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  • Original Article 2015-12-30 2015-12-30 \ 0 \ 348 \ 173

    Commissioning Experience of Tri-Cobalt-60 MRI-guided Radiation Therapy System

    Jong Min Park, So-Yeon Park, Hong-Gyun Wu, Jung-in Kim

    Abstract
    The aim of this study is to present commissioning results of the ViewRay system. We verified safety functions of the ViewRay system. For imaging system, we acquired signal to noise ratio (SNR) and image uniformity. In addition, we checked spatial integrity of the image. Couch movement accuracy and coincidence of isocenters (radiation therapy system, imaging system and virtual isocneter) was verified. Accuracy of MLC positioing was checked. We performed reference dosimetry according to American Association of Physicists in Medicine (AAPM) Task Group 51 (TG-51) in water phantom for head 1 and 3. The deviations between measurements and calculation of percent depth dose (PDD) and output factor were evaluated. Finally, we performed gamma evaluations with a total of 8 IMRT plans as an end-to-end (E2E) test of the system. Every safety system of ViewRay operated properly. The values of SNR and Uniformity met the tolerance level. Every point within 10 cm and 17.5 cm radii about the isocenter showed deviations less than 1 mm and 2 mm, respectively. The average couch movement errors in transverse (x), longitudinal (y) and vertical (z) directions were 0.2 mm, 0.1 mm and 0.2 mm, respectively. The deviations between radiation isocenter and virtual isocenter in x, y and z directions were 0 mm, 0 mm and 0.3 mm, respectively. Those between virtual isocenter and imaging isocenter were 0.6 mm, 0.5 mm and 0.2 mm, respectively. The average MLC positioning errors were less than 0.6 mm. The deviations of output, PDDs between mesured vs. BJR supplement 25, PDDs between measured and calculated and output factors of each head were less than 0.5%, 1%, 1% and 2%, respectively. For E2E test, average gamma passing rate with 3%/3 mm criterion was 99.9%±0.1%.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 292 \ 101

    Evaluation of 3DVH Software for the Patient Dose Analysis in TomoTherapy

    Ju-Young Song, Yong-Hyeob Kim, Jae-Uk Jeong, Mee Sun Yoon, Sung-Ja Ahn, Woong-Ki Chung, Taek-Keun Nam

    Abstract
    The new function of 3DVH software for dose calculation inside the patient undergoing TomoTherapy treatment by applying the measured data obtained by ArcCHECK was recently released. In this study, the dosimetric accuracy of 3DVH for the TomoTherapy DQA process was evaluated by the comparison of measured dose distribution with the dose calculated using 3DVH. The 2D diode detector array MapCHECK phantom was used for the TomoTherapy planning of virtual patient and for the measurement of the compared dose. The average pass rate of gamma evaluation between the measured dose in the MapCHECK phantom and the recalculated dose in 3DVH was 92.6±3.5%, and the error was greater than the average pass rate, 99.0±1.2%, in the gamma evaluation results with the dose calculated in TomoTherapy planning system. The error was also greater than that in the gamma evaluation results in the RapidArc analysis, which showed the average pass rate of 99.3± 0.9%. The evaluated accuracy of 3DVH software for TomoTherapy DQA process in this study seemed to have some uncertainty for the clinical use. It is recommended to perform a proper analysis before using the 3DVH software for dose recalculation of the patient in the TomoTherapy DQA process considering the initial application stage in clinical use.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 171 \ 104

    Effect of Low Magnetic Field on Dose Distribution in the Partial-Breast Irradiation

    Department of Radiation Oncology, Seoul National University Hospital, Seoul, Biomedical Research Institute, Seoul National University Hospital, Seoul, Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea

    Abstract
    he aim of this study is to investigate the effect of low magnetic field on dose distribution in the partial-breast irradiation (PBI). Eleven patients with an invasive early-stage breast carcinoma were treated prospectively with PBI using 38.5 Gy delivered in 10 fractions using the ViewRay system. For each of the treatment plans, dose distribution was calculated with magnetic field and without magnetic field, and the difference between dose and volume for each organ were evaluated. For planning target volume (PTV), the analysis included the point minimum (Dmin), maximum, mean dose (Dmean) and volume receiving at least 90% (V90%), 95% (V95%) and 107% (V107%) of the prescribed dose, respectively. For organs at risk (OARs), the ipsilateral lung was analyzed with Dmean and the volume receiving 20 Gy (V20 Gy), and the contralateral lung was analyzed with only Dmean. The heart was analyzed with Dmean, Dmax, and V20 Gy, and both inner and outer shells were analyzed with the point Dmin, Dmax and Dmean, respectively. For PTV, the effect of low magnetic field on dose distribution showed a difference of up to 2% for volume change and 4 Gy for dose. In OARs analysis, the significant effect of the magnetic field was not observed. Despite small deviation values, the average difference of mean dose values showed significant difference (p<0.001), but there was no difference of point minimum dose values in both sehll structures. The largest deviation for the average difference of Dmax in the outer shell structure was 5.0±10.5 Gy (p=0.148). The effect of low magnetic field of 0.35 T on dose deposition by a Co‐60 beam was not significantly observed within the body for PBI IMRT plans. The dose deposition was only appreciable outside the body, where a dose build‐up due to contaminated electrons generated in the treatment head and scattered electrons formed near the body surface.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 203 \ 108

    Experimental Study for Phase-contrast X-ray Imaging Based on a Single Antiscatter Grid and a Polychromatic X-ray Source

    Yeonok Park, Hyosung Cho, Hyunwoo Lim, Uikyu Je, Chulkyu Park, Heemoon Cho, Kyuseok Kim, Guna Kim, Soyoung Park

    Abstract
    In this work, we performed a proof-of-concept experiment for phase-contrast x-ray imaging (PCXI) based on a single antiscatter grid and a polychromatic x-ray source. We established a table-top setup which consists of a focused-linear grid having a strip density of 200 lines/inch, a microfocus x-ray tube having a focal-spot size of about 5 μm, and a CMOS-type flat-panel detector having a pixel size of 48 μm. By using our prototype PCXI system and the Fourier demodulation technique, we successfully obtained attenuation, scattering, and differential phase-contrast images of improved visibility from the raw images of several selected samples at x-ray tube conditions of 90 kVp and 0.1 mAs. Further, fusion image (e.g., the attenuation+the scattering) may have an advantage in displaying details of the sample’s structures that are not clearly visible in the conventional attenuation image. Our experimental results indicate that single-grid-based approach seems a useful method for PCXI with great simplicity and minimal requirements on the setup alignment.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 306 \ 95

    Evaluation of Dosimetric Characteristics of a Double-focused Dynamic Micro-Multileaf Collimator (DMLC)

    Ae Ran Kim, Jae-Hyuk Seo, Hun-Joo Shin, Hyeong Wook Park, Ki Woong Lee, Jae Choon Lee, Shin-Wook Kim, Ji Na Kim, Hyeli Park, Heui-Kwan Lee, Young-Nam Kang

    Abstract
    Double-focused micro-Multileaf Collimator (μMLC) is able to create radiation fields having sharper dose gradients at the field edges than common MLC. Therefore, μMLC has been used for the stereotactic radio surgery (SRS) and Stereotactic Radiotherapy (SRT). We evaluated the dosimetric characteristics of a double focused Dynamic-μMLC (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.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 220 \ 68

    Response Evaluation after Stereotactic Ablative Radiotherapy for Lung Cancer

    Ji Hoon Choi

    Abstract
    We retrospectively reviewed lung cancer patients who were treated with stereotactic ablative radiotherapy (SABR). We investigated the value of response evaluation after treatment by measuring the volume change of tumors on serial chest computed tomography (CT) examinations. The study included 11 consecutive patients with early-stage (T1-T2aN0M0) non-small cell lung cancer (NSCLC) who were treated with SABR. The median dose of SABR was 6,000 cGy (range 5,000∼6,400) in five fractions. Sequential follow-up was performed with chest CT scans. Median follow-up time was 28 months. Radiologic measurement was performed on 51 CT scans with a median of 3 CT scans per patient. The median time to partial response (TPR) was 3 months and median time to complete remission (TCR) was 5 months. Overall response rate was 90.9% (10/11). Five patients had complete remission, five had partial response, and one patient developed progressive disease without response. On follow-up, three patients (27.2%) developed progressive disease after treatment. We evaluated the the response after SABR. Our data also showed the timing of response after SABR.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 444 \ 193

    Comparison of Dosimetric Parameters of Patient with Large and Pendulous Breast Receiving Breast Radiotherapy in the Prone versus Supine Position

    Sun Young Moon, Myonggeun Yoon, Weon Kuu Chung, Mijoo Chung, Dong Oh Shin, Dong Wook Kim

    Abstract
    The purpose of this study is to analyze dosimetric parameters of patient with large and pendulous breast receiving breast radiotherapy in the prone versus supine position. The patient underwent computed tomography simulation in both prone and supine position. The homogeneity index (HI), conformity index (CI), coverage index (CVI) to the left breast as planning target volume (PTV) and the doses to the lung, heart, and right breast as organ at risk (OAR) were compared by using dose-volume histogram. The lifetime attributable risk (LAR) according to the prone and supine position was measured for the lung and right breast. The HI, CI of the PTV decreased 21.7%, 6.49%, respectively and the CVI increased 10.8% with the prone position. The mean and maximum dose to the left lung decreased 91.6%, 87.0%, respectively and the volume parameters also decreased over 99% with the prone position. The parameters to the right lung were same regardless of the position. The mean and maximum dose to the heart decreased 51.6%, 14.2% with the prone position. But the mean and maximum dose to the right breast increased unlike the other OARs. The LARs to the lung decreased 80.3% (left), 24.2% (right) but the LAR to the right breast doubled with the prone position. The prone position is a favorable alternative for irradiation of breast in patients with large and pendulous breasts.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 325 \ 102

    Feasibility Study for Development of Transit Dosimetry Based Patient Dose Verification System Using the Glass Dosimeter

    Seonghoon Jeong, Myonggeun Yoon, Dong Wook Kim, Weon Kuu Chung, Mijoo Chung, Sang Hyoun Choi

    Abstract
    As radiation therapy is one of three major cancer treatment methods, many cancer patients get radiation therapy. To exposure as much radiation to cancer while normal tissues near tumor get little radiation, medical physicists make a radiotherapy plan treatment and perform quality assurance before patient treatment. Despite these efforts, unintended medical accidents can occur by some errors. In order to solve the problem, patient internal dose reconstruction methods by measuring transit dose are suggested. As feasibility study for development of patient dose verification system, inverse square law, percentage depth dose and scatter factor are used to calculate dose in the water-equivalent homogeneous phantom. As a calibration results of ionization chamber and glass dosimeter to transit radiation, signals of glass dosimeter are 0.824 times at 6 MV and 0.736 times at 10 MV compared to dose measured by ionization chamber. Average scatter factor is 1.4 and Mayneord F factor was used to apply percentage depth dose data. When we verified the algorithm using the water-equivalent homogeneous phantom, maximum error was 1.65%.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 259 \ 129

    Development of Manual Multi-Leaf Collimator for Proton Therapy in National Cancer Center

    Nuri Lee, Tae Yoon Kim, Dong Yun Kang, Jae Hyock Choi, Jong Hwi Jeong, Dongho Shin, Young Kyung Lim, Jeonghoon Park, Tae Hyun Kim, Se Byeong Lee

    Abstract
    Multi-leaf collimator (MLC) systems are frequently used to deliver photon-based radiation, and allow conformal shaping of treatment beams. Many proton beam centers currently make use of aperture and snout systems, which involve use of a snout to shape and focus the proton beam, a brass aperture to modify field shape, and an acrylic compensator to modulate depth. However, it needs a lot of time and cost of preparing treatment, therefore, we developed the manual MLC for solving this problem. This study was carried out with the intent of designing an MLC system as an alternative to an aperture block system. Radio-activation and dose due to primary proton beam leakage and the presence of secondary neutrons were taken into account during these iterations. Analytical calculations were used to study the effects of leaf material on activation. We have fabricated tray model for adoption with a wobbling snout (30×40 cm2) system which used uniform scanning beam. We designed the manual MLC and tray and can reduce the cost and time for treatment. After leakage test of new tray, we upgrade the tray with brass and made the safety tool. First, we have tested the radio-activation with usually brass and new brass for new manual MLC. It shows similar behavior and decay trend. In addition, we have measured the leakage test of a gantry with new tray and MLC tray, while we exposed the high energy with full modulation process on film dosimetry. The radiation leakage is less than 1%. From these results, we have developed the design of the tray and upgrade for safety. Through the radio-activation behavior, we figure out the proton beam leakage level of safety, where there detects the secondary particle, including neutron. After developing new design of the tray, it will be able to reduce the time and cost of proton treatment. Finally, we have applied in clinic test with original brass aperture and manual MLC and calculated the gamma index, 99.74% between them.
  • Original Article 2015-12-30 2015-12-30 \ 0 \ 156 \ 125

    Feasibility of Automated Detection of Inter-fractional Deviation in Patient Positioning Using Structural Similarity Index: Preliminary Results

    Hanbean Youn, Hosang Jeon, Jayeong Lee, Juhye Lee, Jiho Nam, Dahl Park, Wontaek Kim, Yongkan Ki, Donghyun Kim

    Abstract
    The modern radiotherapy technique which delivers a large amount of dose to patients asks to confirm the positions of patients or tumors more accurately by using X-ray projection images of high-definition. However, a rapid increase in patient’s exposure and image information for CT image acquisition may be additional burden on the patient. In this study, by introducing structural similarity (SSIM) index that can effectively extract the structural information of the image, we analyze the differences between daily acquired x-ray images of a patient to verify the accuracy of patient positioning. First, for simulating a moving target, the spherical computational phantoms changing the sizes and positions were created to acquire projected images. Differences between the images were automatically detected and analyzed by extracting their SSIM values. In addition, as a clinical test, differences between daily acquired x-ray images of a patient for 12 days were detected in the same way. As a result, we confirmed that the SSIM index was changed in the range of 0.85∼1 (0.006∼1 when a region of interest (ROI) was applied) as the sizes or positions of the phantom changed. The SSIM was more sensitive to the change of the phantom when the ROI was limited to the phantom itself. In the clinical test, the daily change of patient positions was 0.799∼0.853 in SSIM values, those well described differences among images. Therefore, we expect that SSIM index can provide an objective and quantitative technique to verify the patient position using simple x-ray images, instead of time and cost intensive three-dimensional x-ray images.
Korean Society of Medical Physics

Vol.35 No.2
2015-12-30

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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