• The Journal of Korean Society for Radiation Therapy
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• v.30 no.1_2
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• pp.129-138
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• 2018

Purpose : An aim of this study was to compare the effect of multi leaf collimator(MLC) types for high dimension radiotherapy in treatment sites used clinically. Material and Method : 70 patients with lung cancer, spine cancer, prostate cancer, whole pelvis, head and neck, breast cancer were included in this study. High definition(HD) MLC of TrueBeam STx (Varian Medical system, Palo Alto, CA) and millenium(M) MLC of VitalBeam (Varian Medical system, Palo Alto, CA) were used. Radiotherapy plans were performed for each patient under same treatment goals with Eclipse (Version 13.7, Varian Palo Alto USA, CA). To compare the indicators of the radiotherapy plans, planning target volume(PTV) coverage, conformity index(CI), homogeneity index(HI), and clinical indicators for each treatment sites in normal tissues were evaluated. To evaluate low dose distribution, $V_{30%}$ values were compared according to MLC types. Additionally, length and volume of targets for each treatment sites were investigated. Result : In stereotatictic body radiotherapy(SBRT) plan for lung, the average value of PTV coverage was reduced by 0.52 % with HD MLC. With SBRT plan using HD MLC for spine, the average value of PTV coverage decreased by 0.63 % and maximum dose decreased by 1.13 %. In the test of CI and HI, the values in SBRT plan with HD MLC for spine were 1.144, 1.079 and the values using M MLC were 1.160, 1.092 in SBRT plan for lung, The dose evaluation of critical organ was reduced by 1.48 % in the ipsilateral lung mean dose with HD MLC. In prostate cancer volumetric modulated arc therapy(VMAT) with HD MLC, the mean dose and the $V_{30}$ of bladder and the mean dose and the $V_{25}$ of rectum were reduced by 0.53 %, 1.42 %, 0.97 %, and 0.69 %, respectively (p<0.05). The average value of heart mean dose was reduced by 0.83 % in breast cancer VMAT with M MLC. Other assessment indices for treatment sites showed no significant difference between treatment plans with two types of MLC. Conclusion : Using HD MLC had a positive impact on the PTV coverage and normal tissue sparing in usually short or small targets such as lung and spine SBRT and prostate VMAT. But, there was no significant difference in targets with long and large such as lung, head and neck, and whole pelvis for VMAT.

• The Journal of Korean Society for Radiation Therapy
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• v.15 no.1
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• pp.1-9
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• 2003

I. Purpose The multileaf collimator(MLC) has many advantages, but use of the MLC increased effective penumbra and isodose undulation in dose distribution compared with that of an alloy block. In this work, we introduced the HD-270 MLC, which can improve the above disadvantages of MLC, and reported its feasibility study. II. Method and Materials The HD-270 MLC is a technique which combines the use of the existing Siemens multileaf collimator(3D MLC) with patient translation perpendicular to the leaf plane. The technique produces a smoothed isodose distribution with the reduced isodose undulation and effective penumbra. To assess the efficacy of the HD-270 technique and determine the appropriate resolution, a polygonal shaped MLC field was made to produce field edge angles from 0 degree to 75 degree with a step of 15 degree. Each HD-270 group was generated according to the allowed resolution, i. e., 5, 3, and 2mm. The experiment was carried out on Primus, a Siemens linear accelerator configured with HD-270 MLC. The total 60 MU of 6 MV photon beam was delivered to X-Omat film(Kodak, USA) at a SAD of 100 cm and 1.5 cm depth in solid water phantom. Exposed films were scanned by Lumiscan75(LUMISYS) and analyzed using RIT113 software(Radiological Imaging Technology Inc., USA). To test the mechanical accuracy of table movement, the transverse, longitudinal, and vertical positions were controlled by a consol with ${\pm}5\;mm,\;{\pm}4\;mm,\;{\pm}3\;mm,\;and\;{\pm}2\;mm$ steps, and then measured using a dial gauge with an accuracy of 0.001 inch. During the experiments, the table loaded with about 50Kg human phantom to simulate the real treatment situation. III. Results The effective penumbra and isodose undulation became larger with increase the resolution and field edge angle. The accuracy of the table movement on each direction is good within the ${\pm}1\;mm$. IV. Conclusion Clinical use of the MLC can be increased by using of the HD-270 MLC which complements to the disadvantages of the MLC.

• Progress in Medical Physics
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• v.15 no.3
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• pp.167-172
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• 2004

A Siemens HD-270 MLC$^{TM}$, a virtual-micro MLC, allows to the application of a smooth field edge method due to the finite leaf-width of MLC. This technique was implemented into a Pinnacle planning system in order to evaluate the dose distributions during the planning stage. The necessary dosimetric aspects, such as undulation and effective penumbra, were investigated with variations in the resolutions of a virtual-micro MLC and field edge angle. The positional accuracy of the couch movement was also assessed for clinical implementation. The overhead time for planning and treatment was confirmed as negligible.e.

• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.863-870
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• 2022

DLG (Dosimetric Leaf Gap) and transmission factor are important parameters of MLC modeling in treatment planning system. In this study, DLG and transmission factor of HD-MLC were measured using detector with different measuring volumes, and the accuracy of the treatment plans was evaluated according to the DLG values. DLG was measured using the dynamic sweeping gap method with Semiflux3D and MicroDiamond detectors. Then, 10 radiation treatment plans were generated to optimize the DLG value and compared with the measurement results. Photon energies 6, 8, 10 MV, the DLG measured by Semiflux3D were 0.76, 0.83, and 0.85 mm, and DLG measured by MicroDiamond were 0.78, 0.86, and 0.9 mm. All plans were measured by portal dosimetry and analyzed using Gamma Evaluation. In the 6 MV photon beams, the average gamma passing rate were 94.3% and 98.4% for DLG 0.78 mm and 1.15 mm. In the 10 MV photon beam, the average gamma passing rate were 91.2% and 97.6% for DLG 0.9 mm and 1.25 mm. HD-MLC needs accurate modeling in the treatment planning system. DLG could be used measured data using small volume detector. However, for better radiation therapy, DLG should be optimized at the commissioning stage of LINAC.

• 대한방사선치료학회:학술대회논문집
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• 2003.03a
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• pp.10-11
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• 2003

• Progress in Medical Physics
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• v.34 no.4
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• pp.48-54
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• 2023

Purpose: In this study, the dosimetric characteristics of lung stereotactic body radiotherapy (SBRT) plans using the new Halcyon system were analyzed to assess its suitability. Methods: We compared the key dosimetric parameters calculated for the Halcyon SBRT plans with those of a conventional C-arm linear accelerator (LINAC) equipped with a high-definition multileaf collimator (HD-MLC)-Trilogy Tx. A total of 10 patients with non-small-cell lung cancer were selected, and all SBRT plans were generated using the RapidArc technique. Results: Trilogy Tx exhibited significant superiority over Halcyon in terms of target dose coverage (conformity index, homogeneity index, D_{0.1 cc}, and D_95%) and dose spillage (gradient). Trilogy Tx was more efficient than Halcyon in the lung SBRT beam delivery process in terms of the total number of monitor units, modulation factor, and beam-on time. However, it was feasible to achieve a dose distribution that met SBRT plan requirements using Halcyon, with no significant differences in satisfying organs at risk dose constraints between both plans. Conclusions: Results confirm that Halcyon is a viable alternative for performing lung SBRT in the absence of a LINAC equipped with HD-MLC. However, extra consideration should be taken in determining whether to use Halcyon when the planning target volume setting is enormous, as in the case of significant tumor motions.

• Progress in Medical Physics
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• v.26 no.3
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• pp.168-177
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• 2015

For evaluating the treatment planning accurately, the quality assurance for treatment planning is recommended when patients were treated with IMRT which is complex and delicate. To realize this purpose, treatment plan quality assurance software can be used to verify the delivered dose accurately before and after of treatment. The purpose of this study is to evaluate the accuracy of treatment plan quality assurance software for each IMRT plan according to MLC DLG (dosimetric leaf gap). Novalis Tx with a built-in HD120 MLC was used in this study to acquire the MLC dynalog file be imported in MobiusFx. To establish IMRT plan, Eclipse RTP system was used and target and organ structures (multi-target, mock prostate, mock head/neck, C-shape case) were contoured in I'mRT phantom. To verify the difference of dose distribution according to DLG, MLC dynalog files were imported to MobiusFx software and changed the DLG (0.5, 0.7, 1.0, 1.3, 1.6 mm) values in MobiusFx. For evaluation dose, dose distribution was evaluated by using 3D gamma index for the gamma criteria 3% and distance to agreement 3 mm, and the point dose was acquired by using the CC13 ionization chamber in isocenter of I'mRT phantom. In the result for point dose, the mock head/neck and multi-target had difference about 4% and 3% in DLG 0.5 and 0.7 mm respectively, and the other DLGs had difference less than 3%. The gamma index passing-rate of mock head/neck were below 81% for PTV and cord, and multi-target were below 30% for center and superior target in DLGs 0.5, 0.7 mm, however, inferior target of multi-target case and parotid of mock head/neck case had 100.0% passing rate in all DLGs. The point dose of mock prostate showed difference below 3.0% in all DLGs, however, the passing rate of PTV were below 95% in 0.5, 0.7 mm DLGs, and the other DLGs were above 98%. The rectum and bladder had 100.0% passing rate in all DLGs. As the difference of point dose in C-shape were 3~9% except for 1.3 mm DLG, the passing rate of PTV in 1.0 1.3 mm were 96.7, 93.0% respectively. However, passing rate of the other DLGs were below 86% and core was 100.0% passing rate in all DLGs. In this study, we verified that the accuracy of treatment planning QA system can be affected by DLG values. For precise quality assurance for treatment technique using the MLC motion like IMRT and VMAT, we should use appropriate DLG value in linear accelerator and RTP system.

• Progress in Medical Physics
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• v.27 no.3
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• pp.111-116
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• 2016

This study is to evaluate the dosimetric impact of dosimetric leaf gap (DLG) and transmission factor (TF) at different measurement depths and field sizes for high definition multileaf collimator (HD MLC). Consequently, its clinical implication on dose calculation of treatment planning system was also investigated for pancreas stereotactic body radiation therapy (SBRT). The TF and DLG were measured at various depths (5, 8, 10, 12, and 15 cm) and field sizes ($6{\times}6$, $8{\times}8$, and $10{\times}10cm^2$) for various energies (6 MV, 6 MV FFF, 10 MV, 10 MV flattening filter free [FFF], and 15 MV). Fifteen pancreatic SBRT cases were enrolled in the study. For each case, the dose distribution was recomputed using a reconfigured beam model of which TF and DLG was the closest to the patient geometry, and then compared to the original plan using the results of dose-volume histograms (DVH). For 10 MV FFF photon beam, its maximum difference between 2 cm and 15 cm was within 0.9% and it is increased by 0.05% from $6{\times}6cm^2$ to $10{\times}10cm^2$ for depth of 15 cm. For 10 MV FFF photon beam, the difference in DLG between the depth of 5 cm and 15 cm is within 0.005 cm for all field sizes and its maximum difference between field size of $6{\times}6cm^2$ and $10{\times}10cm^2$ is 0.0025 cm at depth of 8 cm. TF and DLG values were dependent on the depth and field size. However, the dosimetric difference between the original and recomputed doses were found to be within an acceptable range (<0.5%). In conclusion, current beam modeling using single TF and DLG values is enough for accurate dose calculation.

• Progress in Medical Physics
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• v.33 no.4
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• pp.150-157
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• 2022

Purpose: Elekta synergy^® was commissioned in the Seoul National University Veterinary Medical Teaching Hospital. Recently, Chung-Ang University Gwang Myeong Hospital commissioned Elekta Versa HD^TM. The beam characteristics of both machines are similar because of the same Agility^TM MLC Model. We compared measured beam data calculated using the Elekta treatment planning system, Monaco^®, for each institute. Methods: Beam of the commissioning Elekta linear accelerator were measured in two independent institutes. After installing the beam model based on the measured beam data into the Monaco^®, Monte Carlo (MC) simulation data were generated, mimicking the beam data in a virtual water phantom. Measured beam data were compared with the calculated data, and their similarity was quantitatively evaluated by the gamma analysis. Results: We compared the percent depth dose (PDD) and off-axis profiles of 6 MV photon and 6 MeV electron beams with MC calculation. With a 3%/3 mm gamma criterion, the photon PDD and profiles showed 100% gamma passing rates except for one inplane profile at 10 cm depth from VMTH. Gamma analysis of the measured photon beam off-axis profiles between the two institutes showed 100% agreement. The electron beams also indicated 100% agreement in PDD distributions. However, the gamma passing rates of the off-axis profiles were 91%-100% with a 3%/3 mm gamma criterion. Conclusions: The beam and their comparison with MC calculation for each institute showed good performance. Although the measuring tools were orthogonal, no significant difference was found.

• Progress in Medical Physics
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• v.29 no.4
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• pp.164-172
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• 2018

We evaluated the performance of various detectors for small-field dosimetry with field sizes defined by a high-definition (HD) multileaf collimator (MLC) system. For small-field dosimetry, diodes referred to as "RAZOR detectors," MOSFET detectors, and Gafchromic EBT3 films were used in this study. For field sizes less than $1{\times}1cm^2$, percent depth doses (PDDs) and lateral profiles were measured by diodes, MOSFET detectors, and films, and absolute dosimetry measurements were conducted with MOSFET detectors. For comparison purposes, the same measurements were carried out with a field size of $10{\times}10cm^2$. The dose distributions were calculated by the treatment planning system Eclipse. A comparison of the measurements with calculations yielded the percentage differences. With field sizes less than $1{\times}1cm^2$, it was shown that most of the percentage difference values were within 5% for 6-MV and 15-MV photon beams with the use of diodes. The measured lateral profiles were well matched with those calculated by Eclipse as the field sizes increased. Except for the depths of 0.5 cm and 20 cm, there was agreement in terms of the absolute dosimetry within 10% when MOSFET detectors were used. There was good agreement between the calculations and measurements conducted using diodes and EBT films. Both diode detectors and EBT3 films were found to be appropriate options for relative measurements of PDDs and for lateral profiles.