3D-recurrence-patterns of glioblastomas after CT-planned postoperative irradiation

Background and purpose: The introduction of computed-tomography as an advanced planning tool for the irradiation of intracranial tumours led to a controversial discussions about the optimal target-volume for the primary and postoperative treatment of malignant gliomas. This study analyses the three-dimensional tumour regrowth pattern relative to the treated volume which included the macroscopic preoperative tumour and 2-cm safety margin. Materials and methods: Seventy-nine patients with histologically-confirmed Glioblastoma multiforma and documented recurrence who were irradiated in our department between 1990 and 1996 were reviewed. With the help of a computer program written for this purpose, the PTV of the CT-based treatment plan was reconstructed and its spatial outline compared with the reconstructed volume of the recurrent tumour in the control CT-study. Results: In 33 out 34 patients for which the CT-study showing tumour-recurrence was available the recurrence was completely situated within the original 90%-isodose. Only one tumour surpassed the outside surface of the PTV but was predominantly situated within the original tumourbed and suggests a tumour-regrowth within the high dose volume. Conclusions: The above results show that target-volumes based on the preoperative size of the enhanced tumour mass well cover the site of recurrence in nearly all cases. The findings suggest dose escalation to a more restricted volume. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.