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Title
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In vivo estimation of extracranial doses in stereotactic radiosurgery with the Gamma Knife and Novalis systems
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Author
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Abstract
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| Objective: The purpose of this work is to investigate the extracranial doses in vivo during intracranial treatments comparing the Gamma Knife system with the Novalis system for identical pathologies. The analysis is limited to single fraction stercotactic radiosurgeries. Methods: Measurements were performed with TL dosimeters positioned on the lateral canthus, thyroid, breasts and gonads to obtain the dose received to these anatomical regions. Based on these observations, an estimate of the risk for cancer induction and detriment will be proposed. The measured doses were normalized to 24 Gy, and the influence of target maximum dose, reference isodose volume, equivalent treatment time (which is related to the activity of the "Co sources for the Gamma Knife) and distance on extracranial doses are analyzed. Results: The average extracranial dose with a normalized prescription dose of 24 Gy is comparable for both machines. Gamma Knife: For the lateral canthus, thyroid, breast and gonads the median doses were 435, 103, 48, and 6 mGy, respectively. Novalis: For the lateral canthus, thyroid, breast and gonads the median doses were 234, 79, 45, and 3 mGy, respectively. For the Gamma Knife system as well as the Novalis system no correlation could be found between maximum dose, reference isodose volume and extracranial doses. On the other hand, for the Gamma Knife system the equivalent treatment time and distance have a significant influence on doses received on extracranial sites. For the Novalis system only the distance and the geographical placement of the arcs will influence the extracranial dose. Conclusions: Doses to extracranial sites are small, ranging from 1.4% of the prescribed dose (24 Gy) for the lateral canthus to 0.02% for the gonads for the Gamma Knife and in the range of 0.97% of the prescribed dose (24 Gy) for the lateral canthus, to 0.01% for the gonads for the Novalis. According to ICRP-60, the risk for cancer induction after a radiosurgical treatment is estimated to about 0.2% for both the Gamma Knife and Novalis systems; the risk for detriment is estimated at 0.3% for both systems. Although these risks are very small, they must be kept to a minimum value for long life expectancy patients, by choosing the appropriate treatment strategy. Copyright (c) 2006 S. Karger AG, Basel. |
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Language
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English
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Source (journal)
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Radiosurgery, Vol 6
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Source (book)
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7th Meeting of the International-Stereotactic-Radiosurgery-Society, 2005, Brussels, BELGIUM
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Publication
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Basel
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Karger
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2006
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ISBN
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3-8055-8105-X
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DOI
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10.1159/000093714
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Volume/pages
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6
(2006)
, p. 36-49
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ISI
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000239488700004
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Full text (Publisher's DOI)
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