Following radiation therapy to the oral cavity, pharynx, or larynx, the mucous membranes can become erythematous within 1 week, and develop areas with white pseudomembranes (mucositis) at about 2 weeks.5 The patches of mucositis may coalesce by the third week.5 This acute mucosal reaction usually heals within 2 to 4 weeks following completion of radiotherapy, although ulceration and necrosis can occur.4 Late effects of radiation on the mucosa are characterized by thinning or atrophy of the epithelium, telangiectasia, dryness, a loss of mucosal mobility, submucosal induration, and occasionally chronic ulceration and necrosis.6 The mucosa is fragile and more susceptible than normal to mechanical injury.5 Edema is seen in the subcutaneous or submucosal soft tissue in the early phase following radiotherapy, can persist for 6 to 12 months,7 and can become chronic.3,8 Fibrosis, one of the most common delayed radiation-associated manifestations, usually appears in subcutaneous tissues within 6 to 12 months of treatment,5 although it can occur as early as 4 to 12 weeks.6 The fibrosis tends to be slowly progressive,5 nonhomogeneous, and variable in extent and severity from site to site.9 The severity of the fibrosis increases when high total doses of radiation and large fraction sizes are used.4 The risk of developing moderate to severe fibrosis has been reported to be about 40%.3 The affected soft tissue loses elasticity and subcutaneous fat6 and is indurated to palpation.1,6 In the presence of moderate to severe fibrosis, contracture of the tissues also occurs.1 In severe cases, the soft tissues develop a woody consistency and may form a hard mass fixed to skin and underlying muscle or bone (Figure 33-1).5 Obstructive lymphedema may also be associated with fibrosis.5 Radiation therapy to the neck can produce a limitation of neck extension (Figure 33-2).6,10 High-dose irradiation of metastatic cervical lymphadenopathy results in more subcutaneous fibrosis in the neck than does a comparable dose in the absence of palpable lymphadenopathy.5