Cranial dose distribution

The dose distribution in the cranium, with special emphasis in the region subjacent to the skull, has been studied as a function of beam quality and the amount of extension of the radiation field beyond the scalp. Thermoluminescent dosimetry (TLD) measurements were made in a phantom, as well as ion chamber measurements in a water-filled plastic head phantom. Cobalt-60, 6 MV, and 25 MV photon beams were used. The results show the radiation distribution to be essentially independent of the amount of overlap. It does depend, however, on the shape of the skull and on beam quality. For the cobalt-60 and 6 MV beams, a 10 % increase in dose in the frontal region of the cranium was noted. For the 25 MV beam, the radiation dose was diminished relative to the midline dose for a depth of several centimeters.