Dose Distribution Verifications of IMRT for NPC

In order to explore a dose distribution verification procedure of intensity modulated radiation therapy （IMRT） for nasopharyngeal carcinoma （NPC） and establish its evaluation criteria, we performed 35 two-dimensional （2D） patient-specific IMRT verifications over the year i006. The percent of pixels passing 7 and the normalized agreement test （NAT） index were mainly used to represent the agreement between the measured and computed dose distributions with three criteria （2%/2 mm, 3%/3 mm and 5%/3 mm） as recommended in the literature. The results were that all cases passed through verifications with three criteria except that the NAT index of one case was beyond the limitation, and the three tolerance levels of 2%/2mm, 3%/3 mm and 5%/3 mm produced similar clinical verification results but led to different percent of pixels passing Y and NAT index. Our data showed that the percent of pixels passing y and the NAT index were complementary to evaluate future IMRT verifications as two significant metrics. Due to the influence of the noise and the trait of the software, we considered an IMRT plan as acceptable in case of the percent ofpixels passing y 〉95% and the NAT index 〈5 with the 5%/3 mm criteria for IMRT patient-specific quality assurance （QA）.

Application of Statistical Process Control for Setting Action Thresholds as Quality Assurance of Dose Verifications in External Beam Radiotherapy

Purpose: To test the concept of Statistical Process Control (SPC) as a Quality Assurance (QA) procedure for dose verifications in external beam radiation therapy in conventional and 3D Conformal Radiotherapy (3D-CRT) treatment of cervical cancer. Materials and Methods: A study of QA verification of target doses of 198 cervical cancer patients undergoing External Beam Radiotherapy (EBRT) treatments at two different cancer treatment centers in Kenya was conducted. The target doses were determined from measured entrance doses by the diode in vivo dosimetry. Process Behavior Charts (PBC) developed by SPC were applied for setting Action Thresholds (AT) on the target doses. The AT set was then proposed as QA limits for acceptance or rejection of verified target doses overtime of the EBRT process. Result and Discussion: Target doses for the 198 patients were calculated and SPC applied to test whether the action limits set by the Process Behavior Charts could be applied as QA for verified doses in EBRT. Results for the two sub-groups of n = 3 and n = 4 that were tested produced action thresholds which are within clinical dose specifications for both conventional AP/PA and 3D-CRT EBRT treatment techniques for cervical cancer. Conclusion: Action thresholds set by SPC were within the clinical dose specification of ±5% uncertainty for both conventional AP/PA and 3D-CRT EBRT treatment techniques for cervical cancer. So the concept of SPC could be applied in setting QA action limits for dose verifications in EBRT.

Delivered Dose Verification for Lung Cancer Stereotactic Body Radiotherapy Using Cone-Beam CT

Purpose: Verified the delivered dose distribution of lung cancer Stereotactic Body Radiotherapy (SBRT) using the cone-beam CT images. Methods: Twenty lung cancer patients who underwent SBRT with 100 CBCT images were enrolled in this study. Delivered dose distributions were recalculated on CBCT images with the deformed and non-deformed methods, respectively. The planned and delivered dose distributions were compared using the dose-volume histograms. Results: The delivered target coverage (V100) per patient inside target volume deviated on average were 0.83% ± 0.86% and 1.38% ± 1.40% for Pct vs. Pcbct and Pct vs. Pdcbct, respectively. The Conformity Index (CI) and Gradient Index (GI) showed a good agreement among the plans. For the critical organs, only minor differences were observed between the planned dose and the delivered dose. Conclusions: CBCT images were a useful tool for setup and dose delivery verification for lung cancer patients who underwent SBRT.

Data analysis of dose map verification for IMRT

In this paper we analyze the results of dose map verifications for patient’s IMRT (Intensity-modulated radiation therapy) plans and study the factors that may influence the accuracy of verification. MapCHECK, a two-dimensional diode array, was used to measure the dose maps for 1242 plans (14540 fields) from May 2004 to August 2008. The plans were designed with Pinnacle3 planning system. The passing rate of beams was determined when the acceptance criterion was 2%/2 mm, 3%/3 mm and 4%/4 mm. And the data with 3%/3 mm criteria was analyzed in more detail. The considered factors were beam modeling, optimization mode and treatment site. The median passing rate of total fields was 93.5%, 98.8%, and 100% when the acceptance criterion was 2%/2 mm, 3%/3 mm and 4%/4 mm, and the interquartile range were 11.1%, 3.8%, and 1.3%, respectively. The results of direct machine parameter optimization (DMPO) planning mode was better than those of multiple-step mode and beam modeling of new accelerators was better than that of old accelerators. These indicate that beam modeling is the key point of improving passing rate of IMRT verification and the influence of treatment site was little. The factors, the total number of segments, minimum area of segments and minimum monitor unit (MU) of segments, also influence the dosimetric accuracy of IMRT plan verification.

Research Progress of Two-d imensional Matrix Detectors in IMRT Dose Verification

With the continuous development of science and technolog ies in China,radiotherapy technology in medical field has been very significant ly developing,and intensity modulated radiation therapy(IMRT)technology has been the most widely used.This paper first introduces the components and types of two-dimensional matrix detector,two-dimensional ionization chamber matrix detector and two-dimensional semiconductor matrix detector,then analyzes the dosimetric characteristics of the two-dimensional matrix detector.In the end,the various applications of the two-dimensional matrix detector are analyzed and discussed in detail.The paper aims to promote the two-dimensional matrix detector’s development in the field of radiotherapy in China.

Dose reconstruction with Compton camera during proton therapy via subset-driven origin ensemble and double evolutionary algorithm

Compton camera-based prompt gamma(PG) imaging has been proposed for range verification during proton therapy. However, a deviation between the PG and dose distributions, as well as the difference between the reconstructed PG and exact values, limit the effectiveness of the approach in accurate range monitoring during clinical applications. The aim of the study was to realize a PG-based dose reconstruction with a Compton camera, thereby further improving the prediction accuracy of in vivo range verification and providing a novel method for beam monitoring during proton therapy. In this paper, we present an approach based on a subset-driven origin ensemble with resolution recovery and a double evolutionary algorithm to reconstruct the dose depth profile(DDP) from the gamma events obtained by a cadmium-zinc-telluride Compton camera with limited position and energy resolution. Simulations of proton pencil beams with clinical particle rate irradiating phantoms made of different materials and the CT-based thoracic phantom were used to evaluate the feasibility of the proposed method. The results show that for the monoenergetic proton pencil beam irradiating homogeneous-material box phantom,the accuracy of the reconstructed DDP was within 0.3 mm for range prediction and within 5.2% for dose prediction. In particular, for 1.6-Gy irradiation in the therapy simulation of thoracic tumors, the range deviation of the reconstructed spreadout Bragg peak was within 0.8 mm, and the relative dose deviation in the peak area was less than 7% compared to the exact values. The results demonstrate the potential and feasibility of the proposed method in future Compton-based accurate dose reconstruction and range verification during proton therapy.

Verification of Dosimetric and Positional Accuracy of Dynamic Tumor Tracking Intensity Modulated Radiation Therapy

Purpose: We performed both, dosimetric and positional accuracy verification of dynamic tumor tracking (DTT) intensity modulated radiation therapy (IMRT), with the Vero4DRT system using a moving phantom (QUASAR respiratory motion platform;QUASAR phantom) and system log files. Methods: The QUASAR phantom was placed on a treatment couch. Measurement of the point dose and dose distribution was performed for conventional IMRT, with the QUASAR phantom static and moving;for DTT IMRT, this was performed with the phantom moving for pyramid shaped, prostate, paranasal sinus, and pancreas targets. The QUASAR phantom was driven by a sinusoidal signal in the superior-inferior direction. Furthermore, predicted positional errors induced by the Vero4DRT system and mechanical positional errors of the gimbal head, were calculated using the system log files. Results and Conclusion: For DTT IMRT, the dose at the evaluation point was within 3% compared with the verification plan, and the dose distribution in the passing rates of γ was 97.9%, with the criteria of 3% dose and 3 mm distance to agreement. The position error calculated from the log files was within 2 mm, suggesting the feasibility of employing DTT IMRT with high accuracy using the Vero4DRT system.

基于标定和计算的电子射野影像系统剂量重建

提出了一种基于标定和计算的电子射野影像系统(EPID)剂量重建算法。首先,对连续采集模式的EPID原始数据进行暗场校正和增益校正,然后通过亮场灰度特征确定射野边界。其次,对EPID数据进行MU标定、离轴标定和射野大小标定,并根据标定后的叠加通量和加速器机头蒙特卡罗模型进行剂量重建。最后,选取9例IMRT计划,分别使用EPID和MapCheck对计划进行验证测量,并在不同γ标准下比较两种验证工具的通过率。针对选取的1例计划病例,两种标准下使用MapCheck对多个病例验证的通过率分别为99.02%±1.28%、90.84%±4.49%;使用EPID重建模型的平均通过率分别为98.86%±1.19%、91.39%±4.80%。本文提出的标定和剂量计算相结合的EPID重建算法,与主流剂量验证软件MapCheck相比,对IMRT计划的验证通过率没有统计学差异(P>0.05),符合剂量验证的临床要求。

A preliminary study of a new high-resolution detector matrix applied to three-dimensional dose verification in intensity-modulated radiotherapy

Objective:To test the basic dosimetry characteristics of a new high-resolution matrix and to perform a preliminary study on the three-dimensional(3D)dose verification of intensity-modulated treatment(IMRT).Methods:The dosimetry characteristics of the new matrix were investigated,including repeatability,dose-rate response,and dose linearity.Twenty cases of nasopharyngeal carcinoma(NPC)and 20 cases with lung cancer were randomly selected for IMRT plans,and the novel matrix was employed for 3D dose verification.The measured results were evaluated using the gamma passing rate(GPR)and dose volume histogram(DVH).The action limit(AL)and tolerance limit(TL)of the target volume and each organ at risk(OAR)were calculated with reference to the American Association of Physicists in Medicine(AAPM)TG218 report.Results:The matrix performed well for all dosimetry characteristic tests,with a deviation of<1%.The average GPRs of the body were(99.32±0.32)%,(98.36±0.59)%,and(96.27±1.20)%for NPC,and(99.17±0.74)%,(98.09±1.33)%,and(95.83±2.22)%for lung cancer at the gamma standards of 3%/3 mm,3%/2 mm,and 2%/2 mm.The average GPRs difference between the head-neck and thorax-abdomen plans were<1%for the same gamma standard.For both the target volumes and OARs,the average GPRs were>90%under the relatively strict standard of 2%/2 mm.The DVH showed that the measurement results of D_(98) and D_(95) for the target volumes were slightly lower and D_(2) were higher than those of treatment planning system(TPS)(P<0.01).In addition,with the same standard,there may be significant differences in the values of AL and TL between different structures for target volumes and OARs,especially small-volume OARs such as the chiasma and optic nerve-L.Conclusions:The new matrix showed good dosimetry characteristics and can be effectively applied to the treatment planning dose verification of the head-neck and lung cancer.Further research is needed to establish how to analyze the GPR and DVH of the target volume and OARs,and to determine more precise dose verification standards combined with the parameters of AL and TL to better guide 3D dose verification in clinic.

PTW Detector7293种剂量验证方法在调强放射治疗中的对比研究

目的 :对比PTW Detector729 3种验证方法在调强放射治疗(intensity modulated radiation therapy,IMRT)剂量验证中的差异。方法:回顾性选取2022年1—12月于某院完成放射治疗的鼻咽癌、肺癌、乳腺癌、宫颈癌和全脑放射治疗患者共50例,使用PTW Detector729二维电离室矩阵配合PTW RW3固体水与PTW Ocavius 4D旋转模体对50例患者的IMRT计划分别进行归零机架角2D剂量验证、实际机架角2D剂量验证和实际机架角3D剂量验证。将剂量评估阈值设为10%,统计3种验证方法在3%/1 mm、2%/2 mm、3%/2 mm和3%/3 mm 4种评估标准下的γ通过率。采用SPSS 22.0统计学软件进行数据分析。结果:在10%剂量评估阈值标准下,归零机架角2D剂量验证的γ通过率最高,差异有统计学意义(P<0.05);实际机架角2D剂量验证的γ通过率高于实际机架角3D剂量验证,差异有统计学意义(P<0.05)。3种验证方法的γ通过率在3%/1 mm、2%/2 mm、3%/2 mm和3%/3 mm 4种标准下逐渐升高,且在3%/2 mm标准下均超过90%,结果满足临床放射治疗要求。结论:3种验证方法的验证结果均能达到IMRT剂量验证实践指南要求,根据IMRT开展情况选择合适的验证方法,对确保治疗方案安全、有效实施具有重要意义。

基于电子射野影像系统的光栅位置和剂量验证研究

目的 使用基于电子射野影像系统(electronic portal imaging device,EPID)的质控系统,在Primus和VenusX加速器上实现光栅位置及剂量验证。方法 通过灰度值最大梯度方法计算光栅位置,评估偏差。使用剂量标定和剂量计算相结合的算法对EPID采集的图像进行剂量重建,将EPID和MapCheck/PTW得到的数据,分别与计划系统剂量进行γ通过率分析。结果 VenusX加速器光栅误差小于1 mm,Primus重新标定后误差明显减小。重建的剂量,在3%/3 mm,阈值10%和2%/2 mm,阈值10%的2种标准下,Primus加速器γ平均通过率分别为98.86%和91.39%;VenusX加速器γ平均通过率分别为98.49%和91.11%。结论 基于EPID的质控系统,可提高加速器质控效率,减轻物理师工作负担。

独立验证中剂量差异分布及其与肿瘤类型相关性的初步研究

目的:对调强放射治疗(IMRT)计划进行分类独立验证,探讨计划剂量差异分布及其与肿瘤类型的相关性,并建立预测模型。方法:收集180例头颈部、胸部及腹部肿瘤患者固定野IMRT计划,采用独立样本t检验对治疗计划系统中初始计算剂量与独立验算剂量进行一致性分析,以评估独立验证的可行性。比较不同肿瘤间计划靶区(PTV)的剂量差异分布。采用相关性分析及多元线性回归方法分析PTV剂量差异与靶区适形度指数(CI)、均匀性指数间相关性。结果:头颈部、胸部及腹部肿瘤PTV剂量差异均在±1.2%以内,初始剂量与验算剂量间3%/3 mm平均γ通过率>99.5%,显示独立验证与治疗计划系统的剂量分布具有良好一致性。头颈部、胸部及腹部计划中PTV剂量差异分布不同,且与CI显著相关。根据CI可在独立验证中初步判断PTV剂量差异,基于CI及均匀性指数的多元回归方程可用于预估IMRT计划的剂量验算差异。结论:独立验证可快速实现放疗计划治疗前验证,提高放疗计划质量控制的效率。基于剂量差异的预估对放疗计划的优化起到一定指导作用。

独立验证软件Arc QA与Veri QA在调强放疗计划验证中的剂量学比较

目的评估并比较基于蒙特卡罗算法的Arc QA和Veri QA 2款独立剂量验证软件在调强计划验证中的剂量学差异。方法收集87例行调强放疗患者的放疗计划,包括头颈部17例、胸部46例、腹部24例,所有放疗计划均通过了临床剂量验证。分别使用Arc QA和Veri QA对调强计划进行独立剂量计算,采用γ通过率(3%/3 mm)分析二者与治疗计划系统(Treatment Planning System,TPS)间的剂量分布,并对比二者的靶区剂量-体积直方图参数(最小剂量、最大剂量、平均剂量和D95%)剂量验算差异和γ通过率。结果Arc QA和Veri QA与TPS间关于靶区的剂量差异均在±2.5%以内,2款软件在头颈、胸及腹部中的平均γ通过率分别为98.90%±1.99%和99.21%±0.85%、95.74%±3.16%和99.37%±0.77%以及97.10%±2.41%和99.84%±0.17%,二者在胸腹部差异均有统计学意义(t=-5.972,P<0.05;t=-5.133,P<0.05)。结论Arc QA和Veri QA与TPS均有良好的剂量学一致性,能满足临床验证需要,可作为调强计划的独立验证工具。

基于点云分布的光学发射层析系统响应矩阵计算方法

为满足放射治疗的三维剂量实时测量验证需求,基于闪烁体发光的三维剂量测量技术被提出。该技术利用闪烁体受辐射发光的原理,将三维剂量分布转换为三维光分布,并通过相机和光学发射层析技术进行三维光分布的测量与重建。基于光学发射层析的三维重建需要使用迭代算法,而系统响应矩阵是迭代重建的重要参数。本文基于小孔成像模型提出了基于点云分布的系统响应矩阵计算方法,该方法将体素转化成随机点云,计算点云投影至像素内的数量作为体素对像素的响应。在模拟成像的对比中,相较于传统的基于投影面积的计算方法,该方法抑制了模拟图像上的条纹状误差,提升了模拟成像的均匀性和梯度均匀性,改善了模拟精度,有利于提升三维重建的准确性。

Compass验证系统在乳腺癌保乳术后调强放射治疗计划验证中的应用及相关影响因素分析

目的利用Compass三维验证系统对乳腺癌保乳术后调强放射治疗计划进行剂量验证,研究其影响因素并进行分类分析。方法选择乳腺癌保乳放射治疗女性患者20例,年龄45~74岁,中位年龄59岁;侧别,左侧10例,右侧10例。用Compass系统进行计划剂量验证,包括独立核算验证和实测重建剂量验证;将Monaco计划系统蒙卡算法计算的剂量(MCD)、Compass卷积/超分割算法独立核算剂量(CCD)和Compass实测重建剂量(CRD)三者之间两两剂量验证结果进行两两比较(CCD-MCD、CRD-CCD、CRD-MCD),比较参数包括靶区剂量最大限值10%生成区域的γ结果及剂量体积直方图(DVH)结果。结果CRD-MCD与CRD-CCD的γ通过率和平均γ值差异均有统计学意义[(95.23±2.38)%vs(96.33±2.72)%、(94.78±2.56)%vs(95.97±2.95)%、0.41±0.04 vs 0.37±0.04、0.42±0.04 vs 0.38±0.04。P<0.05],CRD-MCD与CCD-MCD的γ通过率和平均γ值差异也均有统计学意义[(95.23±2.38)%vs(99.29±0.46)%、(94.78±2.56)%vs(99.26±0.46)%、0.41±0.04 vs 0.26±0.03、0.42±0.04 vs 0.27±0.03。P<0.05],CRD-CCD与CCD-MCD的γ通过率和平均γ值差异也均有统计学意义[(96.33±2.72)%vs(99.29±0.46)%、(95.97±2.95)%vs(99.26±0.46)%、0.37±0.04 vs 0.26±0.03、0.38±0.04 vs 0.27±0.03。P<0.05]。计划肿瘤靶区(PGTV)的D_(98%)和计划靶区(PTV)的D_(mean)、健侧乳腺的D_(mean)、V5和患侧肺的V20、V30的剂量体积相对偏差在CRD-MCD与CRD-CCD比较,差异有统计学意义[(2.01±1.27)%vs(2.60±1.05)%、(2.84±0.55)%vs(2.55±0.71)%、(-11.15±7.87)%vs(-18.29±7.91)%、(-1.45±5.45)%vs(-2.76±3.83)%、(-0.85±0.36)%vs(-0.65±0.23)%、(-0.56±0.37)%vs(-0.38±0.27)%。P<0.05]。PGTV的D98%、D_(2%)、D_(mean),PTV的D_(98%)、D_(2%)、D_(mean),心脏的D_(mean)、健侧乳腺的D_(mean)、V_(5),健侧肺的V_(5)和患侧肺的V_(5)、V_(20)、V_(30)的剂量体积相对偏差在CRD-MCD与CCD-MCD比较,差异均有统计学意义[(2.01±1.27)%vs(-0.51±0.54)%、(2.86±1.22)%vs(-0.002±0.92)%、(2.63±0.75)%vs(-0.19±0.40)%、(2.17±0.82)%vs(0.38±1.01)%、(2.81±0.95)%vs(-0.17±0.70)%、(2.84±0.55)%vs(0.29±0.43)%、(-17.39±7.79)%vs(0.87±3.30)%、(-11.15±7.87)%vs(9.27±4.87)%、(-1.45±5.45)%vs(2.01±1.30)%、(-0.24±0.80)%vs(0.01±0.04)%、(-4.60±0.87)%vs(0.27±0.59)%、(-0.85±0.36)%vs(-0.21±0.21)%、(-0.56±0.37)%vs(-0.22±1.34)%。P<0.05]。PGTV的D_(98%)、D_(2%)、D_(mean),PTV的D_(98%)、D_(2%)、D_(mean),心脏的D_(mean)、健侧乳腺的D_(mean)、V_(5),健侧肺的V_(5)和患侧肺的V5、V20、V30的剂量体积相对偏差在CRD-CCD与CCD-MCD比较,差异均有统计学意义[(2.60±1.05)%vs(-0.51±0.54)%、(2.88±1.12)%vs(-0.002±0.92)%、(2.83±0.68)%vs(-0.19±0.40)%、(1.81±0.90)%vs(0.38±1.01)%、(2.87±0.82)%vs(-0.17±0.70)%、(2.55±0.71)%vs(0.29±0.43)%、(-18.10±7.40)%vs(0.87±3.30)%、(-18.29±7.91)%vs(9.27±4.81)%、(-2.76±3.83)%vs(2.01±1.30)%、(-0.25±0.81)%vs(0.01±0.04)%、(-4.90±1.03)%vs(0.27±0.59)%、(-0.65±0.23)%vs(-0.21±0.21)%、(0.38±0.27)%vs(-0.22±1.34)%。P<0.05]。结论不同算法在高剂量区、低剂量区和肺等组织密度比较大或者含空腔的组织中计算精度偏差更加显著;机器的稳定性状态对剂量差异亦有影响。

基于锥形束CT下肺癌立体定向放疗摆位误差研究及剂量验证

目的研究不同手臂固定方式对于肺癌立体定向放射治疗(SBRT)中患者体位误差的影响及剂量验证分析。方法选取2019年3月至2022年12月在中南大学附属湘雅三医院肿瘤科收治的34例肺部SBRT治疗患者,分别采用双手交叉握杆(对照组)和双手抱肘置于前额(观察组)的方式固定手臂进行体位固定。每例患者每次治疗时均采用锥形束计算机断层扫描(CBCT),将CBCT扫描图像与CT模拟定位时的图像进行自动匹配,并结合靶区和骨性标志进行调整,计算患者在X、Y、Z轴方向上的误差并进行分析研究,同时选取阈值标准为(2%,2 mm,10%)和(3%,3 mm,10%)的条件下分析比较ArcCHECK模体理论计算剂量和ArcCHECK模体实测剂量之间的差异。结果34例研究对象共得到510组CBCT影像。其中对照组患者和观察组患者每次治疗前体位误差分别为左右方向LAT(1.69±4.43)和(2.25±1.54),头脚方向LNG(1.88±1.39)和(2.40±1.61),腹背VRT(1.26±0.98)和(1.70±1.08)。对照组在X、Y、Z三个方向上的误差数值均小于观察组,差异均有统计学意义(P<0.05)。当阈值标准为(2%,2 mm,10%)时,两组SBRT计划的绝对通过率均大于95%;当阈值标准为(3%,3 mm,10%)时,两组SBRT计划的绝对通过率均大于90%,均满足临床治疗要求。结论在肺癌SBRT治疗中,两种手臂固定方式基于ArcCHECK模体验证的绝对剂量通过率均满足临床要求,但双手交叉握杆的手臂固定方式对于患者体位的重复性和精准性更好。

SRS MapCHECK与EDOSE在立体定向放疗计划剂量验证中的对比

目的:使用SRS MapCHECK和EDOSE对立体定向放疗(SRT)计划进行剂量验证,并比较它们的验证结果。方法:首先比较两种系统在不同方野(2 cm×2 cm、4 cm×4 cm、6 cm×6 cm、10 cm×10 cm)的γ通过率(3%/3 mm),然后选择29例SRT计划,分析两种系统在不同γ标准下的绝对剂量通过率,最后分析EDOSE建立的4种不同物理模型对SRT计划剂量验证的影响。结果:SRS MapCHECK在所有方野和29例SRT计划的绝对剂量γ通过率均高于EDOSE,两者的验证结果有统计学差异(P<0.05);SRS MapCHECK及EDOSE在29例SRT计划的γ通过率(2%/2 mm)分别是为98.60%±2.14%和96.53%±2.41%。基于EDOSE的不同物理模型验证结果有统计学差异,平均γ通过率(2%/2 mm)偏差为1.8%~5.1%。结论:SRS MapCHECK和EDOSE系统均满足SRT计划剂量验证的要求,且SRS MapCHECK的剂量验证通过率优于EDOSE;不同的EDOSE物理模型对SRT计划剂量验证有影响。

A method for direct conversion of EPID images to incident fluence for dose reconstruction

A direct incident fluence measurement method based on amorphous silicon electronic portal imaging device(a-Si EPID) has been developed for pretreatment verification of intensity-modulated radiation therapy(IMRT).The EPID-based incident fluence conversion method deconvolves EPID images to the primary response distribution based on measured lateral scatter kernels in the EPID detector using Conjugate Gradient algorithm.The primary response is converted to the incident fluence based on measured fluence conversion matrix which corrects for off-axis position dependence of the a-Si EPID response and the "horn" beam profile caused by flatting filter. To verify feasibility and accuracy of this method, square fields of various sizes and two IMRT plans were delivered. The dose distributions computed based on EPID-derived incident fluence were compared with the measurement data. For all square field sizes except the smallest field(2 cm), the mean dose differences in cross-line dose profiles were within 1% excluding the penumbra region, and gamma passing percentages with a 2%/2 mm criterion were about 99%. For two IMRT plans, the least gamma passing percentage for all eight IMRT fields was 98.14% with 2%/3 mm criteria. It can be concluded that our direct EPID-based incident fluence conversion method is accurate and capable of being applied to pretreatment dose verification in clinical routines.

基于Edose系统的鼻咽癌调强放疗三维剂量验证

目的:探讨Edose系统在鼻咽癌调强放疗三维剂量验证中的应用。方法:随机选取17例鼻咽癌患者的调强放疗计划,将计划传输至Edose系统中,使用Edose系统在CT中重建三维剂量分布并将剂量计算结果标记为R,Edose系统实测剂量标记为E,并计算绝对百分剂量偏差D%。统计各计划的计划靶区(planning target volume,PTV)和危及器官的R和E,并分析Gamma通过率。采用SPSS 22.0软件进行统计学分析。结果:各PTV的D%都在2%以内。危及器官的D%较PTV的差异大,最大的为小体积的晶体,为(12.47±7.43)%,其次是眼球,为(10.29±7.74)%,其余各危及器官的D%均在5%以内。3%/3 mm、3%/2 mm和2%/2 mm的Gamma通过率分别为(99.20±0.63)%、(98.61±0.86)%和(96.39±1.89)%,均符合临床要求。结论:仅依靠Edose系统的Gamma通过率比较有时并不能完全反映治疗计划是否符合临床治疗的要求,需要全面评估基于三维影像解剖结构的剂量误差对临床计划执行的影响,从而为临床放疗计划的三维剂量验证提供依据。

Inter-Fraction and Intra-Fraction Variation in the Absorbed-Dose Delivery during Interstitial High Dose Rate Brachytherapy—A Study Using MicroMOSFET <i>In-Vivo</i>Dosimeter

Background: The delivered dose has to be checked and verified with planned dose since precise and accurate dose delivery is essential in Brachytherapy. Sources of uncertainty during Brachytherapy are intra-fraction, inter-fraction and inter-application variations. In-vivo dosimetry is the direct method to monitor the radiation dose delivered to a patient during radiotherapy. In this study, assessment of the inter-fraction and intra-fraction variations in the interstitial Brachytherapy was done with microMOSFET. Aim: To analyze the inter-fraction variations in dose delivery during interstitial HDR Brachytherapy and to compare the measured point dose with the TPS-calculated point dose, intra-fraction variation, using the microMOSFET in-vivo dosimeter. Materials and Methods: From May 2014 to February 2016, 22 patients with Head and Neck cancers and 8 patients with Soft-Tissue Sarcomas (STS) were selected for this study. All these patients underwent CT imaging more than 24 hours after the application. Brachyvision 3DTPS and GammaMed Plus iX HDR unit were used for treatments. MicroMOSFET in-vivo dosimeter after calibration was used for the measurements of dose inside the treated volume. Intra & Inter-fraction variations were analyzed and reported. Results: The SD of inter-fraction variation among 22 Head & Neck patients ranges from 2.14% to 14.26%. Minimum & maximum dose variation with first fraction dose of patients ranged from -22.33% to +26.71% and the mean doses were -6.42% to +19.76%. Differences of TPS dose and microMOSFET measured first fraction dose, intra-fraction variation, ranged from -12.36% to +5.05%. The SD of inter-fraction variation for 8 STS patients was from 2.81% to 14.43%. Minimum and maximum doses vary from -38.72% to +25.74% and mean dose varies from -21.5% to +12.53%. Differences of point doses of TPS and measured, intra-fraction variation, were from -5.86% to 4.88%. Conclusions: MicroMOSFET has the potential to minimize the gross errors during multi-fractionated Interstitial Brachytherapy. Edema, applicator displacements and placement of microMOSFET are the main influencing factors for inter-fraction uncertainty in dose delivery. Re-planning with re-simulated images should be considered whenever the microMOSFET readings vary more than ±10% of the planned dose inside the CTV measured in two successive fractions.