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

damage can be minimized with preimplantion dental care, proper case selection, adequate implant technique, intensive treatment planning with appropriate optimization [7] and bone shielding during treatment (Figure 10). Tumors invading bone tissue are usually advanced cases not suitable for brachytherapy alone or combined with EBRT. However, smaller lesions adjacent to the bone can be treated with brachytherapy provided that there is a minimal space of a few millimeters between the CTV and the cortical bone. In lesions closer to the bone, the general rule is that no more than 2 catheters should be placed in contact with the mandible. Alternative options in case of closer proximity to the mandible include narrowing the catheter interspacing to minimize high dose regions extending into the cortical bone tissue. This is especially important in bones with a high mechanical stress such as the mandible, namely in the area adjacent to the mandibular angle.

Fig 4. Neurovascular anatomy of the neck. Taken from http://pinterest.com

5. STAGING

Radiation vascular damage can be minimized by using a shorter intercatheter distance in the area of the CTV occupied by the vessels and by placing the catheters alongside the vessels rather than directly over the vessels. This allows to decrease the volume of the high-dose region as well as to displace the high-dose regions (V 150 ) towards less vulnerable areas, such as those that have not been surgically dissected. Vessel stumps are more vulnerable than intact vessels to high-dose irradiation and should be identified at implantation and during dosimetry [6]. If catheters need to be placed on the vessels, a narrow sheet (1-2 mm) of biodegradable material or tissue (i.e, fat, muscle, etc.) should be interposed to avoid vessel wall exposure to very high dose regions (V 200 ). 4.2.2. Bone Damage Lesions adjacent to themandible carry the risk of osteoradionecrosis (Figure 5). In addition, bone absorption of the 192 Ir photons is much higher due to the predominance of the photoelectric effect at low radiatiion energies that is proportional to the atomic number (Z 3 ) instead of Compton or Pair production that is the most frequent absorption mechanism at high radiation energies such as megavoltage EBRT. Bone damage in other head and neck sites treatedwith brachytherapy such as the upper maxilla, hard palate, etc. is infrequent. Bone

5.1. Local and Regional assessment 5.1.1. Local

A thorough ENT examination is crucial to determine which tumors are suitable candidates for HN BT. In general, good candidates for brachytherapy in the head and neck area are not essentially different from ideal candidates in other anatomical sites. Unifocal, well-defined lesions of ≤ 3cm of diameter that are technically implantable and without fixation to neurovascular structures or bone should be considered. Direct assessment with bimanual palpation and with inspection is crucial in all accessible lesions. ENT endoscopy is necessary for the examination of the naso-, oro- and hypopharyngeal structures that cannot be done through direct vision as well as to rule out multifocality and/or second primary tumours. In case the tumour is treated with a combination of EBRT and brachytherapy, the tumour limits may be tattooed or indicated by clips. Finally, clinical palpation and visual findings requires a comprehensive interpretation with CT or MRI imaging that may better delineate the full extension of the GTV in most head and neck sites. MRI is more sensitive at detecting muscle infiltration and at showing invasion of the medullary space of the mandible and tumour spread along the inferior alveolar nerve.

Fig 5. Osteoradionecrosis of the left mandible. Oral view (left); Bone fragment removed (middle); X-ray (right). Courtesy Prof.D.Peiffert.