Validation of new transmission detector transmission factors for online dosimetry: an experimental study
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RESEARCH
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Validation of new transmission detector transmission factors for online dosimetry: an experimental study So-Yeon Park1,2, Jong Min Park2,3,4, Jung-in Kim2,3,4, Sungyoung Lee4 and Chang Heon Choi2,3,4*
Abstract Background: The demand for dose verification during treatment has risen with the increasing use of intensitymodulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) in modern radiation therapy. This study aims to validate the transmission factors of a new transmission detector, the Dolphin online monitoring system (IBA Dosimetry, Schwarzenbruck, Germany), for clinical use. Methods: The transmission factors of the Dolphin detector were evaluated using 6 MV, 6 flattening filter free (FFF), 10 MV, and 10 FFF clinical beams from a TrueBeam STx linear accelerator system. Two-dimensional (2D) dose distributions were measured through portal dosimetry with and without Dolphin to derive the transmission factors. The measurements were performed using 10 IMRT and 10 VMAT treatment plans. The transmission factors were calculated using a non-negative least squares problem solver for the 2D dose matrix. Normalized plans were generated using the derived transmission factors. Patient-specific quality assurance with normalized plans was performed using portal dosimetry and an ArcCheck detector to verify the transmission factors. The gamma passing rates were calculated for the 2%/2 mm and 1%/1 mm criteria. Results: The transmission factors for the 6 MV, 6 FFF, 10 MV, and 10 FFF beams, were 0.878, 0.824, 0.913, and 0.883, respectively. The average dose difference between the original plan without Dolphin and the normalized plan with Dolphin was less than 1.8% for all measurements. The mean passing rates of the gamma evaluation were 98.1 ± 2.1 and 82.9 ± 12.6 for the 2%/2 mm and 1%/1 mm criteria, respectively, for portal dosimetry of the original plan. In the case of the portal dosimetry of the normalized plan, the mean passing rates of the gamma evaluation were 97.2 ± 2.8 and 79.1 ± 14.8 for the 2%/2 mm and 1%/1 mm criteria, respectively. Conclusions: The Dolphin detector can be used for online dosimetry when valid transmission factors are applied to the clinical plan. Keywords: Transmission detector, Transmission factors, Portal dosimetry, Online dosimetry
Background In modern radiation therapy, intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic ablative radiotherapy (SABR) are used for precise radiation delivery [1, 2]. These techniques can generate a sophisticated dose distribution, delivering high doses to the target with lower doses to * Correspondence: [email protected] 2 Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea 3 Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea Full list of author information is available at the end of the article
critical organs. Such dose distributions are delivered using a beam sequence with
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