L Moghaddasi1,2, E Bezak2,3, W Harriss-Phillips1,2. 1. 1 Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA, Australia. 2. 2 School of Chemistry & Physics, University of Adelaide, Adelaide, SA, Australia. 3. 3 School of Health Sciences, University of South Australia, Adelaide, SA, Australia.
Abstract
OBJECTIVE: Determination of an optimal clinical target volume (CTV) is complex and remains uncertain. The aim of this study was to develop a glioblastoma multiforme (GBM) model to be used for evaluation of current CTV practices for external radiotherapy. METHODS: The GBM model was structured as follows: (1) a Geant4 cellular model was developed to calculate the absorbed dose in individual cells represented by cubic voxels of 20 μm sides. The system was irradiated with opposing 6 MV X-ray beams. The beams encompassed planning target volumes corresponding to 2.0- and 2.5-cm CTV margins; (2) microscopic extension probability (MEP) models were developed using MATLAB(®) 2012a (MathWorks(®), Natick, MA), based on clinical studies reporting on GBM clonogenic spread; (3) the cellular dose distribution was convolved with the MEP models to evaluate cellular survival fractions (SFs) for both CTV margins. RESULTS: A CTV margin of 2.5 cm, compared to a 2.0-cm CTV margin, resulted in a reduced total SF from 12.9% ± 0.9% to 3.6% ± 0.2%, 5.5% ± 0.4% to 1.2% ± 0.1% and 11.1% ± 0.7% to 3.0% ± 0.2% for circular, elliptical and irregular MEP distributions, respectively. CONCLUSION: A Monte Carlo model was developed to quantitatively evaluate the impact of GBM CTV margins on total and penumbral SF. The results suggest that the reduction in total SF ranges from 3.5 to 5, when the CTV is extended by 0.5 cm. ADVANCES IN KNOWLEDGE: The model provides a quantitative tool for evaluation of different CTV margins in terms of cell kill efficacy. Cellular platform of the tool allows future incorporation of cellular properties of GBM.
OBJECTIVE: Determination of an optimal clinical target volume (CTV) is complex and remains uncertain. The aim of this study was to develop a glioblastoma multiforme (GBM) model to be used for evaluation of current CTV practices for external radiotherapy. METHODS: The GBM model was structured as follows: (1) a Geant4 cellular model was developed to calculate the absorbed dose in individual cells represented by cubic voxels of 20 μm sides. The system was irradiated with opposing 6 MV X-ray beams. The beams encompassed planning target volumes corresponding to 2.0- and 2.5-cm CTV margins; (2) microscopic extension probability (MEP) models were developed using MATLAB(®) 2012a (MathWorks(®), Natick, MA), based on clinical studies reporting on GBM clonogenic spread; (3) the cellular dose distribution was convolved with the MEP models to evaluate cellular survival fractions (SFs) for both CTV margins. RESULTS: A CTV margin of 2.5 cm, compared to a 2.0-cm CTV margin, resulted in a reduced total SF from 12.9% ± 0.9% to 3.6% ± 0.2%, 5.5% ± 0.4% to 1.2% ± 0.1% and 11.1% ± 0.7% to 3.0% ± 0.2% for circular, elliptical and irregular MEP distributions, respectively. CONCLUSION: A Monte Carlo model was developed to quantitatively evaluate the impact of GBM CTV margins on total and penumbral SF. The results suggest that the reduction in total SF ranges from 3.5 to 5, when the CTV is extended by 0.5 cm. ADVANCES IN KNOWLEDGE: The model provides a quantitative tool for evaluation of different CTV margins in terms of cell kill efficacy. Cellular platform of the tool allows future incorporation of cellular properties of GBM.
Authors: Eric L Chang; Serap Akyurek; Tedde Avalos; Neal Rebueno; Chris Spicer; John Garcia; Robin Famiglietti; Pamela K Allen; K S Clifford Chao; Anita Mahajan; Shiao Y Woo; Moshe H Maor Journal: Int J Radiat Oncol Biol Phys Date: 2007-02-15 Impact factor: 7.038
Authors: Jan Unkelbach; Bjoern H Menze; Ender Konukoglu; Florian Dittmann; Matthieu Le; Nicholas Ayache; Helen A Shih Journal: Phys Med Biol Date: 2014-01-20 Impact factor: 3.609
Authors: Anitha Priya Krishnan; Isaac M Asher; Delphine Davis; Paul Okunieff; Walter G O'Dell Journal: Int J Radiat Oncol Biol Phys Date: 2008-06-04 Impact factor: 7.038
Authors: Irwin H Lee; Morand Piert; Diana Gomez-Hassan; Larry Junck; Lisa Rogers; James Hayman; Randall K Ten Haken; Theodore S Lawrence; Yue Cao; Christina Tsien Journal: Int J Radiat Oncol Biol Phys Date: 2008-10-01 Impact factor: 7.038
Authors: Vassilis P Antipas; Georgios S Stamatakos; Nikolaos K Uzunoglu; Dimitra D Dionysiou; Roger G Dale Journal: Phys Med Biol Date: 2004-04-21 Impact factor: 3.609