14 Nasopharynx Cancer

Nasopharynx Cancer

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

thenmade in this mould using an acrylic compound.The applicator surface is carefully smoothedwith a grinder and a double nylon cord is attached to its lower posterior aspect to be used later for applicator removal from the nasopharynx. Two rubber strips are attached at its upper anterior aspect at the level of the small projections, which extends into the posterior choanae, where the paste overflowed. These strips would hold the applicator in positionwhen brought out through the nostrils and tied together anterior to the nasal septum. At the time themold technique was employed, iridium (Ir192) wire source afterloading was used. Based on the tumour topography imprinted on the applicator, the radiation oncologist specifies the configuration of the blind-ended plastic tubes upon which wire sources are to be loaded.The tubes are oriented sagittally and spaced 10-15 mm. The radiation oncologist determines the appropriate source lengths and may require 2-4 tubes in an averaged-sized nasopharynx, depending on the tumour extent. Once the applicator has been assembled, the endoluminal trajectory is checkedwith dummy sources.The applicator is inserted in a similar fashion as for the dummy applicator and fixed using immobilization buttons applied on the anterior rubber strips. The positioning in the nasopharyngeal cavity is documented with orthogonal films and the projected dosimetry is verified. The Ir192 wires are then loaded as prescribed. (Figures 4 and 5). 8.1.2 Endoscopy-Based Mould Technique: Hong Kong In contrast to the French approach, this approach only entailed customization of the size of the applicator relative to the dimensions of the nasopharynx of the patient as measured during endoscopy but not of the configuration of the source paths relative to the tumour configuration (Figures 6-8). The endoscopy procedure may entail tumour debulking for better visualization andmeasurement of the nasopharyngeal cavity, as well as to allow better fitting of the applicator and eventual dosimetry. The earlier, preloading version is built on a foam base, while the later, afterloading version is built on a two-jointed silicon and plastic base that allowed for greater flexibility. The insertion procedure is similar to that described for the French approach. 8.1.3 Massachusetts General Hospital Technique The procedure uses two paediatric endotracheal tubes with inner and outer diameters of 5 and 6.8 mm, respectively. After topical anaesthesia of the nasal and the nasopharyngeal mucosa, endotracheal tubes are introduced into the nasopharynx through the nostrils. Under fluoroscopic control, the distal tip of each dummy slugs is placed at the free edge of the soft palate posteriorly and at the posterior wall of the maxillary sinus anteriorly. The inflated balloon, which is attached to the distal end of the endotracheal tube, is used to anchor the tubes and to create a distance between the radiation sources and the nasopharyngeal vault to obtain a better depth dose. The entire implant treatment can be performed as an outpatient procedure (Figures 9 and 10) [Wang, 1987; Wang 1991]. 8.1.4 Nasopharyngeal Balloon Applicators The balloon applicator, inserted transnasally [Slevin, 1997, McLean, 1998] is fixed in place by inflating a balloon concentrically around the catheter (Figure 11).This does not allowpreferential displacement of the catheter away from the soft palate and towards the nasopharynx (Figure 12). Eccentrically placed balloons have been proposed to allow better apposition of the catheter against the nasopharynx [Chang, 2001].These applicators are not compatible withmultiple treatments over several days as the relation of the balloon catheters is not stable or fixed.

8.1.5 Rotterdam Nasopharyngeal Applicator The Rotterdamnasopharyngeal applicator (RNA) is a commercial applicator, made out of soft silicone, which is well-tolerated by the patient (Figure 13)[Levendag, 1997]. It is suitable for applications with stepping-source afterloaders for PDR- or HDR-brachytherapy, as well as for classical low-dose-rate (LDR) techniques. The applicator can remain in situ for the duration of the treatment, which varies from2 to 6 days and can be performed on an outpatient basis in case of HDR brachytherapy. The RNA consists of two silicone tubes fixed on a silicone base that maintains a curved path following the curvature of the nasopharyngeal recess and displaces the catheters away from the soft palate. After local anaesthesia of the nasal cavities and the oropharynx with a 2% xylocaine spray, a flexible guide wire is introduced into one nasal cavity. The end is recuperated with forceps through the oropharynx and brought outside the mouth. The procedure is repeated at the other side. The applicator is then advanced over the guide wires, fixed to them by clamps, and pulled gently through the mouth and the oropharynx into the nasopharynx. The legs of the applicator exit through the nostrils and are fixed with a silicone bridge, pushed against the nasal septum. The applicator tubes are then brought into the applicator and fixed. The applicator placement is secured externally using a silicone flange (Figure 14). A newer design features displacement of the two catheters laterally and away from each other allowing a better coverage of the nasopharyngeal recess [Levendag, 1997]. The tubes have an outer diameter of 15 French (5 mm) and an inner diameter of 9 French (3 mm) and can accommodate standard 6 French afterloading catheters. In both designs, the catheters are inserted into the tubes but are not optimally displaced towards the recess as they are fixed upon the base, the maximum height of which is limited by the diameter of the naso-oropharyngeal passage, that is, the passage bounded by the posterior and lateral walls of the pharynx and the soft palate. Development of newer applicator designs should ideally allow for deployable catheters that can be advanced closer to the nasopharynx and away from the soft palate [Bacorro, 2018]. The procedure is performed under general anesthesia and entails splitting the palate to access the nasopharynx, interstitial implantation radioactive gold grains, and closure of the palate in three layers (Figure 15). This technique has been associated with brisk nasopharyngeal ulceration and necrosis whichmay persist for two to three weeks, and velopalatal insufficiency due to fistulisation or atrophy in 11-19% of the cases [Choy, 1992; Kwong, 2000] 8.2.2 Transnasal Permanent Interstitial Implants The procedure is performed under general anaesthesia [Vikram, 1984]. The soft palate is retracted forward with a retractor, and the nasopharynx is visualised, by means of a fiber optic nasopharyngoscope. After satisfactory visualisation of the tumour site has been obtained, hollow afterloading needles are introduced into the nasal passages and are advanced through the posterior choanae, and inserted into the mucosal surface. Radioactive I-125 seeds are then introduced submucosally through these needles, and the needles are withdrawn. (Figure 16) 8.2.3 Transnasal, Endoscopy-Guided HDR Interstitial Implants The procedure is performed using endoscopic guidance via the 8.2 Interstitial Approaches 8.2.1 Split-palate Interstitial Implantation