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

Background and purpose: The introduction of computed-tomography as an advan ced planning tool for the irradiation of intracranial tumours led to a cont roversial discussions about the optimal target-volume for the primary and p ostoperative treatment of malignant gliomas. This study analyses the three- dimensional tumour regrowth pattern relative to the treated volume which in cluded 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 ou r department between 1990 and 1996 were reviewed. With the help of a comput er 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-recurr ence was available the recurrence was completely situated within the origin al 90%-isodose. Only one tumour surpassed the outside surface of the PTV bu t was predominantly situated within the original tumourbed and suggests a t umour-regrowth within the high dose volume. Conclusions: The above results show that target-volumes based on the preope rative size of the enhanced tumour mass well cover the site of recurrence i n nearly all cases. The findings suggest dose escalation to a more restrict ed volume. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.