Management of Xerostomia Related to Radiotherapy for Head and Neck Cancer

By
JONATHAN A. SHIP, DMD
Professor, Department of Oral
& Maxillofacial Pathology, Radiology, Medicine
Director, Bluestone Center for Clinical Research
New York University College of Dentistry
Professor
Department of Medicine
New York University School of Medicine
New York, New York | December 1, 2005

In 2005, an estimated 29,370 new cases of oral cavity and pharyngeal cancers were diagnosed in the United States, accounting for 2.14% of all cancer cases.[1] Over 7,000 individuals will die from these cancers in this country in 2005- approximately one death per hour. Many advances have been made in the diagnosis and treatment of these cancers, yet the mortality rate remains high (5-year survival rate of ~50%). Probably the most important approach is early detection, since early-stage tumors are associated with markedly better survival rates than late-stage cancers that have already spread to regional tissues and lymphatics. Treatment Sequelae
Treatment of oral and pharyngeal cancers generally consists of a combination of radiation therapy and surgery, with chemotherapy recently becoming an accepted treatment option.[2,3] The challenge of effective therapy is to eradicate metaplastic tissue while preserving, as much as possible, a person's quality of life. This requires a large multidisciplinary team of cooperating clinicians working together under extreme time constraints. The therapeutic modalities of surgery, radiotherapy, and chemotherapy cause a multitude of short- and long-term oral and pharyngeal sequelae that lead to an impaired quality of life.[4-6] The most common problems affecting the oral cavity are salivary hypofunction, xerostomia, and mucositis. Radiotherapy dosages in excess of 24 to 26 Gy can cause permanent salivary gland hypofunction,[ 7] and the addition of chemotherapy (eg, cisplatin(Drug information on cisplatin)) to external-beam radiotherapy is associated with grade 3 xerostomia.[2,3] Further oral and pharyngeal disorders include esophagitis, dysphagia, dysgeusia, oral and pharyngeal infections, dental caries, trismus, radiation dermatitis, facial/ esthetic compromises, and myalgia. Patients experience difficulties with phonation, mastication, wearing removable dental prostheses, and restricted head and neck muscular movements. Radiotherapy dosages in excess of 60 Gy to the mandible also increase the risk of patients developing osteoradionecrosis.[8] Management Strategies
The overall approach to the management of radiotherapy-induced salivary hypofunction and xerostomia involves a well-coordinated effort involving multiple health-care providers, starting with the initial diagnosis. Significant oral and pharyngeal adverse events can be reduced and sometimes even prevented if dentists, medical and radiation oncologists, nurses, dietitians, speech and swallowing experts, social workers, and other specialists can coordinate care throughout the course of diagnosis and multimodal therapy.[9,10] The first strategy involves frequent dental evaluations due to the prevalence of complications.[11] Maintenance of proper oral hygiene and hydration are essential, as well as ensuring a low-sugar diet and daily topical fluoride use to prevent dental caries.[12] Dry mucosal surfaces and dysphagia are managed with oral moisturizers, lubricants, and artificial saliva, as well as careful use of fluids during eating. If there are remaining viable salivary glands after radiotherapy (eg, if parotid-sparing techniques were used), stimulation using sugarfree chewing gums, candies, and mints can enhance salivary output.[13] Artificial saliva and lubricants may ameliorate some xerostomic symptoms and improve oral functioning.[14,15] Treating xerostomia with medications that enhance salivation is another therapeutic option for the individual who has sufficient remaining exocrine tissue following cancer-associated surgery and radiotherapy. Pilocarpine(Drug information on pilocarpine) is a nonselective muscarinic agonist that can improve salivary output and reduce xerostomic complaints when used following the completion of radiotherapy.[ 16,17] Alternatively, when pilocarpine was administered for xerostomia during radiotherapy, the drug was either not beneficial[18] or only modestly effective.[19] Cevimeline (Evoxac) is another muscarinic agonist used for the reduction of xerostomia in patients with Sjögren's syndrome[20,21] and has been suggested for radiotherapyinduced xerostomia.[22,23] It reportedly has a higher affinity for M1 and M3 muscarinic receptor subtypes.[24] Since M2 and M4 receptors are located on cardiac and lung tissues, cevimeline could enhance salivary secretions while minimizing adverse effects on pulmonary and cardiac function. Another approach is to consider concomitant polypharmacy. The majority of head and neck cancer patients are age 50 years or older,[25] and many are taking medications that cause salivary gland dysfunction.[12] Reducing the use of drugs associated with anticholinergic side effects or substituting with drugs that may have fewer xerostomic side effects is preferred. Furthermore, timing of medication use to avoid nocturnal xerostomia or dividing drug dosages to avoid unwanted side effects from a large single dose should be considered.[26] Over the past decade, there has been some interest in using acupuncture techniques to enhance salivation,[ 27-29] with data suggesting that acupuncture therapy can maintain an improvement in stimulated saliva up to 6 months after the completion of radiotherapy.[30] Preventive Techniques
One of the best hopes for treatment of these disorders is the use of preventive techniques. Salivary-sparing radiotherapy using three-dimensional treatment planning and dose-delivery techniques including intensity-modulated radiotherapy (IMRT) have proven successful in limiting radiation exposure to salivary glands, reducing salivary hypofunction and xerostomia, and preserving a person's quality of life.[31-33] There is an exponential relationship between saliva flow reduction and mean parotid dose for each gland,[34] demonstrating the exquisite sensitivity of salivary glands to radiation dosages. Importantly, it appears that reducing the dose to the salivary glands does not impair radiation efficacy with respect to tumors and lymph nodes considered to be at risk for cancer spread, and that long-term survival may not be reduced with these radiation-sparing techniques.[7,35] Prevention may also include a new category of cytoprotective drugs that could protect oral mucosal and salivary gland tissues during chemotherapy and head and neck radiotherapy. The most commonly used is amifostine(Drug information on amifostine) (Ethyol), a broad-spectrum cytoand radioprotectant that provides mucosal and organ protection against myelotoxicity, nephrotoxicity, mucositis, and xerostomia associated with various chemotherapy and radiotherapy modalities.[36,37] Amifostine used prior to each radiation treatment in head and neck cancer patients reduces the incidence of xerostomia,[ 38,39] and may prove to be useful for patients receiving IMRT[40] and combined radiochemotherapy.[ 41] Two surgical approaches may assist in the prevention of oral complications of cancer treatments. High- dose-rate intraoperative radiation therapy can deliver a large dose of radiation while the tumor bed is precisely defined, diminish toxicity, shorten overall treatment time, and reduce radiation dosages directly to salivary glands.[41-43] A second technique involves transferring a submandibular gland to the submental region, which can shield the gland from the damage induced by external- beam radiation.[44,45] Finally, new research in the field of gene therapy may make it possible to prevent damage to as well as correct already damaged salivary glands.[46-48] Transferring genes to salivary glands has been demonstrated in animal models. The close access to salivary gland cells via intraoral cannulation of the main excretory ducts permits relatively noninvasive delivery of vectors and gene transfer. With increased pathobiologic understanding and biotechnologic improvements, gene transfer could become a viable treatment modality.[49] Conclusions
In conclusion, the treatment of radiotherapy- induced salivary hypofunction and xerostomia requires a well coordinated approach using multiple health-care practitioners and techniques. With no single modality that has proven entirely efficacious, the best paradigm may involve concomitant treatments, such as salivarysparing radiotherapy, cholinergic agonists, cytoprotective agents, and gene therapy.

SHANNON T. KAHN, BS, MAC and PETER A.S. JOHNSTONE, MD, MA

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Management of Xerostomia Related to Radiotherapy for Head and Neck Cancer

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