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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.
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Objective:Based on the AAPM-TG218 report, the dose verification of intensity-modulated radiotherapy (IMRT) plans were classified to understand the current status, establish the process and determine the limits of dose verification in our hospital.Methods:Different combinations of tumor locations, accelerators, treatment planning systems and verification devices in our hospital were verified and compared to determine the tolerance limits and action limits of each combination. The measurement requirement was adopted according to the AAPM-TG218 report, and 80 cases were selected for each measurement. The measurement procedures were implemented based upon the AAPM-TG218 report and clinical experience of our hospital.Results:The clinical action limits of IMRT plans in our hospital could meet the recommended range of the AAPM-TG218 report, and the tolerance limits were slightly lower than the AAPM-TG218 report′s recommendation (93.94% for 3%/2 mm). The measurement of verification devices was related to the sensitivity. The tolerance limits measured by EPID were higher than ArcCHECK, especially when the dose/distance requirements were more stringent (94.12% and 92.03% for 3%/2 mm, P=0.074; 86.82% and 74.61% for 2%/2 mm, P=0.017). Conclusion:Through the AAPM-TG218 report, the work flow of IMRT dose verification and the limit range are established in our hospital, providing guidance for subsequent clinical dosimetric measurement.
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Objective To investigate the effect of respiratory movement of different amplitude,period and direction on the dose distribution of target area in dynamic intensity modulated radiation therapy.Methods A total of 30 cases of lung cancer were selected and divided into three groups according to the volume size of the target area,including groups A (72.0-200.2 cm3),B (271.7-380.0 cm3) and C (498.9-684.9 cm3).The average volume was 151.5,327.1 and 583.3 cm3,respectively.Breathing motion simulation platform was used to drive the mode body with two-dimensional ionization chamber matrix along the Gun-Target direction,then turn the collimator to 0° and 90°,respectively.The doses were collected at the central level in different amplitudes of 0,4,8,12 and 15 mm,periodic respiratory movement at the intervals of 3,4 and 5 s and respiratory motion measurement with a cycle of 4 s 5 times.The difference of dose distribution between the collected dose and TPS output was analyzed by taking the absolute dose and γ-passing rate (3 mm/3％) as indicators.Results In the two-sided upward,respiratory movement reduced the dose at the medial edge of the target area and increased the dose at the lateral edge of the target area.The difference of γ-passing rate between respiration cycle was up to 3.54％ (t=2.301,P＜0.05),and when the respiration movement was more than 8 mm,the γ-passing rate was less than 90％ and decreased with the increase of amplitude.The difference of γ-passing rate between static and respiratory motion was negatively correlated with the volume of target area,and the average γ-passing rate of A,B and C three groups increased gradually.The γ-passing rate of 5 composited dose was higher than that of single dose,and the difference was statistically sigificant(t=-9.36--5.95,P＜0.05).Conclusions The dose distribution of dynamic IMRT target area is mainly influenced by respiration range and its own volume,and the respiration cycle has an effect on dose distribution under partial amplitude.After implementing the multiple doses,some single dose implementation errors can be eliminated.Physicians need to expand the target area reasonably according to the range of respiratory movement,and optimize the amount of marginal tissue in the target area in the direction of respiratory movement.For patients with small target volume and large respiratory movement,respiratory management technology should be adopted to improve the accuracy of target dose implementation.
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Objective To evaluate the effect of carbon fiber couch on dose distribution of radiotherapy planning and verification pass rate.Methods Establishing the carbon fiber treatment couch model in Pinnacle8.0m Treatment Planning system (TPS),and then this model was used to correct dose calculations of oblique fields in the treatment plans of 10 cases of nasopharyngeal carcinoma,10 cases of breast cancer and 10 cases of lung cancer and evaluate the effect of carbon fiber couch on the whole dose distribution of the plans.Then these plans were measured by three-dimensional dose verification equipment Delta4 to confirm the improvement extent of Gamma pass rate after considering the carbon fiber treatment couch.Results For the majority of plans,when the carbon fiber couch was taken into consideration,the target doses was significantly reduced (4772 cGy-7266 cGy vs.4859 cGy-7347 cGy,P=0.000-0.002) and the relative deviation of D95 was 1％ to 3％.Measurement results of Delta4 showed that Gamma pass rate (3 mm/3％ criteria) increased in all plans (96.4％-98.8％ vs.93.4％-97.3％,P =0.000),some of that were up to 5 percentage when the couch model was applied.Conclusions Target doses will be overestimated if the treatment couch is ignored in TPS measurement.,However it should arouse enough attention when the disease with smaller doses corresponding gradient.
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Objective To study the effect of the uncertain deflection of the Delta4 phantom (ScandiDos AB,Sweden) in setting up on the Gamma index passing rate during the VMAT plan verification.Methods Two patients with head and neck cancer,two with lung cancers and one with pelvic cancer receiving VMAT radiotherapy were randomly chosen.By means of Eclipse8.6 TPS the treatment plans elaborated for the five patients were picked up to make the verification plans and Delta4 was used to perform dose verification On VARIAN Clinac Ⅸ.The Delta4 phantom was precisely set up first,and then it was deflected in a given angle towards the horizontal direction in relation to the center of the linear accelerator isocenter to perform the dose verification for 11 times successively.To figure out the relationship between the deflection angle of the Delta4 phantom and the Gamma index passing rate.Results As the Delta4 phantom was deflected by 0.0°,0.2°,0.4°,0.6°,0.8°,1.0°,1.2°,1.4°,1.6°,1.8° and 2.0° in sequence,the measured Gamma index passing rates presented a slight decline,but all greater than 90％ (DD 3％,DTA 3 mm).Conclusions In the VMAT plan verification,the Gamma index passing rate of Delta4 has no dependence on the uncertain deflection of the Delta4 phantom provided that the uncertain deflection of the Delta4 phantom is no greater than 2°,but the passing rates of DD and DTA vary significantly with the uncertain deflection of the Delta4 phantom.
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Objective To verify IMRT plans in point,planar and 3D dose,and to concretely analyze the dose differences of 3D anatomic structure based on Gamma passing rate.Methods Thimble ion-chamber,Matrixx and ArcCheck were separately used to measure six nasopharyngeal carcinoma treatment plans and six lung cancer treatment plans.The dose measurement deviation of the center point was compared as well as the Gamma passing rate of dose verification under the criteria of both 3％/3 mm and 2％/2 mm,the group t-test and one-way ANOVA were also proceeded.3DVH system was used to analyze the dose measurement deviation of target volume (TV) and organ at risk (OAR) through DVH.Results For IMRT and VMAT treatment plans,the mean deviation of point dose was (0.59 ± 1.31) ％ and (-1.00 ± 1.03)％ respectively,and the maximum deviation was less than 3％.Under the criterion of 3％/3 mm,the Gamma passing rate measured by Matrixx,ArcCheck and 3DVH for IMRT plans was 96.28％,97.55％ and 99.02％ respectively,and for VMAT plans,the corresponding results of three different detectors were 97.24％,99.67％ and 98.48％.The results analyzed and compared by 3DVH showed that even under the condition of high Gamma pass rate (more than 95％ for a Gamma criterion of 3％/3 mm),the DVH metrics of both TV and OAR in two cases (account for 16.7％ of the total plan) were significantly different on the clinical parameters,including GTV,spinal cord and brain stem etc.Conclusions The analysis of dose difference of the measurement results based on Gamma pass rate and on anatomic structure of 3D images can more effectively evaluate the influence of dose error to the implementing of clinical plan and the impact to the clinical treatment.
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Objective To investigate the factors of effecting with yindex analysis of delivery for helical tomotherapy (HT).Methods Measuring γindex with the ArcCheck device for introduced errors in HT.The errors include setup errors in three-dimensional,the gantry angle error,calculating the dose in the phantom,low dose rate.All the results were compared with the 3％/3 mm and 2％/2 mm criteria.The effect of the accuracy in the application of kilovoltage computed tomography (KVCT) and mega-voltage computed tomography (MVCT) images in HT was also analyzed.Paired-t test method was used for difference compared.Results When the errors were introduced to the HT,theγpassing rate of left-right,superior-inferior,anterior-posterior direction dropped 2.7％,7.2％,3.6％ under the 3％/3 mm criteria (P =0.002,0.022,0.007),with 4.6％,15.7 ％,7.6％ under the 2％/2 mm criteria (P =0.001,0.003,0.002) respectively.There was no statistical significance for theγpassing between scanning the ArcCheek phantom with the KVCT and MVCT under the 3％/3 mm and 2％/2 mm criteria (98.6％ vs 98.7％,P =0.859 and 92.7％ vs 92.8％,P =0.984).Conclusions The errors of the setup position and machine paraments can lead to the dose delivery errors in HT,the quality accurance of machine and plan should be enhanced to minimize the dose errors.The results also showed that there is no difference of KVCT and MVCT image on the delivery of HT.