[Method of cranial irradiation of children with leukemia].

Abstract

By an irradiation of the neurocranium with doses from 12 to 30 Gy during the combined treatment of ALL in children, an essential reduction of the leukemic manifestation on the meninges as well as an improved curability have been achieved during the last few years. The precision of the irradiation technique is of vital importance, i.e. the occurrence of recurrences on the central nervous system during complete remission after skull irradiation are preponderantly due to a defective irradiation technique. The important factors are a daily reproducible positioning and fixation of the head in an irradiation mask and the adjustment within three dimensions by means of a laser light system. Only cobalt-60 gamma radiation or the ultrahard photons of a linear accelerator with an energy of 4 to 6 MV should be applied. The irradiation is performed with laterally opposite, coplanar and coaxial fields in an isocentric adjustment. The field shape is regulated by individual absorbers adjusted under visual control in a defined position to the patient on a plexiglas plate at the therapy simulator. In order to guarantee an homogeneic dose also to the meninges situated at the field borders and to prevent a "geographic miss", the field borders should exceed the cranial calotte by 1 to 2 cm at the frontal, vertical and occipital side. At the base of the skull, special consideration must be given to a sufficient irradiation of the retrobulbar spaces, the frontal meninges situated in the region of the lamina cribrosa and the temporal meninges situated in the region of the deep inner cranial fossae. The dose specification is made in the central ray in the center of the skull. Generally single doses of 2 Gy and weekly doses of 10 Gy are applied. The total dose depends on age, risk group, and treatment aim. Recent studies indicate that in case of simultaneous intrathecal administration of methotrexate, the single dose can be reduced from 1.8-2.0 Gy to 1.2-1.5 Gy and the total dose from 24 Gy to 18 Gy without any unfavorable effect on the rate of recurrences at the central nervous system and the survival rate. Within the scope of an aggressive combination therapy, this self-restraint of the radio-therapeutist is of great importance with regard to acute and chronic complications in the brain and the growing skeleton.