单次曝光法在调强放疗位置验证片拍摄中的应用探讨

目的 通过使用自制射野“十”字板拍摄放疗位置验证片显示中心“十”字,对单次曝光拍摄放疗位置验证片的方法进行尝试.方法 首先确定图像上显示的十字与束流中心轴的位置关系,其次使用单次曝光成像方法拍摄20例患者治疗位置验证片与数字重建影像（DRR）片比较,离线评价患者摆位误差.结果 射野中心“十”字与束流中心轴的位置关系＜2 mm,标尺刻度准确性＜2 mm.头颈部左右方向最小、最大误差分别为1.0、2.0 mm,平均值1.01 mm,标准差0.12 mm;前方向最小、最大误差分别为1.0、3.0 mm,平均值1.25 mm,标准差0.47 mm;头脚方向最小、最大误差分别为1.0、2.0 mm,平均值1.22 mm,标准差0.34 mm.结论 单次曝光法可以拍摄放疗位置验证片,操作简单,可缩短验证时间,减少患者受照剂量,影像轮廓清晰,骨性标记明显,射野中心“十”字及标尺明显,能直观判断肿瘤深度,达到放疗位置验证.     

利用拍摄射野验证片测量鼻咽癌放射治疗实施过程的误差

目的 探讨鼻咽癌放射治疗过程中通过拍摄射野验证片来实施质量控制和分析误差产生的相关因素.方法 利用双曝光照相技术拍摄验证片,将验证片上标记点的影像("+"字金属点)连成参考坐标系,与计划片对比,测量和分析验证片与计划片之间的误差.结果 等中心处位移矢量,偏转角度.射野内解剖骨性结构及周围危及器官(OAR)射野形态变化大于3 mm的位移或绕射束中心旋转轴的变化大于3度.不予治疗查找原因.判断出是放射治疗时摆位误差,抑或是挡块制作时形状和位置的误差,加以针对性纠正.结论 拍摄验证片是较有效的放射治疗质量控制方法,同时可验证患者个体化射野不规则挡块的位置和形变.具有"+"连接注入五个铅金属点的有机玻璃刻度板的使用,使射野验证片参考标记点可量化到具体数据.对分析误差尤为重要.     

三次曝光技术在后颈电子线补量中的应用

目的:IP板与自制十字板合用,采用三次曝光照相技术拍摄射野证实片,用于后颈电子线补量照射范围的确定。方法:将自制十字补板和IP板放置在相应位置,分三次曝光拍摄射野证实片,确定电子线后颈量的照射范围,然后在模拟机下同体位拍摄复合定位片,评价照射范围是否符合治疗要求。结果:8例需要后颈电子线补量的病人使用三次曝光方法拍摄射野证实片,经模拟定位机同治疗体位拍摄复合定位片证实,经主管医生确认电子线后颈补量照射野范围均符合治疗要求,PTW 2D-ARRAY729矩阵验证剂量误差符合要求。结论:采用三次曝光技术确定电子线照射野的方法,可用于鼻咽癌及其他口咽部肿瘤治疗时对后颈电子线补量,该方法操作简单方便、实用。     

关于放疗位置验证方式的探讨

目的:探讨放疗全程进行位置验证的意义。方法:测量使用0.6 MU的剂量拍摄位置验证片时患者实际的吸收剂量,用计划系统计算患者整个疗程吸收剂量的改变。每次治疗前采用单次曝光成像技术拍摄正、侧位位置验证片,与首次位置验证片比对,记录左右、腹背和头脚方向的误差值,若超出误差阈值则纠正摆位后再进行治疗。前五次误差,首次、中间和末次误差以及全程位置验证的误差利用方差分析方法进行统计分析。结果:获取位置验证图像过程中患者平均吸收剂量为0.3 cGy,经过计划系统重新计算剂量分布,对靶区剂量无影响。三种位置验证方式中,全程位置验证的左右、腹背和头脚方向的误差均为最大,且差异有统计学意义(P＜0.05)。三种位置验证方法中,腹背方向的误差均值最小,左右方向的误差均值最大,且差异有统计学意义(P＜0.05)。结论:全程位置验证对于保证病人靶区位置的精确性是有意义的。     

IP板在拍摄射野验证片中的应用

肿瘤放疗中位置验证是重要质量保证环节和措施,为此笔者进行IP板双曝光成相技术拍摄放疗射野位置验证片研究,结果报道如下。     

双曝光照相技术在鼻咽癌放射治疗的临床应用

目的　探索鼻咽癌放射治疗实施过程的质量控制方法。方法　采用KodakEC -Loncologycassettes片盒和KodakEC -Lfilm胶片对在直线加速器治疗的鼻咽癌病人进行照射野的双曝光拍片 ,然后与模拟定位机的治疗计划片比较。结果　双曝光照相技术成像清晰 ,遮挡组织和未遮挡组织经过两次曝光的成像反差明显 ,应用在直线加速器下治疗的鼻咽癌病人 ,检验定位与治疗摆位的照射野及组织位移的变化。结论　采用双曝光照相技术及验证可以减少摆位误差 ,确保放射治疗计划实施的准确性     

双曝光照相技术在鼻咽癌放射治疗的临床应用

目的：探索鼻咽癌放射治疗实施过程的质量控制方法。方法：采用Kodak EC-L oncology cassettes片盒和Kodak EC-L film胶片对在直线加速器治疗的鼻咽癌病人进行照射野的双曝光拍片，然后与模拟定位机的治疗计划片比较。结果：双曝光照相技术成像清晰，遮挡组织和未遮挡组织经过两次曝光的成像反差明显，应用在直线加速器下治疗的鼻咽癌病人，检验定位与治疗摆位的照射野及组织位移的变化。结论：采用双曝光照相技术及验证可以减少摆位误差，确保放射治疗计划实施的准确性。     

拍片验证在腹部肿瘤放射治疗的可行性分析

目的:探讨拍片验证在腹部肿瘤放射治疗的可行性和意义.方法:运用OPTIVUETM(平板电子射野验证成像设备)对第一次放射治疗或每周位置精度验证的病人进行拍片.结果:在113个腹部肿瘤的病人进行的放射治疗期间所拍的500张的验证片与RTT图象(CT扫描合成的参考图象)对比,在200张的调强放射治疗验证片中误差＞3mm占7%(14/200);在300张的适型放射治疗验证片中误差＞5mm占9%(27/300);在113个腹部肿瘤的病人中因肿瘤部位不同造成的摆位误差:上腹部肿瘤39个病人摆位误差的平均值2.15mm;中腹部肿瘤27个病人摆位误差的平均值 2.89mm;下腹部肿瘤40个病人摆位误差的平均值 1.42mm.结论:验证拍片在腹部肿瘤放射治疗中有帮助.     

放射治疗射野片的拍摄和分析

目的　讨论如何实施和完善放射治疗射野片的拍摄和分析。方法　采用双曝光技术进行放射治疗射野片的拍摄 ;在首次曝光时加入射野参考坐标标记点 ;以铅点影像所勾画成的十字线为实际射野的参考坐标 ,与模拟机的计划摄片进行比较分析。结果　射野片上铅点和挡块轮廓的影像都较为清晰 ,但射野内组织影像的分辨率和图像对比度逊于常规的模拟机摄片。不过 ,仍可以从射野片上分辨出照射野内各组织的结构和位置 ,从而分析和判断实际照射野是否达到放射治疗计划的要求。结论　射野片的实时性不如电子射野影像系统 ,但其具有成本低廉、容易实施的特点 ,可成为放射治疗执行阶段中重要的质量控制手段 ;参考标记点的设置是射野片分析工作中不容忽视的环节。     

130例放疗病人摆位误差分析

目的:利用MV级电子射野影像系统（EPID）对130例放疗病人摆位误差进行分析。方法:选取头颈部肿瘤放疗患者30例,胸部肿瘤放疗患者50例,盆腔肿瘤放疗患者50例,使用6MV X线通过EPID获得0°和 90°两射野的实时位置验证片,并与计划系统产生的数字化重建影像的验证片进行对照,计算并分析所测定的摆位误差。结果:3%的头颈部患者摆位误差超过3mm,20%的胸部患者摆位误差超过5mm,10%的盆腔患者摆位误差超过5mm,对这些超过误差范围的患者重新调整位置,达到治疗要求。各部位在X轴（左右方向）、Y轴(头脚方向)、Z轴（前后方向）三个方向的平均摆位误差分别为头颈部1.59mm、1.38mm、1.42mm,胸部2.40mm、2.52mm、2.01mm,盆腔2.11mm、2.35mm、1.98mm。结论:利用EPID可以有效检测放射治疗中的摆位误差,提高摆位的准确性和重复性,是放射治疗质量保证的重要手段。     

Patient position verification with oblique radiation beams.

PURPOSE: In this study we investigated whether the position of head and neck cancer patients during radiotherapy could be determined from portal images of oblique radiation beams. Currently applied additional anterior posterior (AP) and lateral verification beams could then be abandoned. METHOD: The patient position was determined from portal images of the oblique radiation beams and compared with that determined from AP and lateral verification beams. Seven hundred and fifty-one portal images of 18 different patients were analyzed. RESULTS: The set-up errors of patients that were treated with oblique gantry angles could be determined with the same accuracy from the oblique beams as from the AP and lateral verification beams in the ventrodorsal and craniocaudal direction. An additional AP beam was necessary to obtain the same accuracy in the lateral direction, because the used beam directions were relatively close to lateral. The position verification of patients treated with both oblique gantry angles and isocentric table rotations was more accurate if AP and lateral verification beams were used. CONCLUSIONS: For patients treated with an irradiation technique with oblique gantry angles (and no isocentric table rotations) position verification can be performed by using these oblique radiation beams.     

X-ray volume imaging in bladder radiotherapy verification

PURPOSE: To assess the clinical utility of X-ray volume imaging (XVI) for verification of bladder radiotherapy and to quantify geometric error in bladder radiotherapy delivery. METHODS AND MATERIALS: Twenty subjects undergoing conformal bladder radiotherapy were recruited. X-ray volume images and electronic portal images (EPIs) were acquired for the first 5 fractions and then once weekly. X-ray volume images were co-registered with the planning computed tomography scan and clinical target volume coverage assessed in three dimensions (3D). Interfraction bladder volume change was described by quantifying changes in bladder volume with time. Bony setup errors were compared from both XVI and EPI. RESULTS: The bladder boundary was clearly visible on coronal XVI views in nearly all images, allowing accurate 3D treatment verification. In 93.5% of imaged fractions, the clinical target volume was within the planning target volume. Most subjects displayed consistent bladder volumes, but 25% displayed changes that could be predicted from the first three XVIs. Bony setup errors were similar whether calculated from XVI or EPI. CONCLUSIONS: Coronal XVI can be used to verify 3D bladder radiotherapy delivery. Image-guided interventions to reduce geographic miss and normal tissue toxicity are feasible with this technology.     

Feasibility of geometrical verification of patient set-up using body contours and computed tomography data.

BACKGROUND AND PURPOSE: Body contours can potentially be used for patient set-up verification in external-beam radiotherapy and might enable more accurate set-up of patients prior to irradiation. The aim of this study is to test the feasibility of patient set-up verification using a body contour scanner. MATERIAL AND METHODS: Body contour scans of 33 lung cancer and 21 head-and-neck cancer patients were acquired on a simulator. We assume that this dataset is representative for the patient set-up on an accelerator. Shortly before acquisition of the body contour scan, a pair of orthogonal simulator images was taken as a reference. Both the body contour scan and the simulator images were matched in 3D to the planning computed tomography scan. Movement of skin with respect to bone was quantified based on an analysis of variance method. RESULTS: Set-up errors determined with body-contours agreed reasonably well with those determined with simulator images. For the lung cancer patients, the average set-up errors (mm)+/-1 standard deviation (SD) for the left-right, cranio-caudal and anterior-posterior directions were 1.2+/-2.9, -0.8+/-5.0 and -2.3+/-3.1 using body contours, compared to -0.8+/-3.2, -1.0+/-4.1 and -1.2+/-2.4 using simulator images. For the head-and-neck cancer patients, the set-up errors were 0.5+/-1.8, 0.5+/-2.7 and -2.2+/-1.8 using body contours compared to -0.4+/-1.2, 0.1+/-2.1, -0.1+/-1.8 using simulator images. The SD of the set-up errors obtained from analysis of the body contours were not significantly different from those obtained from analysis of the simulator images. Movement of the skin with respect to bone (1 SD) was estimated at 2.3 mm for lung cancer patients and 1.7 mm for head-and-neck cancer patients. CONCLUSION: Measurement of patient set-up using a body-contouring device is possible. The accuracy, however, is limited by the movement of the skin with respect to the bone. In situations where the error in the patient set-up is relatively large, it is possible to reduce these errors using a computer-aided set-up technique based on contour information.     

自制脚部固定器在下肢肿瘤等放疗中的应用

目的 探讨自制脚部固定器在下肢肿瘤等放疗中的应用价值。方法 31例患者下肢放疗时应用脚部固定器定位固定,放疗中每周拍摄验证片,通过验证片和模拟定位片或计划系统生成的数字重建影像比较分析摆位误差。配对t检验差异。结果 患者上下、前后、左右方向摆位误差分别为(2.39±2.21)、(0.22±2.73)、(0.20±2.71) mm,上下方向偏移较前后、左右方向大(P=0.000、0.000)。结论 下肢肿瘤等放疗中应用脚部固定器具有良好准确性和重复性,值得推广。     

In vivo dosimetry during external photon beam radiotherapy

In this critical review of the current practice of patient dose verification, we first demonstrate that a high accuracy (about 1-2%, 1 SD) can be obtained. Accurate in vivo dosimetry is possible if diodes and thermoluminescence dosimeters (TLDs), the main detector types in use for in vivo dosimetry, are carefully calibrated and the factors influencing their sensitivity are taken into account. Various methods and philosophies for applying patient dose verification are then evaluated: the measurement of each field for each fraction of each patient, a limited number of checks for all patients, or measurements of specific patient groups, for example, during total body irradiation (TBI) or conformal radiotherapy. The experience of a number of centers is then presented, providing information on the various types of errors detected by in vivo dosimetry, including their frequency and magnitude. From the results of recent studies it can be concluded that in centers having modern equipment with verification systems as well as comprehensive quality assurance (QA) programs, a systematic error larger than 5% in dose delivery is still present for 0.5-1% of the patient treatments. In other studies, a frequency of 3-10% of errors was observed for specific patient groups or when no verification system was present at the accelerator. These results were balanced against the additional manpower and other resources required for such a QA program. It could be concluded that patient dose verification should be an essential part of a QA program in a radiotherapy department, and plays a complementary role to treatment-sheet double checking. As the radiotherapy community makes the transition from the conventional two-dimensional (2D) to three-dimensional (3D) conformal and intensity modulated dose delivery, it is recommended that new treatment techniques be checked systematically for a few patients, and to perform in vivo dosimetry a few times for each patient for situations where errors in dose delivery should be minimized.     

应用密度填充及伪影消减技术提高带金属植入物患者IMRT剂量准确度研究

目的探讨提高带金属植入物患者放射治疗计划剂量计算准确度的方法。方法利用具有金属伪影消减技术的CT模拟机对插入金属棒的CIRS调强模体和8例椎体中植入了钢钉并接受放疗的患者进行扫描,在获得的常规CT图像、金属伪影消减技术CT图像及对其金属区域进行密度填充的图像上设计治疗计划。在模体中比较单个射野及IMRT计划的计算结果与剂量测量结果,同时对患者IMRT计划中金属植入物及其伪影对照射剂量产生的影响进行分析。结果基于常规CT图像的放疗计划中,射野入射路径未通过金属区域时,单个射野的剂量计算误差为3.85%,通过金属区域时射野计算误差范围达4.46%~74.11%。IMRT计划中存在入射路径通过金属区域的射野时,其误差可能超出临床可接受的范围,计算误差随这种射野所占剂量权重的增加而变大。当采用密度填充及伪影消减技术处理图像后,上述单个射野的计算误差分别为1.23%和0.89%~4.73%,IMRT计划的剂量误差为1.84%。若单独采用密度填充技术处理金属区域,IMRT计划的剂量误差为1.88%。基于常规CT图像的患者IMRT计划中,受金属植入物及其伪影的影响,实际靶区受到的最小剂量、平均剂量及处方剂量覆盖率较计划结果下降,危及器官剂量相近。结论基于常规CT图像的放疗计划中,入射路径通过金属区域的射野可能产生较大的剂量计算误差。如果植入的金属材料已知,在计划系统中对金属区域进行密度填充能有效提高计划的剂量计算准确度。伪影消减技术能显著改善图像质量,进一步减少剂量计算误差,对于配备这种功能的CT机进行带金属植入物患者的模拟定位时应作为常规技术。     

A technique for optimization of digitally reconstructed radiographs of the chest in virtual simulation

INTRODUCTION: Virtual simulation (VS) of radiotherapy uses CT data. Digitally reconstructed radiographs (DRRs) are a critical element of this process, and the quality of these images is frequently suboptimal. We present techniques to improve DRR quality for clinical purposes. The results of two approaches to DRR optimization are presented. METHODS AND MATERIALS: One approach to DRR optimization is to use traditional radiographs as a guide and to adjust the algorithm parameters based on image and objective contrast to produce images that more closely resemble traditional radiographs (Method 1). Another approach is to focus on the visibility of specific anatomic structures. Using this method, two DRR images are optimized manually by interactively adjusting reconstruction parameters, then they are combined into a single composite image (Method 2). DRRs for the chest region, generated using both methods, were evaluated by clinical staff based on usability for treatment verification and field definition. RESULTS: Using Method 1, the resulting DRRs more closely resembled traditional radiographs. This technique allows DRR quality to be improved with little user interaction. These DRRs are generally adequate for clinical use, but not optimal for sites such as the chest. Images generated using Method 2 were considered clinically superior in terms of visibility of specific anatomic structures. These images also compare well with traditional radiographs, although they show an increased contrast level between bone and lower density structures. CONCLUSION: Both Methods 1 and 2 can be used to improve DRR quality for clinical purposes. For the chest region, the additional effort required by Method 2 to achieve a more detailed image appears justified.     

Comparison of megavoltage position verification for prostate irradiation based on bony anatomy and implanted fiducials.

PURPOSE: The patient position during radiotherapy treatment of prostate cancer can be verified with the help of portal images acquired during treatment. In this study we quantify the clinical consequences of the use of image-based verification based on the bony anatomy and the prostate target itself. PATIENTS AND METHODS: We analysed 2025 portal images and 23 computed tomography (CT) scans from 23 patients with prostate cancer. In all patients gold markers were implanted prior to CT scanning. Statistical data for both random and systematic errors were calculated for displacements of bones and markers and we investigated the effectiveness of an off-line correction protocol. RESULTS: Standard deviations for systematic marker displacement are 2.4 mm in the lateral (LR) direction, 4.4 mm in the anterior-posterior (AP) direction and 3.7 mm in the caudal-cranial direction (CC). Application of off-line position verification based on the marker positions results in a shrinkage of the systematic error to well below 1 mm. Position verification based on the bony anatomy reduces the systematic target uncertainty to 50% in the AP direction and in the LR direction. No reduction was observed in the CC direction. For six out of 23 patients we found an increase of the systematic error after application of bony anatomy-based position verification. CONCLUSIONS: We show that even if correction based on the bony anatomy is applied, considerable margins have to be set to account for organ motion. Our study highlights that for individual patients the systematic error can increase after application of bony anatomy-based position verification, whereas the population standard deviation will decrease. Off-line target-based position verification effectively reduces the systematic error to well below 1 mm, thus enabling significant margin reduction.