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The original version of this article [1] unfortunately contained a mistake. [ABSTRACT FROM AUTHOR]

Background: Conventional phantom-based planar dosimetry (2D-PBD) quality assurance (QA) using gamma pass rate (GP (%)) is inadequate to reflect clinically relevant dose error in intensity-modulated radiation therapy (IMRT), owing to a lack of information regarding patient anatomy and volumetric dose distribution. This study aimed to evaluate the dose distribution accuracy of IMRT delivery for nasopharyngeal carcinoma (NPC), which passed the 2D-PBD verification, using a measurement-guided 3D dose reconstruction (3D-MGR) method.Methods: Radiation treatment plans of 30 NPC cases and their pre-treatment 2D-PBD data were analyzed. 3D dose distribution was reconstructed on patient computed tomography (CT) images using the 3DVH software and compared to the treatment plans. Global and organ-specific dose GP (%), and dose-volume histogram (DVH) deviation of each structure was evaluated. Interdependency between GP (%) and the deviation of the volumetric dose was studied through correlation analysis.Results: The 3D-MGR achieved global GP (%) similar to conventional 2D-PBD in the same criteria. However, structure-specific GP (%) significantly decreased under stricter criteria, including the planning target volume (PTV). The average deviation of all inspected dose volumes (DV) and volumetric dose (VD) parameters ranged from - 2.93% to 1.17%, with the largest negative deviation in V100% of the PTVnx of - 15.66% and positive deviation in D1cc of the spinal cord of 6.66%. There was no significant correlation between global GP (%) of 2D-PBD or 3D-MGR and the deviation of the most volumetric dosimetry parameters (DV or VD), when the Pearson's coefficient value of 0.8 was used for correlation evaluation.Conclusion: Even upon passing the pre-treatment phantom based dosimetric QA, there could still be risk of dose error like under-dose in PTVnx and overdose in critical structures. Measurement-guided 3D volumetric dosimetry QA is recommended as the more clinically efficient verification for the complicated NPC IMRT. [ABSTRACT FROM AUTHOR]

Abstract: Background and objective: Respiratory-gated techniques are based on controlling the linear accelerator and limiting the beam-on time to only a small portion of the patient’s breathing cycle. For each beam-on, the machine must spend a start-up time (ST) to set up a stable and correct RF field in the waveguide and get the right beam current, etc. That might cause an obvious variation on the beam dosimetric characteristic, including the beam quality and profile, when the duration of ST is un-ignorable to the beam-on time. The purpose of this study is to investigate this kind of impact for various duty cycles (DC) of breathing-gated operation. Materials and method: A respiratory motion phantom and a Real-time Position Management System (RPM) were used to simulate the patient respiration and to control the beam gating. Measurements were performed on a Varian 600C/D linac with 6 MV photons, using different DCs of 5%, 7%, 10%, 12%, 20%, 50%, 75%, and 100% to a 6-s breathing cycle (BC) simulation. The beam quality, flatness, symmetry were evaluated for these conditions. Output reproducibility and dose linearity were measured and evaluated for different MUs at 400 MU/min dose rate and 30% DC as well. Results: For gated delivery in the above selected DCs and BC, the maximum changes in beam quality, symmetry, flatness were −0.181%, 0.124%, −0.17%, compared with non-gated data respectively. The coefficient of dispersion of output was less than 0.3% and good dose linearity was obtained for the tested gating operation condition. Conclusion: For situation similar to our experiment, the duty cycle effect to beam characteristics is ignorable that the beam modeling based on non-gated delivery can be directly used for respiratory gating therapy. Otherwise, the beam characteristics should be carefully checked individually. [Copyright &y& Elsevier]