Treatment of medulloblastoma using a computer-controlled tracking cobalt unit

Radiation therapy of the length of the spinal column presents various clinical and physical problems. The completed plan may be complicated to set up, be time-consuming and require daily variation to achieve reasonable dose homogeneity. A case of medulloblastoma is used to illustrate the steps in producing a plan for dynamic treatment using a computer-controlled tracking cobalt unit. After definition by computed tomography, the target is considered in segments in order to develop a plan which keeps the spinal cord constantly positioned at the beam isocentre. The main computer is used to develop the patient treatment file and information is transferred to a second computer which controls and monitors the safe functioning of the cobalt unit. The cranial fields are treated separately in a conventional way. Good and consistent control of the dose distribution is achieved along the entire target volume. This technique is a marked improvement over all existing methods of treating the spinal axis.