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Dosimetric Evaluation of Proper Width of Respiratory Gating Window According to Dose Distribution of EBT2 Film

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S Lee

S Lee1,2*, S Park2, H Lee2,3, S Shin2, H Kim1,2, T Kim2, M Kim2, H Jung2, K Kim1,2, Y Ji1,2, (1) University of Science & Technology, Daejeon, Korea (Republic Of) (2) Korea Institute of Radiological and Medical Sciences, Seoul, Korea (Republic Of) (3) Yonsei University, Wonju, Korea (Republic Of)

SU-E-J-156 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: We analyzed dose distribution depending on the width of gating window to determine the proper width of gating window in gated radiation therapy.

Methods: A three dimensional breathing simulator with house phantom was built to simulate periodic sinusoidal breathing motion of 4 seconds/cycle and 3cm fan shape movement. This was driven synchronized with Real-time Position Management (RPM) system (Varian Medical Systems, Palo Alto, CA, USA), and thereafter 4D-CT images were acquired. Three treatment fields (0°, 120°, 240°) with gating plan using treatment planning system (Eclipse, Varian, USA) were performed aimed to be exposed 200cGy to isocenter. Dose evaluations regarding static, non-gated motion, 60% (phase of 20%-80%), 40% (phase of 30%-70%), 30% (phase of 40%-70%), 20% (phase of 40%-60%) and 15% (phase of 40%-55%) of gated motion were carried out using EBT2 film, and extents of field size, high dose exposed, penumbra were analyzed.

Results: In most cases, dose differences compared to static were getting decreased as the width of gating window was decreased. Non-gated motion showed -74.5% dose discrepancies compared to static exposed, whereas 15% respiratory gating window showed within 1% dose difference. Dose differences of 40% gating window was -30.7% whereas 30% gating window showed -6.3% dose discrepancies. Dose difference was rapidly reduced from 30% gating window against non-gated motion to 40% gating window in all cases of field size, high dose area, and penumbra.

Conclusions: 15% respiratory gating window was regarded the most ideal width of gating window, but it will significantly increase beam delivery time over a conventional treatment. Therefore, considering beam delivery time and dose distributions of high dose area, field size, and penumbra, 30% respiratory gating window would be recommended.

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