胃食管结合部腺癌术前放疗胃充盈状态与肿瘤分次内动度和分次间动度的关系

目的 探索胃食管结合部腺癌(AEG)术前放疗,胃充盈状态与肿瘤分次内动度和分次间动度的关系。方法 前瞻性纳入2018—2019年间行全新辅助治疗的10例局部晚期AEG患者,均于治疗前在胃镜下标记肿瘤上下界,共获20枚钛夹。全部患者均在定位及治疗期间行空腹和充盈两种状态下的4DCT扫描,每次扫描均由系统自动重建出0%~90%呼吸时相的10套图像,每个患者可获得100套图像。结果 胃充盈状态并不显著影响肿瘤近胸端的分次内动度与分次间动度,而在肿瘤远胸端,空腹状态下头脚方向的分次间动度较充盈状态下更大[(6.22±4.67) mm∶(4.13±3.68) mm,P=0.013]。为保证AEG的近胸端在放疗期间90%的CTV累积剂量接受95%处方剂量,口服300ml半流质后胃充盈状态下建议左右、腹背、头脚方向分别外放9、8.5、12.1mm。另纳入有近胸端钛夹的6例AEG术前放疗患者作为验证组,显示治疗期间93%的钛夹在外扩范围内。结论 对于AEG的术前放疗,也可考虑定量充盈胃的方式完成放疗。     

术前放疗中食管胃结合部病灶移动度分析

目的 探索食管胃结合部(GEJ)腺癌在术前放疗过程中移动度范围。方法 纳入接受GEJ腺癌术前同步放化疗14例患者,胃镜直视下于肿瘤上、下缘或四周分别置入钛夹标记肿瘤边缘。8例患者采用4DCT定位共获得位于GEJ的8个钛夹分次内图像98套供分析,12例患者在放疗前5次、第7、12、17、22次分别进行CBCT共获得分次间图像90套供分析。配对t检验差异。结果 肿瘤分次内动度在左右、腹背、头脚方向上分别为(0.92±0.95)、(2.27±2.73)、(9.95±5.48) mm,分次内动度头脚方向大于左右方向(P=0.000)和腹背方向(P=0.000),腹背方向大于左右方向(P=0.000)。肿瘤分次间动度在左右、腹背、头脚方向上分别为(6.56±4.19)、(5.69±3.29)、(6.49±4.37) mm,分次间动度左右方向和头脚方向均大于腹背方向(P=0.031、0.044),左右方向和头脚方向差异不显著(P=0.956)。为保证90%肿瘤体积接收95%处方剂量,在GEJ病灶的左右、腹背、头脚方向分别外放19.4、14.6、27.2 mm,可在术前放疗期间较好覆盖肿瘤分次内和分次间的移动度。结论 GEJ肿瘤在术前放疗中分次内和分次间移动度均较大,需在精确治疗中给予考虑并寻找新方法限制肿瘤移动。     

胸段食管癌IGRT分次内误差对靶区剂量的影响

目的 使用CBCT测量食管癌IGRT分次内误差,评价其对靶区和周围OAR剂量的影响。方法 应用CBCT采集 23例胸段食管癌放疗前后摆位图像,获取分次内误差。将分次内误差模拟治疗计划2和计划3,与原始计划1比较,分析其对靶区和OAR剂量学影响,并用单因素方差分析和配对t检验。结果 胸上段、胸中段、胸下段食管癌IGRT分次内平均误差在左右方向分别为(1.2±1.5)、(1.0±1.0)、(1.0±1.0) mm (P=0.138),在上下方向分别为(1.2±1.0)、(1.1±1.0)、(1.2±1.0) mm (P=0.656),在前后方向分别为(1.3±1.1)、(1.2±1.0)、(0.8±0.7) mm (P=0.003)。全部患者3 mm内误差发生频率在左右、上下、前后方向分别占95.2%、94.5%、93.9%。计划3与计划1相比,GTV V_100%下降5.55%,有 3例患者PTV D_95%下降超过原始计划处方的5%。计划3中全肺 V₃₀为(15.24±2.24)%,低于计划1的(15.67±2.28)%(P=0.033)。计划2中 4例脊髓>4500 cGy (D_max为4517.2 cGy),计划3中 19例脊髓>4500 cGy (D_max为5045.2 cGy)。结论 IGRT分次内误差对患者靶区剂量分布有一定影响。脊髓为串行器官,对分次内误差相对敏感,可能会导致部分患者脊髓超过最大耐受量。     

分次内和分次间摆位误差在宫颈自适应放疗中的研究

目的:在图像引导的自适应放疗中,评估宫颈癌患者分次内、分次间的摆位误差。方法:从2014年1月至9月选取16例诊断为IIb-IIIb期的宫颈癌患者,所有病人均未行手术治疗,而是采用三维调强放疗作为根治性治疗。每个病人在放疗前后行10次20个CBCT扫描图像,与计划CT进行配准融合,得到三维方向矢量误差,用X（左右）、Y（腹背）、Z（头脚）、CR（旋转角度）表示。计算摆位误差的平均变化及标准差。结果:收集320套CBCT图像,每个病人平均20套。所选CBCT扫描图像显示:患者在左右、头脚、腹背方向的分次内摆位误差分别为(0.11±0.14)cm、(0.17±0.18)cm、(0.20±0.19)cm;在左右、头脚、腹背方向的分次间摆位误差分别为(0.11±0.13）cm、（0.17±0.20）cm、（0.25±0.20）cm。结论:在图像引导的自适应放疗中,患者在各个方向的摆位误差均数为0.15cm,这一大幅度的误差需要在放疗中被考虑到。     

基于放疗中重复四维CT的食管癌大体肿瘤体积位移变化的比较研究

目的 基于重复四维CT (4DCT)模拟定位增强扫描探讨放疗中胸段食管癌原发肿瘤分次放疗内靶区位移变化。方法 29例胸段食管癌患者分别于放疗前及放疗10、20、30次时行4DCT模拟定位增强扫描,获得各时相原发肿瘤大体肿瘤体积(GTV)及内大体肿瘤体积(IGTV)。比较同次4DCT扫描所得胸上、中、下段食管癌GTV三维方向位移差异,各时段4DCT扫描所得同段食管癌GTV间同一方向位移差异及疗程中IGTV空间位置和体积变化。结果 胸中段患者初次及放疗20次时GTV位移在左右、前后、上下方向均不同(P=0.000~0.016),放疗10次时GTV位移上下与左右、前后方向均不同(P=0.000~0.006);胸下段患者初次及放疗10、20次时GTV位移上下与前后方向也不同(P=0.004~0.013);放疗疗程中不同治疗时段间GTV同一方向位移均相似(P=0.102~0.823)。疗程中IGTV空间位置变化不明显(P=0.689~0.999),而其体积在放疗20次时缩小最明显(P=0.012~0.029)。结论 放疗疗程中不同时段同一部位食管癌同一方向位移变化并不明显,尽管放疗20次时IGTV明显缩小但疗程中其空间位置变化不大。     

前列腺癌大分割精确放疗分次治疗间和分次治疗内位置变动分析

目的 了解前列腺癌精确大分割放疗时分次间和分次内前列腺靶区位移情况。方法 对 2013—2016年间28例接受5 Gy9次放疗的前列腺癌患者,定位前2周B超引导下经直肠穿刺前列腺内植入纯金标记3颗,仰卧位体膜固定充盈膀胱并直肠内插置直肠扩张球囊充气60 ml后CT定位,Pinnacle系统制定放疗计划。23例患者Synergy加速器治疗,每次疗前CBCT校位,扫描图像与计划图像行骨配准记录摆位误差,然后通过前列腺内金标位置配准记录前列腺位移误差,两次之差为分次间位移。5例患者Novalis加速器治疗,通过前列腺内金标配准,疗中ExacTrac系统实时跟踪金标位置变化,观察前列腺分次内位移。结果 23例患者每次疗前均测量位移共计207次,左右、上下、前后位移平均值分别为(0.05±0.10)、(0.20±0.22)、(0.19±0.18) cm;3个方向>0.3 cm位移分别为1、52、49次,>0.5 cm位移分别为1、29、16次。5例患者每次疗时监测测量金标位置移动5次共计225次,左右、上下、前后位移平均值分别为(0.61±0.50)、(0.68±0.69)、(0.70±0.67) mm,各方向>3 mm移动分别为0、1、1次。结论 前列腺癌精确大分割放疗时分次间位移远远大于分次内位移,分次间位移必须校正后才能放疗。分次内靶区位移尽管变化较小,但仍有必要监测分次内靶区位移,以防患者体位变动造成靶区脱靶照射。直肠内球囊插入对前列腺位置具有固定作用。     

肺部肿瘤大分割放疗分次内体位移动影响因素分析

目的 应用IGRT技术,探讨肺部恶性肿瘤患者大分割放疗过程中分次内体位移动情况及相关影响因素。方法 选择江苏省肿瘤医院收治的 96例肺部恶性肿瘤接受大分割治疗的患者。每次治疗前常规行千伏级CBCT扫描并在线配准,校正误差后进行治疗。治疗后再次行CBCT扫描并配准,记录治疗后患者左右、上下、前后方向上的体位变化,应用多元线性回归分析相关影响因素与治疗后体位偏差的关系。结果 上下和前后方向随着分割序数增大分次内体位偏差减小(P=0.000);左右方向随治疗时间延长则分次内移动度增大(P=0.010),体重较大者则移动度较小(P=0.003)。相对于真空体膜,采用热塑网膜固定分次内左右移动度明显增大(P=0.009)。结论 肺部肿瘤大分割放疗分次内存在一定体位误差;这种误差不同方向上有不同的影响因素。改进相关因素,可减少分次内体位误差,提高治疗精度。     

脑转移瘤立体定向放疗分次间和分次内摆位误差及残余误差分析

目的 分析脑转移患者立体定向放疗ExacTrac X线图像,计算分次间和分次内摆位误差及残余误差,分析进行逐弧位置验证的必要性。方法 通过对过去2年在本中心采用头部立体定向放疗的脑转移瘤病例的回顾性分析,配准其数字重建图像和ExacTrac正交kV级验证图像,计算患者3个方向的平移误差和旋转误差。数据包含分次间摆位误差、分次内摆位误差和残余误差。结果 75例116个病灶进行了337次头部立体定向放疗。分次间、分次内平移摆位误差分别为左右方向x (0.93±0.86)、(0.15±0.59) mm,头脚方向y (1.83±1.27)、(0.25±0.73) mm,腹背方向z (0.96±0.80)、(0.14±0.56) mm;分次间、分次内旋转摆位误差分别为矢状面Rx (0.65°±0.62°)、(0.19°±0.40°),横断面Ry (0.97°±0.94°)、(0.13°±0.25°),冠状面Rz (0.92°±0.71°)、(0.10°±0.29°)。残余平移误差左右、头脚、腹背方向分别为(0.06±0.23)、(0.08±0.24)、(0.08±0.22) mm;残余旋转误差矢状面、横断面、冠状面分别为(0.12°±0.27°)、(0.09°±0.18°)、(0.06°±0.19°)。337次分次间摆位误差99.1%超过误差阈值(0.7 mm,0.7°)需要至少校正1次;1 006组分次内摆位误差33.6%在治疗床转到位验证无需误差校正,66.4%需要校正至少1次。结论 头部立体定向放疗患者要重视分次间摆位误差和分次内摆位误差,进行逐弧体位验证是非常必要的。     

应用锥形束CT研究盆腔肿瘤放射治疗分次间及分次内的摆位误差

[目的]研究盆腔肿瘤放疗分次间及分次内的摆位误差,计算临床靶区(CTV)到计划靶区(PTV)的外放边界(MPTV)。[方法]应用ELEKTA Synergy IGRT直线加速器系统治疗盆腔肿瘤24例,通过锥形束CT(CBCT)影像技术获得患者左右(X)、头脚(Y)、前后(Z)方向线性摆位误差以及分别以X、Y、Z轴旋转形成相应的U、V、W旋转摆位误差,分析分次间、分次内的摆位误差,计算MPTV。[结果]24例患者共行365次首次摆位后CBCT扫描,系统误差(均数)±随机误差(标准差)在X、Y、Z方向上分别为(0.73±1.67)mm、(0.11±4.69)mm、(-1.77±2.60)mm,U、V、W方向上分别为(0.81°±1.11°、-0.01°±1.18°、0.39°±0.88°;纠正后摆位误差显著低于首次摆位后摆位误差(P<0.05),治疗后摆位误差较纠正后显著增加(P<0.05);纠正前X、Y、Z方向的MPTV分别为4.93mm、12.63mm、7.06mm,纠正后X、Y、Z方向的MPTV分别为1.25mm、2.43mm、1.67mm。[结论]盆腔肿瘤放疗时Y方向摆位误差最大,Z方向次之,X方向最小,旋转误差一般不超过3°;应用CBCT实施IGRT,可在线实时纠正分次间的摆位误差,提高放疗的精确度;应用CBCT引导放疗时,MPTV可缩小至所有方向均为3mm。     

主动呼吸控制系统在非小细胞肺癌精确放疗中的应用

背景与目的:呼吸运动是影响非小细胞肺癌放射剂量提升的重要因素。本研究观察使用主动呼吸控制(activebreathingcontrol,ABC)系统对非小细胞肺癌原发肿瘤运动的影响,研究其在精确放疗中减少放射性肺损伤方面作用。方法:选择ⅢA～Ⅳ期周围型肺鳞癌或腺癌患者7例,使用ABC系统控制呼吸进行三维适形放疗定位及治疗,在患者吸气量达到平静呼吸最大吸气量的80%时强制屏气,分别计算分次放疗时、分次放疗间的肿瘤运动范围,保持相同体位患者平静呼吸,重复扫描计算出平静呼吸时的肿瘤运动范围。制定适形放疗计划,比较两种状态下内边界、V20、Dmean、大体靶区(grosstargetvolumol,GTV)的体积及双侧肺的体积(totalvolume,TV)的不同,用t检验进行统计学分析。结果:7例患者在主动呼吸控制时分次放疗时左右方向(X)、前后方向(Y)和头脚方向(Z)的运动幅度分别为(0.79±0.45)mm、(0.98±0.52)mm、(0.50±0.75)mm,分次放疗间的三维方向的运动幅度分别为(0.91±0.69)mm、(1.02±0.77)mm、(0.74±1.0)mm,平静呼吸(freebreathing,FB)时的三维运动幅度分别为(1.09±0.61)mm、(1.71±0.82)mm、(2.73±1.08)mm。分别制定ABC和FB状态下的放疗计划,其DVH显示V20分别为(10.0±3.7)%、(17.0±6.5)%(P=0.015),Dmean分别为(539±247)cGy、(844±390)cGy(P=0.012),GTV的体积分别为(26.1±22.0)cm3、(30.0±23.9)cm3(P=0.02),双肺的总体积分别为(3522.8±1020.0)cm3、(3240.7±876.7)cm3(P=0.045)。结论:使用ABC系统控制呼吸,可有效缩小肿瘤运动幅度和内边界,缩小周围型肺癌周围正常组织的受照体积;使用吸气期屏气进行定位和放射治疗,可增加全肺体积,从而降低受照射肺组织的密度,减少放射性肺损伤的发生率。     

Intrafractional gastric motion and interfractional stomach deformity during radiation therapy.

BACKGROUND AND PURPOSE: To evaluate intrafractional gastric motion and interfractional variability of the stomach shape during radiation therapy (RT) for gastric lymphoma. MATERIALS AND METHODS: For 11 patients with gastric lymphomas, we undertook fluoroscopic examinations at the time of the simulation, and once a week during RT to evaluate inter- and intrafractional gastric variations. We recorded anteroposterior and left to right X-ray images at inhale and exhale in each examination. We gave coordinates based on the bony landmarks in each patient, and identified the most superior, inferior, lateral, ventral, and dorsal points of the stomach on each film. The interfractional motion was assessed as the distance between a point at inhale and the corresponding point at exhale. We also analyzed interfractional variation based on each point measured. RESULTS: The intrafractional gastric motion was 11.7+/-8.3, 11.0+/-7.1, 6.5+/-6.5, 3.4+/-2.3, 7.1+/-8.2, 6.6+/-5.8mm (mean+/-SD) for the superior, inferior, right, left, ventral and dorsal points, respectively, which was significantly different between each point. The interfractional variability of stomach filling was -2.9+/-14.4, -6.0+/-13.4, 9.3+/-22.0mm for the superior-inferior (SI), lateral (LAT), and ventro-dorsal (VD) directions, respectively, and the differences of variabilities were also statistically significant. Thus, the appropriate treatment margins calculated from both systematic and random errors are 30.3, 41.0, and 50.8mm for the SI, LAT, and ventro-dorsal directions, respectively. CONCLUSIONS: Both intrafractional gastric motion and interfractional variability of the stomach shape were considerable during RT. We recommend regular verification of gastric movement and shape before and during RT to individualize treatment volume.     

Evaluation of respiratory-induced target motion for esophageal tumors at the gastroesophageal junction.

PURPOSE: To quantify the internal motion margin requirements for radiotherapy of tumors near the gastroesophageal junction (GEJ). METHODS AND MATERIALS: Four-dimensional computed tomography (4DCT) scans were obtained for 25 patients with primary tumors located near the GEJ. The gross tumor volume (GTV) was manually contoured on the exhale-phase image from the 4DCT image set. A deformable image registration method was used to automatically propagate the contours to other phases of the 4DCT images. To quantify target motion, we measured the displacement of the GTV centroid and the variations in the target boundary and volume. Internal margins were calculated in the lateral (RL), anterior-posterior (AP), and superior-inferior (SI) directions. RESULTS: The mean+/-standard deviation peak-to-peak GTV centroid motion was 0.39+/-0.27cm (range, 0.04-1.09cm) in the RL, 0.38+/-0.23cm (range, 0.10-0.94cm) in the AP, and 0.87+/-0.47cm (range, 0.43-2.63cm) in the SI directions, respectively. On average, the internal target volume was 72% (range, 9-172%) larger than the GTV defined on a single-phase CT image. Variations in tumor boundaries due to tissue motion and deformation suggested asymmetric margins: 1.0cm left [toward the stomach], 0.8cm right, 1.1cm anterior, 0.6cm posterior, 1.0cm superior (toward the distal esophagus), and 1.6cm inferior (toward the stomach). CONCLUSION: Because tumors near the GEJ are subject to a marked but asymmetric amount of respiratory-induced intrafractional tumor motion, the use of asymmetric internal margins may be beneficial.     

Set-up errors due to endorectal balloon positioning in intensity modulated radiation therapy for prostate cancer.

PURPOSE: To investigate the set-up errors and deformation associated with daily placement of endorectal balloons in prostate radiotherapy. MATERIALS AND METHODS: Endorectal balloons were placed daily in 20 prostate cancer patients undergoing radiotherapy. Electronic portal images (EPIs) were collected weekly from anterior-posterior (AP) and lateral views. The EPIs were compared with digitally reconstructed radiographs from computed tomography scans obtained during pretreatment period to estimate displacements. The interfraction deformation of balloon was estimated with variations in diameter in three orthogonal directions throughout the treatment course. RESULTS: A total of 154 EPIs were evaluated. The mean displacements of balloon relative to bony landmark were 1.8mm in superior-inferior (SI), 1.3mm in AP, and 0.1mm in left-right (LR) directions. The systematic errors in SI, AP, and LR directions were 3.3mm, 4.9 mm, and 4.0mm, respectively. The random (interfraction) displacements, relative to either bony landmarks or treatment isocenter, were larger in SI direction (4.5mm and 4.5mm), than in AP (3.9 mm and 4.4mm) and LR directions (3.0mm and 3.0mm). The random errors of treatment isocenter to bony landmark were 2.3mm, 3.2mm, and 2.6mm in SI, AP, and LR directions, respectively. Over the treatment course, balloon deformations of 2.8mm, 2.5mm, and 2.6mm occurred in SI, AP, and LR directions, respectively. The coefficient of variance of deformation was 7.9%, 4.9%, and 4.9% in these directions. CONCLUSIONS: Larger interfractional displacement and the most prominent interfractional deformation of endorectal balloon were both in SI direction.     

Inter- and intrafractional movement-induced dose reduction of prostate target volume in proton beam treatment

PURPOSE: To quantify proton radiotherapy dose reduction in the prostate target volume because of the three-dimensional movement of the prostate based on an analysis of dose-volume histograms (DVHs). METHODS AND MATERIALS: Twelve prostate cancer patients underwent scanning in supine position, and a target contour was delineated for each using a proton treatment planning system. To simulate target movement, the contour was displaced from 3 to 15 mm in 3-mm intervals in the superior-to-inferior (SI), inferior-to-superior (IS), anterior-to-posterior (AP), posterior-to-anterior (PA), and left-to-right (LR) directions. RESULTS: For both intra- and interfractional movements, the average coverage index and conformity index of the target were reduced in all directions. For interfractional movements, the magnitude of dose reduction was greater in the LR direction than in the AP, PA, SI. and IS directions. Although the reduction of target dose was proportional to the magnitude of intrafractional movement in all directions, a proportionality between dose reduction and the magnitude of interfractional target movement was clear only in the LR direction. Like the coverage index and conformity index, the equivalent uniform dose and homogeneity index showed similar reductions for both types of target movements. CONCLUSIONS: Small target movements can significantly reduce target proton radiotherapy dose during treatment of prostate cancer patients. Attention should be given to interfractional target movement along the longitudinal direction, as image-guided radiotherapy may be ineffective if margins are not sufficient.     

Prostate position relative to pelvic bony anatomy based on intraprostatic gold markers and electronic portal imaging

PURPOSE: To describe the relative positions and motions of the prostate, pelvic bony anatomy, and intraprostatic gold fiducial markers during daily electronic portal localization of the prostate. METHODS AND MATERIALS: Twenty prostate cancer patients were treated supine with definitive external radiotherapy according to an on-line target localization protocol using three or four intraprostatic gold fiducial markers and an electronic portal imaging device. Daily pretherapy and through-treatment electronic portal images (EPIs) were obtained for each of four treatment fields. The patients' pelvic bony anatomy, intraprostatic gold markers, and a best visual match to the target (i.e., prostate) were identified on simulation digitally reconstructed radiographs and during daily treatment setup and delivery. These data provided quantitative inter- and intrafractional analysis of prostate motion, its position relative to the bony anatomy, and the individual intraprostatic fiducial markers. Treatment planning margins, with and without on-line localization, were subsequently compared. RESULTS: A total of 22,266 data points were obtained from daily pretherapy and through-treatment EPIs. The pretherapy three-dimensional (3D) average displacement of the fiducial markers, as a surrogate for the prostate, was 5.6 mm, which improved to 2.8 mm after use of the localization protocol. The bony anatomy 3D average displacement was 4.4 mm both before and after localization to the prostate (p = 0.46). Along the superior-inferior (SI), anterior-posterior (AP), and right-left (RL) axes, the average prostate displacement improved from 2.5, 3.7, and 1.9 mm, respectively, before localization to 1.4, 1.6, and 1.1 mm after (all p < 0.001). The pretherapy to through-treatment position of the bony landmarks worsened from 1.7 to 2.5 mm (p < 0.001) in the SI axis, remained statistically unchanged at 2.8 mm (p = 0.39) in the AP axis, and improved from 2.0 to 1.2 mm in the RL axis (p < 0.001). There was no significant intrafractional displacement of prostate position or bony anatomic landmarks. An intermarker distance was identified for all fiducial markers, and 96 were followed daily. Seventy-nine percent had a standard deviation of <1 mm, and 96% were <1.5 mm. Margins were 5.1, 7.3, and 5.0 mm in the SI, AP, and RL axes, respectively, before localization and 2.7, 2.9, and 2.8 mm after localization. CONCLUSIONS: Significant interfractional motion exists for patients' prostate and pelvic bony anatomy. However, these move independently, so the pelvic bony anatomy should not be used as a surrogate for prostate motion. Fiducial markers are stable within the prostate and allow significant margin reduction when used for on-line localization of the prostate.     

Intrafraction prostate motion during IMRT for prostate cancer

PURPOSE: Although the interfraction motion of the prostate has been previously studied through the use of fiducial markers, CT scans, and ultrasound-based systems, intrafraction motion is not well documented. In this report, the B-mode, Acquisition, and Targeting (BAT) ultrasound system was used to measure intrafraction prostate motion during 200 intensity-modulated radiotherapy (IMRT) sessions for prostate cancer. METHODS AND MATERIALS: Twenty men receiving treatment with IMRT for clinically localized prostate cancer were selected for the study. Pre- and posttreatment BAT ultrasound alignment images were collected immediately before and after IMRT on 10 treatment days for a total of 400 BAT alignment procedures. Any ultrasound shifts of the prostate borders in relation to the planning CT scan were recorded in 3 dimensions: right-left (RL), anteroposterior (AP), and superior-inferior (SI). Every ultrasound procedure was evaluated for image quality and alignment according to a 3-point grading scale. RESULTS: All the BAT images were judged to be of acceptable quality and alignment. The dominant directions of intrafraction prostate motion were anteriorly and superiorly. The mean magnitude of shifts (+/-SD) was 0.01 +/- 0.4 mm, 0.2 +/- 1.3 mm, and 0.1 +/- 1.0 mm in the left, anterior, and superior directions, respectively. The maximal range of motion occurred in the AP dimension, from 6.8 mm anteriorly to 4.6 mm posteriorly. The percentage of treatments during which prostate motion was judged to be 5 mm. The extent of intrafraction motion was much smaller than that of interfraction motion. Linear regression analysis showed very little correlation between the two types of motion (r = 0.014, 0.029, and 0.191, respectively) in the RL, AP, and SI directions. CONCLUSION: Using an ultrasound-based system, intrafraction prostate motion occurred predominantly in the anterior and superior directions, but was clinically insignificant. Intrafraction motion was much smaller than interfraction motion, and the two types of movement did not correlate.     

A comparison of the use of bony anatomy and internal markers for offline verification and an evaluation of the potential benefit of online and offline verification protocols for prostate radiotherapy

PURPOSE: To evaluate the utility of intraprostatic markers in the treatment verification of prostate cancer radiotherapy. Specific aims were: to compare the effectiveness of offline correction protocols, either using gold markers or bony anatomy; to estimate the potential benefit of online correction protocol's using gold markers; to determine the presence and effect of intrafraction motion. METHODS AND MATERIALS: Thirty patients with three gold markers inserted had pretreatment and posttreatment images acquired and were treated using an offline correction protocol and gold markers. Retrospectively, an offline protocol was applied using bony anatomy and an online protocol using gold markers. RESULTS: The systematic errors were reduced from 1.3, 1.9, and 2.5 mm to 1.1, 1.1, and 1.5 mm in the right-left (RL), superoinferior (SI), and anteroposterior (AP) directions, respectively, using the offline correction protocol and gold markers instead of bony anatomy. The subsequent decrease in margins was 1.7, 3.3, and 4 mm in the RL, SI, and AP directions, respectively. An offline correction protocol combined with an online correction protocol in the first four fractions reduced random errors further to 0.9, 1.1, and 1.0 mm in the RL, SI, and AP directions, respectively. A daily online protocol reduced all errors to <1 mm. Intrafraction motion had greater impact on the effectiveness of the online protocol than the offline protocols. CONCLUSIONS: An offline protocol using gold markers is effective in reducing the systematic error. The value of online protocols is reduced by intrafraction motion.