• Progress in Medical Physics
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• v.19 no.3
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• pp.186-190
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• 2008

In this study, we describe the preliminary application for the delineation of a metal object using cone-beam reconstruction (CBR) based on limited electronic portal imaging device (EPID) projections. A typical Feldkamp, Davis and Kress (FDK) reconstruction algorithm accompanying the edge preserving smoothing filter was used as only a few projections are acquired for reconstruction. In a correlation study of the projection numbers, we found that the size of the seeds and their location depicted by these CBR images were almost identical. Limited views were used for CBR, and our method is inexpensive and competitive for use in clinical applications.

• Progress in Medical Physics
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• v.30 no.4
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• pp.120-127
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• 2019

Purpose: This study was designed to evaluate the dosimetric performance of Mobius3D by comparison with an aSi-based electronic portal imaging device (EPID) and Octavius 4D, which are conventionally used for patient-specific prescription dose verification. Methods: The study was conducted using nine patients who were treated by volumetric modulated arc therapy. To evaluate the feasibility of Mobius3D for prescription dose verification, we compared the QA results of Mobius3D to an aSi-based EPID and the Octavius 4D dose verification methods. The first was the comparison of the Mobius3D verification phantom dose, and the second was to gamma index analysis. Results: The percentage differences between the calculated point dose and measurements from a PTW31010 ion chamber were 1.6%±1.3%, 2.0%±0.8%, and 1.2%±1.2%, using collapsed cone convolution, an analytical anisotropic algorithm, and the AcurosXB algorithm respectively. The average difference was found to be 1.6%±0.3%. Additionally, in the case of using the PTW31014 ion chamber, the corresponding results were 2.0%±1.4%, 2.4%±2.1%, and 1.6%±2.5%, showing an average agreement within 2.0%±0.3%. Considering all the criteria, the Mobius3D result showed that the percentage dose difference from the EPID was within 0.46%±0.34% on average, and the percentage dose difference from Octavius 4D was within 3.14%±2.85% on average. Conclusions: We conclude that Mobius3D can be used interchangeably with phantom-based dosimetry systems, which are commonly used as patient-specific prescription dose verification tools, especially under the conditions of 3%/3 mm and 95% pass rate.

• The Journal of Korean Society for Radiation Therapy
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• v.31 no.1
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• pp.33-41
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• 2019

Purpose : To evaluate the effectiveness of Jaw-tracking(JT) technique in Intensity-modulated radiation therapy(IMRT) and Volumetric-modulated arc therapy(VMAT) for radiation therapy of esophageal cancer by analyzing volume dose of perimetrical normal organs along with the low-dose volume regions. Materials and Method: A total of 27 patients were selected who received radiation therapy for esophageal cancer with using $VitalBeam^{TM}$(Varian Medical System, U.S.A) in our hospital. Using Eclipse system(Ver. 13.6 Varian, U.S.A), radiation treatment planning was set up with Jaw-tracking technique(JT) and Non-Jaw-tracking technique(NJT), and was conducted for the patients with T-shaped Planning target volume(PTV), including Supraclavicular lymph nodes(SCL). PTV was classified into whether celiac area was included or not to identify the influence on the radiation field. To compare the treatment plans, Organ at risk(OAR) was defined to bilateral lung, heart, and spinal cord and evaluated for Conformity index(CI) and Homogeneity index(HI). Portal dosimetry was performed to verify a clinical application using Electronic portal imaging device(EPID) and Gamma analysis was performed with establishing thresholds of radiation field as a parameter, with various range of 0 %, 5 %, and 10 %. Results: All treatment plans were established on gamma pass rates of 95 % with 3 mm/3 % criteria. For a threshold of 10 %, both JT and NJT passed with rate of more than 95 % and both gamma passing rate decreased more than 1 % in IMRT as the low dose threshold decreased to 5 % and 0 %. For the case of JT in IMRT on PTV without celiac area, $V_5$ and $V_{10}$ of both lung showed a decrease by respectively 8.5 % and 5.3 % in average and up to 14.7 %. A $D_{mean}$ decreased by $72.3{\pm}51cGy$, while there was an increase in radiation dose reduction in PTV including celiac area. A $D_{mean}$ of heart decreased by $68.9{\pm}38.5cGy$ and that of spinal cord decreased by $39.7{\pm}30cGy$. For the case of JT in VMAT, $V_5$ decreased by 2.5 % in average in lungs, and also a little amount in heart and spinal cord. Radiation dose reduction of JT showed an increase when PTV includes celiac area in VMAT. Conclusion: In the radiation treatment planning for esophageal cancer, IMRT showed a significant decrease in $V_5$, and $V_{10}$ of both lungs when applying JT, and dose reduction was greater when the irradiated area in low-dose field is larger. Therefore, IMRT is more advantageous in applying JT than VMAT for radiation therapy of esophageal cancer and can protect the normal organs from MLC leakage and transmitted doses in low-dose field.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.2
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• pp.297-303
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• 2014

Purpose : The purpose of this study is reproducibility evaluation of deep inspiration breath-hold(DIBH) technique by respiration data and heart position analysis in radiation therapy for Left Breast cancer patients. Materials and Methods : Free breathing(FB) Computed Tomography(CT) images and DIBH CT images of three left breast cancer patients were used to evaluate the heart volume and dose during treatment planing system( Eclipse version 10.0, Varian, USA ). The signal of RPM (Real-time Position Management) Respiratory Gating System (version 1.7.5, Varian, USA) was used to evaluate respiration stability of DIBH during breast radiation therapy. The images for measurement of heart position were acquired by the Electronic portal imaging device(EPID) cine acquisition mode. The distance of heart at the three measuring points(A, B, C) on each image was measured by Offline Review (ARIA 10, Varian, USA). Results : Significant differences were found between the FB and DIBH plans for mean heart dose (6.82 vs. 1.91 Gy), heart $V_{30}$ (68.57 vs. $8.26cm^3$), $V_{20}$ (76.43 vs. $11.34cm^3$). The standard deviation of DIBH signal of each patient was ${\pm}0.07cm$, ${\pm}0.04cm$, ${\pm}0.13cm$, respectively. The Maximum and Minimum heart distance on EPID images were measured as 0.32 cm and 0.00 cm. Conclusion : Consequently, using the DIBH technique with radiation therapy for left breast cancer patients is very useful to establish the treatment plan and to reduce the heart dose. In addition, it is beneficial to using the Cine acquisition mode of EPID for the reproducibility evaluation of DIBH.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.2
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• pp.65-73
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• 2017

Purpose: Machine Performance Check (MPC) is a self-checking software based on the Electronic Portal Imaging Device (EPID) to measure daily beam outputs without external installation. The purpose of this study is to verify the usefulness of MPC by comparing and correlating daily beam output of QA Beamchecker PLUS. Materials and Methods: Linear accelerator (Truebeam 2.5) was used to measure 10 energies which are composed of photon beams(6, 10, 15 MV and 6, 10 MV-FFF) and electron beams(6, 9, 12, 16 and 20 MeV). A total of 80 cycles of data was obtained by measuring beam output measurement before treatment over five months period. The Pearson correlation coefficient was used to evaluate the consistency of the beam output between the MPC and the QA Beamchecker PLUS. In this study, if the Pearson correlation coefficient is; (1) 0.8 or higher, the correlation is very strong (2) between 0.6 and 0.79, the correlation is strong (3) between 0.4 and 0.59, the correlation is moderate (4) between 0.2 and 0.39, the correlation is weak (5) lower than 0.2, the correlation is very weak. Results: Output variations observed between MPC and QA Beamchecker PLUS were within 2 % for photons and electrons. The beam outputs variations of MPC were $0.29{\pm}0.26%$ and $0.30{\pm}0.26%$ for photon and electron beams, respectively. QA Beamchecker PLUS beam outputs were $0.31{\pm}0.24%$ and $0.33{\pm}0.24%$ for photon and electron beams, respectively. The Pearson correlation coefficient between MPC and QA Beamchecker PLUS indicated that photon beams were very strong at 15 MV, and strong at 6 MV, 10 MV, 6 MV-FFF and 10 MV-FFF. For electron beams, the Pearson correlation coefficient were strong at 16 MeV and 20 MeV, moderate at 9 MeV and 12 MeV, and very weak at 6 MeV. Conclusion: MPC showed significantly strong correlation with QA Beamchecker PLUS when testing with photon beams and high-energy electron beams in the evaluation of daily beam output, but the correlation when testing with low-energy electron beams (6 MeV) appeared to be low. However, MPC and QA Beamchecker PLUS are considered to be suitable for checking daily beam output, as they performed within 2 % of beam output consistency during the observation. MPC which can perform faster than the conventional daily beam output measurement tool, is considered to be an effective method for users.

• The Journal of Korean Society for Radiation Therapy
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• v.30 no.1_2
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• pp.73-81
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• 2018

Purpose : The aims of this study were to compare and assess the effectiveness of Volumetric Modulated Arc Therapy(VMAT) using jaw tracking(JT) and fixed jaw(FJ) in radiation therapy of multiple brain metastasis. Methode and material : Among the patients with Multiple Brain Metastasis treated with jaw tracking, 10 patients with more than 6 tumors and with the size of radiation field $14{\times}14cm^2$ or more were included. Each Treatment plans with jaw tracking(JT) and fixed jaw(FJ) was established with Eclipse (Ver. 13.6 Varian, USA). Gamma Index (3 mm, 3 % confidence interval - 95 %) and maximum dose difference were measured with an electronic portal imaging device(EPID). The $D_{max}$ and $D_{mean}$ of Organ At Risk(OAR) were assessed and compared, and the Conformity Index(CI) and Homogeneity Index(HI) were evaluated. Result : Evaluating jaw tracking(JT) and fixed jaw(FJ) outcomes, in all cases, Gamma Index met the permissible standard of 3 mm, 3 % confidence intervals of 95 %. The maximum dose difference value from the areas with leaf end transmission was measured at a maximum of 98.4 % and an average of 43.6 % in clockwise(CW), and 67.9 % and 41.0 % for each in Counter-Clockwise(CCW). With jaw tracking, the maximum value of $D_{max}$ for each normal organ in OAR decreased in 15.36 %~74.59 % with the average value decreasing in 2.84 %~39.80 %. The maximum value of $D_{mean}$ in OAR decreased in 27.90 %~65.23 %, with the average value decreasing in 7.70 %~41.71 %. No change has been found in Conformity Index and Homogeneity Index values. Conclusion : When Jaw tracking is used in treating patients with multiple brain metastasis with VMAT, the unnecessary exposure due to leakage and transmission of radiation in unspecified areas was reduced, without affecting the dose distribution of the planning target volume(PTV), and the availability of radiation therapy with lower doses in normal organs is expected.

• Radiation Oncology Journal
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• v.27 no.1
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• pp.42-48
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• 2009

Purpose: The introduction of image guided radiation therapy/four-dimensional radiation therapy (IGRT/4DRT) potentially increases the accumulated dose to patients from imaging and verification processes as compared to conventional practice. It is therefore essential to investigate the level of the imaging dose to patients when IGRT/4DRT devices are installed. The imaging dose level was monitored and was compared with the use of pre-IGRT practice. Materials and Methods: A four-dimensional CT (4DCT) unit (GE, Ultra Light Speed 16), a simulator (Varian Acuity) and Varian IX unit with an on-board imager (OBI) and cone beam CT (CBCT) were installed. The surface doses to a RANDO phantom (The Phantom Laboratory, Salem, NY USA) were measured with the newly installed devices and with pre-existing devices including a single slice CT scanner (GE, Light Speed), a simulator (Varian Ximatron) and L-gram linear accelerator (Varian, 2100C Linac). The surface doses were measured using thermo luminescent dosimeters (TLDs) at eight sites-the brain, eye, thyroid, chest, abdomen, ovary, prostate and pelvis. Results: Compared to imaging with the use of single slice non-gated CT, the use of 4DCT imaging increased the dose to the chest and abdomen approximately ten-fold ($1.74{\pm}0.34$ cGy versus $23.23{\pm}3.67$cGy). Imaging doses with the use of the Acuity simulator were smaller than doses with the use of the Ximatron simulator, which were $0.91{\pm}0.89$ cGy versus $6.77{\pm}3.56$ cGy, respectively. The dose with the use of the electronic portal imaging device (EPID; Varian IX unit) was approximately 50% of the dose with the use of the L-gram linear accelerator ($1.83{\pm}0.36$ cGy versus $3.80{\pm}1.67$ cGy). The dose from the OBI for fluoroscopy and low-dose mode CBCT were $0.97{\pm}0.34$ cGy and $2.3{\pm}0.67$ cGy, respectively. Conclusion: The use of 4DCT is the major source of an increase of the radiation (imaging) dose to patients. OBI and CBCT doses were small, but the accumulated dose associated with everyday verification need to be considered.

• Progress in Medical Physics
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• v.23 no.4
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• pp.317-325
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• 2012

The Varian PORTALVISION (Varian Medical Systems, US) shows significant overresponses as the off-center distance increases compared to the predicted dose. In order to correct the dose discrepancy, the off-axis correction is applied to VARIAN iX linear accelerators. The portal dose for $38{\times}28cm^2$ open field is acquired for 6 MV, 15 MV photon beams and also are predicted by PDIP algorithm under the same condition of the portal dose acquisition. The off-axis correction is applied by modifying the $40{\times}40cm^2$ diagonal beam profile data which is used for the beam profile calibration. The ratios between predicted dose and measured dose is modeled as a function of off-axis distance with the $4^{th}$ polynomial and is applied to the $40{\times}40cm^2$ diagonal beam profile data as the weight to correct measured dose by EPID detector. The discrepancy between measured dose and predicted dose is reduced from $4.17{\pm}2.76$ CU to $0.18{\pm}0.8$ CU for 6 MV photon beam and from $3.23{\pm}2.59$ CU to $0.04{\pm}0.85$ CU for 15 MV photon beam. The passing rate of gamma analysis for the pyramid fluence patten with the 4%, 4 mm criteria is improved from 98.7% to 99.1% for 6 MV photon beam, from 99.8% to 99.9% for 15 MV photon beam. IMRT QA is also performed for randomly selected Head and Neck and Prostate IMRT plans after applying the off-axis correction. The gamma passing rare is improved by 3% on average, for Head and Neck cases: $94.7{\pm}3.2%$ to $98.2{\pm}1.4%$, for Prostate cases: $95.5{\pm}2.6%$, $98.4{\pm}1.8%$. The gamma analysis criteria is 3%, 3 mm with 10% threshold. It is considered that the off-axis correction might be an effective and easily adaptable means for correcting the discrepancy between measured dose and predicted dose for IMRT QA using EPID in clinic.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.3
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• pp.44-51
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• 2009

It is very important to verify generated setup errors in cancer therapy by using a high energy radiation and to perform the precise radiation therapy. Specially, the verification of treatment position is very crucial in special therapies like fractionated stereotatic radiotherapy (FSRT). The FSRT uses normally high-dose, small field size for treating small intracranial lesions. To estimate the developed FSRT system, the isocenter accuracy of gantry, couch and collimator were performed and a total of inaccuracy was less than ${\pm}1mm$. Precise beam targeting is crucial when using high-dose, small field size FSRT for treating small intracranial lesions. The EPID image of the 3mm lead ball mounted on the isocenter with a 25mm collimator cone was acquired and detected to the extent of one pixel (0.76mm) after comparing the difference between the center of a 25mm collimator cone and a 3 mm ball after processing the EPID image. In this paper, the radiation treatment efficiency can be improved by performing precise radiation therapy with a developed video based EPID and FSRT at near real time

• Progress in Medical Physics
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• v.30 no.3
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• pp.65-73
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• 2019

Purpose: We evaluated the motion-induced dosimetric effects on the field-in-field (FIF) technique for whole-breast irradiation (WBI) using actual patient organ motion data obtained from cine electronic portal imaging device (cine EPID) images during treatment. Materials and Methods: Ten breast cancer patients who received WBI after breast-conserving surgery were selected. The static FIF (SFIF) plan involved the application of two parallel opposing tangential and boost FIFs. To obtain the amplitude of the internal organ motion during treatment, cine EPID images were acquired five times for each patient. The outside contour of the breast (OCB) and chest wall (CW) contour were tracked using in-house motion analysis software. Intrafractional organ motion was analyzed. The dynamic FIF (DFIF) reflecting intrafractional organ motion incorporated into the SFIF plan was calculated and compared with the SFIF in terms of the dose homogeneity index (DHI_90/10) for the target and V₂₀ for the ipsilateral lung. Results: The average motion amplitudes along the X and Y directions were 1.84±1.09 mm and 0.69±0.50 mm for OCB and 1.88±1.07 mm and 1.66±1.49 mm for CW, respectively. The maximum motion amplitudes along the X and Y directions were 5.53 and 2.08 mm for OCB and 5.22 and 6.79 mm for CW, respectively. Significant differences in DHI_90/10 values were observed between SFIF and DFIF (0.94 vs 0.95, P<0.05) in statistical analysis. The average V₂₀ for the lung in the DFIF was slightly higher than that of the SFIF in statistical analysis (19.21 vs 19.00, P<0.05). Conclusion: Our findings indicate that the FIF technique can form a safe and effective treatment method for WBI. Regular monitoring using cine EPID images can be effective in reducing motion-induced dosimetric errors.