Limitations in Dose Specification of Brachytherapy Combined With External Beam Irradiation

Technological progress in brachytherapy has fostered expanded use of interstitial or intracavitary implants combined with external beam radiotherapy in the management of many malignant neoplasms. However, the methodologies of brachytherapy and teletherapy have developed rather independently and attempts to identify conceptual and practical approaches for combining external beam irradiation with brachytherapy represent a fairly recent effort in the development of radiation therapy. Only with the advent of supervoltage and megavoltage equipment after 1950 was there evolution towards the radiobiological rationale on which modern radiotherapy is based. Large empirical clinical experiences have been the basis for developing operation approaches for combining external beam with either interstitial or intracavitary brachytherapy for a wide range of specific clinical problems. These empirical approaches, combined with the lack of universal agreement on dose specification and reporting methods for brachytherapy, as well as the lack of relevant laboratory studies, are impediments to integrating the two modalities at the clinical level. The intent of this article is to examine some of the complex historical, physical, and radiobiological considerations contributing to a dichotomy that impedes effective comparison of the clinical results of such combined approaches.