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KMID : 1164220170290020053
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Journal of Korean Society for Radiotherapeutic Technology
2017 Volume.29 No. 2 p.53 ~ p.64
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Evaluation on the Usefulness of 6DoF Couch in V-MAT on Patients with Long length of Target
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Choi Young-Se
Park Hyo-Kuk
Kim Se-Young
Kim Joo-Ho
Lee Sang-Kyu
Yoon Jong-Won
Cho Jeong-Hee
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Abstract
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Purpose: To evaluate the usefulness of the HexaPOD™ evo RT system(6DoF couch) and the tendency of dose difference according to size of rotational direction error for volumetric rotational modulated radiotherapy(V-MAT) in patients with long target lengths. Therefore, it is suggested to recommend the need for rotational error correction.
Materials and Methods: Ten patients with Esophagus cancer or Breast cancer including SCL treated with HexaPOD 6DoF(Six-Degree of Freedom) couch were included in this study. 6DoF couch was used to measure the difference in dose according to the rotation error in the directions of Rx(pitch), Ry(roll), and Rz(yaw). Each rotation error was applied. Positioning variation on x, y and z axis was verified and random variations were made by 6DoF couch with positioning
variation. Modified DQA is conducted and point dose and gamma value are analyzed and compared. In addition, after applying the rotation error every 1° to treatment plans of each target with a diameter of 3 cm, 5, 10, 15, and 20 cm respectively, gamma passing rate is being monitored by its aspect of change according to types and sizes of the target length and rotation error.
Results: Mean error of the point dose and Gamma passing rate when the position variation was applied were 2.50±1.11 % and 84.1±7.39 % in the Rx direction, 2.36±1.16 %, and 81.0±8.49 % in the Ry, 2.35±1.10 % and 84.4±6.99 % in the Rz direction, respectively. As a result of analysis on gamma passing rate according to types and sizes of the target length and rotation error, the gamma passing rate tended to decrease with increasing rotation error in the Rx and Rz directions except Ry direction. In particular, the lowest gamma passing rate (74.2 %) was in the case of 2.5° rotation error in Rz direction of the target of 10 cm.
Conclusion: The correction of the rotational error is needed for volumetric modulated radiotherapy of the treatment area with a long target length, and the use of 6DoF couch will improve the reproducibility of the patient position and the quality of the treatment.
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KEYWORD
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V-MAT , 6DoF couch , SI direction , DQA
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