13 Head and Neck - Oropharynx

Head and Neck - Oropharynx

14

THE GEC ESTROHANDBOOKOF BRACHYTHERAPY | Part II Clinical Practice Version 1 - 15/02/2021

8.6 Perioperative Brachytherapy Preoperatively, the surgeon decides jointly with the brachytherapy expert the best surgical approach for tumour resection in the individual case.The possible intraoperative implantation geometry of the target area sometimes needs unusual surgical approaches – this will be discussed. In the course of the operation, the surgeon demonstrates for the brachytherapy expert the subregion(s), where potentially micro-macroscopic residuals are or will be left. Using this target information, the interventional radiotherapy expert performs the implantation of the jointly defined target area to obtain an optimal applicator geometry. The tumour bed is the tissues left behind around the primary tumour and the tissue around the neck nodes with a substantial probability of extracapsular spread. In the oropharyngeal area it is essentially muscle and fat. In the neck, the tumour bed may contain large vessels and nerves, depending upon the location of the enlarged node(s). Most oropharyngeal implants can be undertakenwith button-ended catheters with the entry point in the skin of the neck and the exit point in the oral mucosa beyond the tumour bed. Catheters are usually inserted in the lower neck and then passed upwards into the oropharynx. This allows the neck nodes to be covered (if they need to be treated: multiple N+ or ECS+) and the primary tumour bed with a single set of catheters. If the neck does not need to be treated the entry point will usually follow the submental route. It is advisable to pass the catheters just below the surface of the tumour bed wherever possible at certain intervals (i.e, every 1-1.5 cm). This improves geometry, implant stability and speeds up the procedure avoiding the use of absorbable stitches. When the wound closure involves a huge tissue displacement the catheters are more stable in this way than left just lying in the bed. If there is a flap it will usually interfere with implant placement and therefore brachytherapy needs to be done before the flap (Figure 24). However, if a free flap is used, careful attention needs to be paid to catheters interfering with vascular anastomosis of the flap in the neck. If this is the case, the trajectory and location of all the catheters need to be discussed with the surgeon before catheter placement. In certain locations large or medium sized arterial vessels are part of the CTV and need to be irradiated. It is very important to avoid mechanical trauma from the catheters.This is usually accomplished by placing the catheters alongside the vessels and not perpendicular to them. In addition, it is important to locate hot spots outside the vessels by placing the catheters a couple of millimeters away from the vessel. If this is not possible it is advisable to create a muscle flap or a fat pad 2 to 3 mm thick to be interposed between the vessel wall and a catheter. If this is not possible then haemostatic material (i.e. Surgicel) can be used to create a biological spacer. If vessels are at risk, it is recommended that they are delineated during treatment planning to minimize the dose while keeping if possible, a reasonable CTV coverage. Figure 25 shows the dose distribution for perioperative implantation. The technique of permanent seed implantation for the oropharyngeal cancer is beyond the scope of this chapter.

Figure 24: Tumour bed after resection of a base of tongue tumour. Tumour bed implanted with button-ended catheters. Surgical defect reconstructed with a free flap

Figure 25: Dose distribution of perioperative brachytherapy (Martinez Fernandez et al)