(Saturday, 4/7/2018)
Room: Foyer
Purpose: TrueBeam becomes the linear accelerator of choice in the present years. The 2 models available are with high definition multi leaf collimation with 2.5 mm thick MLC for the central 10 cm x 10 cm fields size and 5 mm thick MLC for the first 10 cm X 10 cm field size. We want to show the significance of this difference and methods to minimze it via optimization procedures
Methods: 25 patients were chosen that were treated for lung lesions using SBRT with 3-5 high dose fractions. The patients were chosen from 2 different centers who are using the 2 TrueBeam types. New plans were generated in using the type of MLC that was not used in the initial plan applying identical optimization parameters. A dosimetric analysis has been performed for the 2 plans and a radiobiological analysis. We compared the biological effective dose (BED), the equivalent uniform dose, the tumor control probability for lung lesions and the normal tissue complications probability (NTCP) for the healthy lung and the surrounding healthy tissue. The homogeneity of the dose distribution, the conformity and the conformality indexes were evaluated
Results: A considerable improvement in planning target volume (PTV) coverage has been seen and a better dose distribution uniformity in the PTV in the treatment plans that used the HD-MLC. We could not detect the same degree of improvement to the normal tissue surrounding the PTV. The dosimetrical differences due to the use of these 2 types of MLCs are significant in lung treatment plans.
Conclusion: PTV coverage and its dose distribution uniformity when using the HD-MLC make the TrueBeam machine that carry those, a better tool in radiation therapy. The normal structures did not display a significant dose distribution improvement. Changing optimization constraints we can improve the outcome to the normal tissue
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