TH-C-AUD-05: Monte Carlo Simulation and Measurment Investigations of Motorized Multi-Leaf Collimator for Electron Beam Delivery

Nassiri, Mikaël Ghadimi; Bouchard, Hugo; Mercure, S; Carrier, Jean‐François

doi:10.1118/1.2761664

Cited by 3 publications

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“…Due to the clinically unacceptable diffused field edges at the patient surface, Karlsson and Karlsson (2002) and Blomquist et al (2002) investigated the use of helium in the treatment head and Moran et al (1997), Klein (1998) and Plessis et al (2006) tested source-tosurface distances (SSDs) of 60 to 85 cm to reduce electron scattering in air. In addition, two types of add-on collimators were developed: a few-leaf electron collimator (FLEC) consisting of four motorized copper blades to approximate conformal shapes by rectangular beams designed by Al-Yahya et al (2005a) and various prototypes of an electron multileaf collimator (eMLC) presented by Leavitt et al (1989), Lee et al (2000), Ma et al (2000), Ravindran et al (2002), Hogstrom et al (2004), Gauer et al (2006), Nassiri et al (2007) and Jin et al (2007). However, with the exception of the prototype of Leavitt et al (1989) and more recently the prototypes of Al-Yahya et al (2005a) and Nassiri et al (2007), the collimators are manually driven and aside from the versions of Leavitt et al (1989) and Jin et al (2007) not yet usable at oblique beam incidence.…”

Section: Introductionmentioning

confidence: 99%

Characterization of an add-on multileaf collimator for electron beam therapy

et al. 2008

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An add-on multileaf collimator for electrons (eMLC) has been developed that provides computer-controlled beam collimation and isocentric dose delivery. The design parameters result from the design study by Gauer et al (2006 Phys. Med. Biol. 51 5987-6003) and were configured such that a compact and light-weight eMLC with motorized leaves can be industrially manufactured and stably mounted on a conventional linear accelerator. In the present study, the efficiency of an initial computer-controlled prototype was examined according to the design goals and the performance of energy- and intensity-modulated treatment techniques. This study concentrates on the attachment and gantry stability as well as the dosimetric characteristics of central-axis and off-axis dose, field size dependence, collimator scatter, field abutment, radiation leakage and the setting of the accelerator jaws. To provide isocentric irradiation, the eMLC can be placed either 16 or 28 cm above the isocentre through interchangeable holders. The mechanical implementation of this feature results in a maximum field displacement of less than 0.6 mm at 90 degrees and 270 degrees gantry angles. Compared to a 10 x 10 cm applicator at 6-14 MeV, the beam penumbra of the eMLC at a 16 cm collimator-to-isocentre distance is 0.8-0.4 cm greater and the depth-dose curves show a larger build-up effect. Due to the loss in energy dependence of the therapeutic range and the much lower dose output at small beam sizes, a minimum beam size of 3 x 3 cm is necessary to avoid suboptimal dose delivery. Dose output and beam symmetry are not affected by collimator scatter when the central axis is blocked. As a consequence of the broader beam penumbra, uniform dose distributions were measured in the junction region of adjacent beams at perpendicular and oblique beam incidence. However, adjacent beams with a high difference in a beam energy of 6 to 14 MeV generate cold and hot spots of approximately 15% in the abutting region. In order to improve uniformity, the energy of adjacent beams must be limited to 6 to 10 MeV and 10 to 14 MeV respectively. At the maximum available beam energy of 14 MeV, radiation leakage results mainly from the intraleaf leakage of approximately 2.5% relative dose which could be effectively eliminated at off-axis distances remote from the field edge by adjusting the jaw field size to the respective opening of the eMLC. Additionally, the interleaf and leaf-end leakage could be reduced by using a tongue-and-groove leaf shape and adjoining the leaf-ends off-axis respectively.

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Section: Introductionmentioning

confidence: 99%

Characterization of an add-on multileaf collimator for electron beam therapy

et al. 2008

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“…[1][2][3][4][5][6][7][8] The E-MLC would be attached either on an existing electron applicator or on a retractable applicator. A second approach 9-12 is to use the photon MLC for the collimation of electron beams.…”

Section: Introductionmentioning

confidence: 99%