Dosimetric comparison of an integrated multileaf-collimator versus a conventional collimator

Abstract

The dosimetric characteristics of both a conventional GE collimator (CC) and a GE multileaf collimator (MLC) are compared for different photon beam energies. The integrated GE MLC consists of 32 pairs of tungsten leaves, replacing the lower pair of jaws of the conventional collimator. Measurements were performed with the conventional collimator before this collimator was replaced by the MLC. All parts of the accelerator except the collimator remained the same. Leakage and transmission measurements show good agreement with the manufacturer's specification, stating a leakage between leaves of less than 1% for all energies and a transmission through leaves of less than 0.5%. The dosimetric characteristics of both collimators are very similar for square and rectangular fields. No significant change in beam quality, beam attenuation and depth of maximum dose could be detected within the measurement accuracy. The MLC output ratio variation is smaller than the one measured with the CC. The penumbra difference in the Y direction is less than 0.5 mm at a depth of 5 cm in phantom; in the X direction the penumbra is 1 mm larger for the MLC due to the rounded leaf fronts. As the two leaf banks replace the lower pair of collimator jaws the distance from the collimator end to the isocentre is similar for the two collimators, therefore the MLC does not reduce the flexibility of the treatment unit. For symmetrical and regular collimator settings the MLC can be treated as the CC.

Quality assurance for computed-tomography simulators and the computed-tomography-simulation process: Report of the AAPM Radiation Therapy Committee Task Group No. 66

“…Additional descriptions of various MLCs can be found in the literature. [59][60][61][62][63][64][65][66][67] Collimator rotation should be within Ϯ1°over full rotation ͑360°͒. Accuracy of jaw positions at various collimator angles should be tested.…”

Multileafkollimator: Erweiterte Qualitätssicherung an einem GE-Linearbeschleuniger

“…Das Wellenprofil der Lamellen dient zur Verringerung der Durchlaßstrahlung zwischen einzelnen Lamellen (Abbildung 1) [3][4][5]11]. Die Lamellen ersetzen das untere Blockblendenpaar der konventionellen Blende in X-Richtung gemäß IEC 1217.…”

Fidelity of dose delivery at high dose rate of volumetric modulated arc therapy in a truebeam linac with flattening filter free beams

“…[11] This enables for FFF, a significant improvement in out-of-field dose for small fields, which can be attributed to the change in the photon spectra,[12–14] when the flattening filter is removed from the beamline. [3] The significance of other secondary byproducts, such as neutrons, from interactions of the primary beam with high atomic number materials of the gantry head has been confirmed with computational and experimental studies for higher photon energies.…”