基于4D-CT测定的保乳术后全乳调强放疗靶区位移的相关性研究

目的 探讨基于4D-CT的乳腺癌保乳术后全乳靶区在自由呼吸状态下随呼吸运动位移变化及与术腔中选定银夹、乳头及体表金属标记位移的相关性。方法 13例保乳术后拟行全乳调强放疗的患者,在自由呼吸状态下行大孔径CT模拟定位并获4D-CT图像。在瓦里安Eclipse治疗计划系统中,由同一放疗医师在每例患者10个呼吸时相CT图像上分别行全乳靶区、乳头、最上层银夹、体中线体表标记勾画,获各中心点在三维方向上的位移,分析靶区位移及与银夹、乳头和体表标记相关性。分析各呼吸时相CT图像上肺体积变化及与靶区位移的相关性。结果 全乳靶区x、y、z轴最大位移分别为0.71、0.76、1.29 mm (F=5.755,P<0.05);全乳靶区中心点三维方向位移与靶体积及同侧肺体积变化均不存在相关性;吸气末2个连续时相与呼气末3个连续时相靶区x、y、z轴平均位移相似,全乳靶体积大小相似;在x、z轴上全乳靶区位移与乳头、体中线体表标记、最上层银夹位移均无相关性,在y轴上全乳靶区位移则与乳头、正中体表标记针、最上层银夹位移有相关性的比例分别为8/13、7/11、9/13,但群体性分析显示全乳靶区位移仅与最上层银夹有相关性(r=0.657,P<0.05)。结论 乳腺体积大小和肺体积改变对全乳靶区位移无明显影响;术腔中选定银夹可用以监测靶区活动度,其用以靶区位移测量和校正可靠性优于乳头及体中线处体表标记。     

基于锥形束CT的保乳术后调强放疗在线校正前后分次间位移规律分析

目的 基于锥形束CT（CBCT）探讨乳腺癌保乳术后调强放疗（IMRT）疗程中在线校正分次间位移变化规律。方法 选择保乳术后行全乳IMRT患者18例,共获取452次CBCT图像,获取CBCT校正前后分次间三维方向位移及摆位误差,分析分次间三维方向位移曲线。 结果 患者分次间位移幅度变化较大,同一患者不同方向的分次间位移幅度差异也较大。疗程中左右（LR）、前后（AP）和头脚（SI）方向分次间位移差异最大为0.22、0.49和0.48 cm,CBCT校正后LR、AP和SI方向位移差异最大为0.16、0.21和0.17 cm,CBCT在线校正降低了放疗疗程中患者SI方向的分次间位移（-0.08 cm 和0.03 cm,t=-2.373,P<0.05）和LR、AP、SI方向的随机误差（t=5.302、6.689、4.812,P<0.05）,系统误差差异无统计学意义。CBCT校正前后放疗疗程中患者分次间位移无明显规律性。结论 对于保乳术后IMRT患者,通过自动像素-解剖结构密度配准实施CBCT在线校正降低了放疗过程中患者头脚方向的分次间位移和三维方向的随机误差;由于个体差异性的存在,CBCT在线校正前后患者分次间三维方向位移离散度较大。     

Implagraphy牙颌面锥形束CT不同扫描体位的辐射剂量对比研究

目的 测算Implagraphy牙颌面锥形束CT(CBCT)体模不同扫描体位的组织器官吸收剂量、当量剂量及有效剂量,为相应的防护措施提供客观依据。方法 使用仿真成年男性头颈部体模及热释光剂量计,分别测量Implagraphy CBCT下颌、上颌及颞下颌关节(TMJ)扫描时脑垂体、眼晶状体、腮腺、颌下腺、舌下腺、颅骨板障、下颌松质骨、颈椎松质骨、颊部皮肤、颈部皮肤、甲状腺、食管及口腔黏膜等组织器官的吸收剂量,计算眼晶状体、皮肤的当量剂量,及Implagraphy CBCT不同扫描体位的有效剂量E₁₉₉₀及E₂₀₀₇。结果 Implagraphy CBCT各扫描体位的吸收剂量分别为:下颌扫描(0.99±0.09)~(12.85±0.09)mGy,上颌扫描(0.93±0.01)~(13.07±0.02)mGy,TMJ扫描(0.68±0.01)~(10.18±0.04)mGy,相同组织器官在不同扫描体位的吸收剂量的差异具有统计学意义(F=19.61~30992.27,P<0.05)。在不同扫描体位,眼晶状体及皮肤的当量剂量分别为(1.11±0.07)~(5.76±0.06)mSv和(6.96±0.06)~(10.64±0.07)mSv,差异具有统计学意义(F=4473.02、9385.50,P<0.05)。有效剂量E₁₉₉₀及E₂₀₀₇分别为:下颌扫描(191.35±1.53)和(325.17±2.58)μSv,上颌扫描(106.62±2.17)和(226.28±2.81)μSv,TMJ扫描(104.21±1.02)和(142.36±1.90)μSv。结论 在牙颌面CBCT检查过程中,采用尽可能小的扫描视野、准确地扫描体位,正确使用铅胶帽、围领及防护镜等屏蔽措施,使X射线辐射照射保持在可以合理达到的尽可能低的水平。     

乳腺癌保乳术后静态逆向调强与三维适形野中野放疗的剂量学比较

目的 比较早期乳腺癌保乳术后静态逆向调强(IMRT)与三维适形野中野瘤床同步加量(FIF)两种放疗技术的剂量学差异。方法 选择9例左侧早期乳腺癌保乳术后患者,分别设计IMRT与FIF两组放疗计划,处方剂量为乳房靶区50.4 Gy,分28次,每次1.8 Gy;瘤床靶区61.6 Gy,分28次,每次2.2 Gy。比较两组计划的靶区适形度及危及器官受量,并比较两者的计划优化和治疗时间。结果 IMRT的全乳靶区适形度(CI)为1.82±0.16,低于FIF的2.21±0.15(t=2.08,P<0.05);瘤床靶区适形度为1.19±0.04,低于FIF的1.59±0.11(t=3.97,P<0.05)。两组计划危及器官同侧肺的V₂₀和心脏的V₃₀无明显差异。FIF对侧肺的Dmax和Dmean分别是(5.41±2.76)和(0.51±0.10) Gy, IMRT分别为(25.72±2.61)和(7.46±0.39) Gy(t=-22.44、-21.14,P<0.05)。对侧乳房的Dmax和Dmean,FIF为(8.50±5.61)和(0.46±0.11) Gy,IMRT为(27.73±4.29)和(6.38±0.48) Gy(t=-5.66、-14.83,P<0.05)。对于对侧肺和乳房的低剂量照射区V₅,FIF为(0.09±0.09)%和(0.45±0.45)%,低于IMRT的(84.66±3.06)%和(60.79±4.94)%(t=-28.19、-12.80,P<0.05)。在计划优化及治疗时间方面,FIF与IMRT优化时间分别为(61.57±0.89)min和(241.28±1.06)min,单次治疗时间分别为(16.14±1.42)min和(29.85±0.59) min(t=-32.35、-8.82,P<0.05)。结论 IMRT改善了靶区适形度,但是增加了对侧肺和对侧乳房的受照剂量。FIF在计划优化时间及治疗时间方面有优势。     

榄香烯乳对人肺腺癌A549细胞放射敏感性影响及其机制的研究

目的 探讨榄香烯乳对人肺腺癌A549细胞放射敏感性的影响及其分子机制。方法 克隆形成实验检测10、20 μg/ml榄香烯乳对人肺腺癌A549细胞的放射敏感性影响。细胞分为空白对照组、单纯照射组(4 Gy X射线照射)、单纯药物组(给予10、20 μg/ml榄香烯乳);联合照射组(给予10、20 μg/ml 榄香烯乳24 h后4 Gy X射线照射)。Western blot检测DNA-PKcs、Bcl-2及P53蛋白的表达变化,并分析DNA-PKcs与Bcl-2、P53表达之间的相关性。结果 10 μg/ml榄香烯乳的放射增敏比SER_D0、SER_Dq 为1.54±0.20和1.43±0.15;20 μg/ml榄香烯乳SER_D0、SER_Dq 为1.63±0.32及1.75±0.19。与单纯照射组相比,10、20 μg/ml榄香烯乳联合照射组细胞的DNA-PKcs蛋白表达明显减少(t=7.52、8.33, P<0.05),Bcl-2蛋白表达明显减少(t=10.74、11.33, P<0.05),P53蛋白表达明显增加(t=-9.25、-7.66P<0.05)。DNA-PKcs与P53蛋白表达显著负相关(r=-0.569,P<0.05),与 Bcl-2蛋白表达显著正相关(r=0.755, P<0.05)。结论 榄香烯乳可增加人肺腺癌A549细胞的放射敏感性,其机制与下调DNA-PKcs表达抑制DNA双链损伤修复和上调p53,下调Bcl-2表达促进细胞凋亡有关。     

乳腺癌保乳术后自主呼吸控制全乳腺调强放疗靶区勾画与靶区位移

目的 探讨自主呼吸控制(ABC)辅助适度深吸气呼吸控制(mDIBH)状态下勾画者和勾画时间对乳腺癌保乳术后全乳靶区的影响及放疗分次内和放疗分次间全乳靶区的位移。方法 20例保乳术后拟行全乳调强放疗患者,ABC辅助CT模拟定位获得3个呼吸状态的5套CT图像[自由呼吸(FB)1套、适度深吸气呼吸控制(mDIBH) 2套、深呼气呼吸控制(DEBH)2套]。放疗10~15次再获5套CT图像。5位放疗医师和同一放疗医师不同时间分别在初次定位获得的第1套mDIBH图像上勾画全乳靶区,比较勾画者和勾画时间对全乳靶区影响。分别标记初次定位2套mDIBH图像上术腔中全部银夹,比较全部银夹所构成几何体在分次内位移。分别勾画初次定位2套和重复定位第1套mDIBH图像上近乳腺靶区等中心平面的2条肋骨,通过比较所勾画肋骨感兴趣点(POI)空间位置位移,获得分次内和分次间胸廓扩张差异。结果 同一医师不同时间勾画4次分别所得全乳靶区体积间差异无统计学意义,5位医师分别勾画全乳靶区体积差异有统计学意义(F=19.681,P=0.000);同一mDIBH状态下,分次内全部银夹所构成几何体POI各方向位移差异无统计学意义,分次内肋骨POI各方向位移差异无统计学意义;同一mDIBH状态下,分次间肋骨POI各方向位移差异无统计学意义。结论 不同勾画者所勾画全乳靶区差异是明显的。ABC辅助mDIBH状态下分次内及分次间全乳靶区位移在各个方向上的差异不明显。     

快速旋转调强与五野动态调强在乳腺癌 保乳术后放疗中的剂量学比较

目的 比较乳腺癌保乳术后RapidArc计划与五野动态调强(5F-IMRT)计划的剂量学差异。方法 选择8例左侧乳腺癌保乳术后女性患者,处方剂量为50 Gy/ 25次。分别设计RapidArc计划与5F-IMRT计划。比较两种计划的靶区适形度指数、均匀性指数、靶区覆盖度和危及器官的受照剂量体积,同时比较两组计划实施时的治疗时间和机器跳数。结果 在两种计划的靶区比较中,RapidArc计划的靶区适形度指数为(0.88±0.03),高于5F-IMRT计划的(0.79±0.02)(t=8.28,P<0.05);RapidArc计划的均匀性指数为(9.01±0.73),优于5F-IMRT计划的(10.44±1.08)(t=-2.73,P<0.05)。两组计划在同侧肺受照剂量体积比较中RapidArc计划的D_mean、V₁₀、V₂₀、V₃₀小于5F-IMRT计划(t=-7.53、-7.20、-8.39、-7.80,P<0.05),但RapidArc计划中的V₅较5F-IMRT计划增加了约16% (t=5.67,P<0.05);心脏的受照剂量体积比较中RapidArc计划中的D_mean、V₅、V₁₀均高于5F-IMRT(t=10.46、28.76、5.40,P<0.05),但在RapidArc计划中心脏的V₃₀低于5F-IMRT (t=-6.12,P<0.05)。对侧肺和对侧乳腺的V₅在RapidArc计划中明显高于5F-IMRT计划 (肺:t=21.50,P<0.05;乳腺:t=5.44,P<0.05)。RapidArc计划中机器跳数减少了25%,平均治疗时间节省了60%。结论 乳腺癌保乳术后RapidArc计划与5F-IMRT计划比较提高了靶区的适形度和均匀度,减少了高剂量区的受照体积,降低了机器跳数,缩短了治疗时间,但增加了正常组织低剂量区的受照体积。     

CT和锥形束CT配准范围与精度关系研究

目的 研究锥形束CT（CBCT）图像和CT图像的配准范围对配准精度的影响。方法 对腹部、头部和胸部各5位患者分别进行CBCT和CT扫描,将扫描后各部位图像的配准范围处理成4种模式,模式1为CT配准范围大于CBCT配准范围;模式2为CBCT与CT配准范围相同;模式3是将模式2的CT平移5 cm;模式4是将模式2的CBCT和CT两边同时减少2 cm。4种模式均使用图像分割与配准工具包进行配准,比较4种模式配准后的平均方差测度值,并分析模式2与其他3种模式的关系。结果 平均方差测度值模式3最大,其次是模式1,最小的是模式2和4,且模式2和4的平均方差测度值几乎相等（P>0.05）。对于各部位的模式2与模式1比较,差异有统计学意义（t=-4.586、-4.164、-5.618,P<0.05）;模式2与模式3比较,差异有统计学意义（t=-6.423、-8.109、-19.601,P<0.05）。结论 CBCT和CT图像的配准范围对图像配准精度有一定的影响,CBCT的配准范围与CT的配准范围越接近,配准精度越高。     

双源CT低管电压冠状动脉成像的应用及心率对图像质量和辐射剂量的影响

目的 探讨双源CT低管电压冠状动脉成像技术的应用价值及不同心率对图像质量和辐射剂量的影响。方法 对323例临床怀疑冠心病患者进行双源CT低管电压(100 kVp)和常规管电压回顾性心电门控冠状动脉成像增强扫描,检查前不使用β受体阻滞剂控制心率。按患者扫描时的平均心率对低管电压组201例进行分组,≤59 次/min为A组(50例),60~69次/min为B组(64例),70~91次/min为C组(62例),≥91次/min为D组(25例)。对照组(管电压120 kVp)为E组(122例)。评价各组的最佳重建时相图像,记录各组的增强扫描序列的螺距、CT容积剂量指数(CTDI_vol)、剂量长度乘积(DLP)及有效剂量(E)值,比较各组患者的扫描螺距、图像质量评分和辐射剂量值等,分析心率对图像质量和辐射剂量的影响。结果 A~D 4组螺距分别为(0.24±0.03)、(0.29±0.04)、(0.33±0.05)、(0.38±0.06),差异有统计学意义(F=62.57,P<0.05);A~E 5组CTDI_vol值分别为(21.59±7.97)、(20.24±6.03)、(18.23±7.55)、(18.14±5.75)、(38.62±16.21)mGy(F=85.16, P<0.05);E值分别为(5.31±2.18)、(4.85±1.70)、(4.49±1.86)、(4.37±1.50)、(8.75±4.07)mSv(F=44.83, P<0.05);图像评分分别为(4.65±0.46)、(4.55±0.53)、(4.55±0.53)、(4.47±0.72)、(4.66±0.44)分(F=1.89,P>0.05)。结论 双源CT低管电压(100 kVp)技术冠状动脉成像在不控制心率情况下可获得较好的图像质量;在自动心电门控剂量窗时,中低心率对辐射剂量的影响较小,高心率可使有效辐射剂量降低,但获得优质图像质量的可能性减小。     

基于VoxelMorph无监督缺失图像配准的无标记射束方向观肿瘤跟踪算法

目的 基于机器学习提出可应用于低图像质量、多叶准直器(MLC)遮挡和非刚性变形兆伏级(MV)图像的无标记射束方向观(BEV)肿瘤放疗跟踪算法。方法 采用窗口模板匹配法和Voxelmorph端到端无监督网络,处理MV图像中的配准问题。使用动态胸部模体,验证肿瘤跟踪算法的准确性。将模体质量保证(QA)计划在加速器上手动设置治疗偏移后执行,收集治疗过程中的682幅电子射野影像系统(EPID)图像作为固定图像;同时采集计划系统中对应射野角度的数字影像重建(DRR)图作为浮动图像,进行靶区跟踪研究。收集21例肺部肿瘤放疗的533对EPID和DRR图像进行肿瘤跟踪研究,提供治疗过程中肿瘤位置变化定量结果。图像相似度用于算法的第三方验证。结果 算法可应对不同程度(10%~80%)的图像缺失,且对数据缺失图像的非刚性配准表现较好。模体验证中86.8%的跟踪误差<3 mm,<2 mm的比例约80%作用。配准后标准化互信息(NMI)由1.18±0.02提高到1.20±0.02(t=-6.78,P=0.001)。临床病例肿瘤运动以平移为主,平均位移3.78 mm,最大位移可达7.46 mm。配准结果显示存在非刚性形变,配准后NMI由1.21±0.03增至到1.22±0.03(t=-2.91,P=0.001)。结论 肿瘤跟踪算法跟踪精度可靠且鲁棒性好,可用于无创、实时、无额外设备和辐射剂量的肿瘤跟踪。     

Clinical implementation of kilovoltage cone beam CT for the verification of sequential and integrated photon boost treatments for breast cancer patients

Objective

The objective of this study was to formulate a practical method for the use of cone beam CT (CBCT) for the verification of sequential and integrated tumour bed boosts for early breast cancer patients.

Methods

Partial arc scan geometries were assessed on a treatment unit. Imaging dose measurements on an Elekta Synergy CBCT system were made in a CT dose phantom for scan parameters 100 kV, 25 mA and 40 ms with an S20 collimator. The protocol was used to verify the setup of a cohort of 38 patients, all of whom had surgical clips inserted in the tumour bed. Setup errors with and without an extended no action level (eNAL) protocol were calculated.

Results

Arcs from 260° to 85° (left breast) and 185° to 15° (right breast) were found sufficient to image fiducial markers and anatomy whilst accounting for the physical limits of the equipment. A single treatment and imaging isocentre was found by applying simple constraints: isocentre <8 cm from midline and isocentre–couch distance <30 cm. Contralateral breast doses were ∼2 mGy per scan (right breast) and ∼12 mGy (left breast). Both mean population systematic error and mean population random error were 3 mm prior to correction. The systematic error reduced to 1.5 mm using an eNAL correction protocol, implying that a 5-mm setup margin could be achieved.

Conclusion

An image-guided verification protocol using CBCT for breast cancer boost plans was implemented successfully. Setup errors were reduced with an acceptable imaging dose to the contralateral breast.There is much interest in more sophisticated radiotherapy techniques for early breast cancer treatments, particularly for patient cohorts that can be identified as at a high risk of recurrence, where a simultaneous integrated boost technique may be used to increase the dose to the tumour bed [1]. One example of a prospective randomised trial testing this approach is the UK Intensity Modulated and Partial Organ Radiotherapy (IMPORT) High trial, which was given approval by the Cambridgeshire 4 Research Ethics committee on 30 April 2008 [2]. This trial is designed to test dose-escalated intensity-modulated radiotherapy after conservation surgery for early breast cancer in women with higher-than-average local recurrence risk, with a primary end point of palpable induration of the ipsilateral breast. The trial required a sequential conformal photon boost for the control arm, and an integrated boost in the two trial arms. The planning target volume (PTV) margin for the tumour bed boost was 5 mm, so effective verification protocols were necessary, using more complex imaging methods than standard tangential beam treatment portals (with a typical whole-breast PTV margin of 10 mm). The use of fiducial markers (either surgical clips or gold seeds) to mark the tumour bed was mandatory in order to facilitate the complex planning and for verification imaging. Participating centres were required to provide a clearly defined imaging strategy, which was sufficient to reduce setup error so that a 5-mm tumour bed PTV margin could be achieved. A range of image-guided methods were permitted: orthogonal planar imaging (both MV and kV), and volumetric imaging via kV cone beam CT (CBCT) and MV systems (for example, on a TomoTherapy unit; TomoTherapy Inc., Madison, WI). This work reports a practical method of image-guided radiation therapy (IGRT) using a kV cone beam CT system for sequential, and integrated, photon breast boosts.     

Characterization and registration of 3D ultrasound for use in permanent breast seed implant brachytherapy treatment planning

PurposePermanent breast seed implant (PBSI) brachytherapy is a novel technique for early-stage breast cancer. Computed tomography (CT) images are used for treatment planning and freehand 2D ultrasound for implant guidance. The multimodality imaging approach leads to discrepancies in target identification. To address this, a prototype 3D ultrasound (3DUS) system was recently developed for PBSI. In this study, we characterize the 3DUS system performance, establish QA baselines, and develop and test a method to register 3DUS images to CT images for PBSI planning.Methods and Materials3DUS system performance was characterized by testing distance and volume measurement accuracy, and needle template alignment accuracy. 3DUS-CT registration was achieved through point-based registration using a 3D-printed model designed and constructed to provide visible landmarks on both images and tested on an in-house made gel breast phantom.ResultsThe 3DUS system mean distance measurement accuracy was within 1% in axial, lateral, and elevational directions. A volumetric error of 3% was observed. The mean needle template alignment error was 1.0° ± 0.3 ° and 1.3 ± 0.5 mm. The mean 3DUS-CT registration error was within 3 mm when imaging at the breast centre or across all breast quadrants.ConclusionsThis study provided baseline data to characterize the performance of a prototype 3DUS system for PBSI planning and developed and tested a method to obtain accurate 3DUS-CT image registration for PBSI planning. Future work will focus on system validation and characterization in a clinical context as well as the assessment of impact on treatment plans.     

Displacement of the lumpectomy cavity defined by surgical clips and seroma based on 4D-CT scan for external-beam partial breast irradiation after breast-conserving surgery: a comparative study

Objective:

To compare the displacements of the lumpectomy cavity delineated by the surgical clips and the seroma based on four-dimensional CT (4D-CT) for external-beam partial breast irradiation (EB-PBI) after breast-conserving surgery (BCS).

Methods:

14 breast cancer patients after BCS were recruited for EB-PBI and undertook 4D-CT simulation. On the 10 sets of the 4D-CT images, all the surgical clips in the cavity were delineated. The gross tumour volume (GTV) formed by the clips, the seroma, and both the clips and the seroma were defined as GTV_c, GTV_s and GTV_c+s, respectively. The displacements of the centre of mass (COM) of the clips, GTV_c, GTV_s, GTV_c+s and the selected clips in the three-dimensional (3D) directions were recorded and compared.

Results:

In the left–right, anterior–posterior and superior–inferior directions, the displacements were 2.20, 1.80 and 2.70 mm for the clip COM; 0.90, 1.05 and 1.20 mm for GTV_c; 0.80, 1.05 and 0.80 mm for GTV_s; and 0.90, 1.20 and 1.40 mm for GTV_c+s, respectively. In the 3D directions, the displacements of the clip COM were greater than the GTV_c, GTV_s, GTV_c+s, and the displacements of the clip COM, GTV_c+s, GTV_c and GTV_s were significantly greater than the displacements of the selected clips (p<0.05).

Conclusion:

The displacements of the clip COM were greater than that of the GTV_c, GTV_s, GTV_c+s and the four selected clips. The optimal internal target volume should be defined based on the boundary displacements.

Advances in knowledge:

When the GTV was delineated using the clips and/or the seroma, there was displacement difference between the lumpectomy cavity centre and the boundary for the EB-PBI. The optimal internal target volume should be defined based on the boundary displacements of the lumpectomy cavity.Previous studies have reported that approximately 70–80% of the in-breast tumour recurrences occurred in the vicinity of the tumour bed (TB) and that the absolute risk of ipsilateral breast recurrence away from the primary tumour site is approximately 1.5–3.5% [1–4]. Thus, for early-stage breast cancer patients after breast-conserving surgery (BCS), partial breast irradiation (PBI), treating only the lumpectomy cavity with a suitable margin, may achieve a similar local control rate and an overall survival rate to whole-breast irradiation treating the whole breast. External-beam partial breast irradiation (EB-PBI) is an important approach in PBI, and clinical research has demonstrated that EB-PBI can achieve excellent results after strict patient selection and accurate target volume delineation [5,6].Accurate delineation of the TB is essential for EB-PBI [7]. Surgical clips and seroma were important surrogates in location and displacement measurement of the TB [8–10]. The optimal number of surgical clips, seroma clarity score (SCS), the delineation experience and contouring guidelines were important factors for TB delineation on CT images [10–14]. The target volume was typically defined using surgical clips, the seroma and any post-operative tissue changes when available [9]. The respiratory-induced displacements and set-up error were important components in EB-PBI planning, and the residual error was not >5 mm after online error correction based on cone-beam CT [15]. Therefore, respiratory-induced TB motion is the major component of the planning target volume for EB-PBI [8]. Four-dimensional CT (4D-CT) simulation has enabled CT data acquisition to be correlated with the respiratory cycle. Therefore, 4D-CT was pervasively used in delineating the target volume and forming the internal target volume (ITV) for EB-PBI [16,17].Although the displacements of the target volume delineated based on clips and seroma have been obtained using 4D-CT in prior studies [16,17], the displacement differences among target volumes have not been fully illustrated. In order to investigate the displacement differences among the target volumes delineated based on clips and/or seroma, we measured and compared the three-dimensional (3D) displacements among three target volumes, the centre of mass (COM) of all the surgical clips and four selected boundary clips during free-breathing (FB).     

Decrease of the lumpectomy cavity volume after whole-breast irradiation affects small field boost planning

To determine whether small field boost (SFB) replanning is necessary when the lumpectomy cavity (LPC) decreases during whole-breast irradiation (WBI) and what parameters might predict a change in the SFB plan. Forty patients had computed tomography (CT) simulation (CT1) within 60 days of surgery and were resimulated (CT2) after 37.8–41.4 Gy for SFB planning. A 3-field photon plan and a single en face electron plan were created on both CTs and compared. In the 26 patients who had a ≥5 cm³ and a ≥25% decrease in lumpectomy cavity volume (LCV) between CT scans, the SFB plan using photons was different in terms of normal breast tissue volume irradiated (BTV) (p < 0.001), and field dimensions (p < 0.001). In 20/35 patients, the energy or field size changed for electron plans on CT2, but no tested characteristics predicted for a change. Less BTV was irradiated using electrons than photons in 29% (CT1) to 37% (CT2). SFB replanning needs to be individualized to each patient because of the variety of factors that can impact dosimetric planning. Replanning is recommended when using 3-field photons if the patient has experienced a ≥5 cm³ and a ≥25% decrease in LCV during WBI. Some patients may benefit from electron SFB replanning but no tested characteristics reliably predict those who may benefit the most. The amount of BTV irradiated is less with electrons than in photon plans and this has the potential to improve cosmesis, a clinically important outcome in breast-conserving therapy.     

Evaluation of Elekta 4D cone beam CT-based automatic image registration for radiation treatment of lung cancer

Objective:

The study was aimed to evaluate the precision of Elekta four-dimensional (4D) cone beam CT (CBCT)-based automatic dual-image registrations using different landmarks for clipbox for radiation treatment of lung cancer.

Methods:

30 4D CBCT scans from 15 patients were studied. 4D CBCT images were registered with reference CT images using dual-image registration: a clipbox registration and a mask registration. The image registrations performed in clinic using a physician-defined clipbox, were reviewed by physicians, and were taken as the standard. Studies were conducted to evaluate the automatic dual registrations using three kinds of landmarks for clipbox: spine, spine plus internal target volume (ITV) and lung (including as much of the lung as possible). Translational table shifts calculated from the automatic registrations were compared with those of the standard.

Results:

The mean of the table shift differences in the lateral direction were 0.03, 0.03 and 0.03 cm, for clipboxes based on spine, spine plus ITV and lung, respectively. The mean of the shift differences in the longitudinal direction were 0.08, 0.08 and 0.08 cm, respectively. The mean of the shift differences in the vertical direction were 0.03, 0.03 and 0.03 cm, respectively.

Conclusion:

The automatic registrations using three different landmarks for clipbox showed similar results. One can use any of the three landmarks in 4D CBCT dual-image registration.

Advance in knowledge:

The study provides knowledge and recommendations for application of Elekta 4D CBCT image registration in radiation therapy of lung cancer.     

Accelerated partial breast irradiation: a dosimetric comparison of three different techniques

PURPOSE: We report the first single-institutional dosimetric comparison of patients treated with three forms of accelerated partial breast irradiation: interstitial HDR brachytherapy, the MammoSite balloon apparatus, and 3D conformal external beam quadrant irradiation (3D-CRT). METHODS: A retrospective dosimetric comparison of interstitial HDR brachytherapy, MammoSite balloon brachytherapy, and 3D-CRT was performed. Thirty patients including 10 from each treatment technique were included for a dosimetric comparison of the dose received by the ipsilateral breast, PTV, heart, and ipsilateral lung. Interstitial patients were treated with 4 Gy in 8 fractions to 32 Gy, and the MammoSite patients were treated with 3.4 Gy in 10 fractions to 34 Gy. 3D-CRT patients were treated with 3.85 Gy in 10 fractions to 38.5 Gy using multiple isocentric beams. The CT images from simulation or implant evaluation were transferred into our 3D treatment planning software. The lumpectomy cavities were outlined for every patient, except the MammoSite patients, where the cavity was defined by the balloon edge. The PTV was constructed as a uniform expansion of 1.5 cm for all interstitial HDR patients, 1.0 cm for the MammoSite patients, and a 1.0 cm expansion in addition to the CTV expansion of 1.0 cm (n=2), and 1.5 cm (n=8) for the 3D-CRT patients. The CTV expansion for 3D-CRT and the PTV expansion for the brachytherapy patients were limited to the chest wall and skin. Normal structures including both ipsilateral lung and breast and heart for left-sided lesions were outlined. The lumpectomy cavity was subtracted from the PTV and normal breast tissue for evaluation. To evaluate dose to the ipsilateral breast and lung, PTV, and heart, a dose-volume histogram (DVH) analysis was performed. All histograms were normalized to the volume of the structure (i.e., expressed as percent volume). RESULTS: The average percentage of the breast receiving 100% and 50% of the prescribed dose (PD) was higher in the 3D-CRT group (24% and 48%, respectively) compared with the MammoSite (5% and 18%, respectively) and interstitial patients (10% and 26%, respectively). Improved coverage of the PTV was noted in the 3D-CRT plans compared with the MammoSite and interstitial HDR plans. With the interstitial HDR technique, 58% of the PTV received 100% of the PD compared with 76% with MammoSite and 100% with 3D-CRT techniques. The percentage of the PTV receiving 90% of the PD was 68%, 91%, and 100% for the interstitial HDR, MammoSite, and 3D-CRT patients, respectively. The ipsilateral lung V20 was slightly higher for 3D-CRT at 5% compared with 0% for both brachytherapy techniques. CONCLUSION: In those treated with 3D-CRT, coverage of the PTV was better with 3D-CRT but varied with the definition used. At the coverage at 90% of the PD, no difference was observed between 3D-CRT and MammoSite (which were both better than interstitial). 3D-CRT resulted in better coverage of the PTV compared with MammoSite or interstitial brachytherapy techniques. Better PTV coverage with 3D-CRT came at the cost of a higher integral dose to the remaining normal breast. Dosimetrically, the best partial breast irradiation technique appears to depend on the clinical situation. Of the brachytherapy techniques, MammoSite appears to be superior in PTV coverage. When comparing MammoSite vs. 3D-CRT PTV coverage at 90% of the PD, the difference was not significantly different.     

Interobserver variability of patient positioning using four different CT datasets for image registration in lung stereotactic body radiotherapy

Purpose

To assess the impact of different reference CT datasets on manual image registration with free-breathing three-dimensional (3D) cone beam CTs (FB-CBCT) for patient positioning by several observers.

Methods

For 48 patients with lung lesions, manual image registration with FB-CBCTs was performed by four observers. A slow planning CT (PCT), average intensity projection (AIP), maximum intensity projection (MIP), and midventilation CT (MidV) were used as reference images. Couch shift differences between the four reference CT datasets for each observer as well as shift differences between the observers for the same reference CT dataset were determined. Statistical analyses were performed and correlations between the registration differences and the 3D tumor motion and the CBCT score were calculated.

Results

The mean 3D shift difference between different reference CT datasets was the smallest for AIPvsMIP (range 1.1–2.2?mm) and the largest for MidVvsPCT (2.8–3.5?mm) with differences >10?mm. The 3D shifts showed partially significant correlations to 3D tumor motion and CBCT score. The interobserver comparison for the same reference CTs resulted in the smallest ?3D mean differences and mean ?3D standard deviation for ?AIP (1.5 ± 0.7?mm, 0.7 ± 0.4?mm). The maximal 3D shift difference between observers was 10.4?mm (?MidV). Both 3D tumor motion and mean CBCT score correlated with the shift differences (R_s = 0.336–0.740).

Conclusion

The applied reference CT dataset impacts image registration and causes interobserver variabilities. The 3D tumor motion and CBCT quality affect shift differences. The smallest differences were found for AIP which might be the most appropriate CT dataset for image registration with FB-CBCT.

     

Respiratory Motional Effect on Cone-Beam CT in Lung Radiation Surgery

The cone-beam CT (CBCT), which is acquired using an on-board imager (OBI) attached to a linear accelerator, is used effectively in the verification of setup accuracy for lung radiation surgery. In this study, the respiratory organ motional effect on the CBCT was evaluated with a properly devised phantom system, and the level of possible error in conditions of a real clinical process was assessed. In a comparison study between the CBCT in static status and CBCT images acquired in 20 different motional cases, we confirmed that the image quality and information of CBCT were degraded, with an increase of motional ranges in the region of inhomogeneous structures. The 4D-CT MIP (50～55%) for the planning of lung radiation surgery and the 4D-CT MIP (full phase) were compared with CBCT in the various motional cases for the evaluation of the influence of the motional effect on CBCT in the process of the setup error correction. The average ratio of relative difference between plan CT: 4D-CT MIP (50%～55%) and CBCT was 5.79% and between plan CT: 4D-CT MIP (50%～55%) and 4D-CT MIP (full phase) was 42.95% in the phantom study. In the analysis of clinical cases of lung radiation surgery, the gross tumor volumes were compared in each CT image. The average ratio of relative difference between plan CT: 4D-CT MIP (50～55%) and CBCT was 10.72% and between plan CT: 4D-CT MIP (50～55%) and 4D-CT MIP (full phase) was 28.19%. These results showed that, although a respiratory organ motional effect on CBCT introduced variation in image quality, the error as a result of this variation could be estimated relatively low in the setup error correction for a gated-lung radiation surgery when the planning was performed in 4D-CT MIP (50～55%), which already included a related signal of motional effect.     

Preoperative computed tomography-guided percutaneous hookwire localization of metallic marker clips in the breast with a radial approach: initial experience

Background: Hookwire localization is the current standard technique for radiological marking of nonpalpable breast lesions. Stereotactic directional vacuum-assisted breast biopsy (SVAB) is of sufficient sensitivity and specificity to replace surgical biopsy. Wire localization for metallic marker clips placed after SVAB is needed.

Purpose: To describe a method for performing computed tomography (CT)-guided hookwire localization using a radial approach for metallic marker clips placed percutaneously after SVAB.

Material and Methods: Nineteen women scheduled for SVAB with marker-clip placement, CT-guided wire localization of marker clips, and, eventually, surgical excision were prospectively entered into the study. CT-guided wire localization was performed with a radial approach, followed by placement of a localizing marker-clip surgical excision. Feasibility and reliability of the procedure and the incidence of complications were examined.

Results: CT-guided wire localization surgical excision was successfully performed in all 19 women without any complications. The mean total procedure time was 15 min. The median distance on CT image from marker clip to hookwire was 2 mm (range 0-3 mm).

Conclusion: CT-guided preoperative hookwire localization with a radial approach for marker clips after SVAB is technically feasible.