An MLC calibration method using a detector array
Minor leaf offsets are defined as the spatial offset of each leaf in a leaf bank relative to the reference leaf, leaf 20. Major leaf offsets are defined as the distance of the reference leaf to the radiation center of the beam.
(a) The RDRL method requires precisely known detector positions; small positional errors in the array’s detectors can disrupt this method by introducing false offsets into the leaf positions. The detector offsets are corrected for, which effectively creates uniform detector positions. (b) Two detectors are located in the projection of each leaf and measure the position of the leaf end.
The measurements required to radiographically align the array. The thick solid line shows an open field measurement used for comparing the alignment profiles, the dashed line shows the initial setup of the array, and the thin solid line shows a correct radiographic alignment with the backup jaw after repositioning the array.
(a) Detector offsets relative to a reference detector. The reference detector is chosen based on which detector lies in the projection of the reference leaf. Detectors at −0.4, 4.4, and 10 cm displayed a larger than average offset value as shown by the solid line. After detector replacement, the dashed line shows the nominal offsets. (b) Measurements with each backup jaw located at the CAX position. The mirrored behavior of the three large spikes on the profiles indicates that they are due to positional errors.
MLC leaf offsets relative to leaf number 20, the reference leaf.
Change in the relative MLC offsets after replacement of the primary Mylar mirror.
Calibration of the X1 MLC leaf bank. Measurements show the relative MLC positions before calibration and after two iterations of the RDRL method with the profiler.
List of collimator settings for Profiler 2 measurements of the X1 MLC leaf bank at CAX for minor leaf offsets in Sec. ???. Settings are based on the IEC 1217 Convention.
List of additional collimator settings for Profiler 2 measurements of the major leaf offsets in Sec. ???. The fields listed are for measurement of the X1 reference leaf at retracted, SYM fields, and extended, X1 fields; the CAX fields were measured during the minor leaf offsets in Sec. ???. Settings are based on the IEC 1217 Convention.
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