initially T1, as well as select T2 and T3 disease, after satisfactory response to EBRT or CCRT, and (3) salvage therapy for well-circumscribed and superficial local recurrences limited to the nasopharyngeal space. As basic principle, the gross tumour volume (GTV) at brachytherapy shouldbe delineatedusing information fromendoscopic examination and cross-sectional imaging (ideally MRI). There is not yet a consensus onCTVdelineation for nasopharyngeal brachytherapy.The high-risk CTV (HR-CTV) should cover at least the GTV plus a 5-mmmargin, with or without including the entire nasopharynx. Most tumours are located at the roof (i.e. the soft tissue situated between themucosa and the base of skull) and/or the lateral walls of the nasopharynx. In central tumours, the CTVwould include both roof and the lateral walls, however, in well-lateralised tumours, the CTV could be restricted to the roof and one lateral wall [Mazeron, 2002]. For nasopharyngeal boost, whether upfront or as salvage for persistent disease, an intermediate-risk CTV (IR- CTV) could be defined to include at least the GTV at diagnosis (GTV-D). With endocavitary brachytherapy, the 40% isodose (i.e., 1.4 Gy in a 3.5 Gy fraction) could adequately encompass the inferior third of the sphenoid, the entire clivus, the posterior third of the nasal cavity and maxillary sinus, and the proximal (pre-styloid) parapharyngeal spaces (Figure 2)[Bacorro, 2018; Mejia, 2018]. 7. TUMOUR AND TARGET VOLUMES

The brainstem, spinal cord, pituitary, optic chiasm, retina, clivus, atlanto-axial joint and soft palate are contoured as OARs using the MRI as aid for delineation. The atlanto-axial joint is drawn using the following borders: upper limit of the dens (superior), 2mm below the lower limit of the atlas (inferior), ventral limit of the dens and including the ligaments visualized on the MRI or corresponding area on CT (anterior), dorsal limit of the dens (posterior), and inner limits of the axis including the ligaments visualized on the MRI or corresponding area on CT (lateral). The soft palate is drawn from its junction with the hard palate down to its free border and along its junction with the tonsillar pillars, at least 6mm below the inferior limit of the constructed catheters.

8. BRACHYTHERAPY TECHNIQUES

8.1 Intracavitary Approaches Personalized ICBT applicators required important resources and expertise [Mazeron, 2002; Law, 2002]. Less invasive anterograde trans-nasal insertion techniques employing pediatric endotracheal tubes and commercially available nasopharyngeal balloon applicators [McLean, 1998, Chang 2001], and retrograde trans- oral insertion techniques using the Rotterdam nasopharyngeal applicator (RNA), have been since developed.The RNA, unlike the pediatric endotracheal tubes and balloon applicators, is compatible with multiple treatments and may remain in place for up to six days of treatment [Levendag, 1997 8.1.1 Imprint-Based Mould Technique: France In the customisedmould technique, two to four sagittally oriented plastic tubes are fixed on the surface of a rigid acrylic applicator, made from an individual impression of the nasopharyngeal cavity (Figure 3) [Chassagne, 1962]. The procedure is performed under neuroleptic analgesia, which allows some preservation of pharyngeal reflexes and muscular tonicity and does not require endotracheal intubation that could limit oropharyngeal access. Nasal secretions are suctioned and the mucous membranes anaesthetised with 5% xylocaine spray until it is possible to manipulate the oropharynx without provoking pain or triggering the gag reflex. Rubber Nelaton catheters are then passed through both nostrils and brought out the mouth. The oral end of the catheters is then tied to cords attached to a dummy applicator, which is much smaller than a normal nasopharyngeal cavity and is thickly coated with a quick-setting silicone paste. By pulling the nasal catheters, the dummy applicator is maneuvered retrogradely through the naso-oropharyngeal passage and into the nasopharyngeal cavity. The silicon paste is allowed to set up for a few minutes and is then extracted from the nasopharynx. An exact impression of the nasopharynx is obtained, demonstrating surface details of the tumour. If the impression appears incomplete, the procedure is repeated after adding more paste in the defective areas. Once an acceptable impression is achieved, the patient is kept under light anaesthesia, while the rigid applicator is fabricated from the impression. A bivalve plaster of Paris negative mould is prepared from the impression. The rigid applicator with walls about 2-5 mm thick is

7.1 Benavides Cancer Institute Approach Brachytherapy simulation

With the applicator in place, non-contrast 1-mm thick axial CT scans are obtained and co-registered with gadolinium-enhanced T1-weighted 1-mm thick axial MR scans if the latter are obtained.

7.2Delineation of clinical target volumes (CTV) and organs-at-risk (OAR) The residual gross tumour volume (GTV-R) is delineated as the residual tumour on the CT simulation scan and the co-registered MRI, the high-risk CTV (HR-CTV) as the GTV-R plus 5mm, and the intermediate-risk CTV (IR-CTV) as 5 mm around the HR- CTV plus the initial extent of disease (GTV at diagnosis, GTV-D), carving out bone and air.