Purpose: To evaluate the performances of the motorized remote controlled multi‐leaf collimator for electron (eMLC) prototype developed in our center. To develop a Monte Carlo model of this prototype. To compare measurements and simulated data for various field configurations. Method and Materials: The model of the eMLC and the Elekta linac head for electron beam energies of 6, 8, 10, and 12 MeV was developed using the Monte Carlo package BEAMnrc/EGSnrc. The dose has been calculated in a water phantom using DOSXYZnrc software for different field sizes from 1.4×1.4 to 16.8×16.8 cm2. The measurement have been done using electron silicon diode. The simulated and measured profiles, percentage depth dose and output factor have been used to validate the Monte Carlo model. Physical parameters such as leakage trough the leaves, dose resolution, contamination dose and leaf scatter were investigated. The number of electron histories or the voxels dimensions where chosen to lead to a statistical uncertainty better than 2% (1 SD). Results: For all field configurations, the difference between measured and simulated penumbras is less than 2 mm and the agreement for output factors is within 2 %. The total leakage dose relative to the maximum central axis dose for a 9.8×9.8 cm2 eMLC field size at 12 MeV at the water surface is 1.7 %.and at dmax is 1.5%. We need to close at least two leaves in order to cut 50 % of the dose under the leaves. Conclusion: Our results showed that the eMLC and Linac Monte Carlo model is a realistic model. A combination of the Monte Carlo model and the prototype could be used to develop advanced techniques like modulated electron therapy and mixed‐beam modulated therapy.
Purpose: To develop a motorized multi‐leaf collimator for electrons (eMLC) and to compare preliminary measurements to Monte Carlo simulations. Method and Materials: An eMLC has been developed. It is the first prototype with fully motorized capabilities. The eMLC is remotely controlled by the operator using home brewed and fully graphical software running on a Windows workstation. The control workstation is connected to the eMLC's custom‐built electronic controller which keeps track of the component states and executes various low‐level commands, including leaf displacement orders. There are 36 independent brass leaves on each side of the eMLC and the maximum size of the generated field is 25.2 × 19.5 cm2. The interleaf distance is less than 0.03 mm. The eMLC prototype is an add‐on device for the Elekta Precise linac (Elekta Ltd., England). The actual distance from the source to the bottom of the leaves is 95.3 cm. The eMLC has been modeled using the BEAMnrc Monte Carlo toolkit and every possible leaf positions is reproducible with our Monte Carlo model. Results: Various preliminary measurements were performed: open field, closed field, one leaf profile, interleaf leakage, leaf transmission, and comparison with conventional custom cutouts. For all measurements, comparison to Monte Carlo simulations are carried out. The transmission through the leaves is 2.4% for a 12 MeV field at the surface of a water phantom with SSD=100 cm. The interleaf leakage is negligible as no interleaf pattern is detected on a closed field profile for all the investigated energies (up to 12 MeV). Conclusion: The motorized eMLC prototype is versatile and easy to operate with a computer control from outside the treatment room. Possible applications of the eMLC go from simply replacing the conventional custom cutouts to complex usages like MERT or electron arc therapy.Research sponsored by Elekta Ltd.
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