Residency · Residency · Otolaryngology

Radiation Effects on Head and Neck Tissues

Introduction

Radiation therapy (RT) is a cornerstone of head and neck cancer treatment, used as definitive therapy, adjuvant therapy, or in combination with chemotherapy. While effective for tumor control, radiation causes significant acute and chronic effects on the normal tissues of the head and neck. Understanding these effects is critical for the otolaryngologist who manages patients before, during, and long after radiation treatment.

Principles of Radiation Biology

Mechanisms of Cellular Injury

Direct damage: ionizing radiation breaks DNA double strands, leading to cell death or mitotic failure. Indirect damage: radiation generates free radicals (reactive oxygen species) from water molecules that damage DNA and cellular structures. Rapidly dividing cells (mucosa, bone marrow) are most susceptible to acute effects. Slowly dividing cells (connective tissue, endothelium) manifest late effects.

Treatment Parameters

Total dose: typically 60-70 Gy for definitive treatment; 60-66 Gy for adjuvant. Fractionation: standard fractionation is 2 Gy/fraction, 5 days/week over 6-7 weeks. Intensity-modulated radiation therapy (IMRT): allows dose shaping to minimize exposure to critical structures (parotid glands, spinal cord, brainstem, optic structures). Proton therapy: Bragg peak allows precise dose deposition with reduced exit dose; emerging for sinonasal and skull base tumors.

Acute Effects (During and Shortly After Treatment)

Mucositis

Inflammation and ulceration of the oropharyngeal mucosa. Occurs at approximately 2 weeks into treatment; peaks at weeks 4-6. Grading: WHO Grade 1 (erythema) to Grade 4 (inability to eat or drink). Confluent mucositis is the most common cause of treatment breaks and hospitalization. Management: oral hygiene, bland rinses (baking soda/salt water), topical analgesics (magic mouthwash), systemic pain control, PEG tube for nutrition if needed.

Dermatitis

Erythema, desquamation (dry then moist), and potential ulceration of irradiated skin. Management: gentle skin care, aqueous cream, avoidance of irritants, silver sulfadiazine for moist desquamation.

Acute Salivary Gland Dysfunction

Rapid decline in salivary output within the first week. Serous acinar cells (parotid) are more radiosensitive than mucous cells. Leads to thick, tenacious saliva.

Taste Disturbance (Dysgeusia)

Loss or alteration of taste; occurs early and may persist for months. Taste buds on the anterior tongue are affected when included in the radiation field. Partial recovery is common; full recovery occurs in 60-80% by 12 months.

Laryngeal Edema

Swelling of the supraglottic and glottic mucosa, May compromise the airway; can persist for months. Management: voice rest, anti-reflux measures, corticosteroids; tracheotomy if severe.

Late Effects (Months to Years After Treatment)

Xerostomia

Most common long-term side effect of head and neck radiation. Permanent damage to salivary gland acini at doses >26 Gy (mean parotid dose). IMRT has significantly reduced xerostomia by sparing the contralateral parotid. Consequences: difficulty swallowing, speaking, and eating; increased dental caries; oral candidiasis; reduced quality of life. Management: frequent sips of water, saliva substitutes, sialagogues (pilocarpine 5 mg TID, cevimeline), meticulous dental care. Amifostine: free radical scavenger; FDA-approved for reduction of xerostomia; limited use due to side effects (nausea, hypotension).

Radiation Caries

Accelerated dental decay from xerostomia and altered oral flora. Prevention: daily fluoride trays (lifelong), regular dental evaluations, meticulous oral hygiene. Extraction of non-restorable teeth before radiation to avoid osteoradionecrosis.

Osteoradionecrosis (ORN)

Ischemic necrosis of irradiated bone (most commonly the mandible). Results from radiation-induced hypovascular, hypocellular, hypoxic tissue. Risk factors: dose >60 Gy, dental extractions after RT, poor oral hygiene, tobacco use. Presentation: exposed bone, pain, pathologic fracture, fistula formation. Management: conservative (antibiotics, debridement, pentoxifylline + vitamin E); advanced cases require free flap reconstruction (fibula or scapula). Prevention: pre-radiation dental evaluation and extraction of at-risk teeth; avoid post-radiation extractions when possible; if extraction is necessary, use atraumatic technique with antibiotics and possibly hyperbaric oxygen.

Fibrosis

Progressive fibrosis of skin, subcutaneous tissue, and muscles. Trismus: fibrosis of the masticator muscles and TMJ; incidence 5-38%. Prevention and management: jaw-stretching exercises (TheraBite) during and after treatment. Cervical fibrosis: woody induration of the neck; may limit future surgical options.

Dysphagia and Aspiration

Fibrosis of the pharyngeal constrictors, tongue base, and larynx. Pharyngoesophageal stricture: progressive dysphagia months to years after RT. Management: swallowing therapy (started prophylactically during RT), esophageal dilation, PEG tube. Chronic aspiration may necessitate laryngeal closure or total laryngectomy in severe cases.

Hypothyroidism

Incidence: 20-50% after neck radiation (dose-dependent). From direct gland damage and vascular injury. Screen with TSH every 6-12 months after treatment; lifelong monitoring. Treatment: levothyroxine replacement.

Hearing Loss

From radiation to the temporal bone and cochlea. Sensorineural hearing loss (cochlear damage) and conductive hearing loss (serous otitis media from Eustachian tube dysfunction). Serous effusion is common during and after treatment; may require myringotomy tubes.

Carotid Stenosis

Radiation-accelerated atherosclerosis of the carotid arteries. Occurs years after treatment; significantly increases stroke risk. Screening with carotid duplex ultrasound recommended 2 years post-RT and periodically thereafter.

Secondary Malignancy

Radiation-induced malignancies may occur 10-20 years after treatment. Risk of sarcoma (osteosarcoma, fibrosarcoma) in the irradiated field. Thyroid cancer risk in patients radiated during childhood. Low overall incidence but important for long-term surveillance.

Radiation in the Reirradiation Setting

Retreatment of recurrent head and neck cancer with radiation carries significantly increased toxicity. Cumulative dose to critical structures (spinal cord, brainstem, optic pathways) limits retreatment. Hyperfractionation and IMRT may reduce late effects. Careful patient selection and multidisciplinary planning essential.

Key Clinical Pearls

Pre-radiation dental evaluation is mandatory; extract non-restorable teeth at least 2-3 weeks before starting RT to reduce ORN risk. IMRT has dramatically reduced xerostomia by sparing the contralateral parotid gland — mean parotid dose <26 Gy preserves function. Hypothyroidism is common and often overlooked; screen TSH every 6-12 months for life. Jaw-stretching exercises should begin during radiation to prevent trismus, not after it develops. Post-radiation dental extractions carry a significant risk of ORN; use atraumatic technique and consider hyperbaric oxygen for mandibular extractions in high-dose fields. Carotid stenosis screening should be performed starting 2 years after radiation.

References

1. Strojan P, Hutcheson KA, Eisbruch A, et al. Treatment of late sequelae after radiotherapy for head and neck cancer. Cancer Treat Rev. 2017;59:79-92.
2. Eisbruch A, Harris J, Garden AS, et al. Multi-institutional trial of accelerated hypofractionated intensity-modulated radiation therapy for early-stage oropharyngeal cancer. Int J Radiat Oncol Biol Phys. 2010;76(5):1333-1338.
3. Lyons A, Ghazali N. Osteoradionecrosis of the jaws: current understanding of its pathophysiology and treatment. Br J Oral Maxillofac Surg. 2008;46(8):653-660.
4. Machtay M, Moughan J, Trotti A, et al. Factors associated with severe late toxicity after concurrent chemoradiation for locally advanced head and neck cancer. J Clin Oncol. 2008;26(21):3582-3589.

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