13 Head and Neck - Oropharynx

Head and Neck - Oropharynx

6

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

TABLE 1 T stage as per 8 th UICC TNM staging for HPV Positive oropharyngeal cancer T Category T Criteria T0 No primary identified T1 Tumour 2 cm or smaller in greatest dimension T2 Tumour larger than 2 cm but not larger than 4 cm in greatest dimension T3 Tumour larger than 4 cm in diameter or extension to lingual surface of epiglottis T4 Moderately advanced disease

Tumour extends to larynx, extrinsic muscles of the tongue, medial pterygoid, hard palate or mandible or beyond

TABLE 2 T stage as per 8 th UICC TNM staging for HPV Negative oropharyngeal cancer T stage T Criteria Tx Primary tumour cannot be assessed Tis Carcinoma in situ T1 Tumour 2cm or smaller in greatest dimension T2 Tumour larger than 2 cm but not larger than 4 cm in greatest dimension T3 Tumour larger than 4 cm in diameter or extension to lingual surface of epiglottis T4 Moderately advanced or very advanced disease

Moderately advanced disease Tumour extends to larynx, extrinsic muscles of the tongue, medial pterygoid, hard palate or mandible Very advanced local disease Tumour invades lateral pterygoid muscle, pterygoid plates, lateral nasopharynx, or skull base or encases carotid artery

T4a

T4b

Brachytherapy is not considered when the disease is extending to retromolar trigone, close to or involving hyoid bone, reaching up to pterygoid plates or involving pterygoid muscles. Patients with inadequate mouth opening and those unfit for anaesthesia are also not considered suitable for BT.

by 5-10 mm. CTV to the GTV res may be defined as CTV high risk (CTV HR) and CTV to the initial disease may be defined as CTV intermediate risk (CTV-IR) analogous to the concept of cervical cancer (ICRU 89, 2016). The aimof the BT is to deliver dose to the pretreatment volume with or without margins i.e CTV-IR. With a stepping source afterloader it is now possible to give a higher dose to the CTV HR which can be considered as a boost in boost technique. There is no further PTV in BT as CTV=PTV. While these concepts of contouring have been well established in gynaecological cancer [29] similar data and supporting evidence is lacking in head neck cancer. More work is needed by the head and neck working groups to establish some guidelines for target volume delineation in head neck BT. Often delineation of GTV on the RT planning CT scan is very challenging. There could be change in the anatomy due to post- procedure oedema and also due to presence of catheters at the site of GTV. CT, MRI and PET fusion could also be very challenging in some situations due to these factors. In such situations catheters which are placed at the site of tumour will themselves act as a guide for GTVdelineation as the implant is based on the visualized disease and taking into account preimplant imaging. In some situations, in view of uncertainty in the GTV delineation loading of the reconstructed catheters could be decided directly based on clinical evaluation of the disease and margins.

7. TUMOUR AND TARGET VOLUMES

Gross tumour volume (GTV) is defined at the time of initial diagnosis (GTV init ) and at the time of BT (GTV res ). GTV init is defined based on the information from the clinical diagram, clinical photograph and imaging at the time of diagnosis. MRI is helpful for the soft tissue extensions of the disease. Tumour marker clips at the 4 corners placed before starting EBRT are also useful for delineation of the GTV init on the BT planning CT scan. Image fusion with MRI and PET CT scan may also be considered for improving the target volume delineation. In patients who are considered for EBRT followed by BT fusion with preEBRT imaging such as CT scan, MRI and PETCT is especially useful. In the post EBRT scenario residual disease as evaluated under anaesthesia at the time of BT and as visualised on a post EBRT contrast imaging (CT/MRI) is considered as residual GTV (GTV res ). Clinical target volume (CTV) takes into account the microscopic extensions of the tumour in all directions and typically is grown