Three-dimensional irradiation planning of laryngeal and hypopharyngeal tumours

Three-dimensional dose distributions were computed for the photon radiation therapy of laryngeal and hypopharyngeal cancers, using conventional moving fields: biaxial and eccentric rotations. Treatment plans obtained under various irradiation conditions with a 15 MeV linear accelerator are analyzed and compared. Satisfactory and homogeneous dose delivery to the tumour, and sufficient protection of the myelon can be acheived with both treatment techniques. The eccentric plan is somewhat superior to the biaxial one. Simulations show that extreme care is needed in positioning the isocentre: an accuracy of about ± 3 mm is required in the sagittal plane. (author) 9 refs.; 18 figs