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KMID : 1038620110290030206
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Radiation Oncology Journal
2011 Volume.29 No. 3 p.206 ~ p.213
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Analysis of changes in dose distribution due to respiration during IMRT
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Shin Jung-Suk
Shin Eun-Hyuk
Shin Eun-Hyuk
Han Young-Yih
Ju Sang-Gyu
Kim JIn-Sung
Ahn Sung-Hwan
Kim Tae-Gyu
Jeong Bae-Kwon
Park Hee-Chul
Ahn Young-Chan
Choi Doo-Ho
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Abstract
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Purpose: Intensity modulated radiation therapy (IMRT) is a high precision therapy technique that can achieve a conformal dose distribution on a given target. However, organ motion induced by respiration can result in signifi cant dosimetric error. Therefore, this study explores the dosimetric error that result from various patterns of respiration.
Materials and Methods : Experiments were designed to deliver a treatment plan made for a real patient to an in-house developed motion phantom. The motion pattern; the amplitude and period as well as inhale-exhale period, could be controlled by in-house developed software. Dose distribution was measured using EDR2 fi lm and analysis was performed by RIT113 software. Three respiratory patterns were generated for the purpose of this study; fi rst the ‘even inhale-exhale pattern’, second the slightly long exhale pattern (0.35 seconds longer than inhale period) named ‘general signal pattern’, and third a ‘long exhale pattern’ (0.7 seconds longer than inhale period). One dimensional dose profi le comparisons and gamma index analysis on 2 dimensions were performed.
Results: In one-dimensional dose profi le comparisons, 5% in the target and 30% dose difference at the boundary were observed in the long exhale pattern. The center of high dose region in the profi le was shifted 1 mm to inhale (caudal) direction for the ‘even inhale-exhale pattern’, 2 mm and 5 mm shifts to exhale (cranial) direction were observed for ‘slightly long exhale pattern’ and ‘long exhale pattern’, respectively. The areas of gamma index >1 were 11.88 %, 15.11%, and 24.33% for ‘even inhale-exhale pattern’, ‘general pattern’, and ‘long exhale pattern’, respectively. The long exhale pattern showed largest errors.
Conclusion: To reduce the dosimetric error due to respiratory motions, controlling patient’s breathing to be closer to even inhaleexhale period is helpful with minimizing the motion amplitude.
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KEYWORD
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Intensity modulated radiation therapy, Respiratory patterns, Dosimetric error
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