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Purpose Scanning proton therapy has dosimetric advantage over passive treatment, but has a large penumbra in low-energy region. This study investigates the penumbra reduction when multi-leaf collimators (MLCs) are used for line scanning proton beams and secondary neutron production from MLCs. Methods Scanning beam plans with and without MLC shaping were devised. Line scanning proton plan of 36 energy layers between 71.2 and 155.2 MeV was generated. The MLCs were shaped according to the cross-sectional target shape for each energy layer. The two-dimensional doses were measured through an ion-chamber array, depending on the presence of MLC field, and Monte Carlo (MC) simulations were performed. The plan, measurement, and MC data, with and without MLC, were compared at each depth. The secondary neutron dose was simulated with MC. Ambient neutron dose equivalents were computed for the line scanning with 10 × 10 × 5 cm3 volume and maximum proton energy of 150 MeV, with and without MLCs, at lateral distances of 25–200 cm from the isocenter. The neutron dose for a wobbling plan with 10 × 10 × 5 cm3 volume was also evaluated. Results The lateral penumbra width using MLC was reduced by 23.2% on average, up to a maximum of 32.2%, over the four depths evaluated. The ambient neutron dose equivalent was 18.52% of that of the wobbling beam but was 353.1% larger than the scanning open field. Conclusions MLC field shaping with line scanning reduced the lateral penumbra and should be effective in sparing normal tissue. However, it is important to investigate the increase in neutron dose.

In particle radiotherapy, range uncertainty is an important issue that needs to be overcome. Because high-dose conformality can be achieved using a particle beam, a small uncertainty can affect tumor control or cause normal-tissue complications. From this perspective, the treatment planning system (TPS) must be accurate. However, there is a well-known inaccuracy regarding dose computation in heterogeneous media. This means that verifying the uncertainty level is one of the prerequisites for TPS commissioning. We evaluated the range accuracy of the dose computation algorithm implemented in a commercial TPS, and Monte Carlo (MC) simulation against measurement using a CT calibration phantom. A treatment plan was produced for eight different materials plugged into a phantom, and two-dimensional doses were measured using a chamber array. The measurement setup and beam delivery were simulated by MC code. For an infinite solid water phantom, the gamma passing rate between the measurement and TPS was 97.7%, and that between the measurement and MC was 96.5%. However, gamma passing rates between the measurement and TPS were 49.4% for the lung and 67.8% for bone, and between the measurement and MC were 85.6% for the lung and 100.0% for bone tissue. For adipose, breast, brain, liver, and bone mineral, the gamma passing rates computed by TPS were 91.7%, 90.6%, 81.7%, 85.6%, and 85.6%, respectively. The gamma passing rates for MC for adipose, breast, brain, liver, and bone mineral were 100.0%, 97.2%, 95.0%, 98.9%, and 97.8%, respectively. In conclusion, the described procedure successfully evaluated the allowable range uncertainty for TPS commissioning. The TPS dose calculation is inefficient in heterogeneous media with large differences in density, such as lung or bone tissue. Therefore, the limitations of TPS in heterogeneous media should be understood and applied in clinical practice.

Two full rotating gantries with different nozzles (multipurpose nozzle with MLC, scanning dedicated nozzle) for a conventional cyclotron system are installed and being commissioned for various proton treatment options at Samsung Medical Center in Korea. The purpose of this study is to use Monte Carlo simulation to investigate the neutron dose equivalent per therapeutic dose, H/D, for X-ray imaging equipment under various treatment conditions. At first, we investigated the H/D for various modifications of the beamline devices (scattering, scanning, multi-leaf collimator, aperture, compensator) at the isocenter and at 20, 40 and 60 cm distances from the isocenter, and we compared our results with those of other research groups. Next, we investigated the neutron dose at the X-ray equipment used for real-time imaging under various treatment conditions. Our investigation showed doses of 0.07 ~ 0.19 mSv/Gy at the X-ray imaging equipment, depending on the treatment option and interestingly, the 50% neutron dose reduction was observed due to multileaf collimator during proton scanning treatment with the multipurpose nozzle. In future studies, we plan to measure the neutron dose experimentally and to validate the simulation data for X-ray imaging equipment for use as an additional neutron dose reduction method.

Purpose: A new system for manufacturingproton range compensator (PRC) was developed by using a three‐dimensional printer (3DP). The physical accuracy and dosimetrical characteristics of the new PRC (PRC‐3DP) was compared with conventional PRC (PRC‐CMM) manufactured by computerized milling machine (CMM). Methods: A PRC for braincancer treatment, with passive scattered proton beam, was calculated in the TPS (Eclipse, Varian, USA) and its data was converted into a new format for 3DP (Projet HD3000, 3D Systems, USA), using the in‐house developed software. PRC‐3DP was printed with UV curable acrylic plastic, while PRC‐ CMM was milled into PMMA using a CMM (V‐CNC500, CINCINNATI, USA). We measured the 5 randomly selected points for its physical thickness of both PRCs to evaluate its physical accuracy. Stopping power ratio (SPR), spread‐out bragg peak (SOBP, 90∼90%) and distal fall‐off (DFO, 20∼80%) at the central axis, +2.5, and 2.5 cm in the lateral direction, and FWHM of dose profile in depth 6, 8, and 10 cm were measured to evaluate for its dosimetrical characteristics. All measured data was compared with TPS data. Results:There was no significant difference in the physical depths between the calculated and the measured value of both RPC‐3DP and RPC‐CMM (p

Purpose: We developed a video image‐guided real‐time patient motion monitoring system for helical Tomotherapy (VGRPM‐Tomo), and its clinical utility was evaluated using a motion phantom. Methods: The VGRPM‐Tomo consisted of three components: an image acquisition device consisting of two PC‐cams, a main controlcomputer with a radiation signal controller and warning system, and patient motion analysissoftware, which was developed in house. The system was designed for synchronization with a beam on/off trigger signal to limit operation during treatment time only and to enable system automation. In order to detect the patient motion while the couch is moving into the gantry, a reference image, which continuously updated its background by exponential weighting filter (EWF), is compared with subsequent live images using the real‐time frame difference‐based analysissoftware. When the error range exceeds the set criteria (δ_movement) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.5, and 1.0 cm for 1 and 2 sec, respectively, was used to evaluate the system performance at maximum couch speed (0.196 cm/sec) in a Helical Tomotherapy (HD, Hi‐art, Tomotherapy, USA). We measured the optimal EWF factor (a) and δ_movement, which is the minimum distance that can be detected with this system, and the response time of the whole system.Results: The optimal a for clinical use ranged from 0.85 to 0.9. The system was able to detect phantom motion as small as 0.2 cm with tight δ_movement, 0.1% total number of pixels in the reference image. The measured response time of the whole system was 0.1 sec. Conclusions: The VGRPM‐tomo can contribute to reduction of treatment error caused by the motion of patients and increase the accuracy of treatment dose delivery in HD. This work was supported by the Technology Innovation Program, 10040362, Development of an integrated management solution for radiation therapy funded by the Ministry of Knowledge Economy (MKE, Korea). This idea is protected by a Korean patent(patent no. 10‐1007367).

Purpose The authors developed a video image-guided real-time patient motion monitoring (VGRPM) system using PC-cams, and its clinical utility was evaluated using a motion phantom. Methods The VGRPM system has three components: (1) an image acquisition device consisting of two PC-cams, (2) a main control computer with a radiation signal controller and warning system, and (3) patient motion analysis software developed in-house. The intelligent patient motion monitoring system was designed for synchronization with a beam on/off trigger signal in order to limit operation to during treatment time only and to enable system automation. During each treatment session, an initial image of the patient is acquired as soon as radiation starts and is compared with subsequent live images, which can be acquired at up to 30 fps by the real-time frame difference-based analysis software. When the error range exceeds the set criteria (δ(movement)) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.3, 0.5, and 1.0 cm for 1 and 2 s, respectively, was used to evaluate the system performance. The authors measured optimal δ(movement) for clinical use, the minimum distance that can be detected with this system, and the response time of the whole system using a video analysis technique. The stability of the system in a linear accelerator unit was evaluated for a period of 6 months. Results As a result of the moving phantom test, the δ(movement) for detection of all simulated phantom motion except the 0.1 cm movement was determined to be 0.2% of total number of pixels in the initial image. The system can detect phantom motion as small as 0.2 cm. The measured response time from the detection of phantom movement to generation of the warning signal was 0.1 s. No significant functional disorder of the system was observed during the testing period. Conclusions The VGRPM system has a convenient design, which synchronizes initiation of the analysis with a beam on/off signal from the treatment machine and may contribute to a reduction in treatment error due to patient motion and increase the accuracy of treatment dose delivery.

The purpose of this study was to evaluate the neutron dose equivalent from proton nuclear interactions with the multi-leaf collimator (MLC) during line scanning proton therapy. We generated a wobbling mode plan, a scanning mode plan, and a dynamic MLC with scanning mode plan with a field size of 7 cm and 12 cm, a maximum proton energy of 150 MeV. A Monte Carlo study was performed using the GEANT4 code (version 10.01.p01) [1] for our virtual machine based on the multi-purpose proton nozzle. In the wobbling mode, scanning mode, and scanning mode with dynamic MLC, the neutron dose equivalent generated through the nozzle was compared using the 12 cm diameter receptor. The receptors were located at the distance of r = 0, 25, 50, 100, 150, and 200 cm from the isocenter. In both field size conditions, the neutron dose equivalent in the scanning mode were 96.6%, 98.7%, 98.7%, 98.4%, 98.2%, and 97.9% lower than the wobbling mode in each receptor position, respectively. However, the neutron doses equivalent using line scanning with MLC to reduce the lateral penumbral width were 53.0%, 91.8%, 90.0%, 90.2%, 92.0%, and 91.6%, respectively, compared to the wobbling mode. The use of dynamic MLC in the scanning increases the neutron dose equivalent, but the use of dynamic MLC can reduce the dose to the organ at risk around the target and avoid disadvantages of the conventional scanning proton therapy [2] . However, according to the results of this study, secondary cancer caused by the effect of neutron dose increased when scanning with dynamic MLC is not negligible [3]

Objective. To evaluate the reproducibility of small bowel displacement system (SBDS) volumetrically using weekly CT throughout a regimen of radiotherapy for the treatment of cervical cancer. Methods. From October 2004 to January 2005, 10 consecutive patients who received pelvic radiation therapy for uterine cervical carcinoma with the SBDS were included in this study. With the patient laid prone on the conventional simulator table, the Styrofoam compression device is placed under the lower abdomen of the patient. Next, CT scan images, first two sets of without and with the SBDS, followed by with SBDS once a week for 3 weeks consecutively after the beginning of radiotherapy, were taken. Radiation planning was performed using standard pelvic box fields in 3-dimensional radiation treatment planning system. In each CT sets, we measured the identified organ volumes and the volume of small bowel irradiated in treatment portals. We used the regression analysis to know the correlation of the volume of small bowel irradiated according to the volume variation of bladder during radiotherapy. Results. The mean small bowel volume with SBDS of 10 patients during radiotherapy was reduced by 60.5% (from 32.5% to 78.2%), comparing to the small bowel volume without SBDS. The variation of small bowel volume reduction in each patient was ranged from 7.3% to 38.5% (mean: 20.5%). In spite of using the SBDS, the volume reduction of small bowel irradiated was affected significantly by the volume of bladder during radiotherapy. The variation of small bowel irradiated for five patients who had more than 10% small bowel volume variation was significantly correlated with the volume of bladder, but not for five patients less than 10% small bowel volume variation. Conclusion. We confirm that in spite of the variation of bladder volume during radiotherapy, the SBDS is an effective method that can be used to displace the small bowel continuously away from the irradiated field for cervical cancer.

This study was conducted to evaluate the cumulative dosimetric error that occurs in both target and surrounding normal tissues when treating a moving target in multifractional treatment with tomotherapy. An experiment was devised to measure cumulative error in multifractional treatments delivered to a horseshoe-shaped clinical target volume (CTV) surrounding a cylinder shape of organ at risk (OAR). Treatments differed in jaw size (1.05 vs 2.5 cm), pitch (0.287 vs 0.660), and modulation factor (1.5 vs 2.5), and tumor motion characteristics differing in amplitude (1 to 3 cm), period (3 to 5 second), and regularity (sinusoidal vs irregular) were tested. Treatment plans were delivered to a moving phantom up to 5-times exposure. Dose distribution on central coronal plane from 1 to 5 times exposure was measured with GAFCHROMIC EBT film. Dose differences occurring across 1 to 5 times exposure of treatment and between treatment plans were evaluated by analyzing measurements of gamma index, gamma index histogram, histogram changes, and dose at the center of the OAR. The experiment showed dose distortion due to organ motion increased between multiexposure 1 to 3 times but plateaued and remained constant after 3-times exposure. In addition, although larger motion amplitude and a longer period of motion both increased dosimetric error, the dose at the OAR was more significantly affected by motion amplitude rather than motion period. Irregularity of motion did not contribute significantly to dosimetric error when compared with other motion parameters. Restriction of organ motion to have small amplitude and short motion period together with larger jaw size and small modulation factor (with small pitch) is effective in reducing dosimetric error. Pretreatment measurements for 3-times exposure of treatment to a moving phantom with patient-specific tumor motion would provide a good estimation of the delivered dose distribution.

The authors developed a video image-guided real-time patient motion monitoring (VGRPM) system using PC-cams, and its clinical utility was evaluated using a motion phantom.The VGRPM system has three components: (1) an image acquisition device consisting of two PC-cams, (2) a main control computer with a radiation signal controller and warning system, and (3) patient motion analysis software developed in-house. The intelligent patient motion monitoring system was designed for synchronization with a beam on/off trigger signal in order to limit operation to during treatment time only and to enable system automation. During each treatment session, an initial image of the patient is acquired as soon as radiation starts and is compared with subsequent live images, which can be acquired at up to 30 fps by the real-time frame difference-based analysis software. When the error range exceeds the set criteria (δ(movement)) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.3, 0.5, and 1.0 cm for 1 and 2 s, respectively, was used to evaluate the system performance. The authors measured optimal δ(movement) for clinical use, the minimum distance that can be detected with this system, and the response time of the whole system using a video analysis technique. The stability of the system in a linear accelerator unit was evaluated for a period of 6 months.As a result of the moving phantom test, the δ(movement) for detection of all simulated phantom motion except the 0.1 cm movement was determined to be 0.2% of total number of pixels in the initial image. The system can detect phantom motion as small as 0.2 cm. The measured response time from the detection of phantom movement to generation of the warning signal was 0.1 s. No significant functional disorder of the system was observed during the testing period.The VGRPM system has a convenient design, which synchronizes initiation of the analysis with a beam on/off signal from the treatment machine and may contribute to a reduction in treatment error due to patient motion and increase the accuracy of treatment dose delivery.

Purpose Intensity modulated radiation therapy (IMRT) is a high precision therapy technique that can achieve a conformal dose distribution on a given target. However, organ motion induced by respiration can result in significant dosimetric error. Therefore, this study explores the dosimetric error that result from various patterns of respiration. Materials and Methods Experiments were designed to deliver a treatment plan made for a real patient to an in-house developed motion phantom. The motion pattern; the amplitude and period as well as inhale-exhale period, could be controlled by in-house developed software. Dose distribution was measured using EDR2 film and analysis was performed by RIT113 software. Three respiratory patterns were generated for the purpose of this study; first the 'even inhale-exhale pattern', second the slightly long exhale pattern (0.35 seconds longer than inhale period) named 'general signal pattern', and third a 'long exhale pattern' (0.7 seconds longer than inhale period). One dimensional dose profile comparisons and gamma index analysis on 2 dimensions were performed Results In one-dimensional dose profile comparisons, 5% in the target and 30% dose difference at the boundary were observed in the long exhale pattern. The center of high dose region in the profile was shifted 1 mm to inhale (caudal) direction for the 'even inhale-exhale pattern', 2 mm and 5 mm shifts to exhale (cranial) direction were observed for 'slightly long exhale pattern' and 'long exhale pattern', respectively. The areas of gamma index >1 were 11.88%, 15.11%, and 24.33% for 'even inhale-exhale pattern', 'general pattern', and 'long exhale pattern', respectively. The long exhale pattern showed largest errors. Conclusion To reduce the dosimetric error due to respiratory motions, controlling patient's breathing to be closer to even inhaleexhale period is helpful with minimizing the motion amplitude.

Purpose: In order to enhance the efficiency of respiratory gated 4-dimensional radiation therapy, a respiration training system using head mounted display device was developed and its efficacy was evaluated. Material and Methods: The experiment was designed to measure differences in respiration regularity by using the developed system. Three groups of patients were involved in the experiments.

Purpose: To evaluate the shielding wall design to protect patients, staff and member of the general public for secondary neutron using a simply analytic solution, multi-Monte Carlo code MCNPX, ANISN and FLUKA. Methods: An analytical and multi-Monte Carlo method were calculated for proton facility (Sumitomo Heavy Industry Ltd.) at Samsung Medical Center in Korea. The NCRP-144 analytical evaluation methods, which produced conservative estimates on the dose equivalent values for the shielding, were used for analytical evaluations. Then, the radiation transport was simulated with the multi-Monte Carlo code. The neutron dose at evaluation point is got by the value using the production of the simulation value and the neutron dose coefficient introduced in ICRP-74. Results: The evaluation points of accelerator control room and control room entrance are mainly influenced by the point of the proton beam loss. So the neutron dose equivalent of accelerator control room for evaluation point is 0.651, 1.530, 0.912, 0.943 mSv/yr and the entrance of cyclotron room is 0.465, 0.790, 0.522, 0.453 mSv/yr with calculation by the method of NCRP-144 formalism, ANISN, FLUKA and MCNP, respectively. The most of Result of MCNPX and FLUKA using the complicated geometry showed smaller values than Result of ANISN. Conclusion: Themore » neutron shielding for a proton therapy facility has been evaluated by the analytic model and multi-Monte Carlo methods. We confirmed that the setting of shielding was located in well accessible area to people when the proton facility is operated.« less

Purpose: We developed an offline based organ motion verification system using cine EPIDimages and evaluated its accuracy and availability through phantom study. Methods: The system was designed for import of cine EPIDimages, which are obtained sequentially during treatment through a DICOM format and reconstructed into a live image. For verification of organ motion, a pattern matching algorithm using an internal surrogate was employed in the self‐developed analysissoftware. For the system performance test, we developed a linear motion phantom, which consists of a human body shaped phantom with a fake tumor in the lung and linear motion cart with control software. The phantom was operated with a motion of 2 cm at 4 sec per cycle and cine EPIDimages were obtained at a rate of 3.3 frames/sec with 1024 × 768 pixel counts in a linear accelerator (10 MVX). Organ motion of the target was tracked using self‐developed analysissoftware and compared with data from the RPM system (Varian, USA). For quantitative analysis, we analyzed correlation between two data sets in terms of average cycle, amplitude, and pattern (root mean square, RSM) of motion. Results: Averages for the cycle of motion from cine EPID and RPM system were 3.95±0.02 and 3.98±0.11 sec, respectively, and showed good agreement on real value (4 sec). Average of the amplitude of motion tracked by our system (1.71 ±0.02 cm) showed a slightly different value, compared with the actual value (2 cm), due to time resolution for image acquisition. The value of the RMS from the cine EPIDimage (0.379) grew slightly, by 3.8%, compared with data from the RPM (0.365). Conclusions: Our system showed good representation of its motion in a preliminary phantom study. The system can be implemented for clinical purposes, which include organ motion verification and its feedback for accurate dose delivery to the moving target.

Purpose: The aim of this study was to investigate the gantry angle dependency of the multileaf collimator (MLC) leaf position error. Methods: An automatic MLC quality assurance system (AutoMLCQA) was developed to evaluate the gantry angle dependency of the MLC leaf position error using an electronic portal imaging device (EPID). To eliminate the EPID position error due to gantry rotation, we designed a reference maker (RM) that could be inserted into the wedge mount. After setting up the EPID, a reference image was taken of the RM using an open field. Next, an EPID-based picket-fence test (PFT) was performed without the RM. These procedures were repeated at every 45° intervals of the gantry angle. A total of eight reference images and PFT image sets were analyzed using in-house software. The average MLC leaf position error was calculated at five pickets (-10, -5, 0, 5, and 10 cm) in accordance with general PFT guidelines using in-house software. This test was carried out for four linear accelerators. Results: The average MLC leaf position errors were within the set criterion of

Purpose: To expedite and cross-check the commissioning of the proton therapy nozzles at Samsung Medical Center using TOPAS. Methods: We have two different types of nozzles at Samsung Medical Center (SMC), a multi-purpose nozzle and a pencil beam scanning dedicated nozzle. Both nozzles have been modelled in Monte Carlo simulation by using TOPAS based on the vendor-provided geometry. The multi-purpose nozzle is mainly composed of wobbling magnets, scatterers, ridge filters and multi-leaf collimators (MLC). Including patient specific apertures and compensators, all the parts of the nozzle have been implemented in TOPAS following the geometry information from the vendor.The dedicated scanning nozzle has a simpler structure than the multi-purpose nozzle with a vacuum pipe at the down stream of the nozzle.A simple water tank volume has been implemented to measure the dosimetric characteristics of proton beams from the nozzles. Results: We have simulated the two proton beam nozzles at SMC. Two different ridge filters have been tested for the spread-out Bragg peak (SOBP) generation of wobbling mode in the multi-purpose nozzle. The spot sizes and lateral penumbra in two nozzles have been simulated and analyzed using a double Gaussian model. Using parallel geometry, both the depth dose curve and dose profile have been measured simultaneously. Conclusion: The proton therapy nozzles at SMC have been successfully modelled in Monte Carlo simulation using TOPAS. We will perform a validation with measured base data and then use the MC simulation to interpolate/extrapolate the measured data. We believe it will expedite the commissioning process of the proton therapy nozzles at SMC.

154 This research was supported by the National Research Foundation of Korea (NRF-2011-0022021), Radiation Safety Programs (2011-31115) through the NSSC and Samsung Medical Center grant [GFO1130081]. Submitted September, 2, 2013, Accepted September, 7, 2013 Corresponding Author: Jin Sung Kim, Department of Radiation Oncology, Samsung Medical Center, 50, Ilwon-dong, Gangnam-gu, Seoul 135-710, Korea Tel: 02)3410-3771, Fax: 02)3410-2619 E-mail: jinsung.k@gmail.com Corresponding Author: Youngyih Han, Department of Radiation Oncology, Samsung Medical Center, 50, Ilwon-dong, Gangnam-gu, Seoul, 135-710, Republic of Korea Tel: 02)3410-2604, Fax: 02)3410-2619 E-mail: youngyih@skku.edu Comparison of Intensity-modulated Radiation Therapy (IMRT), Uniform Scanning Proton Therapy (USPT), and Intensity-modulated Proton Therapy (IMPT) for Prostate Cancer: A Treatment Planning Study

Purpose: Using conventional CCDcamera systems, we developed a video image guided real‐time patient's motion monitoring (VGRPM) system; a motion phantom was used for evaluation of its performance for clinical use. Methods: The VGRPM system consists of three parts: an image acquisitiondevice, a main control computer, and in‐house developed patient motion analysissoftware. For development of an intelligent patient motion monitoring system that works only during treatment time and for system automation, the system was designed for synchronization with a beam on/off trigger signal. Patient movement during radiation is detected by real‐time frame difference based in‐house developed analysissoftware. When the error range exceeds the set criteria, (Cmove), a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.5, 1, and 2 cm for 1 and 2 sec, respectively, was used for evaluation of system performance. We measured optimal Cmove for clinical use, minimum distance, which can be detected in this system, and response time of the whole system. The stability of the system in a linear accelerator unit was evaluated for a period of 6 months. Results: : As a result of the moving phantom test, the Cmove for detection of all simulated phantom motion was determined to be 0.5%. The system can detect phantom motion as small as 0.5 cm. The measured response time from detection of phantom movement to warning signal through video analysis was 0.1 sec. During this testing period, no significant functional disorder was observed. Conclusions: The VGRPM system can contribute to reduction of treatment error by patient's motion and increase the accuracy of treatment dose delivery.

Purpose: Treating moving oragan has been an issue due to the dynamic nature of Tomotheapy. Non of study has investigated throughly the multi‐ fractional effects of treatments. Therefore, we designed a study to evaluate the cumulative error in moving target and nearby normal tissues. Methods: A moving phantom whose motion pattern could be rogrammed by a user was produced. Four plans which used different jaw width (1.05 cm, 2.5 cm), pitch (0.660, 0,287) and modulation factor (1.5, 2.5) to deliver 1.49 Gy to 95% of PTV in each fraction were made. For each plan, 5 different motions ( amplitude 1–3cm, Period 3–5sec) and irregular motion were tested. Film measurements for accumulated dose were made with Gafchromic@EBT films from 1 to 5 fractions. Dose distribution on each film was compared with that measured in static phantom. Profile shapes, DoseArea Histogram (DAH)s and gamma index were used for comparison Results: The dose distortion increased up to 3rd fractions and, after 3rd fractions dose distributions in the target and OAR converged to some constant distribution. The distortion level inside the target was affected by motion parameters; larger motion amplitude and larger motion period resulted in increased dose. However dose at the center of the critical organ was rather affected by the motion amplitude than the motion period . The irregularity of the motion was not thought to cause large dose artifact. More complicated plan with larger modulation factor (2.5) resulted in larger dose distortin than the plan with modulation factor 1.5. The observed phenomena is thought to be reproducible since 3 different measurements of accumulated 5 fraction of treatments showed very similar dose distributions Conclusions: When treating moving organ in small number of fractions, verifying the dose artifact is necessary. (This work was supported by Korea Government (MEST, Grant No2010‐0011771)

Purpose: The aims of this study were to clarify the factors causes imaging artifacts and investigate the impact of partial volume and truncation artifacts on volume determination. Method and Materials: Moving cylindrical phantoms with 2cm of diameter with different heights, 0.3cm, 0.5cm, 1cm, 2cm, 3 cm, and 10cm were scanned (scan range 2cm/6cm0 by GE (General Electric Healthcare) LightSpeed. GE Advantage. 4D software was used to create 4D‐CT data sets. The artifacts were then visually and quantitatively analyzed. Scan. The target volume was determined by manual contouring and automatic volume detection using a cutoff value of 250 HU (Hounsfield Unit). The conformity index of the target volume was defined as the ratio of the manually contoured volume to the volume defined by HU cutoff. The ratio of volume from static CT to real volume was calculated in order to investigate the partial volume effect and truncation artifacts. The volumes measured in 10 phases of 4D CTimages were also compared with true volume. Results: The ratio of static cylinder volume in CTimages scanned 2cm length to the real volume was maximally twice by partial volume effect. The correlation between the velocity and target volume was not consistent potentially due to complicate interplay of different artifacts;,partial volume effect, truncation artifact and miss or different matching between adjacent beds . Conclusions: The static CT data volume can be quite different from true volume even in static CTimages. If a lesion size is not enough to overcome the impact of the partial effects, significantly larger volume will be presented on static and 4DCT images. Any strong correlation between the velocity and the volume was not found.. The 4DCT images still presents partial volume and truncation artifact that requires the further improvement of imaging technology.

Purpose: In order to verify the behavior of tumor motion caused by breathing, respiration & tumor motion verification procedure was designed and its feasibility was tested. Method and Materials: Visual software was developed using LabView 7.0 to analyzerespiration by detecting peak/valley points from RPM signals. The software displays the number of detected peaks/valleys, peak/valley locations, amplitude of signals, and 2nd order differential coefficients at each data points. It calculates mean, standard deviation, variance, maximum and minimum of all detected peak/valley points. It can analyze data for user defined intervals and exports the results in excel file. The program performance was tested using known RPM signals which were sine waves with period of 3 and 6 sec with amplitude of 1 and 2 cm. Also irregular signals obtained from patient's breathing were used to generate irregular respiratory signals by moving a phantom and the software performance was tested. In clinical application, the analyzed respiratory data were converted into tumor motion by applying scaling factor defined by tumor‐motion amplitude to respiration amplitude. To determine the scaling factor, gated On‐Board‐Image (OBI)s were acquired at 0% and 50% of respiratory phases and the imaging times were recorded. From the RPM file, the respiratory signal values at imaging times were read and displacement of tumor was measured from the OBI images. The scaling factor was, then, determined as the ratio of tumor displacement between 0% and 50% phases to difference of two respiratory signals values at corresponding phases. Results: The computed results by the software were extremely consistent with true values within 0.1% difference for regular and irregular motions. Conclusion: Developed software was proven to have sufficient accuracy for clinical application. The proposed method has advantages of non‐invasive, fine temporal resolution without extra radiation, thereby providing a useful tool for 4‐dimensional body stereotactic radiotherapy.

Purpose: Accurate delivery of the most‐up‐to‐date treatment techniques, such as intensity‐modulated radiation therapy(IMRT), is essential. An anthropomorphic phantom was designed and constructed for a remote‐audit program that allows evaluation of an institution's accuracy for deliveringIMRT. The dosimetric characteristics in the phantom were investigated. Method and Materials: The phantom has the shape of a cylinder with one target and three organ‐at‐risks (OARs) inside. The target and OARs were shaped analogous to those of nasopharynx cancer patients. TLD holders were inserted inside the target and the OARs for absolute dose measurements. The phantom allows measurements with ion chamber (IC) at the TLD locations, so that inter‐comparison between two dosimeters was possible. For the measurement of relative dose distribution, two film slots were orthogonally placed near the center of the phantom, which also enables inserting inhomogeneities near the target. Measurements with TLDs and ICs were done for four cases. The first was an anterior one‐port 6MV X‐ray (Primus, Siemens, USA) delivery; the second used the same beam geometrically, but with inhomogeneities inserted, and in the third case three ports of beams were distributed in equi‐gantry angle, and the fourth was an IMRT without inhomogeneities. For case 1–3, theoretical predictions were computed by using Monte Carlo code. Results: For anterior one port X‐ray delivery to a homogeneous/ inhomogeneous phantom, the deviation between the IC and TLD measurements, ranged from 1.7% to 2.3%. For three‐port beam delivery, the range was also similar. For IMRTdelivery, the differences were 0.1–2.8%. The differences between the TLD measurements and MC predictions ranged from −0.14–1.8%. Conclusion: The TLD measurements in the developed phantom agreed with IC and MC results within acceptable differences. The developed phantom with TLDdosimeters are feasible to be used for remote monitoring of IMRT. Supported by KFDA Grant No 05102eui BangPum and 06112eui BangAn300.

Purpose: In order for better management of a medicallinear accelerator. the records of the operational failures of Varian CL2100C over ten years were analyzed.Method and Materials: The failures were classified according to the involved functional subunits and each class was rated into three levels depending on operational conditions. The relationship between the failure rate and working ratio and the relationship between the failure rate and outside temperature were investigated. in addition, the average life time of main part and operating efficiency for last 4 years were analysed.Results: Among the recorded failures ( total 587 failures), the most frequent failure, which was 20% of the total, was observed in the parts related to the collimation system including monitor chamber. Regarding to the operational conditions, the 2nd level of failures, that temporally interrupted treatments, was the most frequent. The 3rd level of failures, that interrupted treatment for more than several hours, was mostly caused by the accelerating subunit. The number of failures was increased with number of treatments and used time. The average life‐time of a Klystron and Thyratron became shorter as the working ratio increased, which was 42 and 83% of the expected values, respectively. The operating efficiency of 95% or higher was maintained, but value slightly decreased. There were no significant correlations between the number of failures and outside temperature. Conclusion: Recording equipment problems and failures in detail over a long period of time can provide a good knowledge of equipment function as well as the capability to forecast future failure. More rigorous equipment maintenance is required for old medicallinear accelerator to avoid the serious failure in advance, and improve the patient treatment quality.

Purpose: In order to reduce potential error that can occur in the planning and delivery of brachytherapy treatment, software which is able to be used for three commercial HDR sources was developed. The feasibility of the program was investigated. Method and Materials: This windows based program was developed by Visual‐Basic language. The TG‐43 algorithm was used for the dose computation at interested points. For source geometry, both point source and line source approximations were employed to be capable for most commercial HDR sources. Anisotropy tables for Nucletron microselectron, Gammamed 12i, and Veri Source were included. User is required to select the HDR source type in the beginning of the program, and to enter the number of catheters and dwelling position of a source. The position and the dose at the interested points, such as A and B points, are required to enter. The developed program used the treatment source position and interest point position in the reference frame of the catheters. The computed dose is compared to that in the RTP by calculating the percent dose difference. The accuracy of the code was validated by comparing with commercial RTP computation and hand calculation results for various prototype of treatment ranging from a single catheter to complex multi‐catheter plans as well as clinical plans. Result: The acceptance levels of performed tests were 5.0% for the percent dose difference at each interested point. For few real patient treatment plans using Nucletron sources, results of the developed program agreed with RTP (Plato, Nucletron) results within 3% error. For Veri Source, large difference between the developed program and RTP was observed if anisotropy was not used in the RTP.Discussion: The developed program was adequate for independent dose verification as a part of brachytherapyquality assurance procedure.