Radiation Therapy

An overview of radiation and why you will see a dentist

Radiation therapy (sometimes abbreviated to XRT) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). Radiotherapy may be used for curative or adjuvant (enhancing the action of a medical treatment) cancer treatment. Radiotherapy is used for the treatment of malignant tumors (cancer), and may be used as the primary therapy. It is also common to combine radiotherapy with surgery, chemotherapy, hormone therapy or some mixture of the three. Most common cancer types can be treated with radiotherapy in some way. The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or palliative) will depend on tumour type, location, and stage, as well as the general health of the patient.

Radiation therapy is commonly applied to the cancerous tumour. The radiation fields (the amount of tissue to be treated ) may also include the draining lymph nodes if they are clinically or radiologically involved with tumour, or if there is thought to be a risk of subclinical malignant spread. It is necessary to include a margin of normal tissue around the tumour to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, breathing).

To try to spare normal tissues (such as skin, saliva glands or organs which radiation must pass through in order to treat the tumour), shaped radiation beams are aimed from several angles of exposure to intersect at the tumour, providing a much larger absorbed dose there than in the surrounding, healthy tissue.

Radiation therapy works by damaging DNA of cancer cells.

The amount of radiation used in radiation therapy is measured in gray (Gy), and varies depending on the type and stage of cancer being treated. For curative cases, the typical dose for a solid epithelial tumor (most head and neck cancers) ranges from 60 to 80 Gy, while lymphoma tumors are treated with 20 to 40 Gy.

The total dose is fractionated (spread out over time) for several important reasons. Fractionation allows normal cells time to recover, while tumor cells are generally less efficient in repair between fractions. In North America, Australia, and Europe, the typical fractionation schedule for adults is 1.8 to 2 Gy per day, five days a week.

In some cases, two fractions per day are used near the end of a course of treatment. This schedule, known as a concomitant boost regimen or hyperfractionation, is used on tumors that regenerate more quickly when they are smaller. In particular, tumors in the head-and-neck demonstrate this behavior.

Before treatment, a CT scan is often performed to identify the tumor and surrounding normal structures. The patient is then sent for a simulation so that molds can be created to be used during treatment.

Radiation is delivered in many different ways; two that are highlighted are conventional external beam radiotherapy and Intensity Modulated Radiation Therapy.

Conventional external beam radiotherapy (2DXRT) is delivered via two-dimensional beams using linear accelerator machines. 2DXRT mainly consists of a single beam of radiation delivered to the patient from several directions: often front or back, and both sides.

Intensity-Modulated Radiation Therapy (IMRT) is an advanced type of high-precision radiation. Computer-controlled x-ray accelerators distribute precise radiation doses to malignant tumors or specific areas within the tumor. The radiation dose is consistent with the 3-D shape of the tumor by controlling, or modulating, the radiation beam’s intensity. The radiation dose intensity is elevated near the gross tumor volume while radiation among the neighboring normal tissue is decreased or avoided completely. The customized radiation dose is intended to maximize tumor dose while simultaneously protecting the surrounding normal tissue. This may result in better tumor targeting, lessened side effects, and improved treatment outcomes.

Radiation therapy is in itself painless. Treatment to higher doses causes varying side effects during treatment (acute side effects), in the months or years following treatment (long-term side effects), or after re-treatment (cumulative side effects). The nature, severity, and longevity of side effects depends on the organs that receive the radiation, the treatment itself (type of radiation, dose, fractionation, concurrent chemotherapy), and the patient.

Most side effects are predictable and expected. Side effects from radiation are usually limited to the area of the patient's body that is under treatment. One of the aims of modern radiotherapy is to reduce side effects to a minimum, and to help the patient to understand and to deal with those side effects which are unavoidable.

Acute side effects

Typically the skin starts to become pink and sore several weeks into treatment. The reaction may become more severe during the treatment and for up to about one week following the end of radiotherapy, and the skin may break down. Although this moist desquamation is uncomfortable, recovery is usually quick. Skin reactions tend to be worse in areas where there are natural folds in the skin, such as underneath the female breast, behind the ear, and in the groin.

If the head and neck area is treated, temporary soreness and ulceration commonly occur in the mouth and throat. If severe, this can affect swallowing, and the patient may need painkillers and nutritional support/food supplements. A feeding tube may be placed temporarily if the patient cannot swallow

Tissues which have been irradiated tend to become less elastic over time due to a diffuse scarring process. This can affect the ability to open the mouth as the jaw joint may be affected.

Dryness

The salivary glands and tear glands have a radiation tolerance of about 30 Gy in 2 Gy fractions, a dose which is exceeded by most radical head and neck cancer treatments. Dry mouth (xerostomia) and dry eyes (xerophthalmia) can become irritating long-term problems and severely reduce the patient's quality of life. Xerostomia can lead to rampant decay of all remaining teeth over a short time.

Fatigue

Fatigue is among the most common symptoms of radiation therapy. Lack of energy, reduced activity and overtired feelings are common symptoms.

Why does the patient see a dentist before and after Head and Neck Radiation?

To rule out any underlying dental infections that could delay or compromise radiation treatment. This is done by a thorough history, clinical exam and radiological investigation (dental x-rays of jaws and teeth)
To remove abscessed or compromised teeth before the mold is made so that facial contour is not changed; as the mold is a very precise fitting appliance. In addition, the removal of infected teeth before radiation reduces the possible formation of a radiation induced bone necrosis called osteoradionecrosis.
To improve the health of the oral cavity so as to minimize radiation induced discomfort.
To salvage the dentition from xerostomia induced decalcification cavities by starting a daily life-long application of fluoride onto the teeth
To monitor the patient closely during and after radiation with the plan to eventually refer the patient back to his family dentist for follow-up care.
Extractions, dental implants or periodontal surgery should not be considered after radiation without consulting the cancer centre’s dentists and radiation oncologists.