Real-Time Tracking Of Linac Parameters For Verification Of Dynamic Multileaf Collimator (DMLC) Based Radiotherapy Treatment
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Date
2018-07
Authors
Midi, Nur Shaheera
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Intensity Modulated Radiation Therapy (IMRT) delivers highly conformal dose to tumour using dynamic multileaf collimator (MLC). The complexity of IMRT delivery requires patient specific pre-treatment verification. This study investigates application of real-time tracking data for IMRT verification from two modern radiotherapy linacs of different tracking mechanism. Varian linac uses motor current feedback to track the MLC and logged the data as Varian log file (VLF), whereas Elekta linac uses optical tracking system and logged the data as Elekta log file (ELF). The tracking data from three head and neck (HN) IMRT treatments from both linacs were analysed using algorithms developed with Matlab (MathWorks, Natick, MA). The data structure of the VLF analysed agrees with the literatures. Another algorithm was developed to characterise ELF, based on the VLF algorithm developed. The algorithm was used to evaluate the accuracy of the IMRT plans and the MLC performance delivered from the linac. Analysis of IMRT delivery logged in VLF shows that the MLC error during treatment is between -1.3 to 2.1 mm. The MLC error for IMRT delivery logged in ELF is higher between -3.0 to 3.9 mm. However, only 1% of the error is above the AAPM TG 142 recommended 3.5 mm tolerance value. The discrepancies of other tracked treatment parameters are also within the tolerance. Percentage gamma pass rates of IMRT delivery ranges from 97.46% to 99.76% for VLF and 97.45% to 100% for ELF. Real-time tracking data is useful for verification of dMLC based radiotherapy delivery and evaluation of the MLC performance.
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Keywords
Real-time tracking of linac parameters , verification of dynamic multileaf collimator