Introduction

Post-treatment imaging is carried out when a recurrent tumor is suspected, to confirm the presence of such a lesion and to determine its extent. The extent of a recurrent cancer is important information for determining the possibility of salvage therapy.

Imaging may also be used to monitor tumor response and to try to detect recurrent or persistent disease before it becomes clinically evident, possibly with a better chance for successful salvage. However, early tumor recurrence may be difficult to distinguish from tissue changes induced by therapy. Therefore, the expected changes on imaging studies after treatment of a head and neck cancer should be clearly understood when analyzing images.

Treatment complications are less frequent than tumor recurrences, but these conditions may sometimes be clinically difficult to distinguish. Although definitive distinction between treatment-induced necrosis and recurrent tumor may also be difficult radiologically, imaging findings may be helpful in guiding treatment and assessing response to specific treatment.

Expected tissue changes after radiotherapy

The changes visible on post-treatment computed tomography (CT) and magnetic resonance imaging (MRI) depend on the radiation dose and rate, the irradiated tissue volume and the time elapsed since the end of radiation therapy. Changes which may be seen include (Fig. 8.1):

• thickening of the skin and platysma muscle

• reticulation of the subcutaneous fat and the deep tissue fat layers

• edema in the retropharyngeal space

• increased enhancement of the major salivary glands, followed by size reduction of these glands: postirradiation sialadenitis

• atrophy of lymphatic tissue, in both the lymph nodes and Waldeyer's ring

• […]