Head and neck cancers usually refer to the neoplasms arising from below skull base to the region of thoracic inlet. Structures of the head and neck are responsible for various important functions like vision, hearing, smell, taste, deglutition and breathing. Any neoplasm arising from head and neck jeopardize these functions. The other important aspect is the cosmetic disturbance which affects the individual psychologically and physically.
Head and neck cancers constitute 5% of all cancers worldwide. It is more prevalent in countries like South East Asia, parts of Africa and South America and has low prevalence in U.S.A and Western Europe. In India head and neck cancer is the most common cancer seen in males in the O.P.D. The most common head and neck cancer is of oral cavity and pharynx. The age adjusted incidence in Indian males range from 10.8 to 38.8 per 1 lakh males and in Indian females from 6.4 to 14.9 per 1 lakh females. Overall male and female ratio being 4:1.Mouth and pharynx cancers stand as the third most common cancer in males and fourth most common cancer in females. They are usually seen in the fifth decade and above but salivary gland and nasopharynx tumor are seen at younger age groups.
Radiotherapy is a treatment modality largely used for head and neck malignancies. However high doses of radiation in large areas, including the oral cavity, maxilla, mandible and salivary glands may result in several undesired effects. Mucositis, candidiasis, dysgeusia, radiation caries, osteoradionecrosis, soft tissue necrosis and xerostomia are common radiation sequelae when higher doses are used. But with the advent of Linear Accelerators and using the technique of IMRT the incidence of these accompaniments can be drastically reduced.
Adverse effects of radiotherapy depend upon the volume and area being irradiated, on the total dose, on the fraction size, on the age, on the patient's clinical conditions and on associated treatments. A small increase in the tumor doses is enough for a significant increase on the complication incidence. Acute reactions happen during the treatment and most of the time, they are reversible. Late complications are normally irreversible, leading to permanent incapability and to a worsening of quality of life and they vary on intensity, being normally classified into mild, moderate and severe.
Many head and neck cancer patients are submitted to high doses of radiotherapy on large areas of radiation including the oral cavity, maxilla, mandible and salivary glands. Thus, anti-cancer therapy is associated with several adverse reactions. These reactions can occur in an acute stage (during or at the weeks right afer treatment) or in a chronic stage (months or years after radiotherapy). The severity of acute oral complications will depend on the inclusion degree of these structures on the radiated area.
Mucositis is defined as mucosal irritation. It starts developing after 3rd week of treatment in most of the patients but patients who are heavy smokers, diabetics or hypertensive it may start as early as 1st week. It is painful and leads to significant morbidity. It is usually controlled by pain killers and anti-inflammatory agents. Mucositis also leads to difficulty in swallowing which indirectly leads to improper food intake and weight loss.
Radiation patients are more prone to develops oral infections caused by fungi and bacteria. These patients have higher no. of microbial species esp. Lactobacillus species, Streptococcus aureus and Candida albicans. Oral candidiasis is a common infection in patients being treated for upper airways and digestive tract malignancies. Colonization of oral mucosa can be found in as many as 93% of these patients, whereas Candida infection can be found in 17-29% of patients submitted to radiotherapy. The possible explanation for such high incidence is decrease in salivary flow and reduced phagocytic activity of salivary granulocytes against these micro-organisms. Clinically, candidiasis can be seen both in its pseudomembranous and erythematous forms.
Dysgeusia affects patients from the second or third week of radiotherapy, and may last for several weeks or even months. It occurs because the taste buds are radiosensitive, with the degeneration of their normal histological architecture. The increase of salivary flow viscosity and the saliva biochemical alteration creates a mechanical barrier of saliva which makes it difficult the physical contact between the tongue and foodstuff. It recovers around 3-6 months after the end of radiation. Studies show that dysgeusia is a complaint by approximately 70% of patients submitted to radiotherapy, also implying in the loss of appetite and weight, being the most uncomfortable complication for most radiated patients.
Even patients, who had not experienced tooth decay for some time, may develop radiation caries when submitted to radiotherapy. The main factor for the development of such injuries is the decrease of saliva amount and its qualitative alterations. Besides, radiation has a direct effect on teeth, making them more susceptible to decalcification.
Osteoradionecrosis is a bone ischemic necrosis caused by radiation, being one of the most serious consequences of radiotherapy, causing pain as well as possible substantial loss of bone structure. In most of the cases osteoradionecrosis is associated with soft tissue necrosis also. This is aggravated by trauma such as tooth extraction after radiotherapy. Mandibles are more affected than maxillas.
Soft Tissue Necrosis
It is defined as ulcer located in radiated tissue, without the presence of residual malignancy. The occurrence of soft tissue necrosis is related to dose, time and volume of the radiated gland, when the brachytherapy is used, the risk is higher. Soft tissue necrosis is a normally painful condition and good oral hygiene together with the use of painkillers and often times, antibiotics, are necessary to manage the condition.
Xerostomia or dry mouth is the most long lasting morbidity of head & Neck radiation. It is usually caused by irradiation of both parotids. It causes several complications such as recurrent infections, inability to swallow solid foods, dental decay, taste loss, change in voice and speech and needs treatment with oral artificial saliva, taste stimulants and systemic agents such as pilocarpine or Bethanechol.
Prevention Of Oral Sequaelae : Using Technique Of Imrt
IMRT assigns non uniform intensities to tiny subdivisions of beams called rays or beamlets. These improved dose distributions lead to improved tumor control and less normal tissue toxicity. As IMRT requires the setting of relative intensities of tens of thousands of rays which cannot be done manually, it requires the use of specialized computer aided optimization methods. The biggest advantage of IMRT is in parotid sparing and spinal cord sparing.
Worldwide data in past 10 years has suggested IMRT to be the treatment of choice from Radiotherapy point of view. It spares the parotid glands and hence maintains salivary functions in majority of patients. It also leads to fewer doses to spinal cord and hence patient does not have radiation myelitis. Since it a localised treatment much of the soft tissues and bone can be kept out of the field leading to fewer or negligible incidence of soft tissue or osteoradionecrosis.