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KMID : 1164220100220010033
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Journal of Korean Society for Radiotherapeutic Technology
2010 Volume.22 No. 1 p.33 ~ p.39
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IMRT and IMRS Checking the Dose Distribution in the Small Field Evaluation of Measurement by Changes in SAD
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Ko Seong-Young
Kim Sung-Joon
Park Gir-Yong
Son Mi-Suk
Lee Nam-Ki
Kim Jin-Soo
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Abstract
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Purpose: It is very important to confirm conformance of dose distribution that is formed with treatment planning from IMRS or IMRT. It has been a problem dropped accuracy and conformance when the field size is getting smaller because of character of the 2D ion chamber. Verification of MatriXX Phantom dose distribution with a change in the SAD. Dose distribution measurement and analysis to improve the accuracy and should be useful to evaluate the award.
Materials and Methods: A use of Novalis linear accelerator 6 MV photon beams. In general, IMRS were 25 patients with small field size. The selected patients were divided into three groups on the basis of the field size. SAD was changed from 80 to 130 cm and field size to determine the dose distribution to the change, each dose was measured using MatriXX Phantom. Analysis of measured values obtained from the program for each patient through the treatment planning system comparison and analysis of the dose distribution and gamma values were expressed.
Results: SAD 80, 100, and 120 cm in size in the gamma value to the investigation of patients less than 3㎠ average 0.939, 0.969, and 0.979, respectively. Patients with more than 5㎠ 0.962, 0.983, and 0.988, respectively.5㎠ or more patients 0.982, 0.990, and 0.992, respectively.
Conclusion: The error rate of less than 3㎠ field size is increased rapidly. If the field size is increased, resolution is increased by 2D ion chambers. It has been approved that it can be credible if it is around 3㎠ when measuring dose distribution using MatriXX. Adjusting geometric field size by changing SAD is likely to be very useful when you measure dose distribution using MatriXX.
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KEYWORD
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MatriXX phantom, gamma value, SAD (source-axis distance)
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