Analysis of prostate bed motion using an endorectal balloon and cone beam computed tomography during postprostatectomy radiotherapy
Authors Joo JH, Kim YJ, Kim YS, Cho YP, Lee HY, Jeong CY, Kwak J, Cho BC
Received 12 October 2015
Accepted for publication 31 March 2016
Published 24 May 2016 Volume 2016:9 Pages 3095—3100
Checked for plagiarism Yes
Review by Single-blind
Peer reviewers approved by Dr Colin Mak
Peer reviewer comments 3
Editor who approved publication: Professor Min Li
Ji Hyeon Joo, Yeon Joo Kim, Young Seok Kim, Young Pil Cho, Ho Yeon Lee, Chang Young Jeong, Jungwon Kwak, Byung Chul Cho
Department of Radiation Oncology, Asan Medical Center, University of Ulsan, College of Medicine, Seoul, Republic of Korea
Background: The authors conducted this prospective study to analyze the amount of interfractional prostate bed motion (PBM) and quantify its components with the use of an endorectal balloon (ERB).
Methods: A total of 1,348 cone beam computed tomography images from 46 patients who underwent postprostatectomy radiotherapy were analyzed. For the pilot image, electronic portal imaging, guided by skin marks was performed to ensure proper positioning and inflation of the ERB. Then, for bone matching, manual or automatic registration of the planning and each cone beam computed tomography was performed, based on the bony anatomy of the pelvis. Shifts (bony misalignment [BM]) in three directions were recorded at each treatment session. For prostate bed matching, manual matching was conducted based on the anterior rectal wall and the shift (PBM) was recorded. Total setup error was defined as the shift from the skin mark to the prostate bed matching, based on anterior rectal wall stretched by the ERB. PBM was defined as the difference between the total setup error and BM.
Results: Systematic errors for the total setup error were 1.0, 1.3, and 1.0 mm in the right–left, anterior–posterior, and superior–inferior directions, with random errors of 1.9, 2.4, and 1.9 mm, respectively. Systematic errors were 1.6, 1.6, and 0.3 mm for BM and 0.8, 1.1, and 0.9 mm for PBM, with random errors of 2.4, 2.5, and 1.1 mm for BM and 1.8, 2.2, and 1.9 mm for PBM.
Conclusion: The BM was the main component of the total setup error, suggesting that interfractional PBM was well controlled by the ERB device. Planning target volume margins of <5 mm were needed to include 95% of the interfractional variations when using an ERB.
Keywords: prostate bed motion, endorectal balloon, cone beam computed tomography
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