Intensity Modulated Radiation Therapy Commissioning and Quality Assurance: Implementation of AAPM TG119 / 의학물리

The purpose of this study is to evaluate the accuracy of IMRT in our clinic from based on TG119 procedure and establish action level. Five IMRT test cases were described in TG119: multi-target, head&neck, prostate, and two C-shapes (easy&hard). There were used and delivered to water-equivalent solid phantom for IMRT. Absolute dose for points in target and OAR was measured by using an ion chamber (CC13, IBA). EBT2 film was utilized to compare the measured two-dimensional dose distribution with the calculated one by treatment planning system. All collected data were analyzed using the TG119 specifications to determine the confidence limit. The mean of relative error (%) between measured and calculated value was 1.2+/-1.1% and 1.2+/-0.7% for target and OAR, respectively. The resulting confidence limits were 3.4% and 2.6%. In EBT2 film dosimetry, the average percentage of points passing the gamma criteria (3%/3 mm) was 97.7+/-0.8%. Confidence limit values determined by EBT2 film analysis was 3.9%. This study has focused on IMRT commissioning and quality assurance based on TG119 guideline. It is concluded that action level were +/-4% and +/-3% for target and OAR and 97% for film measurement, respectively. It is expected that TG119-based procedure can be used as reference to evaluate the accuracy of IMRT for each institution.

Two Case of Erythroleukemia and Myelodysplastic Syndrome in a Non-Destructive Inspector / 대한산업의학회지

BACKGROUND: Ionizing radiation is a group 1 carcinogen according to the IARC(International Agency for Research on Cancer) classification. With the development of the radiation related industry, the number of radiation exposed workers has been increasing. There have been several reports on AML(Acute Myeloid Leukemia) on exposure to ionizing radiation; however, there are no reports of occupational malignant lymphohematopoietic disease related to non-destructive inspection. CASE REPORT 1: A 35-years-old male, who had worked for 10 years in non-destructive inspection, was diagnosed with myelodysplastic syndrome. He worked 8 hours a day, for three weeks per months, where he was exposed to 192Ir and 60Co radiation sources. Because he had not worn a film badge for monitoring his radiation exposure dose, the accurate exposure dose was not reported. The estimate exposure dose calculated via a chromosomal study was 1.20 Gy, which exceed the dose limits of Korean radiation dose standards, which are 50 and 100 mSv annually and quinquennially respectively. CASE REPORT 2: A 26-years-old male, who had worked for 2.5 years in the same company was also diagnosed with myelodysplastic syndrome. CONCLUSION: Non-destructive inspection is the main source of ionizing radiation in the workplace, which could be the cause of malignant lymphohematopoietic diseases. Therefore, more practical plans and guidelines are needed to prevent non-destructive inspectors from workplace radiation exposure.

Dose Verification Study of Brachytherapy Plans Using Monte Carlo Methods and CT Images / 의학물리

Most brachytherapy treatment planning systems employ a dosimetry formalism based on the AAPM TG-43 report which does not appropriately consider tissue heterogeneity. In this study we aimed to set up a simple Monte Carlo-based intracavitary high-dose-rate brachytherapy (IC-HDRB) plan verification platform, focusing particularly on the robustness of the direct Monte Carlo dose calculation using material and density information derived from CT images. CT images of slab phantoms and a uterine cervical cancer patient were used for brachytherapy plans based on the Plato (Nucletron, Netherlands) brachytherapy planning system. Monte Carlo simulations were implemented using the parameters from the Plato system and compared with the EBT film dosimetry and conventional dose computations. EGSnrc based DOSXYZnrc code was used for Monte Carlo simulations. Each (192)Ir source of the afterloader was approximately modeled as a parallel-piped shape inside the converted CT data set whose voxel size was 2x2x2 mm3. Bracytherapy dose calculations based on the TG-43 showed good agreement with the Monte Carlo results in a homogeneous media whose density was close to water, but there were significant errors in high-density materials. For a patient case, A and B point dose differences were less than 3%, while the mean dose discrepancy was as much as 5%. Conventional dose computation methods might underdose the targets by not accounting for the effects of high-density materials. The proposed platform was shown to be feasible and to have good dose calculation accuracy. One should be careful when confirming the plan using a conventional brachytherapy dose computation method, and moreover, an independent dose verification system as developed in this study might be helpful.

Dosimetric Influence of Implanted Gold Markers in Proton Therapy for Prostate Cancer / 의학물리

This study examined the dosimetric influence of implanted gold markers in proton therapy and the effects of their positions in the spread-out Bragg peak (SOBP) proton beam. The implanted cylindrical gold markers were 3 mm long and 1.2 mm in diameter. The dosimetric influence of the gold markers was determined with markers at various locations in a proton-beam field. Spatial dose distributions were measured using a three-dimensional moving water phantom and a stereotactic diode detector with an effective diameter of 0.5 mm. Also, a film dosimetry was performed using Gafchromic External Beam Treatment (EBT) film. The GEANT4 simulation toolkit was used for Monte-Carlo simulations to confirm the measurements and to construct the dose-volume histogram with implanting markers. Motion data were obtained from the portal images of 10 patients to investigate the effect of organ motions on the dosimetric influence of markers in the presence of a rectal balloon. The underdosed volume due to a single gold marker, in which the dose was less than 95% of a prescribed amount, was 0.15 cc. The underdosed volume due to the presence of a gold marker is much smaller than the target volume. However, the underdosed volume is inside the gross tumor volume and is not smeared out due to translational prostate motions. The positions of gold markers and the conditions of the proton-beam field give different impacts on the dose distribution of a target with implanted gold markers, and should be considered in all clinical proton-based therapies.

Implementation and Evaluation of the Electron Arc Plan on a Commercial Treatment Planning System with a Pencil Beam Algorithm / 의학물리

Less execution of the electron arc treatment could in large part be attributed to the lack of an adequate planning system. Unlike most linear accelerators providing the electron arc mode, no commercial planning systems for the electron arc plan are available at this time. In this work, with the expectation that an easily accessible planning system could promote electron arc therapy, a commercial planning system was commissioned and evaluated for the electron arc plan. For the electron arc plan with use of a Varian 21-EX, Pinnacle3 (ver. 7.4f), with an electron pencil beam algorithm, was commissioned in which the arc consisted of multiple static fields with a fixed beam opening. Film dosimetry and point measurements were executed for the evaluation of the computation. Beam modeling was not satisfactory with the calculation of lateral profiles. Contrary to good agreement within 1% of the calculated and measured depth profiles, the calculated lateral profiles showed underestimation compared with measurements, such that the distance-to-agreement (DTA) was 5.1 mm at a 50% dose level for 6 MeV and 6.7 mm for 12 MeV with similar results for the measured depths. Point and film measurements for the humanoid phantom revealed that the delivered dose was more than the calculation by approximately 10%. The electron arc plan, based on the pencil beam algorithm, provides qualitative information for the dose distribution. Dose verification before the treatment should be mandatory.

Study on the Compatibility for an Ir-192 Source Manufactured by Korea Atomic Energy Research Institute (KAERI) in GammaMed Brachytherapy Machine / 의학물리

The compatibility with GammaMed-12i brachytherapy machine for an Ir-192 encapsulated source (IRRS20, KAERI, Korea) manufactured by Korea atomic energy research institute (KAERI) has been investigated. As a mechanical testing of compatibility, precise measurement of step movement with channels, measurement of curvature of radius for wire, and emergency return testing were performed. Periodic measurements of air kerma strength for 45 days were carried out to evaluate decay characteristics of Ir-192 radioisotope and comparison of dose distributions in phantom between KAERI and old sources previously used were performed by film dosimetry. KAERI source has a good compatibility with GammaMed12i machine as a result of mechanical testing. There are in good agreement with calculated values in activity characteristics and there were small differences in dose distributions around the source in comparison between KAERI and old source.

Development of Preliminary Quality Assurance Software for GafChromic(R) EBT2 Film Dosimetry / 의학물리

Software for GafChromic EBT2 film dosimetry was developed in this study. The software provides film calibration functions based on color channels, which are categorized depending on the colors red, green, blue, and gray. Evaluations of the correction effects for light scattering of a flat-bed scanner and thickness differences of the active layer are available. Dosimetric results from EBT2 films can be compared with those from the treatment planning system ECLIPSE or the two-dimensional ionization chamber array MatriXX. Dose verification using EBT2 films is implemented by carrying out the following procedures: file import, noise filtering, background correction and active layer correction, dose calculation, and evaluation. The relative and absolute background corrections are selectively applied. The calibration results and fitting equation for the sensitometric curve are exported to files. After two different types of dose matrixes are aligned through the interpolation of spatial pixel spacing, interactive translation, and rotation, profiles and isodose curves are compared. In addition, the gamma index and gamma histogram are analyzed according to the determined criteria of distance-to-agreement and dose difference. The performance evaluations were achieved by dose verification in the 60o-enhanced dynamic wedged field and intensity-modulated (IM) beams for prostate cancer. All pass ratios for the two types of tests showed more than 99% in the evaluation, and a gamma histogram with 3 mm and 3% criteria was used. The software was developed for use in routine periodic quality assurance and complex IM beam verification. It can also be used as a dedicated radiochromic film software tool for analyzing dose distribution.

Multileaf collimator transmission from the first Hi-Art II helical tomotherapy machine in India.

The purpose of this study was to measure the multileaf collimator (MLC) transmission from the first Hi-Art II tomotherapy machine installed at the Advanced Center for Treatment, Research, and Education in Cancer (ACTREC). The MLC transmission was measured with an A1SL ion chamber and the radiographic extended dose range (EDR2) film in virtual water slabs at 1.5-cm depth with a source-to-surface distance of 85 cm. The MLC transmission was measured for 30 s with all leaves open and for 360 s with all leaves closed. The movable jaws were set to the calibration field size of 5 x 40 cm at isocenter. The MLC transmission was found to be 0.3% with the ion chamber and 0.32% with the film. Thus, the MLC transmission value was found well within the manufacturer tolerance of 0.5%. MLC can safely be used for the beam modulation during intensity-modulated radiotherapy (IMRT) to deliver accurate doses to the patients.

Radiation safety issues in fluoroscopy during percutaneous nephrolithotomy

personnel are important. Patient radiation doses are used for comparison with other centers for achieving the best possible radiation practice. In addition, there are performance checks for the fluoroscopy machines so that x-ray emitting machines should work at the optimum level ie, producing good images at minimum possible radiation doses. This is a review of literature and discussion on radiation dose to patients and personnel, and on basic radiation safety tenets and their application in urological interventions of PCNL procedure. Radiation doses during PCNL have gone down over the time due to advances in technology. However, as radiation is hazardous, there is no room for complacency. A hospitals medical physicist may ensure even further reduction of x-ray dose by carrying out regular dosimetry and quality assurance tests on the fluoroscopy machines. A survey meter may provide an easy and quicker but not-so-accurate method for occupation exposure determination. The practice of PCNL procedures seems to be quite safe with radiation point of view. The quick, easy, and economical method of estimation of radiation dose using survey meter may need further calibration with the standard thermoluminescence dosimetry method. Setting optimum x-ray parameters, incorporation of filters, and quality assurance tests are a few areas where medical physicists may help in further reduction of radiation doses

[Evaluation of X-Ray factors and its effect on radiology department staff at Army hospitals in Tehran in the year 1385]

Knowledge of X-Ray related factors connected with individual dosimeter can be beneficial in diminishing the rate of x-ray intake. Keeping in mind the above mentioned goal, we planned and prepared this study with the help of all radiology staff of the hospital. This research is a descriptive, analytic and a sectional study which was performed in the year 1385. All radiology staff of the army hospitals in Tehran was bulk examples. A check list and a questionnaire form were used to collect data and information. We also made use of SPSS software for data purpose. Results obtained in this study indicate that individual maximum dose received individually was 29/0 milisilvert; the rate of this dose was seen in persons who lacked University education. And a minimum dose received was 0/05 millisiurt which was received by individuals who were less than 30 hours in contact with the preparation of unison.. Many medical tests were performed at the following army hospitals: Golestan, 502, 204 and Mostafa Khomeini hospitals. The X-Ray rate at the mentioned hospitals was 100%. Dose received by all individuals as classified parameters expected was standard and acceptable. Therefore organizing X-ray safety workoshops especially in connection with promoting security level of unison production staff at all centers is an absolute must

Dose monitoring of health care workers occupationally exposed to ionizing radiation in Mansoura university hospitals

This study aims at evaluating the efficacy of radiation safety in Mansoura University Hospitals [MUHs] and to establish practical dose constraint [DC] for medical application. The study has been conducted upon health care workers [HCWs] occupationally exposed to ionizing radiation in various diagnostic and therapeutic activities in six health premises of MUHs. Four medical applications [radiotherapy, nuclear medicine, general radiology and interventional radiology] and five specialties [medical doctors, physicists, technicians, nurses and non-classified personals] were accounted. Doses were measured on a quarterly basis using thermoluniscent dosimeters [TLD-badges], while pocket dosimeters were used whenever TLD was not available. The annual doses were collected to build up a data base for years 1994-2005. The results show that TLD-badges were used in best situation in Oncology and Nuclear Medicine Dept. to cover less than one third of the exposed HCWs. The occupational doses showed a highly significant difference [p<0.0001] depending on the field of medical application. It is found that HCWs in radiotherapy were exposed to an average annual dose of 1.36 +/- 0.61mSv/y. For interventional radiology, the mean annual dose was found 2.25 +/- 2.47mSv/y unlike that of general radiology 1.07 +/- 0.65mSv/y. The largest sources of occupational exposure came from fluoroscopic radiology .equipments [1.76 +/- 0.92mS/y] followed by Cobalt-60 teletherapy machine [1.12 +/- 0.72mS/y]. The study showed that about 90% of HCWs received doses less than 2mSv/y and only 1.39% reported doses 5mSv or above. Dose constraint level can be set at 2mSv/y in premises of MUHs that may be considered achievable ceiling value referring to acceptably applied practices rather than optimized ones

Evaluation of x-ray protection methods used in dental offices in Tabriz in 2005-2006

The aim of this study was to evaluate x-ray protection methods in dental offices in Tabriz. In this study 142 dental offices were evaluated. A questionnaire-based method was used. The data was analyzed by descriptive methods. The least commonly used methods were leaded walls [4.9%] and film badges [16.9%] and the most commonly used methods were lead partitions [67.6%] and position-distance rule [68.3%]. The most commonly used patient protection devices were E-speed films [84.5%] and long collimators [66.2%]. The least commonly used methods, in this respect, were automatic processors [2.1%] and rectangular collimators [0%]. Regarding protection methods for the patient, results did not conform to international standards. Mostly, manual processing was used, resulting in extra radiation dose to patients. The methods which reduce the received dose of patients were disregarded in offices compared to educational centers, necessitating optimization of educational programs in these fields

Film dose analysis system and its application in radiotherapy verification / 南方医科大学学报

<p><b>OBJECTIVE</b>To propose a new computer software-based medical image processing technique with high resolution digital scanner for radiotherapy verification.</p><p><b>METHODS</b>Under the platform of Windows 2000, the software, programmed with Visual C++.NET, was developed according to modular design. All data of the films and the treatment planning system could be processed as images or dose curves for a robust result.</p><p><b>RESULTS</b>Many functions such as data acquisition, automatic analysis and computation and image processing were integrated in the system. Both geometric and dosimetric errors could be calculated at the same time to verify the radiotherapy accuracy.</p><p><b>CONCLUSION</b>This system has good accuracy and stability for cost-effective radiotherapy verification.</p>

Enhancement of MD-55-2 radiochromic film sensitivity using a multilayer film technique for applications in the low dose range

MD-55-2 is one of the Radiochromic film models with the sensitivity suitable for dose measurements ranging from 5 to 100 Gy. However, this lower limit makes the film impractical for its applications in many areas such as brachytherapy source dosimetry. n this project, the useful range of the film has been extended by using a multilayer film technique. In this technique, single-, double-, and triple- layers of films were exposed to the doses ranging from 0.5 to 10 Gy using a Co-60 photon beam. Calibration curves for corresponding layers of films were obtained with a spectrophotometer using a 680nm wavelength. The results indicated that the sensitivities of double and triple layers were approximately 200% and 300%, respectively, higher than a single-layer film. The impact of multilayer film arrangement on the energy dependence of the MD-55-2 Radiochromic film has also been examined using 100KVp, 80 KVp, and 6 MV X-ray beams. The results indicated an insignificant [within 5%] change in film responses with the beam energy. Therefore, the multilayer technique enhances the Radiochromic film sensitivity and expands its application to the low dose range in field of brachytherapy source dosimetry

Brachytherapy polymer gel dosimetry with xCT

Polymer gels are an emerging new class of dosimeters which are being applied to the challenges of modern radiotherapy modalities. Research on gel dosimetry involves several scientific domains, one of which is the imaging techniques with which dose data is extracted from the dosimeters. In the current work, we present our preliminary results of investigating capability of X-ray CT for extracting brachytherapy dose distributions from a normoxic gel dosimeter. A normoxic radiosensitive polymer gel was fabricated under normal atmospheric conditions and poured into three phantoms. Using Cs137 brachytherapy sources, the phantoms were irradiated with different dose distributions with a LDR Selectron remote after-loader. To improve SNR, 25 images were obtained of each slice for image averaging and an averaged background image of an un-irradiated gel phantom was then subtracted for artifact removal. To further improve the accuracy, a self-consistent normalized method was used for calibration of the dosimeters based on an assumption of a linear dose response between zero and maximum dose regions in the gel. Although results reveal very similar CT-number gradients to that of brachytherapy dose distributions, but the method does not fulfill brachytherapy dosimetry requirements. This might be due to the high prescribed doses in this study which in turn results in a large change in the CT numbers. This change in the CT numbers of the images can not be considered to have a linear relationship with dose which was the basic assumption of our calibration method, so the results are just qualitatively comparable. In this study, the results of using X-ray CT for brachytherapy polymer gel dosimetry is promising but not still satisfying. Improving a proper calibration method for correlating CT numbers to dose will be significantly helpful for performing measurements with CT. The main limitation for CT is still a low signal to noise ratio especially in lower dose areas

Dosimetric Verification of Dynamic Conformal Arc Radiotherapy / 의학물리

The purpose of this study is to develop the optimization method for adjusting the film isocenter shift and to suggest the quantitative acceptable criteria for film dosimetry after optimization in the dynamic conformal arc radiation therapy (DCAR). The DCAR planning was performed in 7 patients with brain metastasis. Both absolute dosimetry with ion chamber and relative film dosimetry were performed throughout the DCAR using BrainLab's micro-multileaf collimator. An optimization method for obtaining the global minimum was used to adjust for the error in the film isocenter shift, which is the largest part of systemic errors. The mean of point dose difference between measured value using ion chamber and calculated value acquired from planning system was 0.51+/-0.43% and maximum was 1.14% with absolute dosimetry. These results were within the AAPM criteria of below 5%. The translation values of film isocenter shift with optimization were within +/-1 mm in all patients. The mean of average dose difference before and after optimization was 1.70+/-0.36% and 1.34+/-0.20%, respectively, and the mean ratios over 5% dose difference was 4.54+/-3.94% and 0.11+/-0.12%, respectively. After optimization, the dose differences decreased dramatically and a ratio over 5% dose difference and average dose difference was less than 2%. This optimization method is effective in adjusting the error of the film isocenter shift, which is the largest part of systemic errors, and the results of this research suggested the quantitative acceptable criteria could be accurate and useful in clinical application of dosimetric verification using film dosimetry as follows; film isocenter shift with optimization should be within +/-1 mm, and a ratio over 5% dose difference and average dose difference were less than 2%.

Patient Specific Quality Assurance of IMRT: Quantitative Approach Using Film Dosimetry and Optimization / 대한방사선종양학회지

PURPOSE: Film dosimetry as a part of patient specific intensity modulated radiation therapy quality assurance (IMRT QA) was performed to develop a new optimization method of film isocenter offset and to then suggest new quantitative criteria for film dosimetry. MATERIALS AND METHODS: Film dosimetry was performed on 14 IMRT patients with head and neck cancers. An optimization method for obtaining the local minimum was developed to adjust for the error in the film isocenter offset, which is the largest part of the systemic errors. RESULTS: The adjust value of the film isocenter offset under optimization was 1 mm in 12 patients, while only two patients showed 2 mm translation. The means of absolute average dose difference before and after optimization were 2.36 and 1.56%, respectively, and the mean ratios over a 5% tolerance were 9.67 and 2.88%. After optimization, the differences in the dose decreased dramatically. A low dose range cutoff (L-Cutoff) has been suggested for clinical application. New quantitative criteria of a ratio of over a 5%, but less than 10% tolerance, and for an absolute average dose difference less than 3% have been suggested for the verification of film dosimetry. CONCLUSION: The new optimization method was effective in adjusting for the film dosimetry error, and the newly quantitative criteria suggested in this research are believed to be sufficiently accurate and clinically useful.

Patient Specific Quality Assurance of IMRT: Quantitative Approach Using Film Dosimetry and Optimization / 대한방사선종양학회지

PURPOSE: Film dosimetry as a part of patient specific intensity modulated radiation therapy quality assurance (IMRT QA) was performed to develop a new optimization method of film isocenter offset and to then suggest new quantitative criteria for film dosimetry. MATERIALS AND METHODS: Film dosimetry was performed on 14 IMRT patients with head and neck cancers. An optimization method for obtaining the local minimum was developed to adjust for the error in the film isocenter offset, which is the largest part of the systemic errors. RESULTS: The adjust value of the film isocenter offset under optimization was 1 mm in 12 patients, while only two patients showed 2 mm translation. The means of absolute average dose difference before and after optimization were 2.36 and 1.56%, respectively, and the mean ratios over a 5% tolerance were 9.67 and 2.88%. After optimization, the differences in the dose decreased dramatically. A low dose range cutoff (L-Cutoff) has been suggested for clinical application. New quantitative criteria of a ratio of over a 5%, but less than 10% tolerance, and for an absolute average dose difference less than 3% have been suggested for the verification of film dosimetry. CONCLUSION: The new optimization method was effective in adjusting for the film dosimetry error, and the newly quantitative criteria suggested in this research are believed to be sufficiently accurate and clinically useful.

An Effect of Time Gating Threshold (TGT) on the Delivered Dose at Internal Organ with Movement due to Respiration / 의학물리

In this study, we investigated the effect of time gating threshold on the delivered dose at a organ with internal motion by respiration. Generally, the internal organs have minimum motion at exhalation during normal breathing. Therefore to compare the dose distribution time gating threshold, in this paper, was determined as the moving region of target during 1 sec at the initial position of exhalation. The irradiated fields were then delivered under three conditions; 1) non-moving target 2) existence of the moving target in the region of threshold (1sec), 3) existence of the moving target region out of threshold (1.4 sec, 2 sec). And each of conditions was described by the moving phantom system. It was compared with the dose distributions of three conditions using film dosimetry. Although the treatment time increased when the dose distributions was obtained by the internal motion to consider the TGT, it could be obtained more exact dose distribution than in the treatment field that didn't consider the internal motion. And it could be reduced the unnecessary dose at the penumbra region. When we set up 1.4 sec of threshold, to reduce the treatment time, it could not be obtained less effective dose distribution than 1 sec of threshold. Namely, although the treatment time reduce, the much dose was distributed out of the treatment region. Actually when it is treated the moving organ, it would rather measure internal motion and external motion of the moving organ than mathematical method. If it could be analyzed the correlation of the internal and external motion, the treatment scores would be improved.

Optimum Segment Size for Intensity Modulated Radiation Therapy of Lung Region

PURPOSE: In general, it is possible to generate better leaf sequencing from the ideal fluence map or dose distribution close to the optimized results of the radiation treatment planning (RTP) system, from the filed smaller segment size in Intensity modulated radiation therapy (IMRT). Conversely, an intra-treatment organ motion issue, which prevents the smallest segment size from being chosen, always exists. Furthermore, the question has been raised regarding the proper target margin for IMRT cases with a moving target, as the field itself moves while the target moves, unlike traditional static fields. In this study, the effects of intra-treatment target motion on the segment size have been examined. MATERIALS AND METHODS: Various sizes of rectangular patterns were designed for an IMRT fluence map. A leaf sequence was generated using the step and shoot beam delivery method. The intensity ratios between adjacent segments were 0.2, 0.4 and 0.8. The range of target motion was assumed to be +/-0.3~2.0 cm, in a sinusoidal shape. The dynamic leaf motion that reflected the target motion was calculated to simulate the motion. Film dosimetry was performed to analyze the motion effects. RESULTS: The intensity ratios of the adjacent segments were degraded in all cases. The dose distribution with segment sizes less than half the breathing amplitude showed a significantly degraded intensity map. With a beam irradiation time for a segment greater than two breathing cycles, the dose distribution around the target margin showed a similar tendency as the static fields. CONCLUSION: The minimum size of IMRT segments in the fluence map should be chosen taking the intra-treatment organ motion into consideration. The dose distribution with segment sizes less than half the breathing amplitude was degraded significantly in the intensity map. With a beam irradiation time for a segment greater than two breathing cycles, the target margin can be defined as the same as for a conventional static field