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In recent years, ultra-high dose rate (FLASH) radiotherapy has become one of the most advanced research topics in the field of radiotherapy. Experimental data indicate that FLASH radiotherapy can significantly reduce the irradiation damage in normal tissues while being as effective as clinical conventional dose rate radiotherapy in tumor control. The oxygen depletion hypothesis is considered as one of the key mechanisms underlying the FLASH effect. In this article, research progress on the discovery, experimental evidence and reaction principle of oxygen depletion was reviewed, the measurement methods and biological effect modeling methods of the oxygen depletion hypothesis were summarized, and the oxygen depletion difference between normal tissue and tumor was also discussed.
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Purpose@#This study was aimed to investigate long-term survivals and toxicities of early-stage nasopharyngeal carcinoma (NPC) in endemic area, evaluating the role of chemotherapy in stage II patients. @*Materials and Methods@#Totally 187 patients with newly diagnosed NPC and restaged American Joint Committee on Cancer/ International Union Against Cancer 8th T1-2N0-1M0 were retrospectively recruited. All received intensity-modulated radiotherapy (IMRT)±chemotherapy (CT) from 2001 to 2010. @*Results@#With 15.7-year median follow-up, 10-year locoregional recurrence-free survival, distant metastasis-free survival (DMFS), disease-specific survival (DSS), and overall survival (OS) were 93.3%, 93.5%, 92.9% and 88.2%, respectively. Multivariable analyses showed cervical lymph nodes positive and pre-treatment prognostic nutritional index ≥ 52.0 could independently predict DMFS (p=0.036 and p=0.011), DSS (p=0.014 and p=0.026), and OS (p=0.002 and p 45 years (p=0.002) and pre-treatment lactate dehydrogenase ≥ 240 U/L (p 0.05). Unsurprising, patients in IMRT+CT had more acute gastrointestinal reaction, myelosuppression, mucositis, late ear toxicity, and cranial nerve injury (all p < 0.05) than IMRT alone group. @*Conclusion@#Superior tumor control and satisfying long-term outcomes could be achieved with IMRT in early-stage NPC with mild late toxicities. As CT would bring more toxicities, it should be carefully performed to stage II patients.
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Objective@#To assess the interobserver variations in delineating the planning target volume (PTV) and organs at risk (OAR) using different contouring methods during intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC), aiming to provide references for the quality control of multi-center clinical trials.@*Methods@#The PTV and OAR of CT image of 1 NPC patient manually delineated by 10 physicians from 8 different radiation centers were defined as the " manual contour group" , and the OAR auto-contoured using the ABAS software and modified by the physicians were defined as the " auto+ manual contour group" . The maximum/minimum ratio (MMR) of the PTV and OAR volumes, and the coefficient of variation (CV) for different delineated contours were comparatively evaluated.@*Results@#Large variation was observed in the PTV and OAR volumes in the manual contour group. The MMR and CV of the PTV were 1.72-3.41 and 0.16-0.39, with the most significant variation in the PTVnd (MMR=3.41 and CV=0.39 for the PTVnd-L). The MMR and CV of the manually contoured OAR were 1.30-7.89 and 0.07-0.67. The MMR of the temporal lobe, spinal cord, temporomandibular joint, optic nerve and pituitary gland exceeded 2.0. Compared with the manual contour group, the average contouring time in the auto+ manual group was shortened by 68% and the interobserver variation of the OAR volume was reduced with an MMR of 1.04-2.44 and CV of 0.01-0.37.@*Conclusions@#Large variation may occur in the PTV and OAR contours during IMRT plans for NPC delineated by different clinicians from multiple medical centers. Auto-contouring+ manually modification can reduce the interobserver variation of OAR delineation, whereas the variation in the delineation of small organs remains above 1.5 times. The consistency of the PTV and OAR delineation and the possible impact upon clinical outcomes should be reviewed and evaluated in multi-center clinical trials.
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Objective To assess the interobserver variations in delineating the planning target volume (PTV) and organs at risk (OAR) using different contouring methods during intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC),aiming to provide references for the quality control of multi-center clinical trials.Methods The PTV and OAR of CT image of 1 NPC patient manually delineated by 10 physicians from 8 different radiation centers were defined as the "manual contour group",and the OAR auto-contoured using the ABAS software and modified by the physicians were defined as the "auto+manual contour group".The maximum/minimum ratio (MMR) of the PTV and OAR volumes,and the coefficient of variation (CV) for different delineated contours were comparatively evaluated.Results Large variation was observed in the PTV and OAR volumes in the manual contour group.The MMR and CV of the PTV were 1.72-3.41 and 0.16-0.39,with the most significant variation in the PTVnd (MMR=3.41 and CV =0.39 for the PTVnd-L).The MMR and CV of the manually contoured OAR were 1.30-7.89 and 0.07-0.67.The MMR of the temporal lobe,spinal cord,temporomandibular joint,optic nerve and pituitary gland exceeded 2.0.Compared with the manual contour group,the average contouring time in the auto+ manual group was shortened by 68％ and the interobserver variation of the OAR volume was reduced with an MMR of 1.04-2.44 and CV of 0.01-0.37.Conclusions Large variation may occur in the PTV and OAR contours during IMRT plans for NPC delineated by different clinicians from multiple medical centers.Auto-contouring+ manually modification can reduce the interobserver variation of OAR delineation,whereas the variation in the delineation of small organs remains above 1.5 times.The consistency of the PTV and OAR delineation and the possible impact upon clinical outcomes should be reviewed and evaluated in multi-center clinical trials.
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Objective To analyze the 10-year survival outcome and failure patterns for patients with nasopharyngeal carcinoma (NPC) after intensity-modulated radiotherapy (IMRT),aiming to provide reference for optimized treatment for NPC.Methods Clinical data of 866 patients with NPC receiving IMRT from January 2001 to December 2008 were retrospectively analyzed.Survival analysis was performed using the Kaplan-Meier estimator.Univariate analysis was carried out by log-rank test and multivariate analysis was performed using Cox proportional hazards model.Results The median follow-up time was 132 months.The 10-year local recurrence-free survival (LRFS),distant metastasis-free survival (DMFS),progression-free survival (PFS) and disease specific survival (DSS) were 92.0％,83.4％,75.7％ and 78.6％,respectively.A total of 210 patients died including 124 patients (59.0％) from distant metastasis,which was the primary cause of death,and 47 (22.3％) from local regional recurrence.Independent negative factors of DSS included age＞50 years (P=0.00),LDH ≥ 245 IU/L (P=0.00),Hb＜ 120 g/L (P=0.01),T2-T4 staging (P=0.00),N1-N3 staging (P=0.00) and GTV-nx＞20 cm3(P=0.00).The 10-year LRFS,DMFS and DSS of stage Ⅱ NPC patients did not significantly differ after IMRT alone and chemoradiotherapy (P=0.83,0.22,0.23).For patients with stage Ⅲ NPC,the 10-year LRFS and DSS in the chemoradiotherapy arm were significantly higher than those in the IMRT alone (P=0.01,0.01),whereas no statistical significance was observed in the DMFS between two groups (P=0.14).The overall survival of stage Ⅳa+Ⅳb NPC patients is relatively poor.Conclusions IMRT can improve the long-term survival of NPC patients.Distant metastasis is the primary failure pattern.Patients with stage Ⅰ-Ⅱ NPC can obtain satisfactory survival outcomes after IMRT alone.The addition of chemotherapy can further enhance the LRFS and DSS of stage Ⅲ NPC patients.However,the optimal therapeutic strategy remains to be urgently investigated for stage a+ Ⅳb NPC patients.
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Objective To investigate the physics technique and quality assurance (QA) during radiotherapy in the institutions from the East Guangdong province,aiming to provide reference for the construction of radiotherapy discipline and rational allocation of resources in the primary hospitals from the eastern Guangdong province.Methods From March 15 to May 20,2016,the general conditions,radiotherapy equipment,available technique and quality assurance (QA) in the medical institutions from eastern Guangdong were investigated and analyzed by online combined with on-spot surgery.Results There were 8 institutions which provided radiotherapy with 966 ward beds,a daily capacity of 632 patients and 222 radiotherapy practitioners.Radiotherapy equipment included 12 linear accelerators,5 after-loading devices,1γ-knife,8 CT simulators and 9 radiotherapy planning systems.Five institutions performed IMRT/VMAT,IGRT and ART.Dose verification was performed before precision radiotherapy delivery in all institutions except for 1 center.QA procedures were missing for the linear accelerators,CT simulators and after-loading devices.Short-term advanced studies and hand-by-hand teaching were the main approaches for staff professional training.Conclusions The resource allocation for radiotherapy in the medical centers from the eastern Guangdong province is scarce.The technique and QC levels greatly differ among different institutions.Standard QA protocols are urgently to be established and implemented.Extensive attentions should be paid to the the professional training for technicians.
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Objective To develop a MOSAIQ Integration PlatformCHN (MIP) based on the workflow of radiotherapy (RT) and to meet the actual requirements in China and the special needs for the radiotherapy department.Methods MIP used C/S (client-server) structure mode running on the local network in the hospital and its database was based on the Treatment Planning System (TPS) and MOSAIQ database.Five network servers,as the core hardware,supplied data storage and network service based on cloud services.The core software was developed based on Microsoft Visual Studio Platform using C# network programming language.The MIP server could simultaneously offer network service for about 200 workstations,including entry,query,statistics,and print of data.Results MIP had 15 core function modules,such as Notice,Appointment,Billing,Document Management (application/execution),and System Management,which almost covered the whole workflow of radiotherapy.Up to June 2016,the recorded data in the MIP were as follows:13546 patients,13533 plan application forms,15475 RT records,14656 RT summaries,567048 billing records,and 506612 workload records.Conclusions The MIP based on the RT workflow has been successfully developed and used in clinical practice.It is an important part of radiotherapy information system construction with the advantages of intuitive operation,real-time performance,data security,and stable operation.It is digital,paperless,user-friendly,and convenient for the retrieval and statistics of data as well as information sharing and department management,and can significantly improve the efficiency of the department.More functions can be added or modified to enhance its potentials in research and clinical practice.
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Objective To perform a preclinical test of a delineation software based on atlas-based auto-segmentation (ABAS),to evaluate its accuracy in the delineation of organs at risk (OARs) in radiotherapy planning for nasopharyngeal carcinoma (NPC),and to provide a basis for its clinical application.Methods Using OARs manually contoured by physicians on planning-CT images of 22 patients with NPC as the standard,the automatic delineation using two different algorithms (general and head/neck) of the ABAS software were applied to the following tests:(1) to evaluate the restoration of the atlas by the software,automatic delineation was performed on copied images from each patient using the contours of OARs manually delineated on the original images as atlases;(2) to evaluate the accuracy of automatic delineation on images from various patients using a single atlas,the contours manually delineated on images from one patients were used as atlases for automatic delineation of OARs on images from other patients.Dice similarity coefficient (DSC),volume difference (Vdiff),correlation between the DSC and the volume of OARs,and efficiency difference between manual delineation and automatic delineation plus manual modification were used as indices for evaluation.Wilcoxon signed rank test and Spearman correlation analysis were used.Results The head/neck algorithm had superior restoration of the atlas over the general algorithm.The DSC was positively correlated with the volume of OARs and was higher than 0.8 for OARs larger than 1 cc in volume in the restoration test.For automatic delineation with the head/neck algorithm using a single atlas,the mean DSC and Vdiff were 0.81-0.90 and 2.73％-16.02％,respectively,for the brain stem,temporal lobes,parotids,and mandible,while the mean DSC was 0.45-0.49 for the temporomandibular joint and optic chiasm.Compared with manual delineation,automatic delineation plus manual modification saved 68％ of the time.Conclusions A preclinical test is able to determine the accuracy and conditions of the ABAS software in specific clinical application.The tested software can help to improve the efficiency of OAR delineation in radiotherapy planning for NPC.However,it is not suitable for delineation of OAR with a relatively small volume.
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Objective To conduct the 7th investigation by Chinese Society of Radiation Oncology,Chinese Medical Association,and to further investigate the current situation of radiotherapy in mainland China,reasonably allocate personnel and equipment resources,and promote the development of radiotherapy in China.Methods From October 8,2015 to December 2015,the office for investigation of radiotherapy information was established,the list and contact information of radiotherapy units were provided by each province,and a special data submission system was used for a complete,rapid,and efficient investigation through the Internet.Results As of January 20,2016,there were 1 413 radiotherapy units in the mainland China with 52,496 employees in total,among which there were 15 839 radiotherapy physicians (4824 with senior professional titles),8 452 technical therapists (260 with senior professional titles),3 292 physicists (562 with senior professional titles),and 938 maintenance engineers (120 with senior professional titles).In the aspect of radiotherapy equipment,there were 1930 linear accelerators,96 Co-60 teletherapy units,173 X-knife units,212 γ-knife units,382 Ir-192 brachytherapy units,436 Co-60 brachytherapy units,1 051 X-ray simulators,1 353 CT simulators,642 MRI simulators,978 sets of multileaf collimators,1922 sets of treatment planning systems,and 974 sets of radiotherapy network systems.As for quality control devices,there were 1 792 dosimeters,2 143 ionization chambers,935 two-dimensional array dosimeters,540 threedimensional dosimetric verification systems,596 three-dimensional water tanks,844 anthropomorphic phantoms,and 1 168 water equivalent phantoms.In the aspect of therapeutic situation,there were 102,170 beds (including beds in departments of oncology in general hospitals),76612 episodes per day,and 919339 episodes per year.Conclusions The results of this investigation show significant increases in radiotherapy units,personnel,and equipment in recent years in mainland China.The distribution of radiotherapy units and equipment and the structure of radiotherapy personnel are becoming more reasonable,but there are still some problems.In some regions,current radiotherapy equipment cannot meet the medical needs,and there is a lack of professional technical personnel.
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Objective To develop a network management system for tumor radiotherapy information that integrates process management and quality assurance functions, and to investigate its clinical value. Methods Based on the requirements of radiotherapy process quality assurance and control, the client-server ( C-S) pattern, along with SQL SERVER 2008 database structure, international standard DICOM 3.0, DICOM RT, and HL7 protocols, and system hardware and self-developed software in local area network, was adopted to establish the network management system for radiotherapy information, and clinical tests were performed to evaluate the operation performance of this platform.Results ( 1 ) The interactive integrated management platform and client-side functional modules with a uniform interface were developed.( 2) The safe and reliable standardized data interface was developed, which could be connected to accelerators, treatment planning systems, and hospital information systems developed by mainstream manufacturers.( 3) The modules for radiotherapy process management and quality assurance and management were designed and developed.( 4) The platform passed all the tests before operation and had been used in clinical departments for almost 3 years, which confirmed that the system was safe and stable during operation and that all functions designed were realized.Conclusions The integrated management platform meets the requirements for application and management of radiotherapy information and data, improves the overall work efficiency in radiotherapy department and the level of quality assurance and control, and holds promise for clinical application as a good tool for tumor radiotherapy departments.
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Objective To evaluate the impacts of slice thickness and registration frame range on the accuracy of cone-beam computed tomography ( CBCT) image-guided head and neck ( HN) radiotherapy, and to provide a basis for positioning correction in image-guided radiotherapy.Methods A planned CT scan was performed for an anthropomorphic HN phantom with slice thickness of 1 mm and 3 mm and simulated positioning errors in x, y, and z directions on the accelerator.CBCT scan and reconstruction were performed with slice thickness of 1 mm and 3 mm.Two different registration frame ranges were used ( range 1:from C7 to superior orbit;range 2:from C7 to calvaria ) .Automatic bony registration was performed for CBCT and planned CT images with slice thickness of 1 mm and 3 mm.The registration accuracy was evaluated.Results For range 1, the registration errors in x, y, and z directions with a slice thickness of 1 mm were significantly lower than those with a slice thickness of 3 mm (0.5±0.2 mm vs.-0.7±0.2 mm, P=0.00;0.5±0.3 mm vs. 1.0±0.3 mm, P=0.00;-0.1±0.5 mm vs.1.5±0.5 mm, P=0.00).For range 2, the registration errors in x, y, and z directions with a slice thickness of 3 mm were-0.4±0.2 mm, 0.5±0.2 mm, and 0.7±0.4 mm, respectively.Conclusions Engagement of calvaria in registration range can substantially enhance the registration accuracy in CBCT or CT images for HN.The registration error with slice thickness of 1 mm can be controlled within 1 mm.
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Objective To investigate the dosimetric performance of two algorithms for correcting the presence of tissue inhomogeneities,the finite site pencil beam (FSPB) and X-ray voxel Monte Carlo (XVMC) plans were implemented in the MONACO system,with the accuracy of application to clinic treatment of two algorithms were evaluated.Methods In a non-uniform artificial anthropomorphic phantom,regular open fields and intensity modulation radiated therapy (IMRT) plans of the MONACO were measured by using calibrated EBT2 films,and the dose accuracy of the two kinds of plans was analyzed by comparing the planned and measured plane dose.Results In an anthropomorphic phantom,the deviations between the calculated values by XVMC and the measured values by films were less than ± 2％.While the deviations of FSPB values between calculation and measurements was within ± 3％,except at the condition of 15 MV,10 cm ×2 cm field,the dose error in lung was up to 6.51％.The verification of individual IMRT beams based on films showed that the pass rates of calculation by XVMC and FSPB were larger than 90％ with γ criterion of 3％/3 mm and 4％/4 mm,respectively.At 3％/3 mm,the pass rates of FSPB were in the range of 80％-90％.At the same time,the pass rates of all individual fields were higher than 90％.Conclusions The accuracy of dose calculation of XVMC is better than that of FSPB when being in multi-segments and non-uniform media.The error of algorithm can be controlled within ±3％,for the calculation by XVMC.And the dose deficiency of PTV arising from algorithm can be avoided.
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Objective To analyze the relationship between the radiation doses to mediastinal lymph nodes regions and the regional failure patterns when involved field radiation therapy (IFRT) was used for limited-stage small cell lung cancer (SCLC).Methods The mediastinal lymph node regions (group 1 to 10) of the iimited-stage SCLC patients received definitive radiotherapy were contoured in treatment planning system.The intentional or incidental radiation doses to each lymph node regions were recorded.In-field recurrence,marginal recurrence and out-of-field recurrence were respectively defined as the volume of failed lymph nodes located within the 80％ iso-dose lines,in the 80％-20％ iso-dose lines and beyond the 20％ iso-dose lines of prescribed doses.Results A total of 1 216 lymph node regions in 76 patients were contoured.The median follow-up time was 17.4 months.At diagnosis,lymph node regions with metastatic rates ＞50％ were 4R (68.7％),4L (57.9％),10R (57.9％),2R (56.6％) and 7 (51.3％).The positive lymph node regions were all subjected to prescribed doses.The lymph node regions that received incidental radiation doses of more than 3 000 cGy were:3P,4L,7,6,4R,5,2L.The median lymph node failure-free time was 9.8 months.In this study,only 1 patient developed out-of-field mediastinal lymph nodes failure.The rest of out-of-field recurrences and marginal recurrences were developed in the supraclavicular regions or contralateral hila.Conclusions When IFRT is used to treat mediastinal lymph node regions for patients with SCLC,negative mediastinal regions can be subjected to considerable incidental radiation doses.Out-of-field recurrences of the mediastinal lymph node regions are rare.This is contributed by the incidental radiation dose to these regions.
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Objective To investigate the impact of planning parameter settings on plan quality and delivery efficiency of VMAT for nasopharyngeal carcinoma with two treatment planning systems (TPS),as references for clinic plan optimization. Methods 25 patients with nasopharyngeal carcinoma were selected and planned for SIB?VMAT treatment. The same planning aims were used in the two kinds of TPS ( TPS?1 and TPS?2). Multiple planning parameters were set for plan optimization. Dose distribution to the target volumes and organs at risk,monitor unit ( MU) and delivery time were compared. Paired t?test or one?way ANOVA was used for the data which was in accordance to normal distribution;otherwise, nonparametric Wilcoxon signed rank test or nonparametric Friedman test was used. Results More segments lead to better plan quality and less MU but longer delivery time ( Minor impact was observed when segment number was larger than 120) in TPS?1,while it had little impact on both plan quality and delivery efficiency in TPS?2. Comparing to single?arc plans,dual?arc VMAT achieved no significant benefit in plan quality but had more MU and longer delivery time in TPS?1 ( P= 0?000 ) . However, dual?arc VMAT plans had better dose distribution in TPS?2, decreased the maximum and mean dose for spinal cord in 3?9% and 13?7%respectively (P=0?000,0?000).Changing the settings of maximum or minimum dose rate did not affect the plan quality in both of the tested TPSs. Increasing the maximum or minimum dose rate reduced the delivery time but the latter increased the number of MU ( P=0?000,0?000) . Conclusions VMAT plan quality and delivery efficiency is affected significantly and differently by planning parameter settings for two TPSs. Trial test should be conducted for different TPS to determine the optimal parameter settings.
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Objective To explore the feasibility of employing a risk category system in evaluating the treatment outcome of locoregionally advanced nasopharyngeal carcinoma (NPC) treated by intensitymodulated radiation therapy (IMRT) alone,and offering evidence for relevant perspective studies.Methods Totally 185 locoregionally advanced NPC patients were divided into high-risk and low-risk groups for evaluation and comparison.The patients who met at least one of the following criteria were defined as high-risk group and others as low-risk group:GTVnx ＞ 30 cm3;Clinical stage T4N2M0;multiple neck node metastases with 1 node size ＞4 cm,and N3 with any T stage.Results With a median follow up of 110.9 months (6.7-152.4 months),the 5-year overall survival,locoregional relapse-free survival,distant metastasis-free survival for the high-risk group vs.the low-risk group were 61.0％ vs.90.5％ (x2 =30.298,P＜0.05),78.3％ vs.91.5％ (x2 =6.352,P＜0.05)and 71.6％ vs.92.0％ (x2 =16.346,P ＜0.05).Conclusions As a simple and practicable method,the risk category system is helpful for discriminating locoregionally advanced nasopharyngeal carcinoma with different risk-group of treatment failure and in further perspective clinical research.
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Objective To evaluate the accuracy of image registration based on bony structure (RBS) and grey-scale (RGS) in positioning correction of radiation treatment,and their reliability in clinical application.Methods Setup errors of anthropomorphic phantom (chest& abdomen,head& neck) were simulated with x-,y-,z-directions.CBCT images were acquired for each simulation and registered with planning CT.using bony structure and grey-scale registration separately.Geometry accuracy of all registration were then obtained and analyzed.Results The errors of RBS and RGS in x-,y-,z-directions were (-0.65 ±0.22) mm and (-0.70±0.17) mm (P=0.00),(1.02 ±0.27) mm and (0.90±0.20) mm (P =0.00),(1.46 ± 0.53) mm and (1.47 ± 0.47) mm (P =0.54) for head& neck positioning; with (0.82±0.33) mm and (0.79±0.18) mm (P=0.03),(2.45±1.17) mm and (1.61 ±0.84) mm (P =0.00),(1.44 ± 3.25) mm and (0.19 ± 1.11) mm (P =0.00) for chest& abdomen positioning.Conclusions RGS is more accurate and stable than RBS.The accuracy of image registration is a little better for head& neck than that for chest& abdomen.The algorithms of image registration used in clinical application needs to be tested independently and the systematic error needs to be corrected before applying in different treatment techniques according to their accuracy requirement.
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Objective To investigate the volume of prophylactic irradiation to the neck for stage N0 nasopharyngeal carcinoma (NPC) patients treated with intensity-modulated radiotherapy (IMRT).Methods Retrospective analysis was performed on the clinical records of 270 patients with stage N0 NPC (based on the 6th version of AJCC/UICC staging system),who underwent IMRT as the initial treatment in our center from 2003 to 2008.Among all the patients,171 received prophylactic upper-neck irradiation,and 99 prophylactic whole-neck irradiation.All of them received 6-MV X-ray IMRT to the primary focus of NPC and the lymphatic drainage area in the upper neck (Levels Ⅱ,Ⅲ,and Ⅴ A lymph nodes) at doses of 68 Gy/30fractions and 54 Gy/30 fractions over 6 weeks.In addition,the patients receiving prophylactic whole-neck irradiation had the lower neck and supraclavicular fossae treated by anterior neck semi-field conventional technique at a dose of 50 Gy/25 fractions.Results The median follow-up was 65.1 months (range 4-106months),and the follow-up rate was 93％.The patients undergoing prophylactic upper-neck irradiation and prophylactic whole-neck irradiation had 5-year disease specific survival rates of 95.3％ and 91.9％ (x2 =0.76,P =0.384),relapse-free survival rates of 99.4％ and 99.0％ (x2 =1.18,P =0.278),and distant metastasis-free survival rates of 98.8％ and 94.9％ (x2 =2.31,P =0.128).The 5-year distant metastasisfree survival rate was significantly higher in patients without retropharyngeal lymph node (RLN) metastasis than in those with RLN metastasis (99.4％ vs.93.7％,x2 =8.96,P =0.003).Grade 1-2 mucositis and pharyngitis were the most common acute adverse reactions in patients.At 24 months after IMRT,no grade 3 or 4 xerostomia and trismus were developed.Conclusions Prophylactic irradiation to the upper neck may be feasible for stage N0 NPC patients treated with IMRT.It is reasonable in the 7th version of AJCC/UICC staging system that NPC with negative cervical lymph nodes and positive RLNs is reclassified to stage N1.
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Objective To study preliminary the accuracy of clinical target volume (CTV) and internal target volume (ITV) automatically generated by an in-house deformable registration software on fourdimensional CT (4DCT),and evaluate its feasibility of clinical application.Methods Clinic treated one lung cancer patient and one liver cancer patient were selected for the study.CTV was delineated by radiation oncologist according to a single respiratory phase image of 4DCT scanning,and then deformed to the other phases and generated the CTVdefm on each phase image.Differences between the CTVdefm and CTVmanu were then compared.A composite ITVcopm was created by overlapping all the CTVdefm of 10 phases and compared with the ITVMIP which was contoured on the maximum intensity projection (MIP) CT images,including the shape,volume and geometric center position of the ITV contour.Results For the tested lung case,average volume difference between the CTVdefm and CTV was (-2.59 ± 5.02)％ for the all 10 phases,and the vector departure of the two ITV centers was (1.04 ± 0.89) mm.The ITVcomp almost completely matched the ITVMIP on the tested liver case with a volume difference smaller the 1％ and only 1.4 mm vector departure between their geometric centers.Conclusion The validity of the CTVdefm and ITVcomp gained from automatic deformation of manual delineation reference based on 4DCT images were preliminary evaluated and proved to be good enough for clinic planning.
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Objective To study corrective method for displacement in the procedure of electronic portal imaging device (EPID)-based intensity-modulated radiotherapy dose valuation by studying the relative mechanical displacement of different vendor EPID (aS1000,Varian; aS500,Varian; iViewGT,Elekta).Methods A 5 cm × 5 cm field was set up to acquire portal images for three kinds of EPID,then a in house software was used to analysis the portal images.The relative displacement was acquired via analyzing a series of comparation between center positions of gantry angle ranging from 0° to 360° and gantry angle at 0°.Results In the lateral direction,the maximum relative displacement of EPID with aS1000,S500 and iViewGT were (-0.23 ±0.17) mm,(2.94±0.17) mm and (0.35 ±0.09) mm,respectively.In the longitude direction,the displacements were (-4.16 ± 0.20) mm,(-4.15 ± 0.25) mm and (-1.66 ±0.11) mm,respectively.As to longitude direction,the displacements could be well fitted with the usage of quadruplicate empiric function.Conclusions There is a significant difference at the aspect of relative displacement between different vendors EPID at different gantry angles.And the displacement in the longitude direction is obviously larger than in the lateral direction.The relative displacement should be corrected when applying EPID to the intensity-modulated radiotherapy dose verification at different gantry angles.
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Objective To develop an accurate 2D dose reconstruction model using electronic portal imaging device (EPID).2D dosimetric verifications of volumetric intensity-modulated arc therapy (VIMAT)were done using the model.And the results were compared to other dosimeters.Methods The EPID-based dose reconstruction model was using convolve,deconvolve and correction function.The dose profiles which were obtained by the ion chamber were used to determine the model parameters.A total of 12 VIMAT plans for the treatment of anatomical sites of various complexities were chosen.The results obtained from EPID were compared to other dosimeters and treatment planning system (TPS).The ion chamber was used to measure the central point absolute doses.Other dosimeters were used to measure the plane dose distributions.All dosimeters measured the dose at 10 cm depth.The results were analyzed using γevaluation method.Results Regarding absolute central point doses,the ion chamber results were within 1.5％ of the EPID results.For the comparison to Seven29 and Matrixx,the average γ pass rates with 2％and 2 mm criteria were 98.9％ and 99.8％ respectively.For the dose distributions measured by EPID and calculated by TPS,the γ pass rates with 3％ and 3 mm criteria were 99.9％.Conclusions The presented results which were obtained from the comparison of measured and calculated doses show the reliability of our EPID-based dose reconstruction model.With the model,EPID can be a reliable and fast tool for IMRT plan dosimetric verification.The model expanded to the 3D dosimetric verification in the uniform phantom will be considered as the next work.