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Error Detection During Vmat Delivery Using Epid-Based 3D Transit Dosimetry Publisher Pubmed



Mijnheer B1 ; Jomehzadeh A1, 3 ; Gonzalez P1 ; Olacireguiruiz I1 ; Rozendaal R1 ; Shokrani P2 ; Spreeuw H1 ; Tielenburg R1 ; Mans A1
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Authors Affiliations
  1. 1. The Netherlands Cancer Institute, Department of Radiation Oncology, Plesmanlaan 121, CX Amsterdam, 1066, Netherlands
  2. 2. Department of Medical Physics, Isfahan University of Medical Science, Isfahan, Iran
  3. 3. Department of Medical Physics, Kerman University of Medical Sciences, Kerman, Iran

Source: Physica Medica Published:2018


Abstract

Purpose: To investigate the effectiveness of an EPID-based 3D transit dosimetry system in detecting deliberately introduced errors during VMAT delivery. Methods: An Alderson phantom was irradiated using four VMAT treatment plans (one prostate, two head-and-neck and one lung case) in which delivery, thickness and setup errors were introduced. EPID measurements were performed to reconstruct 3D dose distributions of “error” plans, which were compared with “no-error” plans using the mean gamma (γmean), near-maximum gamma (γ1%) and the difference in isocenter dose (ΔDisoc) as metrics. Results: Out of a total of 42 serious errors, the number of errors detected was 33 (79%), and 27 out of 30 (90%) if setup errors are not included. The system was able to pick up errors of 5 mm movement of a leaf bank, a wrong collimator rotation angle and a wrong photon beam energy. A change in phantom thickness of 1 cm was detected for all cases, while only for the head-and-neck plans a 2 cm horizontal and vertical shift of the phantom were alerted. A single leaf error of 5 mm could be detected for the lung plan only. Conclusion: Although performed for a limited number of cases and error types, this study shows that EPID-based 3D transit dosimetry is able to detect a number of serious errors in dose delivery, leaf bank position and patient thickness during VMAT delivery. Errors in patient setup and single leaf position can only be detected in specific cases. © 2018 Associazione Italiana di Fisica Medica
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