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Which One Is More Reliable in Determining Leaf Position Uncertainties: SNC Machineâ„¢ Hancock MLC Test Or AutoCALâ„¢ MLC Test

K Jacobs*, C Yang , Department of Radiation Oncology, University of Mississippi Med. Center, Jackson, MS


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To compare the absolute MLC leaf position tests of SNC Machineâ„¢ Hancock and AutoCALâ„¢.

Methods: The procedure for SNC Machineâ„¢ Version 1.4.5 Hancock and AutoCALâ„¢ v2.4 tests were performed as outlined by the vendor on an Elekta Synergy with MLCi2 MLCs. The SNC Machineâ„¢ Hancock test is comprised of three 1 cm pickets with 10.5 cm between the center of each picket while the AutoCALâ„¢ is a picket fence test with six 3.5 cm abutting pickets that cover 23.5 cm and AutoCAL analyzes the five abutments. Initially these tests were performed with two MLC leaves out of calibration by 1.5 mm. Those leaves were then corrected and the SNC Machineâ„¢ Hancock and AutoCALâ„¢ tests were performed again.

Results: Between the first tests, which had MLC errors, and the second tests, SNC Machineâ„¢ detected the MLC errors while AutoCALâ„¢ did not. SNC Machineâ„¢ Hancock test gives absolute leaf position for each MLC in each of the three pickets while AutoCALâ„¢ gives the distance between the measured position and the expected position of the peak or trough for each MLC in the picket fence pattern. Because of this, the root mean square (RMS) of the positional differences was compared. The mean RMS for each test was calculated to be 0.33 mm and 0.22 mm for SNC Machineâ„¢ Hancock and AutoCALâ„¢ respectively with the MLC error and 0.31 mm and 0.23 mm respectively without the MLC error. The differences between these mean errors were determined to be statistically significant with a 95% confidence interval with P < 0.0001 for both trials.

Conclusion: It can be concluded both statically and for best clinical use that the SNC Machineâ„¢ Hancock test is a more reliable and robust test than AutoCALâ„¢ for absolute MLC position tests.


MLC, Quality Assurance, Linear Accelerator


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