| Investigation of photon beam models in heterogeneous media of modern radiotherapy. | |
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MedLine Citation:
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PMID: 15462585 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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This study investigates the performance of photon beam models in dose calculations involving heterogeneous media in modern radiotherapy. Three dose calculation algorithms implemented in the CMS FOCUS treatment planning system have been assessed and validated using ionization chambers, thermoluminescent dosimeters (TLDs) and film. The algorithms include the multigrid superposition (MGS) algorithm, fast Fourier Transform Convolution (FFTC) algorithm and Clarkson algorithm. Heterogeneous phantoms used in the study consist of air cavities, lung analogue and an anthropomorphic phantom. Depth dose distributions along the central beam axis for 6 MV and 10 MV photon beams with field sizes of 5 cm x 5 cm and 10 cm x 10 cm were measured in the air cavity phantoms and lung analogue phantom. Point dose measurements were performed in the anthropomorphic phantom. Calculated results with three dose calculation algorithms were compared with measured results. In the air cavity phantoms, the maximum dose differences between the algorithms and the measurements were found at the distal surface of the air cavity with a 10 MV photon beam and a 5 cm x 5 cm field size. The differences were 3.8%. 24.9% and 27.7% for the MGS. FFTC and Clarkson algorithms. respectively. Experimental measurements of secondary electron build-up range beyond the air cavity showed an increase with decreasing field size, increasing energy and increasing air cavity thickness. The maximum dose differences in the lung analogue with 5 cm x 5 cm field size were found to be 0.3%. 4.9% and 6.9% for the MGS. FFTC and Clarkson algorithms with a 6 MV photon beam and 0.4%. 6.3% and 9.1% with a 10 MV photon beam, respectively. In the anthropomorphic phantom, the dose differences between calculations using the MGS algorithm and measurements with TLD rods were less than +/-4.5% for 6 MV and 10 MV photon beams with 10 cm x 10 cm field size and 6 MV photon beam with 5 cm x 5 cm field size, and within +/-7.5% for 10 MV with 5 cm x 5 cm field size, respectively. The FFTC and Clarkson algorithms overestimate doses at all dose points in the lung of the anthropomorphic phantom. In conclusion, the MGS is the most accurate dose calculation algorithm of investigated photon beam models. It is strongly recommended for implementation in modern radiotherapy with multiple small fields when heterogeneous media are in the treatment fields. |
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Authors:
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W Ding; P N Johnston; T P Y Wong; I F Bubb |
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Publication Detail:
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Type: Comparative Study; Evaluation Studies; Journal Article; Validation Studies |
Journal Detail:
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Title: Australasian physical & engineering sciences in medicine / supported by the Australasian College of Physical Scientists in Medicine and the Australasian Association of Physical Sciences in Medicine Volume: 27 ISSN: 0158-9938 ISO Abbreviation: Australas Phys Eng Sci Med Publication Date: 2004 Jun |
Date Detail:
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Created Date: 2004-10-06 Completed Date: 2004-11-02 Revised Date: 2006-11-15 |
Medline Journal Info:
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Nlm Unique ID: 8208130 Medline TA: Australas Phys Eng Sci Med Country: Australia |
Other Details:
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Languages: eng Pagination: 39-48 Citation Subset: IM |
Affiliation:
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Department of Radiation Oncology Physics, Austin and Repatriation Medical Centre, Melbourne, Australia. wding@radoncvic.com.au |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Algorithms* Computer Simulation Humans Lung / physiology*, radiation effects* Models, Biological* Photons / therapeutic use Radiometry / methods* Radiotherapy Dosage Radiotherapy Planning, Computer-Assisted / methods* Radiotherapy, Conformal / methods* Reproducibility of Results Sensitivity and Specificity |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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