Polar graphs displaying the programmed dose rate, gantry speed and MLC leaf positions as a function of gantry angle for (a) the Static MLC Twinkle, (b) the Dynamic MLC Twinkle, (c) the Sunrise and (d) the Snooker Cue for machine QA.
Experimental setups for the machine QA tests: (a) Gafchromic film in transversal plane through the isocenter in 10 × 10 cm2 solid water blocks, (b) 2D ion chamber array with inclinometer mounted to the tray holder of the Clinac and (c) EPID with metal rod placed on the treatment couch.
Schematic overview of the MLC shapes and the field sizes used for the basic validation of the dose calculation. The drawings correspond to the Millenium120 MLC setup, but are very similar for the HD MLC. The cross marks the CAX and the δ indicates the leaf gap(s) between opposing leaf tips. The collimator settings are indicated first for the central setup and second for the laterally or longitudinally shifted setup. All measurements were performed at a depth of 5 cm and SSD = 95 cm, except the Static Twinkle and Sunrise test which were performed in the setup shown in Fig. 2.
Some illustrations of the artificial structures contoured in the Octavius: (a) central and off-axis cylinder, (b) spherical prostate with bladder and rectum, (c) horseshoe-shaped head and neck volume with two PTVs, (d) oesophagus and spinal cord tilted cylinders, (e) spiral shaped Snake structure. Heterogeneity tests were performed in the home made inhomogeneous lung phantom displayed in (f).
Examples of machine QA measurements: (a) StarCheck and inclinometer data obtained for the Static MLC Twinkle data for correct delivery (upper polar plot) and delivery with intended errors (lower polar plot). The gray bars indicate the theoretically expected dose rate as a function of gantry angle. The errors shown in the lower part correspond to an artificially induced gantry inertia effect of 3° and a 2° smoothening effect of the gantry angle motion. (b) Film data obtained for the Static MLC Twinkle displaying correct delivery, induced inertia effect and overly smoothened delivery. All comparisons show the expected image, the measured film and the isodoses of the measurement overlayed on the expected image.
Integrated images of one of the subarcs of the Snooker Cue test: displaying the rod in the center of the projected MLC gaps for all gantry angles for the correct delivery (a) and the displaced projection of the metal rod in the vertical lines for the simulated inertia error of 1° (b) and 2° (c) (for all gantry angles except the starting angle).
Effect of the resolution on the calculation accuracy: Measured (film) (black line) and calculated doses (AAA 8.9 with 2.5 mm (dotted line) or 1 mm (solid line) resolution and AAA 10.0 (dashed line) with a 0.3 mm fluence resolution and 1 mm dose calculation resolution) for (a) the central DLG test setup with a 3 mm gap between the leaf tips, (b) the off-axis test setup with a 3 mm gap between the leaf tips and (c) the tongue and groove setup.
Effect of the angular resolution on the calculation accuracy: (a) Sunrise test calculated with 15° (dashed line), 3° (solid line) and 1° (solid black line) angular resolution. The position of the extracted line profiles is shown on the 2D dose images displayed on the right of the graph. (b) Dynamic gantry, sweeping gap test results for film (black line), 2D array (black squares), and AAA 8.9 dose calculations with an angular resolution of 15° (solid line) and 1° (dashed line). (c) Line profiles corresponding to the Tongue and groove arc, measured with film (solid black line) and the 2D array (black squares) and calculated with 1° angular resolution and 1 mm dose grid resolution for a 2.5 mm (dashed line) and 0.3 mm (solid line) fluence map resolution.
Examples of a comparison of calculated and measured data for a number of RapidArc plans made on the artificial structures. (a) Line profiles in the upper part of each quadrant show the film data while the lower part displays the 2D array measurement points compared to AAA 8.9. (b) Isodose overlays and gamma evaluation maps from which the line profiles were extracted. Red points indicate measurement points with a gamma value larger than unity. The black lines indicate the position of the lineprofiles shown in (a).
Measured and calculated data obtained in the heterogeneous lung phantom for the mediastinal and lateral lobe PTV structures. The ion chamber absolute point dose measurement is indicated with a diamond.
Examples of the comparison of predicted (PDIP) and measured (aSi) portal dose images for two arc deliveries (on the Novalis TX treatment unit). The position of the displayed line profiles is indicated on the gamma evaluation map. The upper graph shows the area of poor gamma agreement in the “_v” line profile. The lower graph shows the typical extreme modulation observed in the RA integrated images.
Overview of the used measurement equipment for the different parts of the RA validation protocol. Letters indicate during which phases the setups are used: I = implementation, R = routine, P = problem investigation or U = major upgrade.
Overview of the planning results for a number of RA plans on the artificial structure sets. Different plans listed for the same structure set were all obtained with identical constraints and priorities during the optimization process for meaningful inter comparison. The confirmity Index CI, the lesion coverage fraction, LCF, and the normal tissue overdosage fraction, NTOF, are calculated for the 95% isodose, according to the formulas listed in the manuscript.
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