CRANIOSPINAL AXIS IRRADIATION - AN IMPROVED ELECTRON TECHNIQUE FOR IRRADIATION OF THE SPINAL AXIS

In this work we review the dosimetric features of craniospinal axis ir radiation in the areas of matching cranial and spinal fields, with ref erence to the normal structures within the spinal field. The implicati ons of the use of photon or electron modalities for the spinal port we re evaluated. A novel method of matching the cranial photon and the sp inal electron fields involving a computer-aided junction design is pre sented. The technique involves moving the photon beam in three steps t o degrade its penumbra to match that of the electron field. Thermolumi nescent dosimetry in a Rando phantom and computed tomography-based dos e-volume histogram study for an illustrative paediatric case were used to compare the dose to normal structures within the spinal field. Our results show that the use of electrons for the spinal field leads to better sparing of deep seated normal structures. In the case of bone m arrow, the use of a customized bolus for the spinal field results in a n improved dose distribution, making electrons potentially superior to photons for radiobiological reasons.