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KMID : 0357520100330010061
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Journal of Radiological Science and Technology
2010 Volume.33 No. 1 p.61 ~ p.66
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Evaluation of Dosimetric Characteristics of Small Field in Cone Versus Square Fields Based on Linear Accelerators(LINAC) for Stereotactic Radiosugery(SRS)
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Yoon Joon
Lee Gui-Won
Park Byung-Moon
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Abstract
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In this paper we evaluated small field dose characteristics of exclusive cone fields versus square fields for stereotactic radiosugery (SRS) which is based on linear accelerators (LINAC). For this test, we used a small beam detector (stereotactic fields detector : SFD) with a 6 MV photon beam and a water phantom system (IBA, Germany). Percentage depth dose (PDD) was measured for different field sets (cones : , , ; square fields : , , ) at a source skin distance (SSD) of 100 cm. We measured the point depths at 1.5 cm, 5 cm, 10 cm, 20 cm, and 30 cm. The output factors were measured under the same geometrical conditions of the PDD and normalized at the maximum dose depth. To analyze the penumbra, we measured the dose profile with 95 cm of SSD, 5 cm of depth for each field sizes (, , , and ) using SFD. We obtained the values for every 1 mm interval in the physical field (90%) and 0.5 mm interval in the penumbra region (20 to 80%). The PDD variation of exclusive cones and square fields were 4.3 to 7.9% lesser than the standard field size (. The variation of PDD was reduced while the field size was increased. To compare the beam quality, we analyzed the and the results showed under the 1% of variations for all experiments except for cone and fields. Output factors of exclusive cone were increased 3.1~4.6% than the square fields, and the penumbra region of exclusive cone was reduced 20% as compared to the square fields. As the previous researches report, it is very important for SRS and SFD that precise dosimetry in small beam fields. In this paper, we showed the effectiveness of exclusive cone, compared to square field. And we will study on the various detector characteristics for small beam fields.
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KEYWORD
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Stereotactic Radiosugery (SRS), Stereotactic Field Detector (SFD), SRS cone, Small beam field
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