**3. Radiation techniques in head and neck cancers**

The treatment of head and neck cancer (HNC) using external beam radiotherapy is commonly done with three field techniques, which involves bilateral parallel opposed beams and one anterior lower neck field. Conventional treatment is based on 2D fluoroscopic images where there is no facility to shield the organs at risk like parotid [1]. The most common side effect of such conventional radiotherapy treatment is xerostomia. This damage to salivary glands causes a reduction in saliva, dryness of mouth, difficulty in chewing, and speech alterations [2, 3]. Dental caries, which results in impaired nutrition, weight loss and significant degradation of quality of life, so their management and prevention is important for radiotherapy. The incidence of radiotherapyrelated xerostomia varies depending on the specific radiotherapy technique used and the dose delivered to the parotid glands.

With the advancement in imaging and treatment planning techniques, CT-based conformal radiotherapy has come into existence which delivers radiation to the target with precision and gives minimal dose to the parotids. These techniques involve three-dimensional conformal radiotherapy (3D-CRT), intensitymodulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT). The evolution of imaging methods from 2D portals to 3D-CBCT (Cone beam CT) has established the role of image-guided radiotherapy in improving the inter and intra-fractional variations during Radiotherapy of HNC [4]. These high precision techniques have led to an improvement in dose distribution and significant sparing of OARs (in this case parotid) and reduction in radiation-induced xerostomia [1]. The various radiotherapy treatment planning techniques in HNC have been discussed here.
