Curative Radiotherapy - Head and neck cancers Radiation Therapy
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HNSCC responds to radiation injury through a loss of reproductive capability, resulting in a clonogenic rather than an interphase death. Within the context of a given fractionation schema, the amount of cell killing is essentially an exponential function of radiation dosage. Thus, for a given level of tumor control, the required radiation dose is approximately proportional to the number of clongenic cells in the tumor. In the context of a once-a-day treatment regimen with daily doses in the range of 180 to 200 cGy, subclinical microscopic disease requires a dose of approximately 5,000 cGy, a 1 cm tumor requires approximately 6,500 cGy, and large T3 or T4 tumors require approximately 7,000 to 7,500 cGy. Patients with head and neck tumors are generally treated with shrinking field techniques wherein the various regions at risk receive doses commensurate with the amount of tumor they are thought to contain.
In the past, dosages greater than 7,500 cGy required the use of interstitial radioactive implants to limit the doses received by adjacent normal tissues. Today, however, the use of IMRT and proton beam therapy also allows the clinician to achieve high tumor doses in a safe manner. The study by Laramore describes representative local control rates and survival data for patients with HNSCC treated with definitive radiotherapy delivered in a standard fractionation scheme. Local control rates are excellent for the early-stage tumors, but there is an obvious need for improvement in regard to the more advanced lesions. Hence, altered fractionation approaches and the concomitant use of chemotherapy and radiotherapy are topics of current research interest.
Introduction
Epidemiology
L Risk Factors
L Carcinogenesis
Anatomy
Pathologic Assessment
Diagnosis and Staging
Treatment
L Treatment by site
L Radiation Therapy
L Chemotherapy
Many factors affect the choice between radiotherapy and surgery as the primary definitive form of treatment. For early lesions of the larynx, the two modalities may yield equivalent locoregional control and survival, but radiation therapy is perceived to yield a better functional result, making it the treatment of choice. In certain cosmetically sensitive areas such as the lip or in early lesions of the nose or eyelid, radiation therapy gives a better ultimate result even after reconstructive surgery.
For tumors of the nasopharynx, a site that is surgically unapproachable, radiotherapy is the mainstay of treatment. Fortunately, nasopharyngeal tumors tend to be among the more sensitive of the HNSCCs. For early tumors of the tonsil and the base and lateral aspects of the tongue, the overall results between surgery and radiotherapy are approximately equivalent, and informed patient choice should guide the treatment management decision. Radiotherapy is also given following the diagnosis of SCC metastatic to cervical lymph nodes from an unknown primary head and neck site. The treatment fields encompass the probable sites of tumor origin (nasopharynx, tonsillar fossa, tongue base, and hypopharynx), with patient survivals at 2 to 3 years being in the range of 30% to 60%.
Revision date: July 5, 2011
Last revised: by Tatiana Kuznetsova, D.M.D.
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