Abstract
The aim of this study is to ensure the MLC positional and leaf speed accuracy. To check the MLC positional and leaf speed accuracy picket fence and synchronized segmented stripes test pattern were performed. The relative and absolute dosimetric verification were analyzed in this study. This project was followed by Quality control for Intensity-Modulated Radiation Therapy, as in the Recommendation No.15 from SGSMP. For relative dosimetric verification test such as different dose in same depth, same dose in different depth, chair test and inhomogeneous test were performed. All the plans were followed by Gamma index. To verify absolute dose 0.3 cc SemiFlex chamber along with a PTW solid water phantom was used. In picket fence and synchronized segmented stripes test, match-lines appear at -10.0, -5.0, 0.0, 5.0, 10.0 and -12.0, -8.0, -4.0, 0.0, 4.0, 8.0, 12.0 cm respectively from the center of the field. The Gamma Index for the different dose in same depth, same dose in different depth, chair test and inhomogeneous test were 99.48% & -0.52%, 99.35% & -0.65%, 99.04% & -1.96% and 98.34% & -1.66% at the pixel range of -1.00 to 1.00 & 1.00 to 2.00 respectively. Calculated and measured absolute dose for three cases were 2.050 &1.970 (% deviation 4.06), 1.728 & 1.730 (% deviation -0.011) and 1.270 & 1.250 (% deviation 1.6).
Highlights
The positional accuracy of the Multi leaf collimator (MLC) has a larger impact on delivered dose in intensity modulated radiotherapy (IMRT) than in conventional 3DCRT, where the MLC defines only the outer border of the beam
The positional accuracy of the MLC should be evaluated over the full range of leaf travel and carriage motion that will be clinically employed
Commissioning and quality assurance of dMLC for IMRT application requires considerable time and effort.The positional accuracy of the MLC has a larger impact on delivered dose in IMRT than in conventional 3DCRT, where the MLC defines only the outer border of the beam
Summary
The positional accuracy of the MLC has a larger impact on delivered dose in IMRT than in conventional 3DCRT, where the MLC defines only the outer border of the beam. Quality assurance of the leaf speed, leaf position vs time or monitor units, is only strictly necessary if performing IMRT with the dynamic MLC technique. With this technique exact control of leaf speed is the main condition determining the accuracy of IMRT delivery, and its measurement is a critically important element of the IMRT quality assurance chain for dMLC delivery. Multi leaf collimator (MLC) based intensity modulated radiotherapy is the result of a highly complex automated process of delivering dose to the patient.
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