Investigation of the reliability, accuracy, and efficiency of gated IMRT delivery with a commercial linear accelerator
Dose-MU linearity results from MapCheck diode array measurements of open fields. Data for various BC and DC are presented. The output/MU values are normalized to the value for the ungated delivery with . The output was the average of those diodes with doses higher than 80% of the maximum dose in the field. The error bars show the standard deviation among diodes in terms of normalized output.
Beam flatness as a function of delivered MUs for a field for ungated and gated measurements with different BC and DC settings. Flatness defined as the percent difference between the maximum and minimum readings within the 80% of the field. The measurements were done at effective depth.
Diagonal beam profiles for a field for several gated and ungated deliveries. Gated deliveries have a BC of 24/min and DC of 20%. The dotted line is for the nominal profile obtained from the planning system (ungated). The circles are for delivery with no gating, while the squares are: (a) , (b) , and (c) gated deliveries.
Profiles along the center of each MLC for gated (dotted) and ungated deliveries (solid). The gated delivery is with a BC of 24/min and DC of 20%.
Histograms of percentage deviation from expected values in abutting regions of picket-fence irradiation for: (a) radiographic film, and (b) MapCheck diode array. The measurements were performed with and without gating on a stationary phantom.
Comparison of isodose distributions between gated (light) and ungated (dark) delivery for an IMRT field (Field #1). The data were acquired with films with a stationary phantom, and isodose lines of 90%, 80%, 70%, and 40% are depicted. The gated delivery was with a DC of 20%, and a BC of .
Fractions of reference points in each film with when compared to the gold-standard film dose distribution for and criteria. All data were collected with a stationary phantom for the IMRT field #1. Gated deliveries were made with a BC of .
The profiles measured with a diode array for the two IMRT fields: (a) field #1, and (b) field #2. The continuous lines are the profiles calculated by the treatment planning system, while the scatter points are for the gated (light) and ungated (dark) measurements. The error bars show the variation of diode readings. The measurements were acquired with a stationary phantom. BC and 20%–50% DC were used for gated deliveries.
Histogram of percent differences between gated and ungated deliveries for 50%, 37%, and 20% DC gated operations. The BC is for all deliveries. All measurements were repeated at least three times and averages of repeated measurements were used to calculate the differences.
Comparison of 20%, 45%, 80%, and 95% isodose lines for calculated and measured with film for a phantom IMRT delivery. The IMRT plan was delivered under a series of situations: Phantom with no motion and nongating, no-motion/gated with a 20% DC, motion/gated with a 37% DC, motion/gated with a 55% DC, and motion/ungated. BC of the gated deliveries as well as that of the motion phantom was .
Measured delivery time per MU as a function of the MU of a segment. The data for nongating and gating with 37% and 20% DCs are presented. The machine dose rate was . The dashed lines represents the time/MU calculated by .
Gating time factor as a function of DC.
Comparison of delivery times for a series of plans including 3DCRT with physical wedge, a 3DCRT with virtual wedge, a DAO IMRT with 12 segments, a beamlet IMRT with 23 segments, a beamlet IMRT with 55 segments, a beamlet IMRT with 89 segments, and an IMRT using compensators. All delivery times were computed based on Eq. (2).
Interplay between delivery time, number of segments, and DC for gated IMRT: (a) Dice similarity coefficient for the comparison between target volume and the prescription isodose surface, and (b) The dice similarity coefficient versus the number of segments and DC for a fixed delivery time of . The DC decreases for each curve in fig. (a) from left to right. The IMRT plans considered are beamlet based and have different numbers of segments.
The percentage of diodes that satisfy various agreement criteria for the delivery of two IMRT fields under various situations.
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