• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.77-84
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• 2012

Purpose: To develop a geometrical quality control real-time analysis program using an electronic portal imaging to replace film evaluation method. Materials and Methods: A geometrical quality control item was established with the Eclipse treatment planning system (Version 8.1, Varian, USA) after the Electronic Portal Imaging Device (EPID) took care of the problems occurring from the fixed substructure of the linear accelerator (CL-iX, Varian, USA). Electronic portal image (single exposure before plan) was created at the treatment room's 4DTC (Version 10.2, Varian, USA) and a beam was irradiated in accordance with each item. The gaining the entire electronic portal imaging at the Off-line review and was evaluated by a self-developed geometrical quality control real-time analysis program. As for evaluation methods, the intra-fraction error was analyzed by executing 5 times in a row under identical conditions and procedures on the same day, and in order to confirm the infer-fraction error, it was executed for 10 days under identical conditions of all procedures and was compared with the film evaluation method using an Iso-align$^{TM}$ quality control device. Measurement and analysis time was measured by sorting the time into from the device setup to data achievement and the time amount after the time until the completion of analysis and the convenience of the users and execution processes were compared. Results: The intra-fraction error values for each average 0.1, 0.2, 0.3, 0.2 mm at light-radiation field coincidence, collimator rotation axis, couch rotation axis and gantry rotation axis. By checking the infer-fraction error through 10 days of continuous quality control, the error values obtained were average 1.7, 1.4, 0.7, 1.1 mm for each item. Also, the measurement times were average 36 minutes, 15 minutes for the film evaluation method and electronic portal imaging system, and the analysis times were average 30 minutes, 22 minutes. Conclusion: When conducting a geometrical quality control using an electronic portal imaging, it was found that it is efficient as a quality control tool. It not only reduces costs through not using films, but also reduces the measurement and analysis time which enhances user convenience and can improve the execution process by leaving out film developing procedures etc. Also, images done with evaluation from the self-developed geometrical quality control real-time analysis program, data processing is capable which supports the storage of information.

• The Journal of Korean Society for Radiation Therapy
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• v.20 no.1
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• pp.17-23
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• 2008

Purpose: Cone-beam CT using linear accelerator attached to on-board imager is a image guided therapy equipment. Because it is to check the patient's set-up error, correction, organ and target movement. but imaging dose should be cause of the secondary cancer when taking a image. The aim of this study is investigation of appropriate cone beam CT scan mode to compare and estimate the image quality and skin dose. Materials and Methods: Measurement by Thermoluminescence dosimeter (TLD-100, Harshaw) with using the Rando phantom are placed on each eight sites in seperately H&N, thoracic, abdominal section. each 4 methods of scan modes of are measured the for skin dose in three time. Subsequently, obtained average value. Following image quality QA protocol of equipment manufacturers using the catphan 504 phantom, image quality of each scan mode is compared and analyzed. Results: The results of the measured skin dose are described in here. The skin dose of Head & Neck are measured mode A: 8.96 cGy, mode B: 4.59 cGy, mode C: 3.46 cGy mode D: 1.76 cGy and thoracic mode A: 9.42 cGy, mode B: 4.58 cGy, mode C: 3.65 cGy, mode D: 1.85 cGy, and abdominal mode A: 9.97 cGy, mode B: 5.12 cGy, mode C: 4.03 cGy, mode D: 2.21 cGy. Approximately, dose of mode B are reduced 50%, mode C are reduced 60%, mode D are reduced 80% a point of reference dose of mode A. the results of analyzed HU reproducibility, low contrast resolution, spatial resolution (high contrast resolution), HU uniformity in evaluation item of image quality are within the tolerance value by recommended equipment manufacturer in all scan mode. Conclusion: Maintaining the image quality as well as reducing the image dose are very important in cone beam CT. In the result of this study, we are considered when to take mode A when interested in soft tissue. And we are considered to take mode D when interested in bone scan and we are considered to take mode B, C when standard scan. Increasing secondary cancer risk due to cone beam CT scan should be reduced by low mAs technique.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.57-67
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• 2013

Purpose: Replacing the film which used to be used for checking the set-up of the patient and dosimetry during radiation therapy, more and more EPID equipped devices are in use at present. Accordingly, this article tried to evaluated the accuracy of the position check-up and the usefulness of dosimetry during the use of an electronic portal imaging device. Materials and Methods: On 50 materials acquired with the search of Korea Society Radiotherapeutic Technology, The Korean Society for Radiation Oncology, and Pubmed using "EPID", "Portal dosimetry", "Portal image", "Dose verification", "Quality control", "Cine mode", "Quality - assurance", and "In vivo dosimetry" as indexes, the usefulness of EPID was analyzed by classifying them as history of EPID and dosimetry, set-up verification and characteristics of EPID. Results: EPID is developed from the first generation of Liquid-filled ionization chamber, through the second generation of Camera-based fluoroscopy, and to the third generation of Amorphous-silicon EPID imaging modes can be divided into EPID mode, Cine mode and Integrated mode. When evaluating absolute dose accuracy of films and EPID, it was found that EPID showed within 1% and EDR2 film showed within 3% errors. It was confirmed that EPID is better in error measurement accuracy than film. When gamma analyzing the dose distribution of the base exposure plane which was calculated from therapy planning system, and planes calculated by EDR2 film and EPID, both film and EPID showed less than 2% of pixels which exceeded 1 at gamma values (r%>1) with in the thresholds such as 3%/3 mm and 2%/2 mm respectively. For the time needed for full course QA in IMRT to compare loads, EDR2 film recorded approximately 110 minutes, and EPID recorded approximately 55 minutes. Conclusion: EPID could easily replace conventional complicated and troublesome film and ionization chamber which used to be used for dosimetry and set-up verification, and it was proved to be very efficient and accurate dosimetry device in quality assurance of IMRT (intensity modulated radiation therapy). As cine mode imaging using EPID allows locating tumors in real-time without additional dose in lung and liver which are mobile according to movements of diaphragm and in rectal cancer patients who have unstable position, it may help to implement the most optimal radiotherapy for patients.

• The korean journal of orthodontics
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• v.40 no.1
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• pp.16-26
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• 2010

Objective: The purposes of this study were to evaluate the force and stress depending on the type, deflection and thickness of the materials and to evaluate the mechanical properties of thermoplastic materials after repeated loading. Methods: Four types of thermoplastic products were tested. Force until the deflections of 2.0 mm and the stress when the materials were restoring to its resting position were evaluated. The mechanical properties of thermoplastic materials evaluated after 5 repeated loading cycles. Results: The interaction was observed between the thickness and the deflection (p < 0.05) from the regression equation. Thickness and amount of deflection rather than products and materials showed the largest effect on force and stress. In all products, at least 159 gf of force was required for more than 1.0 mm deflection or when materials with 1.0 mm thickness were deflected. The stress recorded was more than 19 gf/$mm^2$. During repeated loading, each group showed significant difference on the force and the stress (p < 0.01), 10 - 17% reduction of force and 4 - 7% reduction of stress in average. Conclusions: Proper thickness of thermoplastic materials and deflection level of tooth movement should be decided for the physiologic tooth movement. Force decay after repeated loading should be considered for the efficient tooth movement.

• Progress in Medical Physics
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• v.24 no.2
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• pp.85-91
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• 2013

At present, megavoltage computed tomography (MVCT) is the only method used to correct the position of tomotherapy patients. MVCT produces extra radiation, in addition to the radiation used for treatment, and repositioning also takes up much of the total treatment time. To address these issues, we suggest the use of a video image-guided setup (VIGS) system for correcting the position of tomotherapy patients. We developed an in-house program to correct the exact position of patients using two orthogonal images obtained from two video cameras installed at $90^{\circ}$ and fastened inside the tomotherapy gantry. The system is programmed to make automatic registration possible with the use of edge detection of the user-defined region of interest (ROI). A head-and-neck patient is then simulated using a humanoid phantom. After taking the computed tomography (CT) image, tomotherapy planning is performed. To mimic a clinical treatment course, we used an immobilization device to position the phantom on the tomotherapy couch and, using MVCT, corrected its position to match the one captured when the treatment was planned. Video images of the corrected position were used as reference images for the VIGS system. First, the position was repeatedly corrected 10 times using MVCT, and based on the saved reference video image, the patient position was then corrected 10 times using the VIGS method. Thereafter, the results of the two correction methods were compared. The results demonstrated that patient positioning using a video-imaging method ($41.7{\pm}11.2$ seconds) significantly reduces the overall time of the MVCT method ($420{\pm}6$ seconds) (p<0.05). However, there was no meaningful difference in accuracy between the two methods (x=0.11 mm, y=0.27 mm, z=0.58 mm, p>0.05). Because VIGS provides a more accurate result and reduces the required time, compared with the MVCT method, it is expected to manage the overall tomotherapy treatment process more efficiently.

• Progress in Medical Physics
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• v.21 no.4
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• pp.332-339
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• 2010

We aimed to setup an adaptive radiation therapy platform using cone-beam CT (CBCT) and multileaf collimator (MLC) log data and also intended to analyze a trend of dose calculation errors during the procedure based on a phantom study. We took CT and CBCT images of Catphan-600 (The Phantom Laboratory, USA) phantom, and made a simple step-and-shoot intensity-modulated radiation therapy (IMRT) plan based on the CT. Original plan doses were recalculated based on the CT ($CT_{plan}$) and the CBCT ($CBCT_{plan}$). Delivered monitor unit weights and leaves-positions during beam delivery for each MLC segment were extracted from the MLC log data then we reconstructed delivered doses based on the CT ($CT_{recon}$) and CBCT ($CBCT_{recon}$) respectively using the extracted information. Dose calculation errors were evaluated by two-dimensional dose discrepancies ($CT_{plan}$ was the benchmark), gamma index and dose-volume histograms (DVHs). From the dose differences and DVHs, it was estimated that the delivered dose was slightly greater than the planned dose; however, it was insignificant. Gamma index result showed that dose calculation error on CBCT using planned or reconstructed data were relatively greater than CT based calculation. In addition, there were significant discrepancies on the edge of each beam while those were less than errors due to inconsistency of CT and CBCT. $CBCT_{recon}$ showed coupled effects of above two kinds of errors; however, total error was decreased even though overall uncertainty for the evaluation of delivered dose on the CBCT was increased. Therefore, it is necessary to evaluate dose calculation errors separately as a setup error, dose calculation error due to CBCT image quality and reconstructed dose error which is actually what we want to know.

• Journal of radiological science and technology
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• v.35 no.4
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• pp.335-343
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• 2012

Intensity-modulated radiotherapy(IMRT) have the ability to provide better dose conformity and sparing of critical normal tissues than three-dimensional radiotherapy(3DCRT). Especially, with the benefit of health insurance in 2011, its use now increasingly in many modern radiotherapy departments. Also the use of linear accelerator with high-energy photon beams over 10 MV is increasing. As is well known, these linacs have the capacity to produce photonueutrons due to photonuclear reactions in materials with a large atomic number such as the target, flattening filters, collimators, and multi-leaf collimators(MLC). MLC-based IMRT treatments increase the monitor units and the probability of production of photoneutrons from photon-induced nuclear reactions. The purpose of this study is to quantitatively evaluate the dose of photoneutrons produced from 3DCRT and IMRT technique for Rando phantom in cervical cancer. We performed the treatment plans with 3DCRT and IMRT technique using Rando phantom for treatment of cervical cancer. An Rando phantom placed on the couch in the supine position was irradiated using 15 MV photon beams. Optically stimulated luminescence dosimeters(OSLD) were attached to 4 different locations (abdomen, chest, head and neck, eyes) and from center of field size and measured 5 times each of locations. Measured neutron dose from IMRT technique increased by 9.0, 8.6, 8.8, and 14 times than 3DCRT technique for abdomen, chest, head and neck, and eyes, respectively. When using IMRT with 15 MV photonbeams, the photoneutrons contributed a significant portion on out-of-field. It is difficult to prevent high energy photon beams to produce the phtoneutrons due to physical properties, if necessary, It is difficult to prevent high energy photon beams to produce the phtoneutrons due to physical properties, if necessary, it is need to provide the additional safe shielding on a linear accelerator and should therefore reduce the out-of-field dose.

• Progress in Medical Physics
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• v.17 no.1
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• pp.24-31
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• 2006

Automated analysis software was developed to measure the magnitude of the intrafractional and interfractional errors during breast radiation treatments. Error analysis results are important for determining suitable planning target volumes (PTV) prior to Implementing breast-conserving 3-D conformal radiation treatment (CRT). The electrical portal imaging device (EPID) used for this study was a Portal Vision LC250 liquid-filled ionization detector (fast frame-averaging mode, 1.4 frames per second, 256X256 pixels). Twelve patients were imaged for a minimum of 7 treatment days. During each treatment day, an average of 8 to 9 images per field were acquired (dose rate of 400 MU/minute). We developed automated image analysis software to quantitatively analyze 2,931 images (encompassing 720 measurements). Standard deviations ($\sigma$) of intrafractional (breathing motion) and intefractional (setup uncertainty) errors were calculated. The PTV margin to include the clinical target volume (CTV) with 95% confidence level was calculated as $2\;(1.96\;{\sigma})$. To compensate for intra-fractional error (mainly due to breathing motion) the required PTV margin ranged from 2 mm to 4 mm. However, PTV margins compensating for intefractional error ranged from 7 mm to 31 mm. The total average error observed for 12 patients was 17 mm. The intefractional setup error ranged from 2 to 15 times larger than intrafractional errors associated with breathing motion. Prior to 3-D conformal radiation treatment or IMRT breast treatment, the magnitude of setup errors must be measured and properly incorporated into the PTV. To reduce large PTVs for breast IMRT or 3-D CRT, an image-guided system would be extremely valuable, if not required. EPID systems should incorporate automated analysis software as described in this report to process and take advantage of the large numbers of EPID images available for error analysis which will help Individual clinics arrive at an appropriate PTV for their practice. Such systems can also provide valuable patient monitoring information with minimal effort.

• Radiation Oncology Journal
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• v.26 no.2
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• pp.118-125
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• 2008

Purpose: On-line image guided radiation therapy(on-line IGRT) and(kV X-ray images or cone beam CT images) were obtained by an on-board imager(OBI) and cone beam CT(CBCT), respectively. The images were then compared with simulated images to evaluate the patient's setup and correct for deviations. The setup deviations between the simulated images(kV or CBCT images), were computed from 2D/2D match or 3D/3D match programs, respectively. We then investigated the correctness of the calculated deviations. Materials and Methods: After the simulation and treatment planning for the RANDO phantom, the phantom was positioned on the treatment table. The phantom setup process was performed with side wall lasers which standardized treatment setup of the phantom with the simulated images, after the establishment of tolerance limits for laser line thickness. After a known translation or rotation angle was applied to the phantom, the kV X-ray images and CBCT images were obtained. Next, 2D/2D match and 3D/3D match with simulation CT images were taken. Lastly, the results were analyzed for accuracy of positional correction. Results: In the case of the 2D/2D match using kV X-ray and simulation images, a setup correction within $0.06^{\circ}$ for rotation only, 1.8 mm for translation only, and 2.1 mm and $0.3^{\circ}$ for both rotation and translation, respectively, was possible. As for the 3D/3D match using CBCT images, a correction within $0.03^{\circ}$ for rotation only, 0.16 mm for translation only, and 1.5 mm for translation and $0.0^{\circ}$ for rotation, respectively, was possible. Conclusion: The use of OBI or CBCT for the on-line IGRT provides the ability to exactly reproduce the simulated images in the setup of a patient in the treatment room. The fast detection and correction of a patient's positional error is possible in two dimensions via kV X-ray images from OBI and in three dimensions via CBCT with a higher accuracy. Consequently, the on-line IGRT represents a promising and reliable treatment procedure.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.1
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• pp.127-135
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• 2014

Purpose : By taking advantage of each imaging modality, the use of fused CT/MRI image has increased in prostate cancer radiation therapy. However, fusion uncertainty may cause partial target miss or normal organ overdose. In order to complement such limitation, our hospital acquired MRI image (Planning MRI) by setting up patients with the same fixing tool and posture as CT simulation. This study aims to evaluate the usefulness of the Planning MRI through comparing and analyzing the diagnostic MRI image and Planning MRI image. Materials and Methods : This study targeted 10 patients who had been diagnosed with prostate cancer and prescribed nonhormone and definitive RT 70 Gy/28 fx from August 2011 to July 2013. Each patient had both CT and MRI simulations. The MRI images were acquired within one half hour after the CT simulation. The acquired CT/MRI images were fused primarily based on bony structure matching. This study measured the volume of prostate in the images of Planning MRI and diagnostic MRI. The diameters at the craniocaudal, anteroposterior and left-to-right directions from the center of prostate were measured in order to compare changes in the shape of prostate. Results : As a result of comparing the volume of prostate in the images of Planning MRI and diagnostic MRI, they were found to be $25.01cm^3$(range $15.84-34.75cm^3$) and $25.05cm^3$(range $15.28-35.88cm^3$) on average respectively. The diagnostic MRI had an increase of 0.12 % as compared with the Planning MRI. On the planning MRI, there was an increase in the volume by $7.46cm^3$(29 %) at the transition zone directions, and there was a decrease in the volume by $8.52cm^3$(34 %) in the peripheral zone direction. As a result of measuring the diameters at the craniocaudal, anteroposterior and left-to-right directions in the prostate, the Planning MRI was found to have on average 3.82cm, 2.38cm and 4.59cm respectively and the diagnostic MRI was found to have on average 3.37cm, 2.76cm and 4.51cm respectively. All three prostate diameters changed and the change was significant in the Planning MRI. On average, the anteroposterior prostate diameter decrease by 0.38cm(13 %). The mean right-to-left and craniocaudal diameter increased by 0.08cm(1.6 %) and 0.45cm(13 %), respectively. Conclusion : Based on the results of this study, it was found that the total volumes of prostate in the Planning MRI and the diagnostic MRI were not significantly different. However, there was a change in the shape and partial volume of prostate due to the insertion of prostate balloon tube to the rectum. Thus, if the Planning MRI images were used when conducting the fusion of CT/MRI images, it would be possible to include the target in the CTV without a loss as much as the increased volume in the transition zone. Also, it would be possible to reduce the radiation dose delivered to the rectum through separating more clearly the reduction of peripheral zone volume. Therefore, the author of this study believes that acquisition of Planning MRI image should be made to ensure target delineation and localization accuracy.