FBCT与CBCT水模体模拟膀胱体积的准确性研究

目的 基于FBCT、CBCT水模体模拟膀胱显示体积的准确性和稳定性。方法 用已知体积的硬壁水模体和软壁水模体模拟膀胱。FBCT由2排Hispeed dual CT、64排Lightspeed VCT螺旋CT扫描,各自据螺距或床速分别扫描。CBCT据曝光条件分别pelvis、pelvis spotlight、high quality head扫描。每种扫描5次后于TPS重建分析体积差异并与真实值对比,对两种模体结果行独立样本t检验。结果 重建体积与真实值偏差硬壁模体FBCT为－(1.5~0.2)%,CBCT为－(5.1~2.9)%,软壁模体FBCT为－(4.2~0.1)%,CBCT为－(4.0~0.3)%。FBCT重建体积随螺距或床速增加而减小,Hispeed 重建体积大于Lightspeed (硬壁水模体和软壁水模体的P=0.010和0.004)。CBCT扫描pelvis模式重建体积最小(硬壁水模体和软壁水模体的P=0.020、0.013和0.006、0.008)。结论FBCT和CBCT扫描体积相近且均有良好重复性。对于活动性器官(呼吸、充盈等运动) FBCT扫描推荐少排慢扫描模式,CBCT扫描推荐pelvis spotlight和high quality head模式。     

基于头颈部千伏级锥形束CT的剂量计算研究

目的 探讨用机载千伏级锥形束CT (CBCT)对鼻咽癌患者治疗前扫描图像直接进行剂量计算的可行性.方法 选取治疗前行扇形束CT (FBCT)和CBCT扫描的11例鼻咽癌患者,将体位校正后重新扫描的CBCT图像传输至治疗计划系统中.在治疗计划系统中将FBCT和CBCT图像融合,将FBCT的计划移植至CBCT上.选择CBCT图像自己的HU-ED校正曲线重新进行剂量计算,与FBCT计划的靶区和正常器官的剂量体积直方图以及等中心层面剂量分布的γ通过率分析(阈值3%/3 mm)结果进行比较.结果 11例鼻咽癌患者中CBCT和FBCT计划的剂量体积直方图相似,等中心层面剂量分布中平均γ通过率为98.0%±1.33%.FBCT计划和CBCT计划的靶区受量差异都<1%,正常组织器官受量差异<2%.结论 治疗过程中得到的CBCT图像能用来进行剂量计算.

Abstract：

Objective To study the feasibility of dose calculation using kilovoltage X-ray cone-beam CT (KVCBCT) imaging for head-and-neck radiation therapy.Methods 11 patients with nasopharyngeal carcinoma were scanned with KVCBCT to adjust position before treatment, and rescanning images with KVCBCT after correction were input a treatment-planning system.The dose was recalculated by applying the patients′ treatment plans based on planning CT to the KVCBCT images.The dose distributions and dose volume histograms (DVH) of the tumor and critical structures were compared with the original treatment plan.Results The DVH and dose distribution of the plan based on the KVCBCT are compared with that of the planning CT, and they shows a good consistency for the 11 cases.The doses calculated from the planning CT and KVCBCT were compared on the isocenter planes.Using γ analysis with a criterion of 3%/3 mm, 98.0%±1.33% of the points on the isocenter planes in the planning CT and KVCBCT.The difference of the dose to target volume was<1% and to normal structure was<2%.Conclusions This study indicated that CBCT images can be used to make a treatment plan with its individual hounsfield unit-electron density calibration curve.     

迭代锥形线束CT成像模式性能评价的研究

目的综合评价瓦里安加速器新的迭代锥形线束CT(iCBCT)成像模式的性能, 探讨其在临床应用中的优势。方法选用天津医科大学肿瘤医院放射治疗科Halcyon 2.0、Edge和VitalBeam型号加速器的千伏级CBCT成像系统, 其中Halcyon 2.0和Edge配备了iCBCT成像模式。使用Penta-Guide模体评价iCBCT成像模式的配准精度, 使用直尺测量治疗床的到位精度。应用CatPhan604模体分析各成像设备iCBCT和常规CBCT模式的图像质量。测量成像出束时间和重建时间, 评估图像采集效率。采用t检验对两种成像模式图像的均匀度、高对比度分辨率、对比度、对比度噪声比(CNR)、图像采集的出束时间和重建时间进行统计分析。结果 Halcyon 2.0和Edge加速器iCBCT模式图像配准测量结果与理论值最大偏差分别为0.7 mm和0.6 mm, 所有成像设备治疗床到位误差均<1 mm。头部扫描条件下, iCBCT图像主要提高了均匀度和CNR, Halcyon iCBCT较常规CBCT图像均匀度和CNR分别提高了2.50%(P<0.001)和78.85%(P&...     

间歇式屏气CBCT图像采集优选模式研究

目的 旨在建立一种实用型间歇式屏气CBCT图像采集优选模式。方法 利用自制呼吸运动模型模拟肿瘤患者膈肌附近肿块在屏气和自由呼吸状态下的运动情况并行CBCT扫描。扫描模式有常规屏气CBCT扫描(主要分为屏气间隙暂停扫描、进行自由呼吸、自由呼吸不计入扫描过程)及间歇式屏气CBCT扫描Ⅰ型和Ⅱ型(主要分为若干个屏气和自由呼吸时段,以近3∶1比例作间歇式调配并一次完成扫描),将常规屏气CBCT扫描作为标准技术,与2种间歇式屏气CBCT扫描就图像质量及使用该图像实现三维配准的精度进行量化比较分析。间歇式屏气CBCT图像质量参数与常规屏气CBCT图像行配对t检验。结果 2种间歇式屏气CBCT图像均产生运动伪影,其重建像素值与常规扫描相比较为一致(P>0.05),均匀性无明显改变(P=0.02、0.53),但图像信噪比分别减少30%和60%(P<0.05)。图像配准误差除上下方向最大为0.4 cm以外,其余均在0.1 cm以内。结论 在体模研究阶段,间歇式屏气CBCT扫描图像采集模式并未明显降低图像质量和配准精度,其实际临床的可行性还需在大量患者身上进一步得到验证。     

瓦里安新型锥形束迭代重建算法的图像质量分析

目的:定量分析头颈部的锥形束CT（cone-beam CT，CBCT）与新型迭代重建锥形束CT（iterative cone-beam CT，ICBCT）图像之间的质量差异。方法:利用Catphan604模体，客观地分析了瓦里安Halcyon加速器CBCT和ICBCT标准头部扫描模式下两种图像的高对比度分辨率、低对比度分辨率、均匀性、图像噪声及信噪比和对比度噪声比。针对临床患者数据，利用5位头颈部患者的CBCT、ICBCT分别计算了与成对参考CT图像之间的绝对误差（MAE）、均方根误差（RMSE）、峰值信号比（PSNR）、结构相似性（SSIM）。结果:两种图像的高对比度分辨率无明显差异，MTF50的值均为0.41 lp/mm；低对比度分辨率的感兴趣区域均不可见；相比于CBCT，ICBCT图像的整体均匀性更好（9.89 HU vs 9.21 HU）、图像噪声更小（7.29 HU vs 6.50 HU）、信噪比更高（38.69 vs 53.01）以及对比度噪声比更高（16.93 vs 25.98）。对于临床患者影像，ICBCT与CBCT相比，其MAE、RMSE更低，均值分别为(29.27±9.26)HU、(97.75±19.61)HU；PSNR、SSIM更大，均值分别为32.61±1.72、0.93±0.02，且四个指标之间均存在统计学差异（P<0.05）。结论:头颈部ICBCT图像的质量优于传统CBCT图像质量。     

兆伏级锥形束CT影像质量定量分析

目的 定量分析不同成像条件下兆伏级锥形束CT(MVCBCT)的影像质量,为临床应用提供参考.方法 采用西门子ONCOR直线加速器上的MVCBCT设备,在不同的成像条件下扫描影像质昔模体.通过分析影像均匀性、噪声、空间分辨率、对比度分辨率及成像剂量来评估其影像质量,并与常规大孔径CT影像进行定量比较.结果 MVCBCT影像噪声随加速器出束跳数(MU)增加而减少.均匀性指数与成像MU数及重建矩阵无线件关系.空间分辨率上采用256×256重建矩阵除5MU条件下为0.25 lp/mm,其他皆为0.4 lp/mm.随MU数增加对比度分辨率增加.成像剂量上头颈患者接受最大剂量为1.2 cGy/MU,中心位置剂量为0.8～0.9 cGy/MU,腹部最大和中心处分别为1.3cGy/MU和0.7 cGy/MU.结论 MVCBCT的噪声、均匀性、空间分辨率及对比度分辨率都差于常规扇形束CT.通过选择恰当成像参数和重建参数,可在患者接受尽量低成像剂量的同时获得足够分辨率来分辨骨组织、空腔及部分软组织用于影像引导放疗.     

瓦里安23EX加速器附加锥形束CT图像的CT值线性分析

目的 分析瓦里安23EX加速器附加千伏级X线锥形束CT (CBCT)在不同扫描条件下模体图像在不同位置处的CT值线性变化。方法 应用安装在直线加速器上的CBCT系统在标准头(体)部扫描条件下重复扫描不同位置Catphan504模体,将结果传至计划系统及Matlab 7.0,测量不同位置处不同密度插件的CT值线性情况。经与传统扇形束CT重建后图像CT值线性结果进行比较,了解CBCT图像CT值线性空间分布。结果 模体CBCT图像在标准头(体)部扫描条件下,在横断面、矢状面、冠状面及偏中心位置处CT值线性均有良好表现,其线性拟合因子R²值均>0.953。Bowtie滤过器虽然使得被测量物质的CT值不同,但并不改变CBCT图像CT值的线性。结论 瓦里安23EX加速器附加CBCT图像CT值线性良好,如对CT值做进一步校正,使CBCT图像用于治疗计划系统的剂量计算将成为可能。     

乳腺癌放疗中扇形束CT和锥形束CT图像引导放疗的比较研究

目的 比较乳腺癌保乳术后放疗过程中应用扇形束CT(fan beam CT,FBCT)和锥形束CT(cone beam CT,CBCT)图像引导放疗（image-guided radiation therapy,IGRT）方式的摆位误差、时间效率及患者满意度,探索临床更优图像引导方式。方法 按照治疗时间顺序顺位选取河南省人民医院2021年5月至2022年2月20例采用配备FBCT图像验证系统的联影加速器（FBCT组：左乳10例,右乳10例）和20例采用医科达加速器（CBCT组：左乳10例,右乳10例）行乳腺癌保乳术后调强放疗的患者。利用2种位置验证方式对患者进行图像引导,由2名主管技师共同配准后,记录配准误差及图像引导所需时间后进行治疗。回收分析两组患者的满意度调查问卷。结果 FBCT组（133次FBCT扫描）图像引导配准后,左右、头脚和腹背方向的摆位误差分别为（-0.065±0.265）mm、（-0.007±0.263）mm和（-0.119±0.266）mm,CBCT组左右、头脚和腹背方向的摆位误差分别为（-0.033±0.312）mm、（0.083±0.344）mm和（-0.183±...     

4DCT与MR图像形变配准确定原发性肝癌放疗靶区的应用研究

目的 研究应用形变配准技术联合4DCT和MR-T₂图像进行肝癌IGTV制定的可行性。方法 选择2015—2016年间首次放疗的原发性肝癌患者10例,依次完成自由呼吸下4DCT扫描,深吸气状态下MR-T₂像扫描,将4DCT依呼吸时相分为10个序列。应用MIM软件进行图像配准,评价指标为门静脉、腹腔干在三维方向的最大位移及肝脏交叠度。在各序列CT图像上勾画GTV,将4DCT各时相GTV融合为IGTV;将MR-T₂图像形变配准到4DCT各时相图像上,获得10个GTV_DR,并融合为IGTV_DR。配对t检验比较不同靶区体积差异。结果 门静脉和腹腔干在x、y、z轴向位移分别为(0.3±0.8)、(0.5±1.5)、(0.7±1.2) mm和(0.8±1.8)、(0.1±1.0)、(0.6±2.0) mm。肝脏交叠度为(115.4±13.8)%。形变配准后4DCT各时相GTV均大于配准前,平均增加8.18%(P<0.05),且各分时相形变后的GTV与MR-T₂图像中勾画体积基本一致。IGTV_DR显著大于形变配准前IGTV体积,平均增加了9.67%(P<0.05)。结论 MR图像能显示比CT更多的信息且表现出更高对比度。勾画GTV时应将MR图像与4DCT图像相结合,基于此获得的IGTV可更好地确定靶区范围和运动轨迹,提高肝癌靶区勾画精度。     

基于3DCT、4DCT和CBCT增强扫描测量正常食管壁厚度的研究

目的 比较3DCT、4DCT和CBCT增强扫描图像测量的正常食管壁厚度,为食管癌靶区的勾画提供参考。方法 对2009—2016年间50例肺癌或转移性肺癌患者行胸部增强3DCT、4DCT模拟定位扫描,并于首次3DCRT时进行增强CBCT扫描。分别在3DCT、4DCT呼气末时相(4DCT₅₀)、4DCT最大密度投影图像(4DCT_MIP)及CBCT图像上勾画正常食管,逐层测量各段食管壁厚度取平均值。对同段食管在不同CT图像上管壁厚度的比较行成组t检验,对不同段食管在同种CT图像上管壁厚度的比较行单因素方差分析。结果 3DCT与4DCT₅₀图像间胸段及腹段食管壁厚度差异无统计学意义(P=0.056~0.550);3DCT与4DCT_MIP、CBCT图像间胸段和腹段食管壁的厚度差异有统计学意义(P=0.000~0.004);4DCT_MIP与CBCT图像间胸上、中段食管壁厚度差异有统计学意义(P=0.008、0.001)。在3DCT、4DCT_MIP、4DCT₅₀图像上,胸下段食管壁均较胸上、中段厚(P=0.008~0.041),腹段食管壁较胸段厚(P均=0.000);在CBCT图像上,胸上、中、下段之间的差异均无统计学意义(P=0.088~0.945)。结论 在3DCT、4DCT₅₀图像上勾画胸段食管原发肿瘤GTV时正常食管壁厚度的判断可以使用同一标准,但在4DCT_MIP、CBCT图像上采用5 mm作为勾画GTV时正常食管壁厚度的判定标准尚需谨慎。     

Acquisition of MV-scatter-free kilovoltage CBCT images during RapidArc™ or VMAT

Purpose

To perform kilovoltage (kV) cone beam computed tomography (CBCT) imaging concomitant with the delivery of megavoltage (MV) RapidArc treatment, and demonstrate the feasibility of obtaining MV-scatter-free kV CBCT images.

Methods and materials

RapidArc/CBCT treatment and imaging plans are designed, and delivered on the Varian TrueBeam, using its Developer Mode. The plan contains 250 control points for MV-radiation delivery, each over an arc of 0.4-0.7^o. Interlaced between successive MV delivery control points are imaging control points, each over an arc of 0.7-1.1^o. During the 360^o gantry rotation for the RapidArc delivery, CBCT projections of a phantom are acquired at 11 frames per second. The kV projections with minimal MV-scatter are selected, based on gantry angle, and the CBCT_s image reconstructed. For comparison, a reference CBCT_r image is acquired in the normal way. In addition, to examine the effect of MV-scatter we acquire CBCT_c using the same treatment plan without the imaging control points, i.e. with continuous MV delivery during the 360^o rotation. Quantitative evaluation of image qualities is performed based on the concepts of CNR (contrast-to-noise ratio) and NSTD (normalized standard deviation).

Results

The different types of CBCT images were reconstructed, evaluated, and compared. Visual comparison indicates that the image quality of CBCT_s is similar to that of the reference CBCT_r, and that the quality of CBCT_c is significantly degraded by the MV-scatter. Quantitative evaluation of the image quality indicates that MV-scatter significantly decreases the CNR of CBCT (from ∼7 to ∼3.5 in one comparison). Similarly, MV-scatter significantly increases the inhomogeneity of image intensity, e.g. from ∼0.03 to ∼0.06 in one comparison.

Conclusion

We have developed a method to acquire MV-scatter-free kV CBCT images concomitant with the delivery of RapidArc treatment. Engineering development is necessary to improve the process, e.g. by synchronization of the MV and kV beams.     

Comparison of CBCT conversion methods for dose calculation in the head and neck region

The purpose of this study was to compare different methods of CBCT conversion respect to dose calculation accuracy. Twelve head and neck cancer patients treated with VMAT using simultaneous integrated boost technique were selected for the study. For each patient a planning CT (pCT), a control. CT acquired in the fourth week of treatment and a CBCT scan acquired on the closest day with the control CT were used. In order to re-calculate dose directly on CBCT image sets, a population based approach (CBCT_Pop) and a Histogram Matching (HM) approach based on rigid (CBCT_HM-R) and deformable registration (CBCT_HM-D) were used. Additionally, virtual CTs (vCTs) were generated using two deformable image registration algorithms (CT_ELX and CT_ANC) of the planning CT to the CBCT by using two different deformable image registration (DIR) algorithms. The corresponding control CTs were selected as ground truth and dose distributions on CBCT were analyzed using 3D global gamma index analysis applying a threshold of 10% with respect to the prescribed dose. Using the 2%/2 mm gamma criterion, the results were 89.9%(±8.3%), 94.1%(±5.0%), 94.3%(±5.7%), 96.1%(±3.9%), 93.4%(±6.3%) for the CBCT_Pop, CBCT_HM-R, CBCT_HM-D, CT_ELX and CT_ANC, respectively. On average, the HM and DIR techniques showed a higher accuracy compared to the population based approach, but Kruskal–Wallis test did not show significant difference among the investigated dose calculation techniques assuming p < 0.05. More sophisticated CBCT dose calculation methods seem to improve the dose calculation accuracy, but statistical significance remains to be demonstrated.     

Effect of compressed sensing reconstruction on target and organ delineation in cone-beam CT of head-and-neck and breast cancer patients

Background and purpose

Compressed sensing (CS) based cone-beam computed tomography (CBCT) reconstruction techniques have been shown to improve image quality. This study was to investigate possible improvements of CBCT_CS on manual delineation uncertainties of targets and organs-at-risk.

Patients and methods

Eight H&N and eight breast cancer patients were selected. Each H&N or breast cancer patient had planning-CT (pCT), repeat-CT (rCT), and CBCT reconstructed by both Feldkamp (CBCT_FDK) and compressed sensing methods. On each scan, targets and organs-at-risk were delineated by a radiation oncologist. The impact of reconstruction technique was quantitatively assessed by dice similarity coefficient (DSC) and the shortest perpendicular distance (SPD) between contours of two corresponding scans.

Results

The mean CBCT_CS-to-rCT DSC was 7.2% and 8.0% bigger than the CBCT_FDK-to-rCT for H&N and breast cancer patients respectively. The mean CBCT_CS-to-rCT SPD was 16.6% and 25.4% smaller than CBCT_FDK-to-rCT SPD. Due to anatomical changes, delineation accuracy reduced in reference to pCT, but no time trend was observed in CBCT based delineation accuracy in reference to rCT.

Conclusion

This study demonstrated that CBCT_CS has the potential to improve delineation accuracy in H&N and breast cancer patients over CBCT_FDK, and CBCT_CS thus has potential for adaptive radiotherapy.     

Analyzing the Possibility of Utilizing CBCT Radiomics as an Independent Modality: A Phantom Study

Aim:To verify if computed tomography (CT) radiomics were reproducible by cone beam CT (CBCT) radiomics by using Catphan^® 504. Materials and Methods:Catphan^® 504 was imaged using the default IGRT OBI CBCT imaging protocols and CT scanner. Seven known density image regions of the phantom were segmented and image feature was extracted by Imaging Biomarker Explorer (IBEX) software. The 49 selected features from four feature categories were analyzed by considering each region of interest (ROI) segment as individual image set. Correlation was studies using interclass correlation coefficient (ICC) and Pearson’s correlation coefficient. Results:The ICC of the three feature categories, namely intensity, GLCM, and GLRLM was significant (p-value<0.05) in comparison with CT, while the ICC of the fourth feature category, NID, was no significant. The average absolute Pearson’s correlation coefficient from the features of the images was as follows: CT: r=0.679±0.257, CBC_Thead: r=0.707±0.231, CBCT_thorax: r=0.643±0.260, and CBCT_pelvis: r=0.594±0.276. Conclusion: It seems that the various densities of Catphan^® 504 ROI image segments of the CT radiomics are reproducible with CBCT radiomics and CBCT radiomics can be used as an independent modality. Key Words: Texture, quantitative imaging features, cone-beam CT, computed tomography     

Quantitative evaluation of cone-beam computed tomography in target volume definition for offline image-guided radiation therapy of prostate cancer

Purpose

To quantitatively evaluate cone-beam CT (CBCT) in target volume definition in an offline image guidance environment.

Methods and materials

Fifteen patients each with five helical CTs (HCT) and eight CBCTs were included. A single physician manually delineated prostate and seminal vesicles (SVs) on each CT. The clinical target volume (CTV) was prostate for low risk group (G1), plus SVs for intermediate risk group (G2). The internal target volumes (ITVs) on CBCT (ITV_CBCT) were constructed and compared with ITV_HCT. The following comparisons were performed: CTV and ITV in HCT and CBCT; similarity of ITVs using overlap index (OI); surface differences between ITVs; quality assurance of ITV_CBCT using CTV from weekly CBCT; and dosimetric evaluations of ITV_HCT coverage on plans from ITV_CBCT.

Results

There was no statistical significant difference of CTV or ITV. The ITV OIs were 91%/88% for G1/G2 patients. They improved significantly with 1-2 mm margins. Therefore, the ITVs were mostly within 2 mm. The CTVs from weekly CBCT had >95% overlap with ITV_CBCT. The ITV dose differences (D₉₅, and D_mean) were <0.3%.

Conclusions

It is feasible to use CBCT for target definition in offline image guidance, thereby eliminating the separate helical CT scan process.     

千伏级锥形束CT影像进行放疗剂量计算的可行性研究

目的:研究千伏级锥形束CT（kilovoltage cone-beam CT,KVCBCT）影像进行放疗剂量计算的可行性及精确性。方法:用Elekta Synergy医用直线加速器及多层螺旋CT（德国Siomonos AG,SOMATOM Definition AS 40层）分别扫描CIRS-062电子密度模体,获取KVCBCT及扇形束CT（fan beam CT,FBCT）特定区域亨氏单位值（hounsfield unit,HU）,重新刻度亨氏单位值-相对电子密（HU-RED）表。选取我院行调强放疗的肿瘤患者80例（鼻咽癌、肺癌、胃癌及宫颈癌各20例）,将在FBCT影像上进行的三维适形调强放疗（intensity modulated radiation therapy,IMRT）计划在相对应的CBCT影像上以相同的条件再次进行剂量的计算,并将两种影像条件下的计算结果行配对t检验,比较其剂量分布有无明显差异。结果:在KVCBCT及FBCT两种影像条件下的放疗计划的比较中,鼻咽癌、胃癌、宫颈癌的95%PTV无明显差异,而在肺癌的计划中有着明显差异,在脊髓最大剂量(Dmax)、脑干Dmax、腮腺 V30、眼球Dmax、肺 V20、肺 V5、心脏 V30、肝脏平均剂量（Dmean）、直肠 V40、膀胱 V50、小肠Dmax的比较中无明显差异。结论:经过修订HU-RED表后,CBCT影像用于放疗计划的计算是可行的,但在胸部肿瘤即肺癌患者的放疗中还需要进一步研究找到更合适的方法去减少伪影的干扰。CBCT影像能较准确的反应出患者在治疗中的组织结构变化,并能根据变化实时的制定放疗计划,最终为实现自适应放疗（ART）提供准确的影像及剂量保证。     

HT系统兆伏级CT图像质量和剂量计算研究

目的 定量对HT系统兆伏级CT图像质量及剂量计算准确性进行评估。方法 应用兆伏级CT扫描Cheese phantom模体,分别对图像成像几何精度、噪声、图像均匀性、空间分辨率、密度-CT值的转化及剂量计算准确性进行测试,并与常规千伏级CT进行对比分析。结果 兆伏级CT图像的成像几何精度在三维方向均<2 mm,MVCT图像噪声、均匀性、空间分辨率都差于千伏级CT。基于CT图像进行剂量重建的DVH均与千伏级CT计划的DVH有很好一致性。结论 兆伏级CT图像几何尺寸精确,成像剂量低,剂量计算精确,满足于临床要求。