An evaluation of absorbed doses of high energy electromagnetic radiation in radiotherapy of laryngeal cancer.

When 60Co gamma rays or high-energy X-rays are externally applied to treat laryngeal cancer, the absorbed dose at the laryngeal lumen is lower than given dose because of air space, which it should pass through, before reaching the lesion. Specially in case of high-energy X-rays, the loss of dose is considerable. Thus, the influence of the laryngeal air space on radiation dose was studied for 60Co gamma rays, 6MV X-rays and 10MV X-rays by thermoluminescent dosimetry using neck phantoms having an air cavity in the upper air way. At the anterior commissure, absorbed dose are apt to be reduced with 6MV and 10MV more than 60Co, but it is not affected by field size or anterior neck angle. In the vocal cord, the doses of 6MV and 10MV decrease in proportion to field size. In the posterior commissure, the reduction in dose varies according field size and anterior neck angle, but it is not related with radiation energy. From the above results, it is concluded that 60Co is the most suitable for radiotherapy of laryngeal cancer of these three rays, and, when high-energy X-rays above 6MV are applied, the loss of dose more than 60Co in the anterior commissure and the vocal cord should be taken into account.