• Radiation Oncology Journal
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• v.14 no.1
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• pp.77-85
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• 1996

Purpose : Multileaf collimator(MLC) is very suitable tool for conformal radio-therapy and commissioning measurements for a multileaf collimator installed on a dual energy accelerator with 6 and 10MV photons are required, For modeling the collimator with treament planning software, detailed dosimetric characterization of the multileaf collimator including the penumbra width, leaf transmission between leaf leakage and localization of the leaf ends and sides is an essential requirement. materials and Methods : Measurement of characteristic data of the MLC with 26 pair block leaves installed on CLINAC 2100C linear accelerator was performed. Low sensitive radiographic film(X-omatV) was used for the penumbra measurement and separate experiments using radiographic film and thermoluminescent dosimeters were performed to verify the dose distribution, Measured films were analized with a photodensitometer of WP700i scanner. Results : For 6 & 10 MV x-ray energies, approximately $2.0\%$ of photons incident on the multileaf collimator were transmitted and an additional $0.5\%$ leakage occurs between the leaves. Localizing the physical end of the leaves showed less than 1mm deviation from the $50\%$ decrement line and this difference is attributed to the curved shaped end on the leaves One side of a sin히e leaf corresponded to the $50\%$ decrement line, but the opposite face was aligned with a lower value. This difference is due to the tongue and groove used to decrease between leaf leakage. Alignment of the leaves to form a straight edge resulted larger penumbra at far position from isocenter as compare with divergent alloy blocks. When the MLC edge is stepped by sloping field, the isodose lines follow the leaf pattern and Produce scalloping isodose curves in tissue. The effective penumbra by 45 degree stepped MLC is about 10mm at 10cm depth for 6MV x-ray. The difference of effective penumbra in deep tissue between MLC and divergent alloy blocks is small (5mm). Conclusion : Using the characteristic data of MLC, the MLC has the clinlical acceptability and suitability for 3-D conformal radiotherapy except small field size.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2006.08a
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• pp.76-76
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• 2006

• The Journal of Korean Society for Radiation Therapy
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• v.9 no.1
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• pp.29-36
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• 1997

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.2
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• pp.305-312
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• 2014

Purpose : The purpose of this study is to analyze the mechanical and leaf speed accuracy of the dynamic multileaf collimator (DMLC) and determine the appropriate period of quality assurance (QA). Materials and Methods : The quality assurance of the DMLC equipped with Millennium 120 leaves has been performed total 92 times from January 2012 to June 2014. The the accuracy of leaf position and isocenter coincidence for MLC were checked using the graph paper and Gafchromic EBT film, respectively. The stability of leaf speed was verified using a test file requiring the leaves to reach maximum leaf speed during the gantry rotation. At the end of every leaf speed QA, dynamic dynalog files created by MLC controller were analyzed using dynalog file viewer software. This file concludes the information about the planned versus actual position for all leaves and provides error RMS (root-mean square) for individual leaf deviations and error histogram for all leaf deviations. In this study, the data obtained from the leaf speed QA were used to screen the performance degradation of leaf speed and determine the need for motor replacement. Results : The leaf position accuracy and isocenteric coincidence of MLC was observed within a tolerance range recommanded from TG-142 reports. Total number of motor replacement were 56 motors over whole QA period. For all motors replaced from QA, gradually increased patterns of error RMS values were much more than suddenly increased patterns of error RMS values. Average error RMS values of gradually and suddenly increased patterns were 0.298 cm and 0.273 cm, respectively. However, The average error RMS values were within 0.35 cm recommended by the vendor, motors were replaced according to the criteria of no counts with misplacement > 1 cm. On average, motor replacement for gradually increased patterns of error RMS values 22 days. 28 motors were replaced regardless of the leaf speed QA. Conclusion : This study performed the periodic MLC QA for analyzing the mechanical and leaf speed accuracy of the dynamic multileaf collimator (DMLC). The leaf position accuracy and isocenteric coincidence showed whthin of MLC evaluation is observed within the tolerance value recommanded by TG-142 report. Based on the result obtained from leaf speed QA, we have concluded that QA protocol of leaf speed for DMLC was performed at least bimonthly in order to screen the performance of leaf speed. The periodic QA protocol can help to ensure for delivering accurate IMRT treatment to patients maintaining the performance of leaf speed.

• Radiation Oncology Journal
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• v.13 no.4
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• pp.391-396
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• 1995

Purpose : The Conformal Radiation Therapy has bee widely used under favour of development of computer technologies. The delivery of a large number of static radiation fields are being necessary for the conformal irradiation. In this paper we investigate dosimetric characteristics on penumbra regions of a multileaf collimator(MLC), and compare to those of lead alloy block for the optimal use of the system in 3-D conformal radiotherapy. Materials and Methods : The measurement of penumbra by MLC or lead alloy block was performed with 6 or 10 MV X-rays. The film was positioned at a dmax depth and 10 cm depth, and its optical density was determined using a scanning videodensitometer. The effective penumbra, the distance from $80{\%}$ to $20{\%}$ isodose lines and $90{\%}$ to $10{\%}$ were analyzed as a function of the angle between the direction of leaf motion and the edge defined by leaves. Results : Increasing MLC angle ($0-75^{\circ}$) was observed with increasing the penumbra widths and the scalloping effect. There was no definite differences of penumbra width from $80{\%}$ to $20{\%}$ isodose lines, while being the small increase of penumbra width from $90{\%}$ to $10{\%}$ isodose line varing the depth and energy. The effective penumbra width of lead alloy block are agree resonably with those of MLC within 4.8mm. Conclusion : The comparative qualitative study of the penumbra between MLC and lead alloy block demonstrate the clinical acceptability and suitability of the multileaf collimator for 3-D conformal radiotherapy.

• Journal of radiological science and technology
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• v.36 no.2
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• pp.157-163
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• 2013

Multileaf collimators whose Pb leaves are moving in two-dimensional directions have been used. We propose a different concept three-dimensional (3D) collimator with 3D shape that is automatically changeable to modulate the radiation dose even for complex tumors in real time. A voxel collimator, including a hinged Pb plane and a 3D assembly of many voxel collimators, was used. In each frame rotation axis, a motor, which was controlled by a circuit with field-programmable gate array (FPGA) board connected with computer, was operated according to a predetermined plan. Simulations of that, which are generally used for planning, were performed and compared with experimental results.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.2
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• pp.233-238
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• 2014

Purpose : The Varian's Eclipse radiation treatment planning system is able to correct radiation treatment thought leaf gap which is limitation MLC movement for collision with both MLC. In this study, I'm try to analyze dosimetric effect about the leaf gap in treatment planning system. And then apply to clinical implement. Materials and Methods : The Elclipse version is 10.0. In general, the leaf gap set to 0.05~0.3 mm and must measurement each leaf gap. The leaf gap measured by each LINACs and photons. We applied to measured each leaf gap in IMRT and VMAT. Changing the leaf gap, we evaluated treatment plans by Dmax, CI, etc. Results : When the same plan was evaluated with changing the leaf gap, an increase of 2-5% over the value Dmax, CI increases mm to 0.0~0.50 mm leaf gap. Volumetric modulated and intensity modulated radiation therapy plans all showed the same trend was not found significant between each radiation treatment planning. Conclusion : Generally, the leaf gap setting has a unique measure of the Multileaf collimator. However, the aging of the Multileaf collimator, calibration, and can be changed, after inspection and repair of the lip gap should eventually because these values affect the treatment plan must be applied to the treatment after confirmation. In some cases, may be to maintain the initial setting value of the lip gap, which is undesirable because it can override the influence on the treatment plan.

• Journal of radiological science and technology
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• v.39 no.4
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• pp.595-600
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• 2016

The diagnostic multileaf collimator(MLC) was designed for patient dose reduction in diagnostic radiography We used monte carlo simulation code (MCNPX, LANL, USA) to evaluate efficiency of shielding material for making diagnostic MLC as preliminary study. The diagnostic radiography unit was designed using SRS-78 program according to tube voltage (80,100,120 kVp) and acquired energy spectrums. The shielding material was SKD11 alloy tool steel that is composed of 1.6% carbon(C), 0.4% silicon(Si), 0.6% manganese (Mn), 5% chromium (Cr), 1% molybdenum(Mo) and vanadium(V). The density of it was $7.89g/cm^3$.Using tally card 6, we calculated the shielding efficiency of MLC according to tube voltage. The results was that 98.3% (80 kVp), 95.7 %(100 kVp), 93.6% (120 kVp). We certified efficiency of diagnostic MLC fabricated from SKD11 alloy steel by monte calro simulation. Based on the results, we designed the diagnostic MLC and will develop the diagnostic MLC for reduction of patient dose in diagnostic radiography.

• Progress in Medical Physics
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• v.12 no.2
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• pp.185-191
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• 2001

The virtual compensator which are realized using a multileaf collimator(MLC) and three-dimensional radiation therapy Planning(3D RTP) system was designed. And the feasibility study of the virtual compensator was done to verify that it can do the function of the conventional compensator properly. As a model for the design of compensator, styrofoam phantom and mini water phantom were prepared to simulate the missing tissue area and the calculated dose distribution was produced through the 3D RTP system. The fluence maps which are basic materials for the design of virtual compensator were produced based on the dose distribution and the MLC leaf sequence file was made for the realization of the produced fluence map. Ma's algorithm were applied to design the MLC leaf sequence and all the design tools were programmed with IDL5.4. To verify the feasibility of the designed virtual compensator, the results of irradiation with or without a virtual compensator were analyzed by comparing the irradiated films inserted into the mini water phantom. The higher dose area produced due to the missing tissue was removed and intended regular dose distribution was achieved when the virtual compensator was applied.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2006.08a
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• pp.60-60
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• 2006