Elective irradiation of the neck : a three-dimensional CT definition of the target for conformal radiotherapy

When no lymph node metastases are detected clinically in patients with head and neck cancer, the neck is staged as NO. The elective treatment of the NO neck, by either surgery or radiotherapy, results in excellent local control rates. This thesis specifically deals with the use of radiotherapy as a single modality treatment for the clinically negative neck. Given the risk of radiation-induced side effects, elective neck irradiation is advocated in many institutions only if the probability of subclinical disease is considered to be more than 10-20%. The major side effects of the elective irradiation of the neck are the dry mouth syndrome (xerostomia) and dental caries due to damage to the major and minor salivary glands. A major advance in radiotherapy in the last decade has been the development and clinical implementation of conformal radiotherapy. With the introduction of three-dimensional CT-based radiotherapy planning systems, it has become feasible to conform the high dose region to the target volume. In case of elective neck irradiation for example, high doses of radiation can be delivered to the neck with sparing of the salivary glands and other normal tissues such as the spinal cord. The main objective of this thesis is to provide a three-dimensional CT definition of the target of the NO neck which will indeed allow the design of conformal radiotherapy techniques for elective neck irradiation. It is defined and presented in such a way that it can be studied and verified interactively on CD-i. The second goal of this thesis is the development of conformal radiotherapy treatment plans and subsequently, to demonstrate the potential for reducing the side effects of elective neck irradiation by using such conformal techniques. The coverage of the three-dimensional NO neck target and the amount of sparing of the parotid (and submandibular) salivary glands can subsequently be studied interactively with a CD-i, using all CT-, MRI- and anatomical slices obtained from a human cadaver.