This is a helpful reference paper that provides an overview of the biomolecular effects of radiation on the tissues of the upper aero-digestive tract. The authors explain that radiation injuries occur in a repetitive and accruing manner over the duration of treatment and may therefore heal differently from normal wound healing. Clinically these injuries may be classified as acute (less than three months), subacute (three to six months), or chronic (greater than six months) with the acute injuries mainly attributable to cell death and inflammatory processes and chronic effects related to vascular and connective tissue damage. Altering fraction size, dose and volume concentrations may alter the pathophysiology and is currently being explored in various clinical trials. Some patients recover well functionally from the acute effects of treatment, but may go on to develop late effects, while others who experience severe and protracted acute effects may achieve good resolution and recover good swallowing function after six months. Late effects may be consequential (originate from early mucosal reactions to radiotherapy) or generic (originate from direct damage to target tissue). Late dysphagia after radiotherapy may be due to either generic or consequential effects. The authors also summarise selected studies that examined the use of prophylactic swallowing exercises and provide useful commentary about the possible role of exercises in developing metabolic reserve in head and neck patients treated with radiotherapy. They conclude by highlighting gaps in our current understanding of how radiation changes affect swallowing function, and suggest directions for future research on this topic. 

Pathophysiology of radiation-induced dysphagia in head and neck cancer.
King SN, Dunlap NE, Tennant PA, Pitts T.
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Roganie Govender

University College London, Head & Neck Academic Centre, UK.

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