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Radiation Therapy

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what is radiation therapy?

Last reviewed: October 4, 2026

Introduction

Radiation therapy is one of the main treatments for head and neck cancer. It may be the only treatment for an early cancer, it is often combined with chemotherapy for more advanced cancers, and it is frequently given after surgery to lower the chance of the cancer returning [1]. Modern techniques shape the radiation closely around the tumor, which has substantially reduced long-term dry mouth compared with older methods [2].

Radiation works over weeks and its effects on normal tissue continue for months and years, so what a patient does during and after treatment matters: swallowing and jaw exercises, dental care and fluoride, and follow-up for thyroid function and other late effects [3, 4]. The sections below explain how radiation is given, its side effects and how to limit them. A numbered reference list is at the end of the page.

The most common type of radiation therapy, called external beam radiation therapy is a form of cancer treatment in which ionizing radiation (usually high-energy x-rays, called photons, and sometimes electrons or protons) is directed at a cancer to impair the cancer’s ability to survive. Radiation therapy treatment for head and neck cancers is usually administered once or sometimes twice daily over several weeks, Monday through Friday. Each treatment may take only a few minutes. The ionizing radiation is directed at the carefully defined three dimensional cancer target by multiple beams. Tissue in the path of these beams incur damage to DNA. The DNA damage incurred by a cancer is generally greater than that of non-cancerous tissue. An additional method of sparing normal tissues (such as skin or organs which radiation must pass through to treat the tumor), is to use shaped radiation beams aimed from several angles to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding healthy tissue. Besides the tumour itself, the radiation fields may also include the draining lymph nodes if necessary. The high dose radiation field extends around the cancer to include a margin of normal tissue to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, swelling or swallowing motion) and movement of external skin marks relative to the tumor position.

Dose and schedule

For most head and neck cancers treated with radiation, the tumor and involved lymph nodes receive about 70 Gy (gray, the unit of absorbed dose) in 35 daily treatments of 2 Gy, five days a week for about seven weeks; areas at lower risk receive a smaller dose. After surgery the dose is usually 60 to 66 Gy [1]. Altered schedules, such as twice-daily treatment (hyperfractionation), improved five-year survival by about 8 percentage points compared with standard once-daily radiation in a meta-analysis of 33 trials, but this benefit was seen when radiation was given without chemotherapy, and altered schedules were not better than standard radiation combined with chemotherapy [5]. Adding chemotherapy at the same time as radiation improves survival for advanced cancers [6] (see chemotherapy and immunotherapy).

IMRT and proton therapy

Intensity-modulated radiation therapy (IMRT) shapes many small beams of varying strength to match the tumor and avoid nearby structures such as the salivary glands, spinal cord and inner ears. In the PARSPORT trial, moderate or worse dry mouth two years after treatment affected 29% of patients treated with parotid-sparing IMRT compared with 83% treated with conventional radiation, and saliva and quality of life recovered better with IMRT [2]. IMRT is now the standard technique [1].

Proton therapy deposits most of its energy at a set depth, with little dose beyond the target. In a randomized trial of 440 patients with oropharyngeal cancer, intensity-modulated proton therapy controlled the cancer as well as IMRT, and five-year overall survival was 90.9% compared with 81.0% [7]. Protons are not available everywhere, and their role is still being defined for other head and neck sites; they are most often considered for tumors near the eyes, skull base or brain [1].

Other types of radiation therapy include temporary implants of radioactive material into the cancer (called brachytherapy) and oral administration of a radioactive medicine (such as radioactive iodine used to treat thyroid cancer).

Radiation therapy is administered under the care of a Radiation Oncologist, and in the case of radioactive iodine, sometimes by a Medical Oncologist. Note that there are some benign conditions treated with radiation therapy as well.

• National Cancer Institute’s brochure on radiation therapy

minimizing side effects of radiation therapy to the head or neck

The side effects with greatest long-term consequence for head and neck radiation involve the swallowing mechanism, saliva production, dental decay, and loss of range of motion of the jaw and neck. Minimizing major long-term side effects on tissue mobility requires active, effortful, and deliberate movement by the patient during and after the course of radiation therapy. It comes down to “use it or lose it.” Tissue forms scar after injury, including the injury from radiation dose passing through normal tissue on the way to the cancer target. Starting some weeks after radiation begins, and continuing months after radiation ends, stiff scar tissue (fibrosis) gradually develops in tissues exposed to radiation. The tongue, throat muscles, jaw joint, and neck muscles are all potentially susceptible to slowly, insidiously losing their mobility and pliability. A throat that cannot contract and relax muscles to transport food to the esophagus will not swallow effectively or safely. A jaw joint that gets stiff will lead to lock jaw (trismus). And a neck that freezes up prevents normal head turning and posture. Avoiding these problems with immobile muscles requires frequent intentional movement during and after the course of radiation to maintain pliability and avoid long-term loss of function. Involving a speech pathologist for instruction on specific exercises to perform to maintain swallow ability and jaw movement helps greatly. Placement of a gastric feeding tube through the abdominal wall is a common consideration. Neck range of motion may also benefit from a physical therapist’s instruction. During and after radiation therapy, a patient has fatigue and a sore throat and often wishes to simply rest to recover. This is a mistake! Active, effortful, diligent movement exercises, including swallowing frequently despite the pain, is essential to avoid long-term problems.

Side effects during treatment

Most side effects build up over the course of treatment, peak near the end and improve over several weeks afterward [1]:

Mouth and throat soreness (mucositis) affects nearly everyone treated to the mouth or throat, usually starting in the second or third week, and is more severe with chemotherapy (see mucositis).
Skin redness and peeling in the treated area.
Loss of taste and thick saliva or dry mouth; taste usually recovers partly over months (see xerostomia).
Pain with swallowing and weight loss. Nutrition is monitored weekly, and a feeding tube may be needed if weight loss or dehydration cannot be controlled [1].
Fatigue.

Other long-term effects

Narrowing of the carotid arteries. Radiation to the neck can gradually narrow the carotid arteries. In a study of 628 patients, about 30% had narrowing found on imaging and 10% had symptomatic narrowing (such as a stroke or mini-stroke) within ten years, with risk related to the dose the artery received [8]. Control of blood pressure and cholesterol, not smoking, and sometimes ultrasound surveillance are recommended [4].
Hearing loss, especially when the inner ear receives a high dose or cisplatin is given, and stiffness of the neck and jaw (trismus), as described above [4].
Second cancers. Survivors remain at risk for a new cancer of the head and neck, lungs or esophagus, mostly related to tobacco and alcohol, which is one reason for lifelong follow-up [4].

Dental preparation for radiation therapy

If the target cancer is near the mouth, it is essential for the patient to have their teeth evaluated and possibly treated by a dentist specifically for the purpose radiation therapy before starting radiation. The reason for this is that radiation accelerates dental decay and decreases the blood flow and healing ability of the jaws and teeth. If a tooth is anything less than healthy, radiation to this tooth will likely cause the tooth to develop decay, fracture, and die. This is called osteoradionecrosis. Pulling the tooth may be necessary, but after radiation, a tooth socket will not heal well, and the bone may remain exposed. This bone, which heals poorly from the effects of radiation, then can become infected, die, and then fracture. This situation may require significant undertakings of surgery and hyperbaric oxygen, antibiotics and other medicines in an attempt to heal the jaw. It is far safer to have any teeth requiring fillings or extraction to be done prior to radiation therapy. Since it takes about two weeks after any tooth extraction for the normal tooth socket to heal over, seeing a dentist and arranging any needed work must be done as expediently as possible once radiation therapy is chosen.

The 2024 guideline from the International Society of Oral Oncology, the Multinational Association of Supportive Care in Cancer and ASCO on osteoradionecrosis recommends [3]:

A dental examination with X-rays before radiation, ideally by a dentist experienced with cancer patients.
Removal of teeth with a poor long-term outlook in the high-dose area before radiation, ideally at least two weeks before it starts, without delaying cancer treatment.
Daily high-concentration fluoride, often applied with custom trays, for life, along with careful brushing and flossing.
Regular dental visits after radiation, and telling the treating team before any later extraction or oral surgery in the treated area.

Radiation planning that limits the dose to the jaw also lowers the risk [3].

Lymphedema

Lymphedema is the condition of swelling (edema) of tissue relating to insufficient clearance by the lymphatic system. It can occur after treatment, either surgical, radiation, or both. New drainage pathways develop over time, but treatments such as manual lymphatic drainage performed by a physical therapist or a home-use device speed up and improve clearance of lymphedema. When severe and untreated, lymphedema can constrain movement, which can allow scar tissue to develop and limit movement permanently.

• Link to an article explaining lymphedema and its treatment from the American Head and Neck Society website.

Swelling of the face, under the chin or in the neck after head and neck cancer treatment is common and often underrecognized. The American Cancer Society survivorship guideline recommends that survivors be assessed for lymphedema and fibrosis and referred to a therapist trained in lymphedema care, whose treatment combines manual lymphatic drainage, compression, exercises and skin care [4]. More information is on the lymphatics and lymph nodes page.

Hypothyroidism

Hypothyroidism may occur after radiation exposure to the thyroid. For radiation fields that include the thyroid, which is the case for the treatment of many head and neck cancers, monitoring for hypothyroidism is undertaken. The time frame in which hypothyroidism may occur is three years after the completion of radiation. If hypothyroidism sets in, treatment involves use of thyroid hormone, which is available in pill form.

In a prospective study of 105 patients whose neck was treated with radiation, 33% developed an underactive thyroid within two years. The risk was higher with a higher average dose to the thyroid and a smaller thyroid gland [9]. The American Cancer Society survivorship guideline recommends checking thyroid-stimulating hormone (TSH) every 6 to 12 months after radiation to the neck [4]. Symptoms of an underactive thyroid, such as tiredness, feeling cold, weight gain and constipation, overlap with the after-effects of cancer treatment, so blood tests are more reliable than symptoms.

Summary

Radiation for head and neck cancer is usually given daily over six to seven weeks, alone, with chemotherapy, or after surgery [1].
IMRT reduces long-term dry mouth compared with older techniques; proton therapy is an option in some situations [2, 7].
Swallowing and jaw exercises during and after radiation help prevent stiffness and long-term swallowing problems [1].
A dental evaluation before radiation and lifelong fluoride lower the risk of osteoradionecrosis [3].
Thyroid function should be checked every 6 to 12 months, and survivors need follow-up for lymphedema, carotid artery narrowing and second cancers [4, 9, 8].

References

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Head and Neck Cancers. Version 2.2026. nccn.org
Nutting CM, Morden JP, Harrington KJ, et al. Parotid-sparing intensity modulated versus conventional radiotherapy in head and neck cancer (PARSPORT): a phase 3 multicentre randomised controlled trial. Lancet Oncol. 2011;12(2):127-36. doi:10.1016/S1470-2045(10)70290-4 PubMed 21236730
Peterson DE, Koyfman SA, Yarom N, et al. Prevention and Management of Osteoradionecrosis in Patients With Head and Neck Cancer Treated With Radiation Therapy: ISOO-MASCC-ASCO Guideline. J Clin Oncol. 2024;42(16):1975-1996. doi:10.1200/JCO.23.02750 PubMed 38691821
Cohen EE, LaMonte SJ, Erb NL, et al. American Cancer Society Head and Neck Cancer Survivorship Care Guideline. CA Cancer J Clin. 2016;66(3):203-39. doi:10.3322/caac.21343 PubMed 27002678
Lacas B, Bourhis J, Overgaard J, et al. Role of radiotherapy fractionation in head and neck cancers (MARCH): an updated meta-analysis. Lancet Oncol. 2017;18(9):1221-1237. doi:10.1016/S1470-2045(17)30458-8 PubMed 28757375
Lacas B, Carmel A, Landais C, et al. Meta-analysis of chemotherapy in head and neck cancer (MACH-NC): An update on 107 randomized trials and 19,805 patients, on behalf of MACH-NC Group. Radiother Oncol. 2021;156:281-293. doi:10.1016/j.radonc.2021.01.013 PubMed 33515668
Frank SJ, Busse PM, Lee JJ, et al. Proton versus photon radiotherapy for patients with oropharyngeal cancer in the USA: a multicentre, randomised, open-label, non-inferiority phase 3 trial. Lancet. 2026;407(10524):174-184. doi:10.1016/S0140-6736(25)01962-2 PubMed 41391462
Carpenter DJ, Patel P, Niedzwiecki D, et al. Long-term risk of carotid stenosis and cerebrovascular disease after radiation therapy for head and neck cancer. Cancer. 2025;131(1):e35089. doi:10.1002/cncr.35089 PubMed 37897711
Boomsma MJ, Bijl HP, Christianen ME, et al. A prospective cohort study on radiation-induced hypothyroidism: development of an NTCP model. Int J Radiat Oncol Biol Phys. 2012;84(3):e351-6. doi:10.1016/j.ijrobp.2012.05.020 PubMed 22717243

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