B Mijnheer1, A Jomehzadeh2, P González2, I Olaciregui-Ruiz2, R Rozendaal2, P Shokrani3, H Spreeuw2, R Tielenburg2, A Mans2. 1. The Netherlands Cancer Institute, Department of Radiation Oncology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands. Electronic address: b.mijnheer@nki.nl. 2. The Netherlands Cancer Institute, Department of Radiation Oncology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands. 3. Department of Medical Physics, Isfahan University of Medical Science, Isfahan, Iran.
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.
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.
Authors: Igor Olaciregui-Ruiz; Sam Beddar; Peter Greer; Nuria Jornet; Boyd McCurdy; Gabriel Paiva-Fonseca; Ben Mijnheer; Frank Verhaegen Journal: Phys Imaging Radiat Oncol Date: 2020-08-29