主动呼吸控制用于原发性肝癌放射治疗肝脏位置重复性的研究

背景与目的：呼吸运动能造成肝癌放疗靶区的扩大,限制了放疗剂量的增加.主动呼吸控制（active breathing control,ABC）提供了一种减少呼吸运动的简便方法,肝脏位置重复性较好是使用ABC技术减少靶区边界外放的一个重要前题,然而对使用该技术放疗过程中深吸气后肝脏位置的重复性目前尚不明确,因此本研究对ABC用于原发性肝癌放疗肝脏位置的重复性进行了测量.方法：入组本研究的患者共20人,其中16例肝癌碘油沉积良好.所有的患者进行了ABC呼吸训练和ABC控制下的放射治疗.在常规模拟机透视下测量一次屏气过程肝脏位置的稳定性和通过5次反复屏住吸气表示的一次放疗中肝脏位置的重复性.每周用兆伏级X线电子射野影像仪拍摄验证片与放疗计划生成的数字重建图像（digital reconstruction radiograph,DRR）比较测量分次放疗间肝脏位置在头脚方向上的重复性,通过每周在模拟机下体模固定在治疗体位拍摄正、侧位X线片,测量碘油在前后和左右位置上距离脊柱垂直距离的变化值,计算肝脏位置在这两个方向上的重复性.结果：所有患者配合良好,均能全程耐受ABC放疗屏气,没有1例因为不能耐受中断放疗.在平静呼吸状态下,患者膈在头脚方向上运动幅度平均为1.6 cm（范围：1.0～2.6 cm）.在透视下测得一次屏气过程中肝脏上下移动幅度平均为1.3 mm（范围：0.0～2.9 mm）.使用ABC放疗时一次放疗中和分次放疗间肝脏位置在头脚方向上的重复性（标准差）分别为1.6 mm和6.6 mm,前后方向上的重复性分别为0.9 mm和4.2 mm,左右方向上的重复性分别为0.7 mm和5.5 mm.结论：应用主动呼吸控制技术对入选的原发性肝癌患者放疗时肝脏的位置重复性良好.分次放疗间的重复性要差于一次放疗中的.安全的减少计划靶区的外扩需要结合影像引导的放疗并且要考虑肝脏位置的重复性.     

The reproducibility of organ position using active breathing control (ABC) during liver radiotherapy

Purpose: To evaluate the intrafraction and interfraction reproducibility of liver immobilization using active breathing control (ABC).

Methods and Materials: Patients with unresectable intrahepatic tumors who could comfortably hold their breath for at least 20 s were treated with focal liver radiation using ABC for liver immobilization. Fluoroscopy was used to measure any potential motion during ABC breath holds. Preceding each radiotherapy fraction, with the patient setup in the nominal treatment position using ABC, orthogonal radiographs were taken using room-mounted diagnostic X-ray tubes and a digital imager. The radiographs were compared to reference images using a 2D alignment tool. The treatment table was moved to produce acceptable setup, and repeat orthogonal verification images were obtained. The positions of the diaphragm and the liver (assessed by localization of implanted radiopaque intra-arterial microcoils) relative to the skeleton were subsequently analyzed. The intrafraction reproducibility (from repeat radiographs obtained within the time period of one fraction before treatment) and interfraction reproducibility (from comparisons of the first radiograph for each treatment with a reference radiograph) of the diaphragm and the hepatic microcoil positions relative to the skeleton with repeat breath holds using ABC were then measured. Caudal-cranial (CC), anterior-posterior (AP), and medial-lateral (ML) reproducibility of the hepatic microcoils relative to the skeleton were also determined from three-dimensional alignment of repeat CT scans obtained in the treatment position.

Results: A total of 262 fractions of radiation were delivered using ABC breath holds in 8 patients. No motion of the diaphragm or hepatic microcoils was observed on fluoroscopy during ABC breath holds. From analyses of 158 sets of positioning radiographs, the average intrafraction CC reproducibility (σ) of the diaphragm and hepatic microcoil position relative to the skeleton using ABC repeat breath holds was 2.5 mm (range 1.8–3.7 mm) and 2.3 mm (range 1.2–3.7 mm) respectively. However, based on 262 sets of positioning radiographs, the average interfraction CC reproducibility (σ) of the diaphragm and hepatic microcoils was 4.4 mm (range 3.0–6.1 mm) and 4.3 mm (range 3.1–5.7 mm), indicating a change of diaphragm and microcoil position relative to the skeleton over the course of treatment with repeat breath holds at the same phase of the respiratory cycle. The average population absolute intrafraction CC offset in diaphragm and microcoil position relative to skeleton was 2.4 mm and 2.1 mm respectively; the average absolute interfraction CC offset was 5.2 mm. Analyses of repeat CT scans demonstrated that the average intrafraction excursion of the hepatic microcoils relative to the skeleton in the CC, AP, and ML directions was 1.9 mm, 0.6 mm, and 0.6 mm respectively and the average interfraction CC, AP, and ML excursion of the hepatic microcoils was 6.6 mm, 3.2 mm, and 3.3 mm respectively.

Conclusion: Radiotherapy using ABC for patients with intrahepatic cancer is feasible, with good intrafraction reproducibility of liver position using ABC. However, the interfraction reproducibility of organ position with ABC suggests the need for daily on-line imaging and repositioning if treatment margins smaller than those required for free breathing are a goal.     

肝癌肺癌质子重离子治疗中主动呼吸控制技术不确定性研究

目的:研究主动呼吸控制(ABC)技术在质子重离子治疗肝癌、肺癌中的不确定性。方法:治疗前对40例癌症患者治疗部位进行影像拍摄验证片,其中20例肺癌患者共拍摄200张验证片;20例肝癌患者肿瘤周围注有碘油标记物,以标记物位置变化代替肿瘤位置的变化,共拍摄200张验证片。验证片配准均以椎体为主要目标,记录肿瘤位置变化值。结...     

主动呼吸控制与自由呼吸配合bodyfix固定装置用于胸部肿瘤SBRT对比研究

目的:初步比较主动呼吸控制(ABC)技术与自由呼吸(FB)模式配合bodyfix固定装置在胸部肿瘤立体定向放疗(SBRT)的差异。方法:随机选取40例胸部肿瘤行SBRT患者,均分为ABC组和FB组。两组采用bodyfix固定装置固定后CBCT扫描图像与计划参考图像配准,得到左右、头脚、前后方向平移误差。校正摆位误差后S...     

用主动呼吸控制提高肺癌图像引导放疗精度

目的增加使用主动呼吸控制(ABC)系统时屏气时间,结合使用图像引导放疗(IG- RT)提高肺癌患者放疗精度。方法对31例肺癌患者行主动呼吸控制系统训练,训练屏气时接入氧,训练5 d,每日训练约30 min。训练时充分发挥患者的主观能动性,让患者熟练掌握屏气技巧,主动配合治疗。采用立体定向体架固定(SBF),用IGRT的SynergyTM系统锥形束CT(CBCT)与ABC系统配合进行治疗。结果31例中训练后最大屏气时间达40 s以上的24例,平均最大屏气时间为65.5 s,较训练前增加33.9 s。使用ABC时横膈在头脚方向运动平均为1.7 mm,而在自由呼吸时为16.0 mm。首次CBCT采集图像与计划图像比较在左右(x)、头脚(y)、前后(z)方向平均误差分别为3.3、4.8、3.1 mm,调整床后分别为1.0、1.2、1.1 mm。结论通过吸入氧气屏气的呼吸训练,能明显延长患者屏气时间。在IGRT中配合使用ABC系统,可使肺部肿瘤放疗精度控制在2 mm,为提高分次剂量和总治疗剂量,减少肺损伤提供可能。     

自主呼吸控制在乳腺癌术后放疗中的应用研究

目的 探讨自主呼吸控制（ABC）技术在乳腺癌术后放疗中的意义.方法 对22例行保乳术的早期乳腺癌患者（10例左侧,12例右侧）行术后全乳放疗并配合使用ABC技术.对每例患者在自由呼吸（FB）和75%适度深吸气（mDIBH）状态下分别行CT扫描.治疗计划系统设计优化放疗计划,每例患者做2个计划,处方剂量1.8 Gy/次,25次.比较各计划全肺平均受量（MLD）、全肺接受20Gy的体积（V20）、患侧肺V20、左侧乳腺癌患者心脏V30和心脏平均受量（Dmean）等参数.结果 22例患者患侧肺V20,FB时平均为17.0%,mDIBH时平均为16.2%,降低0.8%（t=3.63,P=0.002）;FB时双肺V20平均为8.7%,mDIBH时平均为8.0%,降低0.6%（t=2.78,P=0.011）.10例左侧患者心脏V30,FB时平均为6.1%,mDIBH时平均为3.8%,降低2.3%（t=6.50,P＜0.01）;心脏Dmean由449.58cGy降为332.79cGy（t=5.94,P＜0.01）.结论 乳腺癌术后全乳切线放疗中配合ABC技术使用mDIBH方法控制呼吸不但可减少呼吸运动对乳腺靶区的影响,而且可减少肺和心脏受照体积和剂量,从而大大减轻了对肺和心脏的放射损伤.     

Reproducibility of lung tumor position and reduction of lung mass within the planning target volume using active breathing control (ABC)

PURPOSE: The active breathing control (ABC) device allows for temporary immobilization of respiratory motion by implementing a breath hold at a predefined relative lung volume and air flow direction. The purpose of this study was to quantitatively evaluate the ability of the ABC device to immobilize peripheral lung tumors at a reproducible position, increase total lung volume, and thereby reduce lung mass within the planning target volume (PTV). MATERIALS AND METHODS: Ten patients with peripheral non-small-cell lung cancer tumors undergoing radiotherapy had CT scans of their thorax with and without ABC inspiration breath hold during the first 5 days of treatment. Total lung volumes were determined from the CT data sets. Each peripheral lung tumor was contoured by one physician on all CT scans to generate gross tumor volumes (GTVs). The lung density and mass contained within a 1.5-cm PTV margin around each peripheral tumor was calculated using CT numbers. Using the center of the GTV from the Day 1 ABC scan as the reference, the displacement of subsequent GTV centers on Days 2 to 5 for each patient with ABC applied was calculated in three dimensions. RESULTS: With the use of ABC inspiration breath hold, total lung volumes increased by an average of 42%. This resulted in an average decrease in lung mass of 18% within a standard 1.5-cm PTV margin around the GTV. The average (+/- standard deviation) displacement of GTV centers with ABC breath hold applied was 0.3 mm (+/- 1.8 mm), 1.2 mm (+/- 2.3 mm), and 1.1 mm (+/- 3.5 mm) in the lateral direction, anterior-posterior direction, and superior-inferior direction, respectively. CONCLUSIONS: Results from this study indicate that there remains some inter-breath hold variability in peripheral lung tumor position with the use of ABC inspiration breath hold, which prevents significant PTV margin reduction. However, lung volumes can significantly increase, thereby decreasing the mass of lung within a standard PTV.     

主动呼吸控制结合三维适形放疗非小细胞肺癌的初步研究

目的 探讨医科达公司主动呼吸控制(ABC)系统结合三维适形放疗技术治疗非小细胞肺癌(NSCLC)可行性.方法 29例Ⅱ～Ⅳ期未能手术的NSCLC患者分别在自由呼吸(FB)状态和ABC控制下行CT扫描,并在两个重建图像序列中按同样条件分别设计FB和ABC后的三维适形放疗计划.选择屏气触发方式为吸气后屏气,触发阈值设定为呼吸曲线峰值的80%,每次最长屏气时间为25 s.上叶病灶计划靶体积(PTV)为临床靶体积(CTV)外放0.6 cm;中下叶病灶PTV为CTV外放1.0 cm.采用3～5个野进行共面适形治疗.通过剂量体积直方图评价两个计划的大体肿瘤体积(GTV)、CTV、PTV、双肺体积(V_(lung))、双肺V_(20).和平均肺剂量(MLD).近期疗效按世界卫生组织肿瘤疗后客观效果评分.正常组织急性反应按美国国家癌症研究所CTC3.0标准评价.结果 除1例患者因经济原因中断治疗,其他患者均顺利完成治疗.使用ABe技术后GTV、CTV、PTV均较FB技术有一定缩小[36.35 cm~3:31.40 cm~3(t=9.70,P<0.001)、82.33 cm~3:70.83 cm~3(t=8.19,P<0.001)、230.73 cm~3:197.59 cm~3(t=5.72,P<0.001)],双肺V_(20)、MLD均低于FB技术[21.66%:18.76%(t=11.16,P<0.001)、1329.07 Gy:1143.14 Gy(t=13.24,P<0.001)].总有效率为64%(18例).急性放射性食管炎发生率1、2级分别为68%(19例)、18%(5例);急性放射性肺损伤发生率1、2级分别为82%(23例)、7%(2例);骨髓抑制发生率1、2、3级分别为57%(16例)、25%(7例)、14%(4例);急性心脏损伤1、2级分别为86%(24例)、14%(4例).结论 ABC的临床应用可行,靶区定位更为精确,可减少正常肺组织照射剂量,从而减少放射副反应的发生率.     

呼吸控制技术用于放射治疗的研究进展

随着计算机和三维影像技术的快速发展,精确放射治疗已成为当前放射治疗的主流和今后发展的方向,但照射时,患内部器官自主和不自主运动导致的肿瘤位移在很大程度上限制着此技术的发展。由生理过程引起的内部器官在同次治疗中的运动影响精确放射治疗,肿瘤运动即时间因素的四维放射治疗尤为重要,呼吸运动是同次治疗中最大幅度的器官运动,因此,控制呼吸已成为目前研究的热点。呼吸运动对精确放射治疗的影响主要体现在以下两方面：     

3D-CRT联合主动脉呼吸控制主体定向放射治疗剂量学分析

目的:探讨高剂量率三维适形放疗(three-dimensional conformal radiation therapy,3D-CRT)联合主动呼吸控制技术(active breathing control,ABC)进行早期非小细胞肺癌(non-small cell lung cancer,NSCLC)立体定向放射治疗(ste-reotactic body radiation therapy,SBRT)的剂量学特点。方法:选取接受放射治疗的早期NSCLC患者8例,分别在ABC辅助下适度深吸气末屏气(moderate deep inspiration breath-hold,mDIBH,触发阈值设定为峰值的80%)和自由呼吸(free breathing,FB)状态下行模拟定位CT扫描,分别在2套CT图像上采用高剂量率(剂量率为1 000 Mu/min)的3D-CRT设计SBRT计划。比较2种呼吸状态下大体肿瘤体积(gross tumor volume,GTV)、计划靶体积(planning targetvolume,PTV)、双肺的体积、2种计划方式下PTV的最大剂量(D1%)和最小剂量(D99%)、靶区剂量分布的均匀指数(HI)和适形指数(CI)、正常组织的相关体积-剂量(Vx、Dmean、Dmax)及机器跳数(MU)的差异。结果:PTV体积由FB下平均158.04cm3减少到了mDIBH下的76.90cm3,减少51.34%,P=0.006;GTV FB体积较GTV mDIBH平均减少了约3cm3,差异无统计学意义,P=0.658;mDIBH状态下患侧肺、健侧肺和双肺平均体积分别由FB状态下的1 978.77、1 762.55和3 745.26cm3增加到了2 910.88、2 671.13和5 615.85cm3,分别增加了32.02%、35.36%和33.31%,P值均<0.05。FB及mDIBH状态下的靶区剂量的CI、HI、D1%和D99%均基本相当,P>0.05;mDIBH下3D-CRT计划中患侧肺V5～V40、双侧肺V5～V40及Dmean、胸壁V5～V40及Dmean、脊髓Dmax、绝对剂量体积V60-50、V50-40均小于FB状态,P<0.05;mDIBH下的健侧肺V5～V15、心脏V20～V40、Dmean以及绝对剂量体积V40-30、V30-20较FB略有降低,绝对剂量体积V20-10、V10～V5略有增大,P>0.05;3D-CRT mDIBH的MU及照射时间与3D-CRT FB基本相当,P>0.05。结论:高剂量率的3D-CRT联合ABC技术在早期NSCLC SBRT中可在不影响靶区剂量分布的同时,更好的降低肺组织、胸壁受照剂量。     

Short-term and long-term reproducibility of lung tumor position using active breathing control (ABC)

PURPOSE: To evaluate the short-term and long-term reproducibility of lung tumor position for scans acquired using an active breathing control (ABC) device. METHODS AND MATERIALS: Ten patients with lung cancer were scanned over three sessions during the course of treatment. For each session, two scans were acquired at deep inhale, and one scan each at half of deep inhale and at exhale. Long-term reproducibility was evaluated by comparing the same breathing state scans from two sessions, with setup variation removed by skeletal alignment. Tumor alignment was based on intensity matching of a small volume around the tumor. For short-term reproducibility, the two inhale volumes from the same session were compared. RESULTS: For the short-term reproducibility, the mean and the standard deviation (SD) of the displacement of the center of tumor were 0.0 (1.5) mm in anteroposterior (AP), 0.3 (1.4) mm in superior/inferior (SI), and 0.2 (0.7) mm in right/left (RL) directions. For long-term reproducibility, the mean (SD) were -1.3 (3.1) mm AP, -0.5 (3.8) mm SI, and 0.3 (1.6) mm RL for inhale and -0.2 (2.8) mm AP, 0.2 (2.1) mm SI, and -0.7 (1.1) mm RL for exhale. CONCLUSION: The ABC device demonstrates very good short-term and long-term reproducibility. Increased long-term variability in position, primarily in the SI and AP directions, indicates the role of tumor-directed localization in combination with breath-held immobilization.     

形变配准算法在肺癌自适应放疗中的应用研究

目的 探讨在肺癌自适应放疗中,图像形变配准方法对患者受量评估的影响。方法 在Raystation治疗计划系统平台上,用两种不同的形变配准算法(混合形变配准和生物动力学形变配准)、不同的形变次序(以放疗前图像作为参考图像和以放疗中期图像作为参考图像),共4种不同的形变配准方法为基础计算累积剂量。选择11例接受自适应放疗的肺癌患者,处方剂量在35.0~61.6 Gy之间,用4种形变配准方法分别计算肺、心脏和GTV的D_mean以及GTV的D₉₈和D₂,比较其剂量学差异。结果 用4种不同形变方式计算得到的11例患者肺D_mean的标准差在0.07~0.70 Gy;心脏D_mean的标准差在0.01~0.79 Gy;GTV的D_mean标准差在0.01~2.23 Gy,D₉₈的标准差在0.02~6.51 Gy,D₂的标准差在0.01~0.97 Gy。结论 图像形变配准方式的选择对肺癌自适应放疗的累积剂量计算造成了不可忽视的不确定性。     

Comparison of intensity-modulated radiotherapy planning based on manual and automatically generated contours using deformable image registration in four-dimensional computed tomography of lung cancer patients

PURPOSE: To evaluate the implications of differences between contours drawn manually and contours generated automatically by deformable image registration for four-dimensional (4D) treatment planning. METHODS AND MATERIALS: In 12 lung cancer patients intensity-modulated radiotherapy (IMRT) planning was performed for both manual contours and automatically generated ("auto") contours in mid and peak expiration of 4D computed tomography scans, with the manual contours in peak inspiration serving as the reference for the displacement vector fields. Manual and auto plans were analyzed with respect to their coverage of the manual contours, which were assumed to represent the anatomically correct volumes. RESULTS: Auto contours were on average larger than manual contours by up to 9%. Objective scores, D(2%) and D(98%) of the planning target volume, homogeneity and conformity indices, and coverage of normal tissue structures (lungs, heart, esophagus, spinal cord) at defined dose levels were not significantly different between plans (p = 0.22-0.94). Differences were statistically insignificant for the generalized equivalent uniform dose of the planning target volume (p = 0.19-0.94) and normal tissue complication probabilities for lung and esophagus (p = 0.13-0.47). Dosimetric differences >2% or >1 Gy were more frequent in patients with auto/manual volume differences > or =10% (p = 0.04). CONCLUSIONS: The applied deformable image registration algorithm produces clinically plausible auto contours in the majority of structures. At this stage clinical supervision of the auto contouring process is required, and manual interventions may become necessary. Before routine use, further investigations are required, particularly to reduce imaging artifacts.     

图像引导自主呼吸控制下肝脏肿瘤计划靶区外放研究

目的 图像引导自主呼吸控制（ABC）下肝脏肿瘤适形放疗计划靶体积（刚）外放范围。方法 应用瓦里安公司图像引导放疗（IGRT）系统，对13例经肝动脉栓塞化疗（TACE）的患者，在kV透视测量ABC下碘油影像的稳定性后，以锥形束CT（CBCT）联合ABC技术于每次治疗前采集容积CT图像10次／人。根据碘油影像进行kV-CBCT和计划CT的3D-3D配准，并以此校正摆位误差，设定修正摆位的阈值为3mm。治疗结束后再次采集kV-CBCT和计划CT3D-3D配准验证。结果 ABC kV透视模式下碘油几乎不存在运动。根据stroom公式M=2．0∑＋0．7α和测量结果进行计算，治疗前不加修正和使用ABC技术时肝脏治疗的PTV外放x．y、z轴分别为4．4、5．3、7．8mm。采用以上技术进行在线校正时，PTV外放x,y、z轴分别为2．5、2．6、3．9mm。结论 应用ABC技术的肝脏适形放疗，建议PTV外放x、y、z轴分别为5、6、8mm，应用ABC技术结合图像引导适形放疗系统在线治疗前校正时，PTV外放x,y、z轴分别为3、3、4mm。     

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。     

胃癌术后放疗中呼吸运动及主动呼吸控制对靶区移动影响分析

目的 了解胃癌术后放疗患者中自由呼吸运动对放疗靶区移动程度,分析采用主动呼吸控制(ABC)方法后靶区移动程度及相关因素.方法 22例胃癌患者术中在瘤床或淋巴结引流区放置银夹作为标记,术后采用ABC技术定位放疗.每周重复2次采集自由呼吸和ABC时相0°和90°图像,应用Image J图像处理软件处理图像及标记银夹.测定自由呼吸和采用ABC时银夹在头脚、左右及前后轴向上的移动幅度,包括同次放疗内和分次放疗间移动幅度.结果 自由呼吸和采用ABC后头脚、左右、前后轴向上的移动幅度分别为11.1、1.9、2.5 mm(F=85.15,P=0.000)和2.2、1.1、1.7 mm(F=17.64,P=0.000),头脚、前后方向明显减少(t=4.36,P=0.000;t=3.73,P=0.000);同次放疗内自由呼吸与ABC后同一呼吸相内的无变化,而ABC后异次呼吸相内的分别为3.7、1.6、2.8mm(F=19.46,P=0.000),3个方向均明显增加(t=-4.36,P=0.000;t=-3.52,P=0.000;t=-3.79,P=0.000);ABC后分次放疗间的银央簇中心和银夹最大移动幅度分别为2.7、1.7、2.5 mm(F=4.07,P=0.019)和4.6、3.1、4.2 mm(F=5.17,P=0.007),3个方向均明显增加(t=-4.09,P=0.000;t=-4.46,P=0.000;t=-3.45,P=0.000).结论 胃癌术后自由呼吸状态下放疗靶区移动幅度以头脚方向最大,左右方向最小;采用ABC技术后头脚、前后方向明显减小,而同次治疗内和分次放疗问的也有类似变化.     

Image-guided radiotherapy for liver cancer using respiratory-correlated computed tomography and cone-beam computed tomography

PURPOSE: To evaluate a novel four-dimensional (4D) image-guided radiotherapy (IGRT) technique in stereotactic body RT for liver tumors. METHODS AND MATERIALS: For 11 patients with 13 intrahepatic tumors, a respiratory-correlated 4D computed tomography (CT) scan was acquired at treatment planning. The target was defined using CT series reconstructed at end-inhalation and end-exhalation. The liver was delineated on these two CT series and served as a reference for image guidance. A cone-beam CT scan was acquired after patient positioning; the blurred diaphragm dome was interpreted as a probability density function showing the motion range of the liver. Manual contour matching of the liver structures from the planning 4D CT scan with the cone-beam CT scan was performed. Inter- and intrafractional uncertainties of target position and motion range were evaluated, and interobserver variability of the 4D-IGRT technique was tested. RESULTS: The workflow of 4D-IGRT was successfully practiced in all patients. The absolute error in the liver position and error in relation to the bony anatomy was 8 +/- 4 mm and 5 +/- 2 mm (three-dimensional vector), respectively. Margins of 4-6 mm were calculated for compensation of the intrafractional drifts of the liver. The motion range of the diaphragm dome was reproducible within 5 mm for 11 of 13 lesions, and the interobserver variability of the 4D-IGRT technique was small (standard deviation, 1.5 mm). In 4 patients, the position of the intrahepatic lesion was directly verified using a mobile in-room CT scanner after application of intravenous contrast. CONCLUSION: The results of our study have shown that 4D image guidance using liver contour matching between respiratory-correlated CT and cone-beam CT scans increased the accuracy compared with stereotactic positioning and compared with IGRT without consideration of breathing motion.