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SU‐E‐T‐261: Plan Quality Assurance of VMAT Using Fluence Images Reconstituted From Log‐Files
Author(s) -
Katsuta Y,
Shimizu E,
Matsunaga K,
Majima K
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4888592
Subject(s) - quality assurance , collimator , dosimetry , fluence , nuclear medicine , root mean square , mathematics , fraction (chemistry) , position (finance) , computer science , statistics , physics , optics , medicine , chemistry , laser , external quality assessment , pathology , quantum mechanics , organic chemistry , finance , economics
Purpose: A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi‐leaf collimator (MLC) shapes. One of the main problem in the plan quality assurance is dosimetric errors associated with leaf‐positional errors are difficult to analyze because they vary with MU delivered and leaf number. In this study, we calculated integrated fluence error image (IFEI) from log‐files and evaluated plan quality in the area of all and individual MLC leaves scanned. Methods: The log‐file reported the expected and actual position for inner 20 MLC leaves and the dose fraction every 0.25 seconds during prostate VMAT on Elekta Synergy. These data were imported to in‐house software that developed to calculate expected and actual fluence images from the difference of opposing leaf trajectories and dose fraction at each time. The IFEI was obtained by adding all of the absolute value of the difference between expected and actual fluence images corresponding. Results: In the area all MLC leaves scanned in the IFEI, the average and root mean square (rms) were 2.5 and 3.6 MU, the area of errors below 10, 5 and 3 MU were 98.5, 86.7 and 68.1 %, the 95 % of area was covered with less than error of 7.1 MU. In the area individual MLC leaves scanned in the IFEI, the average and rms value were 2.1 – 3.0 and 3.1 – 4.0 MU, the area of errors below 10, 5 and 3 MU were 97.6 – 99.5, 81.7 – 89.5 and 51.2 – 72.8 %, the 95 % of area was covered with less than error of 6.6 – 8.2 MU. Conclusion: The analysis of the IFEI reconstituted from log‐file was provided detailed information about the delivery in the area of all and individual MLC leaves scanned.