• Progress in Medical Physics
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• v.19 no.2
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• pp.131-138
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• 2008

We evaluated on the calculation accuracy of treatment planning system (TPS) with phantom having convex and concave surface. The TPS is Eclipse (Varian, USA) using both algorithms AAA and PBC for photon dose calculations. PBC algorithms have three corrections of Batho, modified Batho (M-Batho), and equivalent TAR (E-TAR). The field sizes were $10{\times}10\;cm^2$ and $20{\times}20\;cm^2$, and MLC-shaped fields for these fields. We measured doses at three depths 5, 10 and 15cm in phantom of SSD=90cm in the condition of inserted farmer chamber. For given conditions, we have calculated dose with these algorithms and compared them with measured doses. In AAA the calculated doses (dose/MU) were agreed to measured doses within ${\pm}1%$ in flat and convex surface and were under estimated with -1.9% maximum in concave surface. In PBC the calculated doses were over estimated with +1.7% and +4.1% respectively in flat and convex surface and the differences were from -3.1% to +2.1% in concave surface. In comparison of criteria from AAPM and IAEA reports, and statistical analysis for these results, it is found that the AAA's results are in good agreement with measured values and the M-Batho's results are generally good agreed with measured values among PBC algorithms.

• The Journal of Korean Society for Radiation Therapy
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• v.27 no.1
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• pp.87-95
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• 2015

Purpose : This study presents the usefulness assessment of secondary shield for the lens exposure dose reduction during radiation treatment of peripheral orbit. Materials and Methods : We accomplished IMRT treatment plan similar with a real one through the computed treatment planning system after CT simulation using human phantom. For the secondary shield, we used Pb plate (thickness 3mm, diameter 25mm) and 3 mm tungsten eye-shield block. And we compared lens dose using OSLD between on TPS and on simulation. Also, we irradiated 200 MU(6 MV, SPD(Source to Phantom Distance)=100 cm, $F{\cdot}S\;5{\times}5cm$) on a 5cm acrylic phantom using the secondary shielding material of same condition, 3mm Pb and tungsten eye-shield block. And we carried out the same experiment using 8cm Pb block to limit effect of leakage & transmitted radiation out of irradiation field. We attached OSLD with a 1cm away from the field at the side of phantom and applied a 3mm bolus equivalent to the thickness of eyelid. Results : Using human phantom, the Lens dose on IMRT treatment plan is 315.9cGy and the real measurement value is 216.7cGy. And after secondary shield using 3mm Pb plate and tungsten eye-shield block, each lens dose is 234.3, 224.1 cGy. The result of a experiment using acrylic phantom, each value is 5.24, 5.42 and 5.39 cGy in case of no block, 3mm Pb plate and tungsten eye-shield block. Applying O.S.B out of the field, each value is 1.79, 2.00 and 2.02 cGy in case of no block, 3mm Pb plate and tungsten eye-shield block. Conclusion : When secondary shielding material is used to protect critical organ while irradiating photon, high atomic number material (like metal) that is near by critical organ can be cause of dose increase according to treatment region and beam direction because head leakage and collimator & MLC transmitted radiation are exist even if it's out of the field. The attempt of secondary shield for the decrease of exposure dose was meaningful, but untested attempt can have a reverse effect. So, a preliminary inspection through Q.A must be necessary.

• Progress in Medical Physics
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• v.13 no.4
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• pp.202-208
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• 2002

The purpose of this study is to evaluate the monitor unit obtained from various methods for the treatment of superficial cancers using electron beams. Thirty-three breast cancer patients who were treated in our institution with 6, 9, and 12 MeV electron beams, were selected for this study. For each patient, irregularly shaped treatment blocks were drawn on simulation film and constructed. Using the irregular blocks, monitor units to deliver 100 cGy to the dose maximum (dmax) were calculated from measurement and three-dimensional radiation treatment planning (3D RTP) system (PINNACLE 6.0, ADAC Laboratories, Milpitas CA) Measurements were made in solid water phantom with plane parallel (PP) chamber (Roos, OTW Germany) at 100 cm source-to surface distances. CT data was used to investigate the effect of heterogeneity. Monitor units were calculated by overriding CT values with 1 g/㎤ and in the presence of heterogeneity. The monitor unit values obtained by the above methods were compared. The dose, obtained from measurement in solid water phantom was higher than that of RTP values for irregularly shaped blocks. The maximum differences between monitor unit calculated in flat water phantom at gantry zero position were 4% for 6 MeV and 2% for 9 and 12 MeV electrons. When CT data was used at a various gantry angle the agreement between the TPS data with and without density correction was within 3% for all energies. These results indicate that there are no significant difference in terms of monitor unit when density is corrected for the treatment of breast cancer patients with electrons.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.12
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• pp.5019-5024
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• 2015

Background: The purpose of this study was to assess the dosimetric and clinical feasibility of volumetric modulated arc based hypofractionated stereotactic radiotherapy (RapidArc) treatment for large acoustic schwannoma (AS >10cc). Materials and Methods: Ten AS patients were immobilized using BrainLab mask. They were subject to multimodality imaging (magnetic resonance and computed tomography) to contour target and organs at risk (brainstem and cochlea). Volumetric modulated arc therapy (VMAT) based stereotactic plans were optimized in Eclipse (V11) treatment planning system (TPS) using progressive resolution optimizer-III and final dose calculations were performed using analytical anisotropic algorithm with 1.5 mm grid resolution. All AS presented in this study were treated with VMAT based HSRT to a total dose of 25Gy in 5 fractions (5fractions/week). VMAT plan contains 2-4 non-coplanar arcs. Treatment planning was performed to achieve at least 99% of PTV volume (D99) receives 100% of prescription dose (25Gy), while dose to OAR's were kept below the tolerance limits. Dose-volume histograms (DVH) were analyzed to assess plan quality. Treatments were delivered using upgraded 6 MV un-flattened photon beam (FFF) from Clinac-iX machine. Extensive pretreatment quality assurance measurements were carried out to report on quality of delivery. Point dosimetry was performed using three different detectors, which includes CC13 ion-chamber, Exradin A14 ion-chamber and Exradin W1 plastic scintillator detector (PSD) which have measuring volume of $0.13cm^3$, $0.009cm^3$ and $0.002cm^3$ respectively. Results: Average PTV volume of AS was 11.3cc (${\pm}4.8$), and located in eloquent areas. VMAT plans provided complete PTV coverage with average conformity index of 1.06 (${\pm}0.05$). OAR's dose were kept below tolerance limit recommend by American Association of Physicist in Medicine task group-101(brainstem $V_{0.5cc}$ < 23Gy, cochlea maximum < 25Gy and Optic pathway <25Gy). PSD resulted in superior dosimetric accuracy compared with other two detectors (p=0.021 for PSD.

• Progress in Medical Physics
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• v.17 no.3
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• pp.179-186
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• 2006

Purpose: Photon beam data of linear accelerators in Korea are collected, analyzed, and a simple method for checking and verifying the dose calculations in a TPS are suggested. Materials and Methods: Photon beam data such as output calibration condition, output factor, wedge factor, percent depth dose, beam profile, and beam quality were collected from 26 institutions in Korea. In order to verify the accuracy of dose calculation, ten sample planning tests were peformed. These Include square, elongated, and blocked fields, wedge fields, off-axis dose calculation, SSD variation. The planned data were compared to that of manual calculations. Results: The average and standard deviation of photon beam quality for 6, 10, and 15 MV were $0.576{\pm}0.005,\;0.632{\pm}0.004,\;and\;0.647{\pm}0.006$, respectively. The output factors of 6 MV photon beam measured at depth of dose maximum for $5{\times}5cm,\;15{\times}15cm,\;20{\times}20cm\;were\;0.944{\pm}0.006,\;1.031{\pm}0.006,\;and\;1.055{\pm}0.007$. For 10 MV photon beam, the values were $0.935{\pm}0.006,\;1.031{\pm}0.007,\;1.054{\pm}0.0005$. The collected data were not enough to calculate average, the output factors for 15MV photon beam with field size of $5{\times}5cm,\;15{\times}15cm,\;20{\times}20cm\;were\;0.941{\pm}0.008,\;1.032{\pm}0.004,\;1.049{\pm}0.014$. There was seven institutions $e{\times}ceeding$ tolerance when monitor unit values calculated from treatment planning system and manually were compared. The measured average MU values for the machines calibrated at SAD setup were 3 MU and 5 MU higher than the machines calibrated at SSD for 6 MV and 10 MV, respectively except the wedge case. When the wedges were inserted, the MU values to deliver 100 cGy to 5 cm depends on manufactures. When the same wedge angle was used, Siemens machine requires more MUs then Varian machine. Conclusion: In this study, photon beam data are collected and analyzed to provide a baseline value for chocking beam data and the accuracy of dose calculation for a treatment planning system.

• Progress in Medical Physics
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• v.20 no.4
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• pp.269-276
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• 2009

Radiation treatment techniques using photon beam such as three-dimensional conformal radiation therapy (3D-CRT) as well as intensity modulated radiotherapy treatment (IMRT) demand accurate dose calculation in order to increase target coverage and spare healthy tissue. Both jaw collimator and multi-leaf collimators (MLCs) for photon beams have been used to achieve such goals. In the Pinnacle3 treatment planning system (TPS), which we are using in our clinics, a set of model parameters like jaw collimator transmission factor (JTF) and MLC transmission factor (MLCTF) are determined from the measured data because it is using a model-based photon dose algorithm. However, model parameters obtained by this auto-modeling process can be different from those by direct measurement, which can have a dosimetric effect on the dose distribution. In this paper we estimated JTF and MLCTF obtained by the auto-modeling process in the Pinnacle3 TPS. At first, we obtained JTF and MLCTF by direct measurement, which were the ratio of the output at the reference depth under the closed jaw collimator (MLCs for MLCTF) to that at the same depth with the field size $10{\times}10\;cm^2$ in the water phantom. And then JTF and MLCTF were also obtained by auto-modeling process. And we evaluated the dose difference through phantom and patient study in the 3D-CRT plan. For direct measurement, JTF was 0.001966 for 6 MV and 0.002971 for 10 MV, and MLCTF was 0.01657 for 6 MV and 0.01925 for 10 MV. On the other hand, for auto-modeling process, JTF was 0.001983 for 6 MV and 0.010431 for 10 MV, and MLCTF was 0.00188 for 6 MV and 0.00453 for 10 MV. JTF and MLCTF by direct measurement were very different from those by auto-modeling process and even more reasonable considering each beam quality of 6 MV and 10 MV. These different parameters affect the dose in the low-dose region. Since the wrong estimation of JTF and MLCTF can lead some dosimetric error, comparison of direct measurement and auto-modeling of JTF and MLCTF would be helpful during the beam commissioning.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.1
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• pp.57-65
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• 2004

Introduction : The phantom that includes high density materials such as steel was custom-made to fix lung and bone in order to evaluation inhomogeneity correction at the time of conducting radiation therapy to treat lung cancer. Using this, values resulting from the inhomogeneous correction algorithm are compared on the 2 and 3 dimensional radiation therapy planning systems. Moreover, change in dose calculation was evaluated according to inhomogeneous by comparing with the actual measurement. Materials and Methods : As for the image acquisition, inhomogeneous correction phantom(Pig's vertebra, steel(8.21g/cm3), cork(0.23 g/cm3)) that was custom-made and the CT(Volume zoom, Siemens, Germany) were used. As for the radiation therapy planning system, Marks Plan(2D) and XiO(CMS, USA, 3D) were used. To compare with the measurement value, linear accelerator(CL/1800, Varian, USA) and ion chamber were used. Image, obtained from the CT was used to obtain point dose and dose distribution from the region of interest (ROI) while on the radiation therapy planning device. After measurement was conducted under the same conditions, value on the treatment planning device and measured value were subjected to comparison and analysis. And difference between the resulting for the evaluation on the use (or non-use) of inhomogeneity correction algorithm, and diverse inhomogeneity correction algorithm that is included in the radiation therapy planning device was compared as well. Results : As result of comparing the results of measurement value on the region of interest within the inhomogeneity correction phantom and the value that resulted from the homogeneous and inhomogeneous correction, gained from the therapy planning device, margin of error of the measurement value and inhomogeneous correction value at the location 1 of the lung showed $0.8\%$ on 2D and $0.5\%$ on 3D. Margin of error of the measurement value and inhomogeneous correction value at the location 1 of the steel showed $12\%$ on 2D and $5\%$ on 3D, however, it is possible to see that the value that is not correction and the margin of error of the measurement value stand at $16\%$ and $14\%$, respectively. Moreover, values of the 3D showed lower margin of error compared to 2D. Conclusion : Revision according to the density of tissue must be executed during radiation therapy planning. To ensure a more accurate planning, use of 3D planning system is recommended more so than the 2D Planning system to ensure a more accurate revision on the therapy plan. Moreover, 3D Planning system needs to select and use the most accurate and appropriate inhomogeneous correction algorithm through actual measurement. In addition, comparison and analysis through TLD or film dosimetry are needed.

• Progress in Medical Physics
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• v.29 no.2
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• pp.66-72
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• 2018

The proper position of a multi-leaf collimator (MLC) is essential for the quality of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) dose delivery. Task Group (TG) 142 provides a quality assurance (QA) procedure for MLC position. Our study investigated the QA validation of the mechanical leaf gap measurement and the maintenance procedure. Two $VitalBeam^{TM}$ systems were evaluated to validate the acceptance of an MLC position. The dosimetric leaf gaps (DLGs) were measured for 6 MV, 6 MVFFF, 10 MV, and 15 MV photon beams. A solid water phantom was irradiated using $10{\times}10cm^2$ field size at source-to-surface distance (SSD) of 90 cm and depth of 10 cm. The portal dose image prediction (PDIP) calculation was implemented on a treatment planning system (TPS) called $Eclipse^{TM}$. A total of 20 VMAT plans were used to confirm the accuracy of dose distribution measured by an electronic portal imaging device (EPID) and those predicted by VMAT plans. The measured leaf gaps were 0.30 mm and 0.35 mm for VitalBeam 1 and 2, respectively. The DLG values decreased by an average of 6.9% and 5.9% after mechanical MLC adjustment. Although the passing rates increased slightly, by 1.5% (relative) and 1.2% (absolute) in arc 1, the average passing rates were still within the good dose delivery level (>95%). Our study shows the existence of a mechanical leaf gap error caused by a degenerated MLC motor. This can be recovered by reinitialization of MLC position on the machine control panel. Consequently, the QA procedure should be performed regularly to protect the MLC system.

• Progress in Medical Physics
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• v.16 no.3
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• pp.125-129
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• 2005

The first step in the commissioning procedure of a treatment planning system is always verification of the basic beam data. In this work, we have measured POD curves and beam profiles between 1 $\times$ 1 cm$^{2}$ and 40 $\times$ 40 cm$^{2}$ . In an attempt, Pinnacle 7.4f detect discrepancies between predicted dose distribution and delivered dose distribution. The discrepancies between measurement data and caculation data was found. The delivered dose was underestimated in field but overestimated out of field. The D$_{max}$ depth of 1 $\times$ 1 cm$^{2}$ was reduced about 2 mm. For the larger field size ($\geq$4$\times$4 cm$^{2}$, the beam profile and PDD curve showed good agreement between measurement data and calculation data.

• Journal of Radiation Protection and Research
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• v.36 no.2
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• pp.86-92
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• 2011

This study used the optically stimulated luminescence dosimeters (OSLDs), recently, received the revaluation of usefulness in vivo dosimetry, and the diode detecters to measure the skin dose of patient with the rectal cancer. The measurements of dose delivered were compared with the planned dose from the treatment planning system (TPS). We evaluated the clinical application of OSDs in radiotherapy. We measured the calibration factor of OSLDs and used the percent depth dose to verified, also, we created the three point of surface by ten patients of rectal cancer to measured. The calibration factors of OSLD was 1.17 for 6 MV X-ray and 1.28 for 10 MV X-ray, demonstrating the energy dependency of X-ray beams. Comparison of surface dose measurement using the OSLDs and diode detectors with the planned dose from the TPS, The skin dose of patient was increased 1.16 ~ 2.83% for diode detectors, 1.36 ~ 2.17% for OSLDs. Especially, the difference between planned dose and the delivery dose was increased in the perineum, a skin of intense flexure region, and the OSLDs as a result of close spacing of measuring a variate showed a steady dose verification than the diode detecters. Therefore, on behalf of the ionization chamber and diode detecters, OSLDs could be applied clinically in the verification of radiation dose error and in vivo dosimety. The research on the dose verification of the rectal cancer in the around perineal, a surface of intense flexure region, suggest continue to be.