WS531-2017《螺旋断层治疗装置质量控制检测规范》的实施及 评价

目的:依据WS531- 2017《螺旋断层治疗装置质量控制检测规范》,对浙江省首台螺旋断层治疗系统 （Tomotherapy,TOMO）进行年度系统稳定性检测,进一步规范质量控制操作,明确系统的各项性能,保证临床放射治疗的 准确实施。方法:利用8 通道计量仪（TomoElectrometer）、电离室A1SL（Standing Imaging, USA）和A17（Standing Imaging, USA）、圆柱形模体（Cheese Phantom）、等效矩形固体水、二维水箱、EBT3胶片和Vidar胶片分析仪,按照WS531- 2017要求,对TOMO的10个关键指标进行检测。结果:设备静态输出剂量偏差为-0.6%;旋转输出剂量偏差为1.4％。射 线质与计划值偏差为0.8%。射野横向剂量曲线的对称性为-1.2%。射野纵向剂量曲线半高宽偏差为0.7 mm。多叶准直 器横向偏移为-0.6 mm。绿激光灯在虚拟等中心横断面偏移为0.08 mm、矢状面和冠状面的偏移为0.2 mm;红激光灯指示 偏差-0.4 mm。治疗床的移动偏差为0.3 mm。治疗床和机架旋转同步性偏差为-0.6 mm。结论:TOMO的10项关键指标 均满足WS531-2017的评价标准,建议TOMO年检时适当增加必要检测项目,如MVCT图像质量检测等, 以确保系统的正 常工作及良好的稳定性。     

应用两种三维探测器阵列进行螺旋断层调强放疗计划剂量验证

目的:研究分别采用Delta4和Arc Check三维探测器阵列对螺旋断层放疗系统(TOMO)的调强计划实施剂量验证的异同。方法:分别采用Scandi Dos公司Delta4三维半导体探测器阵列和Sun Nuclear公司Arc Check三维半导体探测器阵列对10例患者的TOMO调强放疗计划实施验证。通过TOMO系统MVCT成像和配准消除床面沉降的影响,确保实现两种三维探测器阵列的精确摆位。实施治疗质量保证(Delivery Quality Assurance,DQA)计划照射后将探测器阵列测量获得的平面剂量分布与TOMO计划系统模体计划计算获得的平面剂量分布进行比较。采用Gamma分析方法,选择多个不同的剂量标准分析评估验证情况。结果:阈值水平(Threshold,TH)分别为5%、10%、20%、70%、90%时,采用3%/2 mm、3%/3 mm、3%/4 mm、3%/5 mm四种不同剂量偏差/吻合距离剂量标准,γ≤1的平均通过率均超过94.1%,测量所得剂量分布与计算结果在相应平面的几何分布均呈现出良好的一致性。结论:两种三维探测器阵列各具特点,用于TOMO调强放疗计划验证能够获得令人满意的结果 。     

应用一维、二维、三维探测器阵列进行螺旋断层调强放疗计划剂量验证

目的：比较Tomotherapy标配Cheese模体联合EBT3免冲洗胶片（一维探测器阵列）、Octavius八角模体配合PTW Seven29二维探测器阵列（二维探测器阵列）、Delta4三维探测器阵列用于螺旋断层放疗系统（Tomo Therapy,TOMO）的调强计划实施剂量验证的差异。方法：分别采用一维、二维、三维探测器对10例患者TOMO的调强计划实施验证。通过TOMO系统MVCT成像和配准消除床面沉降的影响,确保实现体模和探测器阵列的精确摆位。实施治疗质量保证（Delivery Quality Assurance,DQA）计划照射后将测量获得的平面剂量分布与TOMO计划系统模体计划计算获得的平面剂量分布进行比较。采用Gamma分析方法,选择多个不同的剂量标准分析评估验证情况。结果：采用3%/2mm、3%/3 mm、3%/4 mm、3%/5 mm四种不同剂量偏差/吻合距离剂量标准,γ≤1的平均通过率均超过95.2%,测量所得剂量分布与计算结果在相应平面的几何分布均呈现出良好的一致性。结论：胶片空间分辨率高于二维、三维探测器阵列,是调强计划验证的＂金标准＂。而二维和三维探测器阵列凭借其操作简便、数据处理快捷的特点可作为一维验证方法的有效补充。     

胰腺癌患者螺旋断层放疗摆位误差分析

目的：通过兆伏级CT（MVCT）在线测量校正胰腺癌患者螺旋断层放疗的摆位误差,确定临床靶区CTV和计划靶区PTV之间的外放距离。方法：2012年5月至12月,21例接受TomoTherapy治疗的胰腺癌患者,每次治疗前均行靶区部位MVCT扫描。并将扫描后的MVCT图像与定位时千伏级CT（kVCT）图像进行配准,分别记录患者左右x、头脚y、腹背z和横断面旋转Roll四个方向的偏差数值,对其误差值进行统计分析。结果：21例患者共行358次MVCT扫描,其摆位误差值在x、y、z和Roll方向分别为：（-0．14±0．60）mm、（-1．21±0．44）mm、（0．69±0．93）mm和（0．02±0．26）。x、y、z方向CTV和PTV之间的外放距离分别为：5．5mm、7．4mm和3．9mm。结论：胰腺癌患者治疗摆位误差较大,Tomotherapy通过在线摆位校正能有效减小摆位误差。临床上建议胰腺癌患者在x、y、z方向上CTV和PTV之间可分别外扩5mm、7mm和4mm,为精确照射提供必要的质量保证。     

Tomotherapy MVCT不同配准方式对头颈部摆位的影响

目的:评估螺旋断层放射治疗（Tomotherapy, TOMO）兆伏级CT（MVCT）不同配准方式对头颈部摆位的影响。方法:首先基于室内激光和体表标记对头颈部模体进行摆位,行MVCT图像引导并自动配准,误差修正后将其作为参考图像。随后进行单、双及3方向移床（-5~5 mm,步长1 mm）,分别用Bone、Bone and Tissue和Full Image方式进行配准,最后记录左右（X）、头脚（Y）、腹背（Z）的摆位误差。结果:不同配准方式下,Bone的摆位误差最小。在Fine 1 mm模式下,Bone和Bone and Tissue配准存在显著差异,摆位误差分别为0.5（0.3, 0.8） mm和0.6（0.4, 0.8） mm;在Fine 2 mm模式下,Bone和Bone and Tissue配准同样存在显著差异,摆位误差分别为0.4（0.3, 0.7） mm和0.5（0.4, 0.8） mm。在Normal 2 mm和Coarse 3 mm模式下,3种配准方式均存在显著差异（P<0.05）。在Fine 2 mm和Normal 2 mm模式下,3种图像配准均无差异（P>0.05）。不同配准方式下,Y方向相关性最低。CTV-PTV外放Margin值在Bone配准方式下,X、Y、Z 3个方向分别为2.1、2.8、2.2 mm;Bone and Tissue配准方式下,X、Y、Z 3个方向分别为2.1、2.7、2.2 mm;Full Image配准方式下,X、Y、Z 3个方向分别为2.2、3.0、2.2 mm。结论:综合3种模式相同的扫描长度、扫描时间和剂量考虑,在TOMO临床治疗头颈部患者时,可选择Normal模式,优先选择Bone配准方式。     

螺旋断层调强放疗进行全中枢神经系统照射时不同部位靶区外放的临床研究

目的:分析使用螺旋断层加速器TOMO进行全中枢神经系统放疗的患者的MVCT图像，以颅骨、颈椎、胸椎、腰椎和整体靶区（PTVROI）为感兴趣区分别进行图像配准和摆位误差统计，计算各感兴趣区的靶区外放。方法:回顾性分析中国医学科学院肿瘤医院2016年~2020年使用TOMO行全中枢神经系统放疗的16例患者的154套MVCT图像，分别以颅骨、颈椎、胸椎、腰椎和PTVROI进行配准，统计不同部位靶区的摆位误差数据，得到5组包含左右（X）方向、头脚（Y）方向、腹背（Z）方向的摆位误差数据，比较颅骨、颈椎、胸椎、腰椎和PTVROI是否有差异，并应用公式M=2.5Σ+0.7σ分别计算不同部位的临床靶区到计划靶区的外放边界。结果:在X方向上的两两比较中，颅骨vs颈椎，差异有统计学意义（P=0.023），其余各组比较均无显著性差异；Y方向上的两两比较均未显示有显著性差异；而在Z方向上，PTVROI vs颅骨、PTVROI vs胸椎，无显著性差异，其他组两两比较，PTVROI vs颈椎（P<0.001）、PTVROI vs腰椎（P<0.001）、颅骨vs颈椎（P=0.007）、颅骨vs胸椎（P=0.017）、颅骨vs腰椎（P<0.001）、颈椎vs胸椎（P<0.001）、颈椎vs腰椎（P<0.001）、胸椎vs腰椎（P<0.001），差异有统计学意义。结论:使用TOMO行全中枢神经系统放疗，Y方向的靶区外放差异较小，X和Z方向的靶区外放边界从头到腰椎呈递增趋势，建议在中枢的不同位置采取不同的PTV外放策略。     

Octavius 1600SRS三维剂量验证系统临床可行性测试

目的:通过模体实验对PTW Octavius 1600SRS三维剂量验证系统进行临床应用前性能测试,评估其对立体定向放射治疗（SBRT）计划进行剂量验证的可行性。方法:选用PTW Octavius 1600SRS体模的CT图像,模拟勾画7个球形靶区,中心靶区（PTV0）直径大小为3 cm,其余各靶区直径大小分别为1.0 cm（2个）、1.5 cm（2个）和2.0 cm（2个）,各靶区中心点距PTV0中心点距离为3~6 cm。设置PTV0的中心点为计划中心,在治疗计划系统中制定SBRT计划（Plan0）,处方剂量为8 Gy×3 F。实验分别对Plan0引入临床常见偏差,包括叶片MLC位置偏差（1、2、3 mm）、计划中心点（ISO）位置偏差（1、2、3 mm）和机架位置偏差（0.5°、1.0°、2.0°）,并生成相应的偏差计划。使用1600SRS验证系统分别对原计划和偏差计划进行测量,比较两者γ通过率和靶区覆盖率的差别,以评估系统对放疗剂量偏差的敏感性。另外,对6例临床SBRT计划进行治疗前剂量验证,并与EPID验证结果进行比较,以评估其临床计划验证性能。结果:1600SRS验证系统对MLC偏差检测非常敏感,当MLC出现1 mm偏差时,其γ通过率与各靶区覆盖率均出现显著下降,且随着MLC偏差变大,其下降越明显。当MLC出现3 mm偏差时,（3 mm/3%）和（2 mm/3%）的γ通过率分别从99.6%和98.0%下降至92.8%和81.7%,7个靶区体积的覆盖率（V98%）平均下降（58.8±6.8）%。1600SRS对机架旋转偏差和ISO平移误差检测亦敏感,在机架旋转出现2°偏差或ISO出现3 mm偏差时,其（2 mm/2%）的γ通过率分别从95.1%下降至89.5%或86.2%。另外,6例临床SBRT放疗计划的（2 mm/3%）γ通过率平均为（95.5±1.5）%。结论:Octavius 1600SRS能敏感地检测出SBRT计划中MLC到位偏差、机架旋转角度偏差与ISO偏差,能较好地应用于SBRT计划的治疗前剂量验证。     

乐园化引导干预可提升儿童放疗摆位精度

目的:探讨乐园化引导干预对儿童放疗摆位精度的影响。方法:选取2020年3月～2022年5月在中山大学肿瘤防治中心放疗的儿童患者作为研究对象,按照是否参与乐园化引导干预分为试验组（24例）和对照组（21例）。试验组儿童患者在每次放疗前进行儿童乐园化诱导心理干预,待儿童患者完成心理适应后进行治疗;对照组实施常规放疗准备后治疗。比较两组儿童患者放疗实施的摆位精度。结果:试验组在左右（LR）、头脚（SI）、腹背（AP）方向的摆位误差分别为（-0.32±2.18）、（-0.12±2.24）、（-0.17±2.32） mm,对照组分别为（-0.93±1.91）、（0.79±1.75）、（-0.63±1.97） mm。两组摆位误差比较,在LR和SI方向的差异有统计学意义（LR:t=2.28, P=0.02;SI:t=-2.58, P=0.01）,而AP方向的差异无统计学意义（LR:t=1.63, P=0.11）。结论:乐园化引导干预可以提高儿童患者放疗的依从性,进而提高放疗的摆位精度,具有显著的临床应用意义和推广价值。     

螺旋断层放射治疗在儿童神经母细胞瘤全颅骨放疗中保护海马的计划设计

目的:用螺旋断层放射治疗(TOMO)的不同模式进行儿童全颅骨照射的计划设计,探讨TOMO全颅骨照射同时保护海马的调强技术。方法:取5例儿童高危神经母细胞瘤颅骨转移病例,全颅骨外扩3 mm且皮下内收3 mm形成计划靶区(PTV),海马区外扩5 mm形成海马保护区。使用Tomo HDTM治疗计划系统设计螺旋模式下的保护全脑(HT-BSRT)、保护海马(HT-HSRT)和6野径照模式下保护全脑(DT-BSRT)、保护海马(DT-HSRT)4种调强计划,处方剂量为21.6 Gy/12F。单因素ANOVA和配对t检验比较靶区、海马区及其他正常组织剂量。结果:5例病例的4种调强方式中,PTV受照95%处方量的体积都大于95%,HT-BSRT、HT-HSRT、DT-BSRT、DT-HSRT均匀性指数分别为0.046 4±0.013 2、0.094 5±0.053 4、0.108 6±0.027 9和0.133 2±0.040 4(P=0.013),适形度指数分别为0.625 40±0.039 88、0.638 30±0.023 40、0.589 00±0.041 40和0.615 00±0.034 19(P=0.198);海马平均剂量分别为(14.92±3.52)、(3.30±0.79)、(17.80±1.78)和(5.13±1.62)Gy(P0.000 1),海马保护区平均剂量分别为(15.38±3.08)、(4.41±1.06)、(17.83±1.55)和(6.41±1.81)Gy(P0.000 1)。结论:全颅骨照射同时保护海马较之仅保护全脑的TOMO调强计划在满足PTV剂量要求下,能显著降低海马区受照剂量,保护儿童神经认知功能。     

基于红外定位系统的放疗摆位偏差预警系统对头颈肩膜形变的分析与研究

目的:通过对放疗红外定位系统（OPS）在摆位期间采集的膜球变形度等数据进行分析,研究头颈肩膜的变形程度。方法:随机选取头颈部癌症患者23例,使用头颈肩热塑膜固定体位。通过使用OPS对膜上的6个定位球进行实时监测,记录摆位期间的各个膜球变形程度。当膜球变形度偏差值小于1.0 mm,则认定膜球变形度在正常范围内,不影响摆位精度。结果:6个定位球偏差在1.0 mm内的占比分别为70.3%、62.0%、57.4%、61.8%、70.5%、65.5%。结论:基于OPS系统的放疗摆位偏差预警系统能实时监测到膜是否发生形变,实验结果显示头颈肩膜形变的发生概率较大,影响了摆位精准度。该预警系统通过及时发现膜的形变程度,有效提高放疗摆位精准度,具有较强的临床价值。     

Optimization of megavoltage CT scan registration settings for brain cancer treatments on tomotherapy

This study aims to determine the settings that provide the optimal clinical accuracy and consistency for the registration of megavoltage CT (MVCT) with planning kilovoltage CT image sets on the Hi-ART tomotherapy system. The systematic offset between the MVCT and the planning kVCT was determined by registration of multiple MVCT scans of a head phantom aligned with the planning isocentre. Residual error vector lengths and components were used to quantify the alignment quality for the phantom shifted by 5 mm in different directions obtained by all 27 possible combinations of MVCT inter-slice spacing, registration techniques and resolution. MVCT scans with normal slices are superior to coarse slices for registration of shifts in the superior-inferior, lateral and anterior-posterior directions. Decreasing the scan length has no detrimental effect on registration accuracy as long as the scan lengths are larger than 24 mm. In the case of bone technique and fine resolution, normal and fine MVCT scan slice spacing options give similar accuracy, so normal mode is preferable due to shorter procedure and less delivered dose required for patient set-up. A superior-inferior field length of 24-30 mm, normal slice spacing, bone technique, and fine resolution is the optimum set of registration settings for MVCT scans of a Rando head phantom acquired with the Hi-ART tomotherapy system, provided the registration shifts are less than 5 mm.     

Optimization of megavoltage CT scan registration settings for thoracic cases on helical tomotherapy

This study aims to investigate the settings that provide optimum registration accuracy when registering megavoltage CT (MVCT) studies acquired on tomotherapy with planning kilovoltage CT (kVCT) studies of patients with lung cancer. For each experiment, the systematic difference between the actual and planned positions of the thorax phantom was determined by setting the phantom up at the planning isocenter, generating and registering an MVCT study. The phantom was translated by 5 or 10 mm, MVCT scanned, and registration was performed again. A root-mean-square equation that calculated the residual error of the registration based on the known shift and systematic difference was used to assess the accuracy of the registration process. The phantom study results for 18 combinations of different MVCT/kVCT registration options are presented and compared to clinical registration data from 17 lung cancer patients. MVCT studies acquired with coarse (6 mm), normal (4 mm) and fine (2 mm) slice spacings could all be registered with similar residual errors. No specific combination of resolution and fusion selection technique resulted in a lower residual error. A scan length of 6 cm with any slice spacing registered with the full image fusion selection technique and fine resolution will result in a low residual error most of the time. On average, large corrections made manually by clinicians to the automatic registration values are infrequent. Small manual corrections within the residual error averages of the registration process occur, but their impact on the average patient position is small. Registrations using the full image fusion selection technique and fine resolution of 6 cm MVCT scans with coarse slices have a low residual error, and this strategy can be clinically used for lung cancer patients treated on tomotherapy. Automatic registration values are accurate on average, and a quick verification on a sagittal MVCT slice should be enough to detect registration outliers.     

Feasibility study of helical tomotherapy for total body or total marrow irradiation

Total body radiation (TBI) has been used for many years as a preconditioning agent before bone marrow transplantation. Many side effects still plague its use. We investigated the planning and delivery of total body irradiation (TBI) and selective total marrow irradiation (TMI) and a reduced radiation dose to sensitive structures using image-guided helical tomotherapy. To assess the feasibility of using helical tomotherapy, (A) we studied variations in pitch, field width, and modulation factor on total body and total marrow helical tomotherapy treatments. We varied these parameters to provide a uniform dose along with a treatment times similar to conventional TBI (15-30 min). (B) We also investigated limited (head, chest, and pelvis) megavoltage CT (MVCT) scanning for the dimensional pretreatment setup verification rather than total body MVCT scanning to shorten the overall treatment time per treatment fraction. (C) We placed thermoluminescent detectors (TLDs) inside a Rando phantom to measure the dose at seven anatomical sites, including the lungs. A simulated TBI treatment showed homogeneous dose coverage (+/-10%) to the whole body. Doses to the sensitive organs were reduced by 35%-70% of the target dose. TLD measurements on Rando showed an accurate dose delivery (+/-7%) to the target and critical organs. In the TMI study, the dose was delivered conformally to the bone marrow only. The TBI and TMI treatment delivery time was reduced (by 50%) by increasing the field width from 2.5 to 5.0 cm in the inferior-superior direction. A limited MVCT reduced the target localization time 60% compared to whole body MVCT. MVCT image-guided helical tomotherapy offers a novel method to deliver a precise, homogeneous radiation dose to the whole body target while reducing the dose significantly to all critical organs. A judicious selection of pitch, modulation factor, and field size is required to produce a homogeneous dose distribution along with an acceptable treatment time. In addition, conformal radiation to the bone marrow appears feasible in an external radiation treatment using image-guided helical tomotherapy.     

Delineation of moving targets with slow MVCT scans: implications for adaptive non-gated lung tomotherapy

Accurate imaging is a prerequisite for adaptive radiation therapy of mobile tumours. We present an evaluation of the performance of slow computed tomography (CT) for mapping and delineating the excursion boundary of a moving object using a tumour phantom scanned with the helical MVCT scanner of a tomotherapy unit. A spherical test object driven by sinusoidal motion in both the lateral and cranial-caudal directions was used to determine how well MVCT images depict the true envelope of the motion. Such information is useful in interpreting the CT images relative to the static object case when radiotherapy gating is to be used or in determining the internal target volume (ITV) when beam gating is not possible. A computer simulation of the CT imaging process was developed which incorporates the third generation fan beam geometry and helical acquisition technique of the tomotherapy MVCT system. Motion artefacts are mainly characterized by the parameter alpha=Tgantry/Trespiration which is interpreted as the period of the gantry rotation (Tgantry) in units of the respiratory period (Trespiration). Experimental tests were performed using a fixed gantry period of 10 s per full rotation and respiratory period ranging from 4.0 (alpha=2.5) to 1.0 (alpha=10) s. These cases represent typical clinical imaging conditions on the tomotherapy unit, as well as an extreme test case where the gantry period is intentionally set to be much greater than the respiratory period (termed an 'ultra-slow' scan). The accuracy of target (ITV) delineation is evaluated by comparing volumes generated using iso-density contours on the MVCT images to the true motion envelope, known a priori in this phantom study. As expected, motion artefacts are present in clinical MVCT images and they are not averaged over the slow gantry period of rotation. Furthermore, artefacts are not significantly affected by scanning with different helical pitch values. Greater distortions from the true density distribution are observed for lateral motion compared to cranial-caudal motion. Volumes generated by iso-density contours yield better agreement with the motion envelope for scans performed under ultra-slow conditions (alpha=10) compared to typical clinical imaging conditions (alpha=2.5). If the MVCT gantry cannot be rotated very quickly due to engineering constraints in order to achieve ultra-fast CT, we suggest an opposite approach as an interim measure for mapping the ITV. Adjusting MVCT scan conditions to a very slow acquisition (alpha=10) may be a good compromise for determining the ITV for non-gated adaptive tomotherapy of moving lung tumours.     

The effect of temporal HU variations on the uncertainty of dose recalculations performed on MVCT images

Over the course of radiation therapy, a patient's anatomy may change substantially. The relatively recent addition of frequent in-room imaging to assist with patient localization has provided a database of images that may be used to recalculate dose distributions for adaptive radiotherapy purposes. The TomoTherapy Hi-Art II unit (Accuray Inc., Sunnyvale, CA, USA) uses a helical scanning geometry and a megavoltage (MV) beam to acquire volumetric patient images. This study evaluated the uncertainty of dose calculations performed on megavoltage CT (MVCT) images as a function of temporal Hounsfield Unit (HU) variations observed in the imaging system over three years on two machines. A baseline error between dose calculations performed on kVCT and MVCT images was established using a series of phantoms. This baseline error ranged from -1.4% to 0.6%. Materials of differing densities were imaged and MVCT numbers were measured periodically. The MVCT number of solid water varied from 5 to 103 HU and consistently increased prior to target replacement. Finally, the dosimetric uncertainty of the temporal HU variation was assessed using MVCT images of typical head and neck, lung and prostate cancer patients. Worst-case MVCT recalculation errors could approach 5%, 7% and 10% for the head and neck, lung and prostate images, respectively. However, if a tolerance of ±30 HU were maintained for the MVCT number of solid water, dosimetric errors were limited to ±2.5%, ±3% and ±4%, respectively.     

影像引导放疗中常用CT设备影像质量的比较分析

目的:分析影像引导放疗中常用的模拟定位螺旋CT(MSCT)、加速器机载锥形束CT(CBCT)和螺旋断层治疗机MV螺旋CT(MVCT)的影像质量。方法:CatPhan600模体测量三种成像设备的CT值均匀性和线性、空间分辨率、低对比度分辨率、3D影像的几何准确性和金属伪影大小。结果:MSCT、CBCT和MVCT的CT值与物质密度均呈线性关系;均匀模体中的CT均匀性分别为1.07%,1.40%,39.81%;空间分辨率分别为8 lp/cm,7 lp/cm,4 lp/cm;MSCT可显示低对比度为1%的3 mm圆孔,CBCT只能略微分辨圆孔,而MVCT则无法显示圆孔,几何准确性均良好;MVCT的金属伪影较小。结论:CBCT和MVCT的成像质量均不如MSCT,但能满足患者治疗体位验证和监测的需要。