• Progress in Medical Physics
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• v.26 no.4
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• pp.223-228
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• 2015

Double-focused micro-Multileaf Collimator (${\mu}MLC$) is able to create radiation fields having sharper dose gradients at the field edges than common MLC. Therefore, ${\mu}MLC$ has been used for the stereotactic radiosurgery (SRS) and Stereotactic Radiotherapy (SRT). We evaluated the dosimetric characteristics of a doublefocused Dynamic-${\mu}MLC$ (DMLC) attached to the Elekta Synergy linear accelerator. For this study, the dosimetric parameters including, Percent Depth Dose (PDD), Leaf leakage and penumbra, have been measured by using of the radiochromic films (GafChromic EBT2), EDGE diode detector and three-dimensional water phantom. All datas were measured on 6 MV x-ray. As a result, The DMLC shows transmission below to 1% and because of double-focused construction of the DMLC, the penumbras of fields with DMLC are independent from the field sizes. In this paper, the resulting dosimetric evaluations proved the applicability of the DMLC attached to the Elekta Synergy linear accelerator.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.1
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• pp.1-10
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• 2012

Purpose: To evaluate dose distribution differences when the dose rates are randomly changed in intensity-modulated radiation therapy using a dynamic multileafcollimator. Materials and Methods: Two IMRT treatment plans including small-field and large-field plans were made using a commercial treatment planning system (Eclipse, Varian, Palo Alto, CA). Each plan had three sub-plans according to various dose rates of 100, 400, and 600 MU/min. A chamber array (2D-Array Seven729, PTW-Freiburg) was positioned between solid water phantom slabs to give measurement depth of 5 cm and backscattering depth of 5 cm. Beam deliveries were performed on the array detector using a 6 MV beam of a linear accelerator (Clinac 21EX, Varian, Palo Alto, CA) equipped with 120-leaf MLC (Millenium 120, Varian). At first, the beam was delivered with same dose rates as planned to obtain reference values. After the standard measurements, dose rates were then changed as follows: 1) for plans with 100 MU/min, dose rate was varied to 200, 300, 400, 500 and 600 MU/min, 2) for plans with 400 MU/min, dose rate was varied to 100, 200, 300, 500 and 600 MU/min, 3) for plans with 600 MU/min, dose rate was varied to 100, 200, 300, 400 and 500 MU/min. Finally, using an analysis software (Verisoft 3.1, PTW-Freiburg), the dose difference and distribution between the reference and dose-rate-varied measurements was evaluated. Results: For the small field plan, the local dose differences were -0.8, -1.1, -1.3, -1.5, and -1.6% for the dose rate of 200, 300, 400, 500, 600 MU/min, respectively (for 100 MU/min reference), +0.9, +0.3, +0.1, -0.2, and -0.2% for the dose rate of 100, 200, 300, 500, 600 MU/min, respectively (for 400 MU/min reference) and +1.4, +0.8, +0.5, +0.3, and +0.2% for the dose rate of 100, 200, 300, 400, 500 MU/min, respectively (for 600 MU/min reference). On the other hand, for the large field plan, the pass-rate differences were -1.3, -1.6, -1.8, -2.0, and -2.4% for the dose rate of 200, 300, 400, 500, 600 MU/min, respectively (for 100 MU/min reference), +2.0, +1.8, +0.5, -1.2, and -1.6% for the dose rate of 100, 200, 300, 500, 600 MU/min, respectively (for 400 MU/min reference) and +1.5, +1.9, +1.7, +1.9, and +1.2% for the dose rate of 100, 200, 300, 400, 500 MU/min, respectively (for 600 MU/min reference). In short, the dose difference of dose-rate variation was measured to the -2.4~+2.0%. Conclusion: Using the Varian linear accelerator with 120 MLC, the IMRT dose distribution is differed a little <(${\pm}3%$) even though the dose-rate is changed.