Delineation of radiation therapy target volumes for patients with postoperative glioblastoma: a review

Abstract

Glioblastoma is the most aggressive and lethal primary malignancy of the brain, and radiotherapy (RT) is a fundamental part of its treatment. However, the optimal radiation treatment conditions are still a matter of debate, and there is no clear consensus concerning the inclusion of peritumoral edema in the clinical target volume calculation. Target delineation calculations that use postoperative residual tumor and cavity volumes plus 2 cm margins result in smaller volumes of normal brain receiving high-dose irradiation, compared to calculations that include expanded edema. Smaller RT fields may be more appropriate than larger RT fields, possibly reducing the risk of late neurological deterioration, especially in patients with significant peritumoral edema. This review focuses on the factors influencing target delineation, such as peritumoral edema, failure patterns, and prognostic factors (clinical and pathological characteristics) of patients with glioblastoma. Based on this information, we make three suggestions for radiation oncologists to refer to in daily practice. Further study is necessary to investigate the unresolved problems related to routine clinical application of RT.

Keywords: glioblastoma; postoperative; radiotherapy; target volume.

Figure 1

Target delineation for GBM. Notes: Figures A and B are MRI images from a 58 year old male patient with GBM with a large residual tumor, who had undergone partial resection. These figures show the two phases of target volume delineation. (A) The initial GTV includes postoperative peritumoral edema based on the axial T2 fluid-attenuated inversion recovery sequence (red line); the initial CTV (green line) includes postoperative peritumoral edema plus a 2 cm expansion in all directions. (B) The boost GTV includes the surgical cavity and residual enhancement based on the axial T1 sequence with gadolinium (red line) and the boost CTV is a 2 cm expansion in all directions (green line). Figure C is a MRI image from a 39 year old female patient with GBM, who had undergone gross total resection. It shows the one phase of target volume delineation. The GTV includes surgical cavity and residual enhancement based on the axial T1 sequence with gadolinium (red line) and CTV is a 2 cm expansion in all directions (green line). Abbreviations: CTV, clinical target volume; GBM, glioblastoma multiforme; GTV, gross target volume; MRI, magnetic resonance imaging.