Application of the gamma evaluation method in Gamma Knife film dosimetry
Drawings of Leksell coordinates: the superior posterior right corner of the patient is the origin (0, 0, 0) and the center coordinate of the Leksell frame is (100, 100, 100). The x axis has a right to left direction, the y axis has a posterior to anterior direction, and the z axis has a cranial to caudal direction relative to the patient. [From Elekta AB, Online Reference Manual Leksell GammaPlan® 8.3 (Document number 1008129), Rev. 01, Copyright © 2008/06 by Elekta Instrument AB. Reprinted by permission of Elekta AB].
Collimator sector configuration for the composite shot, which is a characteristic feature of GK PFX. The 4, 8, and 16 mm shots and blocked sectors were mixed.
Dosimetric phantoms used for GK QA purpose and irradiation sample of the EBT2 film. (a) Old polystyrene phantom and phantom holder; (b) new solid water phantom and EBT2 film in the axial plane configuration; (c) in the coronal plane configuration; and (d) irradiation sample of Gafchromic EBT2 film.
Optical density vs absolute dose curves of EBT2 film in the 0–10 Gy dose range for red, green, and blue channels.
Comparison of isodose lines between planning dose distribution and film measurement in the axial plane. Solid lines are the 20, 50, and 80% isodose lines from the DICOM RT file. Dash lines are measured isodose lines.
Comparison of the line profiles of four test plans and film measurements in the diagonal direction along the anterior-right to posterior-left side of the patient (top left to right bottom side in Fig. 5). The solid lines correspond to DICOM RT data and the dotted lines correspond to film measurement data.
Gamma index map for 0.5 mm/0.5% tolerance criteria in the axial plane.
Dose gamma index histogram in 5% isodose bins for 0.5 mm/0.5% and 0.3 mm/0.3% tolerance criteria in the axial plane.
Dose pass rate histogram in 5% isodose bins for 0.5 mm/0.5% and 0.3 mm/0.3% tolerance criteria in the axial plane.
Pass rates of gamma evaluation within the 20 and 50% isodose lines using four evaluation criteria (2.0 mm/2.0%, 1.0 mm/1.0%, 0.5 mm/0.5%, and 0.3 mm/0.3%; units, %).
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