Use of a Deformable Atlas to Identify Cryptic Critical Structures in the Treatment of Glioblastoma Multiforme

MD Anderson Cancer Center, Department of Radiation Oncology, University of Texas, Houston, Texas, United States of America.
PLoS ONE (Impact Factor: 3.23). 03/2012; 7(3):e32098. DOI: 10.1371/journal.pone.0032098
Source: PubMed


Dose constraints for traditional neural critical structures (e.g. optic chiasm, brain stem) are a standard component of planning radiation therapy to the central nervous system. Increasingly, investigators are becoming interested in accounting for the dose delivered to other non-target neural structures (e.g. hippocampi), which are not easily identified on axial imaging. In this pilot study, a commercially available digital atlas was used to identify cryptic neural structures (hippocampus, optic radiations, and visual cortices) in 6 patients who received intensity modulated radiation therapy (IMRT) as part of multimodal management of glioblastoma multiforme (GBM). The patient's original IMRT plans were re-optimized, with avoidance parameters for the newly identified critical structures. Re-optimization was able to reduce both mean and maximum dose to the volumes of interest, with a more pronounced effect for contralateral structures. Mean dose was reduced by 11% and 3% to contralateral and ipsilateral structures, respectively, with comparable reduction in maximum dose of 10% and 2%, respectively. Importantly, target coverage was not compromised, with an average change in coverage of 0.2%. Overall, our results demonstrate the feasibility of incorporating tools for cryptic critical structure identification into the treatment planning process for GBM.

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    ABSTRACT: BACKGROUND:: Despite improvements in advanced MR imaging and intraoperative mapping, there remain cases where it is difficult to determine if viable eloquent structures are involved by a glioma. A novel software program, deformable anatomic templates (DAT), rapidly embeds the normal location of eloquent cortex and functional tracts in the MR images of glioma-bearing brain. OBJECTIVE:: To investigate the feasibility of the DAT technique in patients with gliomas related to eloquent brain. METHODS:: Forty cases of gliomas (grade II-IV) with minimal mass effect were referred for a prospective pre- and postoperative DAT analysis. The DAT results were compared to the patient's fMRI, DTI, operative stimulation and new postoperative clinical deficits. RESULTS:: Fifteen of the 40 glioma patients had overlap between tumor and eloquent structures. Immediate postoperative neurological deficits were seen in 9 cases in which the DAT showed the eloquent area both within the tumor and within or at the edge of the resection cavity. In 6 cases with no deficits, DAT placed the eloquent area in the tumor but outside of the resection cavity. CONCLUSION:: This is proof-of-concept that DAT can improve the analysis of diffuse gliomas of any grade, by efficiently alerting the surgeon to the possibility of eloquent area invasion. The technique is especially helpful in diffuse glioma, as these tumors tend to infiltrate rather than displace eloquent structures. DAT is limited by tract displacement in gliomas which produce moderate to severe mass effect.
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    ABSTRACT: Radiotherapy (RT) remains the principal component of glioma treatment, and three-dimensional conformal RT (3DCRT) is the current standard of RT delivery. Advances in imaging and in RT technology have enabled more precise treatment to defined targets combined with better means of avoiding critical normal structures, and this is complemented by intensive quality assurance, which includes on-treatment imaging. The refinements of 3DCRT include intensity modulated RT (IMRT), arcing IMRT, and high-precision conformal RT, formerly described as "stereotactic," which can be delivered using a linear accelerator or other specialized equipment. Although proton therapy uses heavy charged particles, the principal application can also be considered as refinement of 3DCRT. The technologies generally improve the dose differential between the tumor and normal tissue and enable more dose-intensive treatments. However, these have not translated into improved survival outcome in patients with low- and high-grade gliomas. More intensive altered fractionation regimens have also failed to show survival benefit. Nevertheless, novel technologies enable better sparing of normal tissue and selective avoidance of critical structures, and these need to be explored further to improve the quality of life of patients with gliomas. Principal clinical advance in RT has been the recognition that less intensive treatments are beneficial for patients with adverse prognosis high-grade gliomas. We conclude that the principal gain of modern RT technology is more likely to emerge as a reduction in treatment related toxicity rather than as an improvement in overall survival; the optimal avoidance strategies remain to be defined.
    Preview · Article · May 2014

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