Medulloblastoma: Treatment technique and radiation dosimetry

Abstract

It is well established that elective cranio-spinal irradiation is beneficial in the treatment of medulloblastoma. However, because of the geometry of the brain and the spinal column, a simple treatment procedure which results in a uniform dose over the entire target volume while maintaining a low dose to other tissues is not easy to perform. This report describes a relatively simple treatment technique which can be administered with radiotherapy apparatus that is available in most treatment centers. Special consideration is given to the dosimetry in the junction regions of the contiguous 60Co fields. Computer dosage calculations were made to check the effectiveness of this technique. This calculated data was verified experimentally with thermoluminescent dosimetry (TLD) in both a rectangular polystyrene phantom as well as the human like Alderson Rando phantom. The dose to critical organs such as the eyes was found to be less than 15% of the tumor dose, while the male gonadal dose was less than 10%. Detailed consideration is given to the factors affecting the overall variation of dose in the entire target volume. It has been estimated that using this technique, the overall dosage variation to the cranio-spinal axis is within ±10% of the prescribed tumor dose for the average adult, while for the average child it is better than ±5k.