The Effects Of Radiation Therapy On Oral Health

Introduction

Radiation therapy (RT) is a type of cancer treatment that uses beams of intense energy to kill cancer cells. At high doses, radiation therapy kills cancer cells by damaging their DNA. Most radiation therapy uses x-ray, but there are other types of radiation therapy, like proton radiation.

Radiation therapy can be used alone or combined with other treatment options like chemotherapy or surgery, it can be recommended at different stages of the treatment:¹

• It can be used alone as primary treatment
• After surgery (adjuvant therapy) with chemotherapy or alone to remove any remaining cancer cells that could have been left out during surgery
• Before surgery (neoadjuvant therapy) with chemotherapy (chemoradiation), or after chemotherapy, to shrink the size of large cancers, which makes less invasive surgeries possible
• With targeted drugs, when chemotherapy and surgery are not recommended.
• Radiation therapy can be used at advanced stages of cancer to ease the symptoms and improve the quality of life (palliative radiotherapy)
• It can also be used for cases of recurrence, when cancer has come back after the treatment

According to the state of mouth UK report 2018/2019, oral cancer is the ninth most common cancer in the UK. There are 8,302 new cases every year and it accounts for just over 2% of all diagnosed cancer cases. Between 34% and 85% of head and neck cancer cases have radiotherapy as part of their treatment plan.²

Types of radiation therapy

There are mainly two types of radiation therapy: external beam and internal. The type of radiation therapy is decided based on several factors like: the size and location of the tumor, how close the tumor is to areas that are sensitive to radiation, and the general health and medical history of the patient.^{3 4}

External beam radiation therapy

The most common type of radiation treatment for oral cancer. It’s an outpatient procedure, where an outside of the body machine is used to send radiation beams to the tumor site. Proton radiotherapy is a type of external beam radiation therapy that uses protons instead of x-ray. There is also another type of external beam radiation called intensity modulated radiation therapy (IMRT) that aims at delivering effective doses of radiation to cancer cells without affecting healthy cells.

Internal radiation therapy

(Also called brachytherapy) is when implants are used to deliver radiation. This is an inpatient procedure, tiny rods of radioactive materials are surgically implanted in or near the cancer cells or tumor, the implant is left for a few days while patients are under supervision at the hospital.

Radiation therapy for head and neck cancer has been proven effective and with significant curing rate whether it was used alone or with other treatment modalities, but high doses of radiation used have a significant acute and chronic side effects as well due to the high turnover of the oral mucosal cells, diversity of the oral microflora, and trauma to the tissues during natural function. And that’s why multidisciplinary management is crucial before and during the radiation treatment, referral to dental professionals is very important for meticulous assessment and effective curative and preventative measures.

The degree, progression and severity of the side effects of radiation therapy vary depending on several factors:⁵

• The radiation doses
• The degree of vascularity and hypocellularity of the tissues
• The age of the patient at the beginning of the diagnosis

The effects of radiation therapy on the oral health can be divided based on their time of occurrence into acute and chronic, the acute adverse effects happen during or just after the radiation, while the chronic ones occur months or even years after the treatment.

There are many oral complications of radiation therapy but the most common side effects are:

Oral mucositis

Mucositis is the most common acute side effect caused by radiation therapy, almost all patients on radiation treatment suffer from mucositis. Young patients and patients with poor oral hygiene and inadequate nutritional intake suffer more incidences of mucositis. The condition is characterized by:

• Erythema (redness of the skin)
• Oedema (fluid retention)
• Ulceration of the oral mucosa

High doses of radiation lead to tissue damage and death of mucosal cells and impairment of their abilities to heal and divide leading to oral mucositis.

The severe pain caused by ulcers can impair the oral intake of food and patients may need hospitalization and insertion of a feeding tube. In severe cases of mucositis, doses of radiation may need to be altered or decreases resulting in poor prognosis.⁶

Salivary gland dysfunction

Salivary glands are usually affected by radiation therapy within one week of treatment. Despite all the efforts to prevent that, the close proximity of the glands to the treatment field leads to physiological dysfunctions and secondary adverse effects that impact the quality of life for cancer patients. The changes in salivary gland physiological functions during RT have been associated with loss of salivary glands acinar cells and glandular shrinkage, and the change of saliva composition due to that, considering that acinar cells are the main provider of water and proteins.^7,8

Radiation therapy induced salivary gland dysfunction results in:

• Hyposalivation (reduction in salivary flow rate by 50 to 60%)
• Xerostomia (sensation of oral dryness)
• Oral infections
• Mucositis
• Functional changes like difficulties in mastication and swallowing, and loss of taste

Radiation induced dental caries

The mechanism of radiotherapy induced dental caries can be explained in the following points:⁹

• Dental caries usually develop when the demineralization and remineralization process of the dental hard tissues are imbalanced, reduction of salivary gland flow caused by radiation treatment can lead to change in saliva composition and low saliva PH which affects the remineralization process of dental tissues
• Radiation can directly affect the dental hard tissues by weakening the enamel-dentin bond and causing demineralization
• Teeth in the radiation field can also be affected by decreased vascularity and low circulation which can cause dental caries

Radiation induced trismus

Trismus is the inability to open your mouth properly due to muscle spasm in the temporomandibular joint region. Radiation therapy is the most common cause of trismus for head and neck cancer patients. Unfortunately, there is no standard treatment for trismus, there are however several exercises methods and jaws mobilizing devices, but their efficacy for radiation induced trismus is still unknown.¹⁰

Osteoradionecrosis

This is the most serious side effect of head and neck radiation, defined as bone death due to radiation, the bone death is caused by decreased vascularity of the bone as a result of the radiation. It mostly affects the lower jaw(mandible), and rarely affects the upper jaw(maxilla).

The risk of developing osteoradionecrosis is high when radiation doses are higher and when the bone is exposed, it is also higher if patients need any dental treatment or extractions after the radiations, and that’s why a meticulous dental assessment is important before the start of radiotherapy.¹¹

Management of oral complications of radiation therapy

Oral assessment and regular follow-ups are very crucial before, during and after radiation treatment, several steps are required to prevent or minimize the side effects of radiation on the soft and hard tissues of the oral cavity. ¹²

Before radiotherapy

• Thorough assessment and applying of preventive treatments to teeth and oral mucosa

• Extraction of badly decayed and unrestorable teeth at least two weeks before the start of treatment to prevent osteoradionecrosis
• Patient education about proper oral hygiene measures is essential

During radiotherapy

• Treatment of hyposalivation by taking pilocarpine hydrochloride, a muscarinic agonist that stimulates secretion of saliva
• Non opioid interventions like mouthwashes and zinc supplements have been used to manage oral mucositis
• Patients are advised to follow up with a dental specialist at least every two weeks for gentle scaling and cleaning
• Dry mouth can be managed at home by staying dehydrated and drinking enough water, and lubricating the mouth with a solution of ½ tablespoon of baking soda in a cup of warm water
• Oral lidocaine is used to treat painful cases of oral ulcers and mucositis

After radiotherapy

• Regular dental visits for prevention and treatment of dental caries, and prevention of post radiation osteoradionecrosis
• Application of topical fluoride
• Use of chlorhexidine mouthwash to reduce the cariogenic bacteria
• Nutritional counseling and following a healthy diet is important to limit the consumption of cariogenic food

Summary

Radiation therapy is one of the most effective treatments of head and neck cancer, external beam radiation and brachytherapy are the main types used for oral cancer, they aim to target and kill cancer cells, but they affect and damage the surrounding healthy tissues despite all precautions taken to prevent that.

The most common adverse effects during radiotherapy are: mucositis and oral infections, decreased salivary gland flow and dysfunction, dental caries, trismus and osteoradionecrosis.

Effective management of oral health is crucial before, during and after radiotherapy, to ensure all existing dental problems are dealt with and preventive measures are applied before the start of radiation treatment, it is also important to educate the patients about proper oral hygiene practices and the importance of regular follow ups.