Erratum to: Experimental measurement of ionization chamber angular response and associated magnetic field correction factors in MR-linac (Medical Physics, (2020), 47, 4, (1940-1948), 10.1002/mp.14025)

The value and uncertainty of conversion factor (Formula presented.) for A1SL ionization chamber obtained directly via water calorimetry has been revised and updated [1]. This update impacts Table II in our 2020 paper [2] and the value of uncertainty for (Formula presented.) and total uncertainty must be changed to provide the corrected Table II below. II Table Uncertainty budget for magnetic field correction factor (Formula presented.) determined from cross-calibration of A1SL (# XW080735) with A19 (# XAQ100622), FC65-G (#1811) and CC13 (# 8306). (Table presented.) Figures 7 and 8 were also impacted, as (Formula presented.) used in cross-calibration was used to generate these figures. The updated figures and the caption to Figure 7 are provided below. 7 Fig. (Figure presented.) “Absolute values of (Formula presented.) as a function of angle between chamber axis and magnetic field for four chambers measured in this study, normalized to directly measured (Formula presented.) = 0.977 ± 0.98% value by D’Souza et al. [1] at 270-degree orientation for A1SL chamber (# XW080735). The overall uncertainty of the relative chamber orientation measurement (0.25%) is shown with the shaded band. The total uncertainty of the absolute measurement of (Formula presented.) (1.17% for A1SL; 1.24% for A19, FC65-G and CC13) is shown with error bars at cardinal angles.” 8 Fig. (Figure presented.) Comparison of magnetic field correction factor, (Formula presented.), measured in this study (red dots) and Monte Carlo study carried out by Malkov and Rogers [9]. Simulated distribution of (Formula presented.) for full geometric sensitive volume (FV) of the chamber is shown with blue diamonds; to account for chamber dead volume, the chamber sensitive volume was reduced by 1 mm away from the stem, and the resulting simulated (Formula presented.) values for reduced sensitive volume (RV) are shown with violet squares. This work, Malkov - FV, Malkov - RV. The (Formula presented.) update also impacts Table IV of the paper. The updated Table IV is shown below. IV Table A comparison table of available Monte Carlo studies and experimental results of beam quality conversion factor, (Formula presented.) and magnetic field correction factors k_B and (Formula presented.) for chambers studied in this work to date. FV and RV in “Method” section refers to the full geometric sensitive volume (FV) and reduced geometric sensitive volume (RV) as defined in the Monte Carlo study by Malkov and Rogers (2018) [9]. ║ (0°) {║ (180°)} refers to the parallel {antiparallel} orientation of chamber’s tip and magnetic field with the radiation beam incident perpendicular to both; ┴ (90°) {┴ (270°)} refers to the parallel {antiparallel} orientation of chamber’s tip and Lorentz force with magnetic field and radiation beam perpendicular to the axis of the chamber (Figure 5). The last column shows % difference between (Formula presented.) obtained from different studies and the associated measured value from this work (Formula presented.). (Table presented.) The update impacts the Results section of the abstract: “We measured the absolute magnitude of the magnetic field correction factor (Formula presented.) for the Exradin-A19, A1SL, IBA FC65-G and CC13 to be 0.938 ± 1.13%, 0.968 ± 0.99%, 0.950 ± 1.13% and 0.975 ± 1.13%, respectively.” should be corrected to: “We measured the absolute magnitude of the magnetic field correction factor (Formula presented.) for the Exradin A19, A1SL, IBA FC65-G and CC13 to be 0.930 ± 1.24%, 0.960 ± 1.17%, 0.942 ± 1.24% and 0.967 ± 1.24%, respectively.” The change also impacts the Result section of the paper in the third paragraph. “We have thus renormalized the entire response distribution of A1SL in Figure 7 at 270° to the experimentally measured (Formula presented.) of 0.985 ± 0.83%.” should be corrected to: “We have thus renormalized the entire response distribution of A1SL in Figure 7 at 270° to the experimentally measured (Formula presented.) of 0.977 ± 0.98%.” and “In this 180-degree orientation, which is the preferred setup for reference dosimetry by several institutions including ours, the (Formula presented.) was measured to be 0.980 ± 1.13%, 0.996 ± 1.13% and 0.990 ± 1.13%, for the Exradin A19, IBA FC65-G, and CC13, respectively.” should be corrected to “In this 180-degree orientation, which is the preferred setup for reference dosimetry by several institutions including ours, the (Formula presented.) was measured to be 0.980 ± 1.24%, 0.988 ± 1.24% and 0.982 ± 1.24%, for the Exradin A19, IBA FC65-G, and CC13, respectively.” The change impacts the Discussion section. “As such, the agreement between Malkov and Rogers’ Monte Carlo simulation and our experimental results for A19 is <0.53% for FV and less than 0.42% for RV for all orientations, as shown in Table IV and Figure 8(b). For the A1SL chamber, Table IV shows a partial agreement between our results and the Monte Carlo work of Malkov and Rogers. The agreement is relatively good, -0.41 %, at 0° for both FV and RV, while it becomes significantly different for 90° (−0.1% for FV vs −1.45% for RV) and 270° (−0.61% for FV vs +0.41% for RV). Table IV only gives a snapshot of a few cardinal orientations. It is only through a full comparison of the curves, as we have provided in Figure 8(a) that one can notice that from 0° to 180°, the data almost overlaps the distribution for FV, while from 180° to 360°, the experimental data is in better agreement with RV.” should be corrected to: “As such, the agreement between Malkov and Rogers’ Monte Carlo simulation and our experimental results for A19 is <0.76% for FV and less than 0.68% for RV for all orientations, as shown in Table IV and Figure 8(b). Within uncertainty, our results also suggest a larger absolute value of conversion factor (Formula presented.) for A19. For the A1SL chamber, Table IV shows a partial agreement between our results and the Monte Carlo work of Malkov and Rogers. The agreement is relatively good, about 0.4%, at 0° for both FV and RV, while it becomes significantly different for 90° (0.7% for FV vs −0.65% for RV) and 270° (0.2% for FV vs 1.21% for RV). Table IV only gives a snapshot of a few cardinal orientations. It is only through a full comparison of the curves, as we have provided in Figure 8(a) that one can notice that from 0° to 180°, the data tracks between two Monte Carlo datasets and more congruent with RV, while from 180° to 360°, the experimental data are in better agreement with FV.” The sixth and seventh paragraph of Discussion section are also impacted: “At parallel orientation, a difference of 1.61% was observed when comparing (Formula presented.) for IBA FC65-G to Monte Carlo study performed by Malkov and Rogers [9].” “Similarly, comparing the magnitude of our measured correction factor for the same chamber at 180° angle against the experimental data by de Prez et al. [17] has shown a disagreement of 1.1%, although for the 90° orientation, the agreement was about 0.42%.” “Finally, the result for the CC13 chamber agrees within 0.6% with the only available Monte Carlo study for this chamber [9].” should be corrected to: “At parallel orientation, a difference of 0.85% was observed when comparing (Formula presented.) for IBA FC65-G to Monte Carlo study performed by Malkov and Rogers [9].” “Similarly, comparing the magnitude of our measured correction factor for the same chamber at 180° angle against the experimental data by de Prez et al. [17] has shown a disagreement of 0.26%, although for the 90° orientation, the agreement was about 0.46%.” “Finally, the result for the CC13 chamber agrees well within 0.16% with the only available Monte Carlo study for this chamber [9].”.