General principles of radiation therapy for head and neck cancer
- Wendy Hara, MD
Wendy Hara, MD
- Clinical Associate Professor, Department of Radiation Oncology
- Stanford University
- Shlomo A Koyfman, MD
Shlomo A Koyfman, MD
- Assistant Professor of Medicine
- Departments of Radiation Oncology and Bioethics
- Cleveland Clinic
- Section Editors
- Bruce E Brockstein, MD
Bruce E Brockstein, MD
- Section Editor — Cancer of the Head and Neck
- Clinical Professor of Medicine
- University of Chicago Pritzker School of Medicine
- David M Brizel, MD
David M Brizel, MD
- Section Editor — Radiation Therapy
- Leonard R Prosnitz Professor of Radiation Oncology
- Professor of Otolaryngology Head & Neck Surgery
- Duke University Cancer Institute
- Marshall R Posner, MD
Marshall R Posner, MD
- Section Editor — Cancer of the Head and Neck
- Professor of Gene and Cell Medicine
- The Tisch Cancer Institute
- Icahn School of Medicine at Mount Sinai
Radiation therapy (RT) is an important and potentially curative modality for head and neck cancers. For many primary sites within the head and neck, RT yields better functional outcomes than surgery and, thus, is often preferred for localized disease. For locoregionally advanced lesions, RT is often used in combination with chemotherapy as a definitive organ function-preserving approach, or after surgery as an adjuvant.
The general principles of RT for head and neck squamous cell carcinoma will be reviewed here. The approach to dose and schedule for definitive RT of head and neck cancer is discussed separately. (See "Definitive radiation therapy for head and neck cancer: Dose and fractionation considerations".)
Ionizing radiation produces its biologic effects by imparting energy to tissues. Free radicals are generated, which cause single-strand and double-strand DNA breaks and loss of cellular reproductive ability.
Some cells die relatively rapidly through apoptosis. However, most cells do not manifest evidence of damage until mitosis occurs, and several divisions may ensue before actual cell death (termed mitotic cell death). The cellular doubling time (typically three to five days for head and neck cancer) also influences the rapidity with which a tumor shrinks. For this reason, most tumors do not show immediate shrinkage after starting RT. While radioresponsive tumors start to shrink in a few days, most head and neck cancers may take weeks or longer to shrink. Some low-grade, slowly proliferating tumors histologically appear to be viable for prolonged periods after irradiation.
The radiation dose is measured in Gray (Gy), which is defined as the absorption of 1 joule of energy per kilogram of matter (water or human tissue). One Gy is equivalent to 100 centigray (cGy) or 100 rad (the formerly used unit of measure). As the radiation beam passes through tissue, its energy is absorbed; the higher the energy of the beam (expressed as megavoltage [MV]), the deeper it penetrates. The depth of tumor in the head and neck area is relatively shallow compared with many other visceral organs. Thus, the energy of the beam used for head and neck cancer treatment is usually lower compared with other visceral sites.
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- GENERAL PRINCIPLES
- EXTERNAL BEAM RADIATION THERAPY
- Linear accelerators
- Imaging for treatment planning and setup
- Three-dimensional conformal RT
- - Intensity-modulated RT
- - Image-guided RT
- - Image-guided adaptive radiation therapy
- - Stereotactic body radiation therapy
- - Charged particle radiation
- INTRAOPERATIVE RADIATION THERAPY
- INFORMATION FOR PATIENTS