Abstract
Motive of the study is to present quantitative and qualitative analysis and comparison of beam data measurement with FF (flattening filter) and FFF (flattening filter free) beam in a Varian TrueBeamTM Medical Linear Accelerator. Critique of beam characterization and evolution of dosimetric properties for 6 MV, 10 MV, 15 MV FF beam and 6 MVFFF, 10 MVFFF FFF beam has been carried out. We performed the comparison of photon beam data for two standard FF photon energy 6 MV, 10 MV verses 6 MVFFF, and 10 MVFFF FFF beam. Determination and comparison of parameter involved PDD (Percentage depth dose), Depth dose profile, Symmetry, Flatness, Quality index, Relative output factor, Penumbra, Transmission factor, DLG (Dosimetric leaf gap), in addition to degree of Un-flatness and off-axis ratio of FFF beam. Outcomes of presenting study had shown that change of various parameters such as Percentage depth dose curves, Shape of the depth dose profile, Transmission, Value of quality index and significant rise in surface dose for FFF in comparison with FF beam. Differences in the output factor at lower and higher field sizes for FFF beam compared to that of FF beam were found. The maximum output factor deviation between 6 MV and 6 MVFFF was found to be 4.55%, whereas in 10 MV and 10 MVFFF was 5.71%. Beam quality TPR20/10 for FFF beam was found to be lesser in magnitude, 5.42% for 6 MVFFF whereas 4.50% for 10 MVFFF compared to 6 MV and 10 MV FF beam respectively. Jaw transmission and interleaf leakage for FFF beam were found to be lesser than FF beam. Also DLG for FFF beam was found to be lesser in magnitude comparable to that of flattened beam. This study is mainly inclined towards evaluation and comparison of the FF and FFF beam. It has been observed that, the outcome of a commissioning beam data generation fully complies with vendor specification and published literature.
Highlights
Installation and commissioning of the Varian TrueBeamTM millennium 120 leaf Medical Linear Accelerator were carried out in Super Specialty Capitol Hospital, Jalandhar Punjab (India)
Delta variation between Flattening Filter (FF) and Flattening Filter Free (FFF) slowly decreases with rise in field size and output factors converges to unity at field size of 10 × 10 cm2.There is no significant difference in Significant differences in output factor (Scp) at smaller field sizes for 6 MVFFF beam compared to 6 MV
Removal flattening filter alters various commissioning associated parameter as Field flatness, Field penumbra, Beam quality, Surface dose, Transmission factor, off axis energy variation and Homogeneity need to be redefined for FFF beam other than FF beam
Summary
Installation and commissioning of the Varian TrueBeamTM millennium 120 leaf Medical Linear Accelerator were carried out in Super Specialty Capitol Hospital, Jalandhar Punjab (India). Varian offers the TrueBeamTM machine in two different versions, one is with millennium 120 leaf MLC (Multi Leaf Collimator) for general purpose and the other is TrueBeamSTX with HD (High definition) 120 leaf MLC having a special purpose for stereotactic radiotherapy, which has at central (8 cm, leaf width projected at isocenter) 32 leaf pairs of MLC having 2.5 mm leaf thickness and outer (14 cm, leaf width projected at isocenter) 28 leaf pairs of MLC having 5 mm leaf thickness to achieve high precise target conformation and minimize the penumbra effect Both TrueBeamTM machines have a feature with FF (Flattening Filter) and FFF (Flattening Filter Free) mode along with electron energy.
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