Intracranial germinoma: on whole-ventricular irradiation

A current focus in the treatment of intracranial germinoma is on decreasing the volume of radiotherapy. We studied the theoretical impact of selecting different target volumes and treatment techniques.

Retrospectively, five cases of localized germinoma were identified. Treatment plans were produced for three target volumes: involved field plans (i.e., targeting only gross disease), whole brain plans, and plans of increasing complexity targeting the ventricles (lateral-opposed, four-field and intensity-modulated (IMRT)). A second series of patients was processed similarly except that no involved field plans were produced.

When target volumes were compared, normal structures were substantially spared by ventricular irradiation but maximally spared by involved field radiation. When treatment techniques were assessed for ventricular irradiation, the greatest gain in tissue sparing occurred when switching from two to four fields. This gain was at the higher doses levels at the expense of an increased volume of tissue irradiated to lower doses. IMRT plans always spared a small additional amount of normal brain. Whole ventricular plans were compared to similar plans excluding the fourth ventricle. Whole brain dose was only improved by 4-6% by excluding the fourth ventricle.

The substitution of whole-ventricular irradiation for whole-brain irradiation can spare a significant amount of normal tissue, thus providing a theoretical advantage with respect to the risk of late effects. Ventricular irradiation is best achieved with at least a four-field 3D configuration, and optimally through an IMRT plan. Exclusion of the fourth ventricle in the target volume had only a minimal impact on normal tissue doses.