Application of EPID-based in vivo dose verification in dynamic intensity-modulated radiotherapy for lung and esophageal cancers / 中华放射医学与防护杂志

Objective:To investigate the factors affecting the accuracy of electronic portal imaging device (EPID)-based in vivo dose verification in radiotherapy for patients with lung and esophageal cancers, and to recommend the workflow and specifications for the application of the in vivo dose verification. Methods:This study randomly selected 32 patients who received radiotherapy for esophageal and lung cancers at the Department of Radiation Oncology, Jinhua Municipal Central Hospital from May to August 2022, including 14 lung cancer cases and 18 esophageal cancer cases. Using a uRT-linac 506c linear accelerator, these patients were treated according to the dynamic intensity-modulated radiotherapy (dIMRT) and EPID-based In vivo dose verification ( In vivo EPID) plans developed with the uRT-TPOIS planning system. The In vivo dose verification performed during the treatment included 238 fractions of In vivo EPID and 80 fractions of image-guided radiotherapy (IGRT) for the lung cancer cases, as well as 414 fractions of In vivo EPID and 105 fractions of IGRT for the esophageal cancer cases. The 2D γ passing rate for each irradiation field was obtained according to the set threshold value. Furthermore, fractioned irradiation fields with γ-passing rates below the threshold value were analyzed, and primary factors decreasing the γ-passing rate were further analyzed by combining the online CT images and 3D reconstruction-derived dose. Results:For lung and esophageal cancers, the mean γ-passing rates were 95.1% ± 5.7% and 96.5% ± 4.5%, respectively at 3 mm/5%; 91.5% ± 8.4% and 92.2% ± 4.9%, respectively at 3 mm/3%, and 79.1% ± 14.7% and 83.7% ± 8.2%, respectively at 2 mm/2%, indicating no statistically significant differences between two cancers ( P > 0.05). The average γ passing rate for beam orientations near 0°/180° (Group A) was higher than those near 90°/270° (Group B) 3 mm/5%: Z = -25.4, P < 0.05; 3 mm/3%: Z = -26.8, P < 0.05). The IGRT correction of setup errors significantly improved the γ passing rates (96.3% ± 5.1% and 96.4% ± 4.9%, respectively at 3 mm/5%, Z = -5.50, P < 0.05; 92.3% ± 8.0% and 91.3% ± 7.7%, respectively at 3 mm/3%, Z = -9.54, P < 0.05). The results of In vivo dose verification were affected by changes in the volumes and motion of tumors and normal tissues, radiotherapy positioning, and adequacy of pre-treatment preparation. Conclusions:EPID-based In vivo dose verification during radiotherapy can avoid incorrect irradiation. However, it is necessary to standardize the workflow of the EPID-based In vivo dose verification to avoid the decrease in the γ passing rate caused by artificial factors.

Clinical application of radiotherapy based on UIH linear accelerators to in vivo dose verification / 中华放射医学与防护杂志

Objective:To explore the clinical application of the electronic portal imaging device (EPID) based on the linear accelerator produced by Shanghai United Imaging Healthcare Co., Ltd. (UIH) to in vivo dose verification. Methods:A total of 68 patients (32 cases with head and neck tumors, 16 cases with chest tumors, and 20 cases with abdomen and pelvis tumors) who were treated with volumetric modulated arc therapy (VMAT) in the Henan Provincial People′s Hospital were selected in this study. Each patient underwent the pre-treatment dose verification using an Arccheck device (Pre Arccheck), the pre-treatment dose verification using an EPID (Pre EPID), and the in vivo dose verification using an EPID (In vivo EPID). Moreover, the position verification based on fan beam computed tomography (FBCT) was also performed for each patient in the first three treatments and then once a week. The patients were treated when the setup error in any direction ( x: left-right, y: head-foot, z: vertical) was less than 3 mm; otherwise, position correction would be conducted. The three-dimensional setup deviation d was calculated according to setup errors x, y, and z. Results:The γ passing rates of dose verifications Pre EPID and In vivo EPID of 68 patients were (99.97±0.1)% and (94.15±3.84)%, respectively, significantly different from that (98.86±1.48)% of the Pre Arccheck dose verification ( t = -6.12, 9.43; P < 0.05). The γ passing rates of the chest, abdomen and pelvis, and head and neck in the In vivo EPID dose verification showed no significant differences ( P > 0.05). The difference in the γ passing rates (5.56±3.72)% between dose verifications Pre EPID and first In vivo EPID was unrelated to the three-dimensional setup deviation d (1.46±1.51 mm) ( P > 0.05). As the treatment proceeded, the γ passing rate of In vivo EPID gradually decreased from (94.15±3.84)% in the first week to (92.15±3.24)% in the fifth week. From the third week to the fifth week, the γ passing rates of In vivo EPID were significantly different from those in the first week ( t = 2.48, 2.75, 3.09, P < 0.05). Conclusions:The setup errors within 3 mm do not affect the γ passing rate of in vivo dose verification. The clinically acceptable threshold for the γ passing rate of in vivo EPID needs to be further determined. In addition, in vivo dose verification can support the clinical application of adaptive radiotherapy to a certain extent.

A markerless beam's eye view tumor tracking algorithm based on structure conversion and demons registration in medical image / 中华放射肿瘤学杂志

Objective:To propose a markerless beam's eye view (BEV) tumor tracking algorithm, which can be applied to megavolt (MV) images with poor image quality, multi-leaf collimator (MLC) occlusion and non-rigid deformation.Methods:Window template matching, image structure transformation and demons non-rigid registration method were used to solve the registration problem in MV images. The quality assurance (QA) plan was generated in the phantom and executed after manually setting the treatment offset on the accelerator, and 682 electronic portal imaging device (EPID) images in the treatment process were collected as fixed images. Meanwhile, the digitally reconstructured radiograph (DRR) images corresponding to the field angle in the planning system were collected as floating images to verify the accuracy of the algorithm. In addition, a total of 533 images were collected from 21 cases of lung tumor treatment data for tumor tracking study, providing quantitative results of tumor location changes during treatment. Image similarity was used for third-party verification of tracking results.Results:The algorithm could cope with different degrees (10%-80%) of image missing. In the phantom verification, 86.8% of the tracking errors were less than 3 mm, and 80% were less than 2 mm. Normalized mutual information (NMI) varied from 1.182±0.026 to 1.202±0.027 ( P<0.005) before and after registration and the change of Hausdorff distance (HD) was from 57.767±6.474 to 56.664±6.733 ( P<0.005). The case results were predominantly translational (-6.0 mm to 6.2 mm), but non-rigid deformation still existed. NMI varied from 1.216±0.031 to 1.225±0.031 ( P<0.005) before and after registration and the change of HD was from 46.384±7.698 to 45.691±8.089 ( P<0.005). Conclusions:The proposed algorithm can cope with different degrees of image missing and performs well in non-rigid registration with data missing images which can be applied in different radiotherapy technologies. It provides a reference idea for processing MV images with multi-modality, partial data and poor image quality.

Preliminary study of physical model test and clinical application based on EPID-based in-vivo dose verification system / 中华放射肿瘤学杂志

Objective:To validate the accuracy of physical model of in-vivo 3D dose verification based on electronic portal imaging device (EPID) using the phantom and preliminarily analyze the clinical application.Methods:Two phantoms (uniform and non-uniform phantoms) were involved in this study. The system of in-vivo 3D dose verification based on EPID was employed to acquire the images of square fields (SF) and combined fields of intensity-modulated radiotherapy (CFIMRT). The physical model of different media was constructed using the system. The factor of γ passing rate under different dose/distance criteria was statistically compared. For clinical cases, the dose-volume histograms were adopted to analyze the dose distribution of target volume and organs at risk (OARs).Results:For the SF in the uniform phantom, the average γ passing rate (3%/3 mm) was (97.49±1.11)%, and (94.06±5.11)% for the SF in the non-uniform phantom ( P>0.05). No statistical significance was noted in IMRT using different delivery methods (all P>0.05). For clinical cases, the average γ passing rate (3%/2 mm) was (97.96±1.84)% in the pre-treatment dose verification, and (90.51±6.96)%(3%/3 mm) for the in-vivo 3D dose verification. For clinical cases, significant dose deviation was observed in OARs with small size and large volume changes. Conclusion:The in-vivo 3D dose verification model based on EPID can be effectively applied in inter-fraction dose verification, providing technical support for adaptive radiotherapy in clinical practice.

Two-dimensional dose reconstruction using scatter correction of portal images

Context: Electronic portal imaging devices (EPIDs) could potentially be useful for patient setup verification and are also increasingly used for dosimetric verification. The accuracy of EPID for dose verification is dependent on the dose-response characteristics, and without a comprehensive evaluation of dose-response characteristics, EPIDs should not be used clinically. Aims: A scatter correction method is presented which is based on experimental data of a two-dimensional (2D) ion chamber array. An accurate algorithm for 2D dose reconstruction at midplane using portal images for in vivo dose verification has been developed. Subjects and Methods: The procedure of scatter correction and dose reconstruction was based on the application of several corrections for beam attenuation, and off-axis factors, measured using a 2D ion chamber array. 2D dose was reconstructed in slab phantom, OCTAVIUS 4D system, and patient, by back projection of transit dose map at EPID-sensitive layer using percentage depth dose data and inverse square. Verification of the developed algorithm was performed by comparing dose values reconstructed in OCTAVIUS 4D system and with that provided by a treatment planning system. Results: The gamma analysis for dose planes within the OCTAVIUS 4D system showed 98% ±1% passing rate, using a 3%/3 mm pass criteria. Applying the algorithm for dose reconstruction in patient pelvic plans showed gamma passing rate of 96% ±2% using the same pass criteria. Conclusions: An accurate empirical algorithm for 2D patient dose reconstruction has been developed. The algorithm was applied to phantom and patient data sets and is able to calculate dose in the midplane. Results indicate that the EPID dose reconstruction algorithm presented in this work is suitable for clinical implementation

Commissioning of portal dosimetry using a novel method for flattening filter-free photon beam in a nontrue beam linear accelerator

Aim: The aim of this study is to commission and validate the portal dosimetry (PD) system using an indirect method for flattening filter free (FFF) photon beam of the upgraded c-series linear accelerator. Background: Varian Medical System clinacs with amorphous-silicon portal imager panel (aSi-1000) do not have PD for FFF beams. Recently, our c-series linear accelerator was upgraded to deliver 6MV FFF (6MVFFF) photon beam with the highest dose rate of 1400 monitor unit (MU)/min. The study, therefore, focuses on the commissioning and validation of PD for the 6MVFFF beam. Materials and Methods: An indirect method was implemented to predict the portal dose for FFF beam in Eclipse as the treatment planning system does not have direct prediction algorithm for FFF beam (version. 11). Dosimetrical characteristics of aSi-electronic portal imaging device (EPID) were evaluated for 6MVFFF beam and validation of PD for 6MVFFF beam was performed for open fields along with pretreatment quality assurance of intensity-modulated radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS) techniques for 30 patients planned with 6MVFFF beam. Results: ASi-EPID saturates between 100 and 130 cm source to detector distance (SDD) for 6MVFFF beam and resolved at more than 140 cm SDD. The squared correlation coefficient (R2) for MU linearity was found to be 1 (R2 = 1), and instantaneous dose response linearity at different SDD's was found to be 0.999 (R2 = 0.999) for the 6MVFFF beam. Maximum gamma area index (GAI) for 3% dose difference and 3 mm distance-to-agreement criteria for IMRT, VMAT, and SRS/stereotactic radiotherapy plans was 97.9% ± 0.3%, 96.3% ± 0.5%, and 98.2% ± 0.2%, respectively. Conclusion: The results reveal that this novel method can be used to commission portal dosimetry for 6MVFFF beam as it is a convenient, faster, and accurate method

Evaluation of positional accuracy of the Varian's exact-arm and retractable-arm support electronic portal imaging device using intensity-modulated radiotherapy graticule phantom

Purpose: The aim of the present study was to compare the positional accuracy of varian's exact-arm (E-arm) and retractable-arm (R-arm) supporting electronic portal imaging device (EPID) systems (amorphous silicon flat-panel detector) using the intensity-modulated radiotherapy (IMRT) graticule phantom. Materials and Methods: The known shifts of 0.5, 1.0, and 1.5 cm were introduced to the given phantom in longitudinal, lateral, and vertical directions, respectively, with respect to treatment couch of medical linear accelerator. The experiment was repeated for different gantry angle and varying source to imager distances (SIDs). The images were acquired for each shift at varying SIDs and beam orientations for both EPID supporting systems. The corresponding shifts obtained from treatment planning system (TPS) were recorded and compared. Results: The known (expected) and observed (recorded from TPS) shifts obtained for different beam angles (namely, 0°, 90°, 180°, and 270° for anterior, left lateral, posterior, and right-lateral portal images, respectively) in the longitudinal, lateral, and vertical direction at varying SID were compared. The maximum shift in the observed value from the expected one was 3 and 2 mm, respectively, out of the all beam configuration for R-arm and E-arm. These shifts were randomly observed for all imager position and beam orientation. Conclusion: The IMRT graticule phantom is an effective tool to check the mechanical characteristic and consistency of different EPID supporting arms. The effect of EPID sag due to gravity (gantry and treatment couch) was not significant for detection of shift in patient's position. The E-arm support EPID has better mechanical stability and accuracy in detection of patient's position than that of R-arm

A comparative study of dosimetric verification of HalcyonTM treatment plans using Varian Portal Dosimetry and PTW array 1500 / 中华放射医学与防护杂志

Objective To compare two pretreatment plan QA methods for HalcyonTM accelerator using Portal Dosimetry (PD),and PTW OCTAVIUS 1500 detector array + Octagonal phantom (Oct 1500)respectively.Methods Parallel measurement-based pretreatment QA using two methods was performed for 22 IMRT/VMAT plans (74 fields) that have been used to treat 20 patients recruited in the Halcyon clinical trial.Several γ 2D comparisons were also applied to provide guidelines for Halcyon planning QA.Results Using Oct1500 method,the γ 2D passing rates for 74 fields in 22 Plans were 95.26±3.59,95.01±3.62 (Local Dose),99.05± 1.35,98.57± 1.96 (Max Dose) respectively.Two-related samples non-parametric tests suggested that the differences between the evaluation criteria were of statistical significance (Z =-7.220,-4.108,P＜0.05).For PD method,the γ 2D passing rates were 84.11％ ± 1.35％ (1 mm/1％),99.07％± 1.35％ (2 mm/2％),and 99.86％ ± 1.35％ (3 mm/3％).Two-related samples non-parametric tests suggested that the differences between evaluation criteria of PD method were statistically significant (Z =-7.475,-7.475,-6.906,P＜0.05).For 74 fields and max dose,3 mm/3％ evaluation criteria,two-related samples non-parametric tests suggested that the differences between PD and Oct1500 method were statistically significant (Z=-5.072,P＜0.05).Conclusions Both methods can be used for Halcyon pretreatment plan QA.PD is superior to Oct1500 with respect to efficiency and spatial resolution-induced verification accuracy.The criteria of 2 mm/2％ for PD,and Max Dose/3 mm/3％ for Oct1500 was suggested.

Application of electronic portal imaging device in postoperative intensity modulated radiotherapy of rectal cancer / 医疗卫生装备

Objective To measure and analyze the set-up errors of postoperative intensity modulated radiation therapy of rectal cancer (PIMRTRC)with electronic portal imaging device (EPID),and to provide theoretical foundation for clinical realizing of accurate PIMRTRC.Methods Totally 30 patients after rectal carcinoma resection underwent sagittal and coronal photographing with EPID before the first time of therapy and one time per week during the treatment course.The obtained images were compared with DRR images in treatment planning system to get the setup errors at X(left-right),Y(head-foot) and Z (front-back)directions,and the extending margins of CTV and PTV in postoperative intensity modulated radiation therapy were calculated.EPID was used for setup correction,and SPSS 19.0 was involved in to execute statistical analysis. Results The linear displacement had the mean values plus/minus standard deviation at X, Y and Z directions before and after error correction being(-1.392 4±3.670 9)mm vs(-0.816 5±2.670 5)mm,(0.969 7±4.076 1)mm vs(0.418 2±2.911 4)mm, and(0.704 4±1.805 6)mm vs(0.471 7±1.641 3)mm respectively;the extending margin had the values being 7 mm vs 5 mm, 6 mm vs 4 mm, and 4 mm vs 3 mm respectively.Conclusion EPID ensures the correctness and accuracy in postoperative intensity modulated radiotherapy of rectal cancer,which makes target area gifted with maximized dose,the surrounding tissue and organs at risk protected adequately,and provides theoretical support for extending CTV margin.[Chinese Medical Equip-ment Journal,2018,39(5):59-63]

Application of EPID-based 3D dose reconstruction in cancer patients / 中华放射肿瘤学杂志

Objective To perform 3D dose reconstruction based on electronic portal imaging device ( EPID) of linear accelerator for the static intensity-modulated using Edose, a dose verification system, Aiming to assist the radiotherapy professionals to better understand the radiotherapy organs at risk and target dose changes. Methods CBCT image was acquired for patients with head and neck cancer and thoracic cancer once a week for a total of six times. Subsequently,CBCT images and planning CT images were subject to rigid registration and exported to the Edose software. According to the setup error, EPID-based three-dimensional dose reconstruction was performed by using Edose software. The gamma passing rate and dose of different organs at risk ( OARs ) were analyzed and statistically compared. Results For patients with nasopharyngeal carcinoma,the intra-fractional Dmax of the spinal cord was more significantly fluctuated and higher compared with the planning dose, whereas the intra-fractional Dmax of the brainstem did not significantly fluctuate. The V30 of the parotid gland significantly changed with a maximum increase of 28. 69％ per fraction. For patients with thoracic tumors,the Dmax of the spinal cord was slightly changed,and the actual doses in the lung and heart were higher than the planning doses. The average deviation of the pulmonary V5 was up to 16. 99％ between the actual and planning doses with statistical significance ( P<0. 05).According to the analysis of gamma passing rate,significant dose changes occurring in the OARs were detected in the 16th fraction for the head and neck cancer and the 24th fraction for the thoracic neoplasms. Conclusions The dose changes in the OARs can be obtained by reconstructing the EPID-based 3D dose distribution using the Edose software for each fraction, which can better protect the OAR, enhance the coverage of target dose and provide certain reference for dose-guided and self-adaptive radiotherapy.

The preliminary comparison of the reconstructed doses with electronic portal imaging device (EPID) and dynalogs files for in vivo phantom dosimetry / 中华放射医学与防护杂志

Objective To study the difference of the constructed doses between electronic portal imaging device (EPID) and dynalogs files of linac for in vivo phantom dosimetry.Methods Twelve pelvic patients treated with volumetric modulated arc therapy (VMAT) plans were selected and the information of each plan was copied to theCheese phantom to recalculate the doses before delivered on Varian RapidArc Linac.TheCheese phantom was placed on the isocenter and the electronic portal image (EPI) formed by the EPID was sent to EPIgray software to reconstruct the actual delivered doses.Meanwhile,dynalogs files were respectively imported to the Mobius software to reconstruct the actual delivered doses too.The point dose in the center of each VMAT plan (the center of the effective sensitive volume of ionization chamber) was measured by the A1SL ionization chamber.At the same time,the dose of sensitive volume of ionization chamber from treatment planning systcm (TPS) was recorded.Results The relative deviation between the dose from TPS and the measurement results by the ionization chamber was 1.13％.The difference between the reconstructed doses of EPID-based or the dynalogs file-based with the measurement results by the ionization chamber was not statistically significant (P ＞ 0.05).Conclusions The two methods of dose reconstruction can provide reference for in vivo dosimetry of VMAT.

The impact of electronic portal imaging device position error on 3D dose verification of volumetric modulated arc therapy / 中华放射医学与防护杂志

Objective To analyze the impact of electronic portal imagingdevice (EPID) position error on three-dimensional dose verification of volumetric modulated arc therapy (VMAT).Metbods Five Suremark SL-20 lead points were fixed on Elekta tray,and EPID images were collected in 0-360° rotation,one image per 5°.The position error relative to the accelerator was analyzed via Matlab.Then the images position error was corrected according to the analysis,and the 3D dose was reconstructed with the corrected images.The dose distributions of double arcs,clockwise arc(arc 1),and counterclockwise arc (arc 2) of 16 nasopharyngeal carcinoma patients' VMAT plan were evaluated by γ analysis,and the results of before and after position error correction were compared.Results Compared to 0° gantry angle,the error of source to the image distance (SID) was maximum (1.20 cm) when the gantry angle was 180°.On account of the SID change,the maximum error along the up-down (y) direction in the iso-center planar was 2.28 mm and the left-right (x) direction error was within ± O.5 mm.The 3D γ analyses of 16 nasopharyngeal carcinoma in VMAT plans were obviously increased after the position error along y was corrected.The double arcs,arc1 and arc 2 were increased by (4.12 ±1.67) ％ (t =-9.86,P＜ 0.05),(3.47±1.64) ％ (t=-8.46,P＜ 0.05) and (5.08±1.30) ％ (t=-15.63,P＜ 0.05) in 5％/3 mm standard,respectively.However,in 3％/3 mm standard,γ value of the double arcs,arc 1 and arc2 were increased by (7.63 ±2.24) ％ (t =-13.63,P＜ 0.05),(6.03 ±2.07) ％ (t =-11.66,P＜ 0.05),(9.17 ±2.23) ％ (t =-16.41,P＜ 0.05),respectively.Since the EPID position error along x was corrected after y,the 3D γ analysis of reconstruction dose indicated that the average of the 5％/3 mm and 3％/3 mm γ value were increased by 0.23％ and 0.24％,respectively.Conclusions EPID motion error along the gantry to table direction of the accelerator can't be ignored.When reconstruct dose based on EPID,a modification should be made for rebuilding more accurate patients' 3D dose distribution.

Improved 2D image registration algorithm applied to head and neck tumor / 中华放射医学与防护杂志

Objective To evaluate the effect of setup errors on the 2D image projection and image registration, and then propose an improved registration method based on mutual information. Methods An anthropomorphic head phantom was used to simulate the rotational and translational setup errors. The geometric disparities were reflected by the changes of mutual information. Known setup errors were intentionally introduced to twenty cases divided into two groups demarcated by 3 mm translation error and 3° rotation error: ten cases with larger errors and ten with smaller errors. Then the anterior-posterior and lateral portal images were captured by the electronic portal imaging device ( EPID ) , based on which the setup errors were calculated using two mutual information registration method respectively: the vender provided one, and the improved method as proposed. The calculated errors were compared with the actual setup errors to evaluate robustness of the method. Results For the ten cases with smaller setup errors, the average translational registration disparities using the conventional method were 0. 3, 0. 4, and 0. 3 mm in x, y and z directions respectively. The rotational disagreements were 0. 4° in both x and z directions. The average time consumption was 28. 7 s. The corresponding discrepancies analyzed using the improved method were 0. 3, 0. 4, 0. 3 mm, 0. 5° and 0. 4°, respectively. On average, 31. 1 s was needed for registration. For the ten cases with larger setup errors, the mean disparities of the conventional method were 0. 9, 0. 7, 0. 8 mm, 0. 9° and 0. 8°, 29. 9 s taken on average. The corresponding result of the improved method was 0. 5, 0. 4, 0. 5 mm, 0. 6° and 0. 5°, 33. 2 s taken on average. Conclusions Regarding smaller setup errors, the two methods showed little difference and both had good performance in imageregistration accuracy. For larger setup errors, however, the improved mutual information registration method exhibited significantly higher accuracy than the conventional method, at cost of clinically acceptable registration time.

Improved 2D image registration algorithm applied to head and neck tumor / 中华放射医学与防护杂志

Objective To evaluate the effect of setup errors on the 2D image projection and image registration, and then propose an improved registration method based on mutual information. Methods An anthropomorphic head phantom was used to simulate the rotational and translational setup errors. The geometric disparities were reflected by the changes of mutual information. Known setup errors were intentionally introduced to twenty cases divided into two groups demarcated by 3 mm translation error and 3° rotation error: ten cases with larger errors and ten with smaller errors. Then the anterior-posterior and lateral portal images were captured by the electronic portal imaging device ( EPID ) , based on which the setup errors were calculated using two mutual information registration method respectively: the vender provided one, and the improved method as proposed. The calculated errors were compared with the actual setup errors to evaluate robustness of the method. Results For the ten cases with smaller setup errors, the average translational registration disparities using the conventional method were 0. 3, 0. 4, and 0. 3 mm in x, y and z directions respectively. The rotational disagreements were 0. 4° in both x and z directions. The average time consumption was 28. 7 s. The corresponding discrepancies analyzed using the improved method were 0. 3, 0. 4, 0. 3 mm, 0. 5° and 0. 4°, respectively. On average, 31. 1 s was needed for registration. For the ten cases with larger setup errors, the mean disparities of the conventional method were 0. 9, 0. 7, 0. 8 mm, 0. 9° and 0. 8°, 29. 9 s taken on average. The corresponding result of the improved method was 0. 5, 0. 4, 0. 5 mm, 0. 6° and 0. 5°, 33. 2 s taken on average. Conclusions Regarding smaller setup errors, the two methods showed little difference and both had good performance in imageregistration accuracy. For larger setup errors, however, the improved mutual information registration method exhibited significantly higher accuracy than the conventional method, at cost of clinically acceptable registration time.

Research progress in electronic portal imaging device-based in vivo dosimetry verification / 中华放射肿瘤学杂志

In vivo dosimetry (IVD) is currently the most direct and effective means of quality assurance.The electronic portal imaging device (EPID) has been widely used for IVD verification owing to its favorable dosimetric properties.In recent years,an increasing number of EPID-based IVD studies have emerged around the world.The purpose of this paper is to give an overview of the present progress in EPID-based IVD studies,and to provide a reference for the subsequent application of EPID in IVD.

Comparison of set-up errors detected by EPID and CBCT using two different immobilization ;techniques for patients with nasopharygeal carcinoma / 中国癌症杂志

Background and purpose: With the development of therapy equipments and technology, the treatment for nasopharyngeal carcinoma(NPC) has entered into the era of precision radiotherapy, and setup errors have become a very important factor affecting treatment effects. The purpose of this study was to analyze the set-up errors detected by the kilovoltage cone beam CT(EPID) and the megavoltage electronic portal imaging device(CBCT) using 2 kinds of different immobilization techniques (pillow+head neck shoulder mask and vacuum bag+head neck shoulder mask) for NPC patients. Methods:A total number of 40 NPC patients were randomly assigned into 2 groups (pillow+head neck shoulder mask group and vacuum bag+neck shoulder mask group). Then each group was further divided into CBCT scan group and EPID group for veriifcation before treatment delivery. We matched the EPID images with the DRRs and acquired the set-up errors in x, y, z axis. Setup errors of CBCT were calculated according to its matched and planned CT images in left-right (x), superior-inferior (y) and anterior-posterior (z) directions. Paired t-test was used to evaluate the differences. Results:In the pillow+head neck shoulder mask group, the set-up errors of CBCT in the x, y, z axis were x (0.67±2.01)mm, y (0.51±1.71)mm and z (0.57±2.04)mm, respectively. The errors of EPID were x (0.69±2.19)mm, y (0.54±2.03)mm and z (0.61±2.11)mm. In the vacuum bag+head neck shoulder mask group, the set-up errors of CBCT in the x, y, z axis were x (0.42±1.81)mm, y (0.33±1.55)mm and z (0.50±1.75)mm, respectively. The errors of EPID were x (0.44±1.87)mm, y (0.43±1.70)mm and z (0.54±1.77)mm. The vacuum bag+head neck shoulder mask ifxed technique was more accurate when compared to the pillow + head neck shoulder mask ifxation method (P<0.05). Conclusion:CBCT and EPID were similar in detecting set-up errors for the NPC patients. However, the vacuum bag+neck shoulder mask ifxed technique was more accurate when compared to the pillow+head neck shoulder mask ifxation method.

CBCT image guided radiation therapy clinical application / 中国医学装备

Objective:Study the effect about cone beam CT(CBCT) image guidance sytem to improve the positioning accuracy and reducing the set-up uncertainty in precise radiotherapy. Methods:Use CBCT system to scan head and neck tumors patients (30 cases) and chest tumor patients (40 cases), including head and neck tumor patients were scaned 90 times, chest tumor patients were scaned 113 times. Setup deviation statistics about anterior and posterior, head and feet, left and right direction. Results:The patients with head and neck cancer, the maximum error of anterior-posterior is 6mm, Three directions errors which greater than 3mm all less than 10%. Patients with chest tumor position error are in the head and foot direction, greater than 5 mm up to 21.51%. Before and after the direction of the error did not exceed 5mm. The left and right direction greater than 5 mm up to 4.53%. Conclusion:It greatly enhances the precision of radiotherapy, improved the curative effect of radiotherapy by using CBCT online image guidance system for the patient position correction. Compared with EPID, patients scaned with CBCT absorb smaller cumulative dose, the image resolution is higher, image matching is more accurate. But compared with the ordinary helical CT,the resolution and scanning range also need to improve.

The electronic portal imaging device for dosimetric verification of intensity-modulated radiation therapy / 中华放射医学与防护杂志

Objective To investigate the feasibility and efficiency of electronic portal imaging device for dosimetric verification of intensity-modulated radiation therapy.Methods 10 patients treated with intensity-modulated radiation therapy were verified using the electronic portal imaging device of aS1000 from Varian and MatriXX from IBA.The gamma pass rate and time needed was recorded and compared.Results The gamma pass rate at 3％/3 mm was 95.82％ (94.77％-96.86％) and 99.08％ (98.72％-99.45％) with aS1000 and MatriXX,respectively.The average time needed for dosimetric verification with aS1000 and MatriXX was 12.7 and 47.8 min,respectively.Conclusions The electronic portal imaging device of aS1000 has the potential as a tool for IMRT dosimetric verification.It is more convenient and efficient than MatriXX.

The study of mechanical movement displacement for three amorphous silicon electronic portal imaging devices / 中华放射肿瘤学杂志

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.

Comparison of infrared mrker-based positioning system and electronic portal imaging device for the measurement of setup errors / 中华放射肿瘤学杂志

ObjectiveTo measure the setup errors with infrared marker-based positioning system (IM-BPS) and electronic portal imaging device (EPID) for patients with esophageal carcinoma and lung cancer and investigate the accuracy and practicality of IM-BPS. MethodsFrom January 2007 to January 2008, 40 patients with esophageal carcinoma and 27 patients with lung cancer received three-dimensional conformal radiotherapy or intensity-modulated radiotherapy, setup errors during the treatment were measured with IM-BPS and EPID, and the data of setup errors were compared with paired t-test and agreement with x2-test. ResultsIt takes 10 - 12 mins to complete the validating for each patient by EPID) system, while IMBPS system only needs 2 -5 mins. The mean setup errors along x, y and z-axis for patients with esophageal carcinoma measured by IM-BPS and EPID were 3.49 mm, 3. 19 mm, 3.31 mm and 4. 03 mm, 3.41 mm, 3.43 mm, respectively. For the patients with lung cancer, the setup errors were 4. 23 mm, 3.51 mm, 3. 39mm and 4. 85 mm, 3. 53 mm, 3.74 mm, respectively. The difference of setup errors meanured by the two systems was within 1 mm for 65％ esophageal carcinoma patients ( x2 =51.09, P =0. 000), and 55％ lung cancer patients ( x2 =53. 35, P =0. 000).Conclusions The measurement results of setup errors for patients with esophageal carcinoma and lung cancer show that IM-BPS is mostly better than EPID. Though validating for patients can be measured accurately and be well quality controlled, IM-BPS is used easily because of macroscopic, homely,spare time and real-time monitoring.