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Dosimetric Analysis On the Effect of Target Motion in the Fixed-Beam IMRT, RapidArc and Tomotherapy

J Song1*, S Cho2, (1) Chonnam National University Medical School, Chonnam, ,KR, (2) Chonnam National University Hwasun Hospital, Chonnam, ,KR

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To analyze the dose variation due to the respiratory motion in the internal target volume (ITV)-based IMRT treatment by comparing with the calculated dose distribution in the plan according to the IMRT performance techniques.
Methods: Three different ITV-based IMRT plans, a fixed-beam (FB) IMRT, a volumetric modulated arc therapy (VMAT), and tomotherapy using helical therapy were prepared separately. Delivery quality assurance (DQA) plans were established for these treatment plans. The dose distribution in the actual motion condition was measured and analyzed using a two-dimensional diode detector placed on a moving phantom capable of simulating breathing movements. The dose variations were compared and analyzed for each treatment method in order to evaluate the effect of a target motion on the IMRT dosimetric error. The dose measurement was performed considering only a uniform target shape and motion in the superior-inferior (SI) direction.
Results: The degree to which the error increased with increasing motion range showed different tendencies according to the treatment method. In the case of tomotherapy, the mean pass rate of gamma evaluation was 83.08±0.78% at the 4-cm motion range and 95.80±0.72% at the 2-cm motion range. In the case of RapidArc, the mean pass rate was 63.68±5.08% at the 4-cm motion range and 81.43±3.81% at the 2-cm motion range. For FB-IMRT, the average pass rate was 61.38±6.49% for 4cm motion range and 82.05±4.67% for 2cm motion range. The pass rate was lowered and the dosimetric error was relatively increased in the case of RapidArc and FB-IMRT, as the target was smaller.
Conclusion: Among the various ITV-based IMRT methods, it was confirmed by real dose measurements under the SI directional motion conditions that the tomotherapy method has a relative advantage in the dosimetric similarity with the original plan compared to the general FB-IMRT or VMAT-type RapidArc methods.

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