Chapter 4

Radiation oncology is the discipline of medicine involving the use of ionizing radiation to treat malignant neoplasias. The radiation oncologist aims to deliver a precise dose of ionizing radiation to a defined tumor volume while minimizing damage to the surrounding normal structures. Due to the increasingly multidisciplinary nature of oncology, an understanding of radiation therapy is crucial to the surgeon involved in the combined-modality treatment of the patient with head and neck cancer.

### External Beam Radiation Therapy (Teletherapy)

Therapeutic ionizing radiation can be divided into two categories: high-frequency electromagnetic radiation (X-rays and γ-rays) and particulate radiation (electrons, neutrons, protons). The amount of radiation absorbed per unit mass of tissue is known as the absorbed dose. The most commonly used unit for absorbed dose is the gray (Gy), which is equivalent to one joule of energy absorbed per kilogram of tissue. One Gy is also equal to 100 cGy, or 100 rads (the previously used unit of absorbed dose).

In the head and neck, primary radiotherapy is most frequently delivered via a linear accelerator with 6-megavolt (MV) photons. Anatomic location and desired depth of penetration are the main criteria used in choosing which type and energy of external beam to employ. Less commonly employed forms of external beam radiotherapy (EBRT) include 6–20 MeV electron beams, 60Co γ-rays, and superficial (40–100 kV) or orthovoltage (250 kV) X-rays.

### Brachytherapy

Brachytherapy is a form of radiotherapy in which a radioactive source is placed inside or adjacent to the area requiring treatment. Selected radioisotopes contained within specialized instruments deliver radiation to the tumor or tumor bed at a short distance. The treatment may involve permanent implantation of the radiation source, or a temporary placement after which the source is withdrawn. Brachytherapy treatment can be delivered via interstitial implants (eg, base of tongue, neck, or tumor bed), intracavitary applicators (eg, recurrent nasopharyngeal cancer), or molds (eg, skin, ...

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

## Subscription Options

### AccessSurgery Full Site: One-Year Subscription

Connect to the full suite of AccessSurgery content and resources including more than 160 instructional videos, 16,000+ high-quality images, interactive board review, 20+ textbooks, and more.