Intensity-modulated radiotherapy using implanted fiducial markers with daily portal imaging: assessment of prostate organ motion

PURPOSE: To assess our single institutional experience with daily localization, using fiducials for prostate radiotherapy. METHODS AND MATERIALS: From January 2004 to September 2005, 33 patients were treated with 1,097 intensity-modulated radiation treatments, using three implanted fiducials. Daily portal images were obtained before treatments. Shifts were made for deviations > or =3 mm in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) dimensions. RESULTS: Of 1,097 treatments, 987 (90%) required shifts. Shifts were made in the LR, SI, and AP dimensions in 51%, 67%, and 58% of treatments, respectively. In the LR dimension, the median distance shifted was 5 mm. Of 739 shifts in the SI dimension, 73% were in the superior direction for a median distance of 6 mm, and 27% were shifted inferiorly for a median distance of 5 mm. The majority of shifts in the AP dimension were in the anterior direction (87%). Median distances shifted in the anterior and posterior directions were 5 mm and 4 mm, respectively. The median percentage of treatments requiring shifts per patient was 93% (range, 57-100%). Median deviations in the LR, SI, and AP dimensions were 3 mm, 4 mm, and 3 mm, respectively. Deviations in the SI and AP dimensions were more often in the superior rather than inferior (60% vs. 29%) and in the anterior rather than posterior (70% vs. 16%) directions. CONCLUSIONS: Interfraction prostate motion is significant. Daily portal imaging with implanted fiducials improves localization of the prostate, and is necessary for the reduction of treatment margins.     

利用电子射野影像装置测量放疗摆位误差的初步研究

目的 利用电子射野影像装置(EPID)对不同部位肿瘤放疗中的摆位误差进行量化分析,了解不同部位的摆位误差,不同医生对摆位误差的接受程度有无差异。方法 2006年1月—2007年12月接受放射治疗的患者中按头颈、胸部、腹盆腔不同部位,及不同医生治疗组随机抽出58例,按部位分别为头及头颈部20例,胸部19例,腹盆部19例。所有病例采用Philips公司AcQ-Sim大孔径CT和/或Nucletron公司Simulix-HQ X线模拟机模拟定位,治疗计划为ADCC公司Pinnacle3 7.4,用Elekta公司的Precise加速器实施放疗,利用Elekta的iViewGT采集图像,采用双曝光法拍摄照射野验证片。参考图像为CT定位后的DRR或X线模拟机定位图像,图像比较采用骨性结构为标志,勾画出参考图像上的骨性结构,与EPID进行最大程度重合后得出在水平、垂直方向上的摆位误差数据并进行分析。结果 得到102组数据,其中EPID为拍摄角度为0° 38组,90° 21组,其他角度43组。摆位误差水平方向为1.02mm±1.15mm(0mm~5mm),垂直方向为1.11mm±1.20mm(0mm~6mm)。90%以上摆位误差小于3mm。头部或头颈部固定摆位误差最小,水平方向和垂直方向分别为0.64mm±0.65mm和0.91mm±0.98mm。不同医生组之间摆位误差有所不同。结论 绝大多数摆位误差在容许范围。需提高EPID在胸、腹盆部的解剖识别率,以减少其对摆位误差的影响。实施治疗前,先行X线模拟机摆位不失为一种缩小摆位误差的有效办法。     

Intra-fraction prostate displacement in radiotherapy estimated from pre- and post-treatment imaging of patients with implanted fiducial markers

Purpose

To determine intra-fraction displacement of the prostate gland from imaging pre- and post-radiotherapy delivery of prostate cancer patients with three implanted fiducial markers.

Methods and materials

Data were collected from 184 patients who had two orthogonal X-rays pre- and post-delivery on at least 20 occasions using a Varian On Board kV Imaging system. A total of 5778 image pairs covering time intervals between 3 and 30 min between pre- and post-imaging were evaluated for intra-fraction prostate displacement.

Results

The mean three dimensional vector shift between images was 1.7 mm ranging from 0 to 25 mm. No preferential direction of displacement was found; however, there was an increase of prostate displacement with time between images. There was a large variation in typical shifts between patients (range 1 ± 1 to 6 ± 2 mm) with no apparent trends throughout the treatment course. Images acquired in the first five fractions of treatment could be used to predict displacement patterns for individual patients.

Conclusion

Intra-fraction motion of the prostate gland appears to be a limiting factor when considering margins for radiotherapy. Given the variation between patients, a uniform set of margins for all patients may not be satisfactory when high target doses are to be delivered.     

Comparison of two methods for anterior–posterior isocenter localization in pelvic radiotherapy using electronic portal imaging

Purpose: The two setup methods commonly used to determine the anterior–posterior isocenter location in pelvic radiotherapy are to align lateral localization lasers with lateral skin tattoos on the patient, or to set the couch height so that the isocenter is at a fixed height (determined during simulation or treatment planning) above the couch top. This study was implemented to determine which technique gives more accurate patient treatment by comparison of the anterior–posterior setup variation measured with electronic portal imaging.

Methods and Materials: Eleven supine prostate patients were treated with tattoo localization and 159 left-lateral portal images were taken during the treatments. The field displacements were then determined by template matching. These patients were compared to nine patients (205 images) set up to a fixed isocenter height. Similarly, eight prone rectal patients (136 right-lateral images) set up to tattoos were compared to six patients (108 images) set up to a fixed height. The patients were not immobilized and were all treated with three field techniques on a hard couch top. The overall mean treatment position deviation and the standard deviation of the displacements (total setup variation) were calculated for each patient group along with the systematic (simulator-to-treatment) and the random (treatment-to-treatment) setup variation.

Results: The mean treatment position deviations were 3.3 mm anterior and 5.2 mm posterior with the tattoo method for the prostate and rectal patients, respectively. These mean position deviations were 0.4/0.1 mm anterior with the fixed height technique. The total setup variations were 4.6/5.2 mm (1 SD) with tattoo localization and 1.7/1.5 mm (1 SD) with the fixed height method. Similarly, random variation was 2.3/3.3 mm (1 SD) with the tattoo method compared to 1.3/1.2 mm (1 SD) with the fixed height method. Systematic variation was 3.7/4.5 mm (1 SD) compared to 1.2/1.1 mm (1 SD).

Conclusion: The fixed height technique gives much more accurate localization of the anterior–posterior isocenter in pelvic radiotherapy than lateral skin tattoos.     

Intrafraction motion of the prostate during external-beam radiation therapy: analysis of 427 patients with implanted fiducial markers

PURPOSE: To analyze the intrafraction motion of the prostate during external-beam radiation therapy of patients with prostate cancer. METHODS AND MATERIALS: Between August 2001-December 2005, 427 patients with Stage T3Nx/0Mx/0 prostate carcinoma received intensity-modulated radiation therapy treatment combined with position verification with fiducial gold markers. For a total of 11,426 treatment fractions (average, 27 per patient), portal images were taken of the first segment of all five beams. The irradiation time of the technique varied between 5-7 min. From these data, the location of gold markers could be established within every treatment beam under the assumption of minimal marker movement. RESULTS: In 66% of treatment fractions, a motion outside a range of 2 mm was observed, with 28% outside a range of 3 mm. The intrafraction marker movements showed that motion directions were often reversed. However, the effect was small. Even with perfect online position-correction at the start of irradiation, intrafraction motion caused position uncertainty, but systematic errors (Sigma) were limited to <0.6 mm, and random errors (sigma) to <0.9 mm. This would result in a lower limit of 2 mm for margins, in the absence of any other uncertainties. CONCLUSIONS: Intrafraction motion of the prostate occurs frequently during external-beam irradiation on a time scale of 5-7 min. Margins of 2 mm account for these intrafraction motions. However, larger margins are required in practice to accommodate other uncertainties in the treatment.     

关于电子荧光类射野影像系统作为出射剂量仪使用的研究

目的研究利用射野影像系统进行出射剂量测量的可能性。以便能进一步把该类系统发展为剂量仪系统。材料与方法使用荧光型电子射野影像系统，探头由金属板—荧光屏和Ｐｌｕｍｂｉｃｏｎ照像机组成。通过与电离室及射野证实片所测结果的比较，建立一套与像素位置对应的灰度校正矩阵。并在多种射野面积和体模厚度下验证，所用射线为６ＭＶ－Ｘ线。结果通过对该系统的各种性能测试，如灰度的稳定性、探头的均匀性、剂量响应曲线、灰度的射野依赖性及对体模厚度的依赖性，发现短期稳定性好于１％，有较明显的灰度饱和性，但需作灰度饱和校正。作为相对剂量仪使用时，只要建立一个探头非均匀性校正矩阵，就能与证实片的剂量结果保持一致，误差小于±５％。结论研究证明，电子射野影像系统完全可以成为一套剂量仪系统。在对靶区的位置进行实时监测的同时，还能通过对影像灰度的计算，得出出射野的剂量分布     

Comparison of daily megavoltage electronic portal imaging or kilovoltage imaging with marker seeds to ultrasound imaging or skin marks for prostate localization and treatment positioning in patients with prostate cancer

PURPOSE: To compare the accuracy of imaging modalities, immobilization, localization, and positioning techniques in patients with prostate cancer. METHODS AND MATERIALS: Thirty-five patients with prostate cancer had gold marker seeds implanted transrectally and were treated with fractionated radiotherapy. Twenty of the 35 patients had limited immobilization; the remaining had a vacuum-based immobilization. Patient positioning consisted of alignment with lasers to skin marks, ultrasound or kilovoltage X-ray imaging, optical guidance using infrared reflectors, and megavoltage electronic portal imaging (EPI). The variance of each positioning technique was compared to the patient position determined from the pretreatment EPI. RESULTS: With limited immobilization, the average difference between the skin marks' laser position and EPI pretreatment position is 9.1 +/- 5.3 mm, the average difference between the skin marks' infrared position and EPI pretreatment position is 11.8 +/- 7.2 mm, the average difference between the ultrasound position and EPI pretreatment position is 7.0 +/- 4.6 mm, the average difference between kV imaging and EPI pretreatment position is 3.5 +/- 3.1 mm, and the average intrafraction movement during treatment is 3.4 +/- 2.7 mm. For the patients with the vacuum-style immobilization, the average difference between the skin marks' laser position and EPI pretreatment position is 10.7 +/- 4.6 mm, the average difference between kV imaging and EPI pretreatment position is 1.9 +/- 1.5 mm, and the average intrafraction movement during treatment is 2.1 +/- 1.5 mm. CONCLUSIONS: Compared with use of skin marks, ultrasound imaging for positioning provides an increased degree of agreement to EPI-based positioning, though not as favorable as kV imaging fiducial seeds. Intrafraction movement during treatment decreases with improved immobilization.     

Daily electronic portal imaging of implanted gold seed fiducials in patients undergoing radiotherapy after radical prostatectomy

PURPOSE: The aim of this study was to measure interfraction prostate bed motion, setup error, and total positioning error in 10 consecutive patients undergoing postprostatectomy radiotherapy. METHODS AND MATERIALS: Daily image-guided target localization and alignment using electronic portal imaging of gold seed fiducials implanted into the prostate bed under transrectal ultrasound guidance was used in 10 patients undergoing adjuvant or salvage radiotherapy after prostatectomy. Prostate bed motion, setup error, and total positioning error were measured by analysis of gold seed fiducial location on the daily electronic portal images compared with the digitally reconstructed radiographs from the treatment-planning CT. RESULTS: Mean (+/- standard deviation) prostate bed motion was 0.3 +/- 0.9 mm, 0.4 +/- 2.4 mm, and -1.1 +/- 2.1 mm in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) axes, respectively. Mean set-up error was 0.1 +/- 4.5 mm, 1.1 +/- 3.9 mm, and -0.2 +/- 5.1 mm in the LR, SI, and AP axes, respectively. Mean total positioning error was 0.2 +/- 4.5 mm, 1.2 +/- 5.1 mm, and -0.3 +/- 4.5 mm in the LR, SI, and AP axes, respectively. Total positioning errors >5 mm occurred in 14.1%, 38.7%, and 28.2% of all fractions in the LR, SI, and AP axes, respectively. There was no significant migration of the gold marker seeds. CONCLUSIONS: This study validates the use of daily image-guided target localization and alignment using electronic portal imaging of implanted gold seed fiducials as a valuable method to correct for interfraction target motion and to improve precision in the delivery of postprostatectomy radiotherapy.     

A magnetic resonance imaging study of prostate deformation relative to implanted gold fiducial markers

PURPOSE: To describe prostate deformation during radiotherapy and determine the margins required to account for prostate deformation after setup to intraprostatic fiducial markers (FM). METHODS AND MATERIALS: Twenty-five patients with T1c-T2c prostate cancer had three gold FMs implanted. The patients presented with a full bladder and empty rectum for two axial magnetic resonance imaging (MRI) scans using a gradient recalled echo (GRE) sequence capable of imaging the FMs. The MRIs were done at the time of radiotherapy (RT) planning and a randomly assigned fraction. A single observer contoured the prostate surfaces. They were entered into a finite element model and aligned using the centroid of the three FMs. RESULTS: During RT, the prostate volume decreased by 0.5%/fraction (p = 0.03) and the FMs in-migrated by 0.05 mm/fraction (p < 0.05). Prostate deformation was unrelated to differential bladder and bowel filling, but was related to a transurethral resection of the prostate (TURP) (p = 0.003). The standard deviation for systematic uncertainty of prostate surface contouring was 0.8 mm and for FM centroid localization was 0.4 mm. The standard deviation of random interfraction prostate deformation was 1.5 mm and for FM centroid variability was 1.1 mm. These uncertainties from prostate deformation can be incorporated into a margin recipe to determine the total margins required for RT. CONCLUSIONS: During RT, the prostate exhibited: volume decrease, deformation, and in-migration of FMs. Patients with TURPs were prone to prostate deformation.     

Migration of intraprostatic fiducial markers and its influence on the matching quality in external beam radiation therapy for prostate cancer

Purpose

To assess the influence of fiducial marker (FM) migration on the matching quality in external beam radiation therapy (EBRT) for prostate cancer.

Materials and methods

The position of FMs were identified using on-board kV imaging (OBI) and their 3-D position established using an in-house reconstruction algorithm for 31 patients with prostate adenocarcinoma. To carry out the match, the positions were overlaid on the digitally reconstructed radiographs (DRR) generated from the planning CT. The distance between each FM was calculated for seven treatments throughout the EBRT course. Four radiotherapy technologists were asked to independently perform and rate the match from OBI to DRR which was then correlated to the extent of FM migration.

Results

All the matches were rated by at least three radiotherapy technologists as “very easy” (“easy” subgroup) for 24 patients (77%), while the other seven patients had their match rated less than “very easy” and considered the “not easy” subgroup. The average daily FM migration was 0.93 ± 0.34 mm for the “easy” subgroup vs. 1.82 ± 0.75 mm for the latter. An average migration >2 mm was seen in five/seven patients in the “not easy” subgroup as compared to none in the “easy” subgroup. There was a trend towards less FM migration and better matching if the planning CT was done later than the day of the FM implant (p = 0.093).

Conclusions

FM migration >2 mm predicts for a more difficult matching process; PTV margins might have to be adjusted or the planning CT repeated.     

电子射野影像装置机械运动的位置误差研究

目的 研究不同类型电子射野影像装置(EPID)机械运动的相对位置偏差,为基于EPID进行调强放疗剂量验证提供位置误差的修正依据。
方法 对3种不同类型EPID (瓦里安aS1000、aS500和医科达iViewGT)采用5 cm×5 cm射野进行照射。通过自编软件系统对EPID采集的射野图像进行分析,并确定射野中心点在EPID上投影。对臂架0°~360°射野中心点在EPID上投影位置进行分析,并与臂架0°时位置比较以确定相对位置偏移。
结果 在瓦里安aS1000、aS500、医科达iViewGT的EPID最大相对偏移左右方向上分别为(－0.23±0.17)、(2.94±0.17)、(0.35±0.09) mm,上下方向上分别为(－4.16±0.20)、(－4.15±0.25)、(－1.66±0.11) mm。对上下方向上的相对位移采用四次方经验函数可较好地进行拟合。
结论 不同类型EPID在不同角度下相对位置误差不同,且在上下方向上明显较左右方向大,应用EPID进行调强验证时必需考虑对在不同臂架角度下相对位置误差进行修正。     

电子射野影像装置对盆腔肿瘤放疗摆位误差的测定

目的利用Elekta iView GT量化测定盆腔肿瘤放疗摆位中的系统误差及随机误差,为放疗计划PTV的设定提供初步的参考依据。方法对12例接受盆腔放疗的病例进行摆位误差量化测定,共获取244组图像数据。所有入组病例均为CT模拟定位及适形放疗。将每日前后野和两侧野的电子射野影像装置(EPID),采用盆腔骨性标志与数字重建图像(DRR)比较,记录在左右、头脚、前后方向上的移动,从得到的数据计算系统和随机误差。结果每日摆位误差的最大值在左右、头脚、前后方向上分别为9.9、14.0、21.1 mm,摆位的系统误差分别为0.5、0.2、2.3 mm。12例病例数据显示,在左右、头脚、前后方向上移动幅度5～10 mm和>10mm的发生频率分别为8%、9%、21%和0%、1%、3%。结论应用EPID测定盆腔肿瘤放疗的摆位误差,为放疗计划PTV的设定提供初步的参考依据。在PTV设定时,考虑由摆位误差而引起的边界(SM)至少需5 mm,但前后方向以扩大到10 mm为好,以达到97%的靶区包绕率,且需注意个体差异。     

扫描液体电离室型电子射野影像装置的剂量响应研究

目的　研究扫描液体电离室型电子射野影像装置 (EPID)的剂量响应特性及其各种影响因素 ,如机架角、照射野大小、图像获取模式 ,以便进一步利用EPID进行剂量验证方面的研究。方法　所有实验均在装备有PortalVisionTMMK2型电子射野影像装置的Varian 6 0 0C/D加速器上实现。为了得到剂量响应曲线 ,需要建立入射到探头的射线强度与EPID像素值之间的关系。首先 ,通过改变源到探头电离室的距离得到不同的射线强度。其次 ,针对任一剂量率条件 ,用EPID拍摄 3幅数字射野图像取平均 ,取射野中心轴附近 11× 11个像素点的平均值作为EPID响应。最后 ,根据相同条件下测得的剂量率和对应的像素值 ,绘制剂量响应曲线。改变机架角、照射野大小和图像获取模式 ,得到一系列剂量响应曲线。结果　EPID输出像素值与入射剂量率之间并非线性关系。EPID剂量响应曲线与图像获取模式关系密切 ,在离轴点略受机架角的影响 ,但不受射野大小的影响。结论　由于射野图像获取模式明显地影响EPID剂量响应曲线的形状 ,所以对不同获取模式应该分别刻度。机架角的影响可通过在不同机架角下刻度加以消除。EPID剂量响应与射野大小无关的事实为日常剂量响应刻度提供了便利 ,即用一种射野条件刻度就可以准确地应用于其它射野条件     

Comparison of localization performance with implanted fiducial markers and cone-beam computed tomography for on-line image-guided radiotherapy of the prostate

PURPOSE: The aim of this work was to assess the accuracy of kilovoltage (kV) cone-beam computed tomography (CBCT)-based setup corrections as compared with orthogonal megavoltage (MV) portal image-based corrections for patients undergoing external-beam radiotherapy of the prostate. METHODS AND MATERIALS: Daily cone-beam CT volumetric images were acquired after setup for patients with three intraprostatic fiducial markers. The estimated couch shifts were compared retrospectively to patient adjustments based on two orthogonal MV portal images (the current clinical standard of care in our institution). The CBCT soft-tissue based shifts were also estimated by digitally removing the gold markers in each projection to suppress the artifacts in the reconstructed volumes. A total of 256 volumetric images for 15 patients were analyzed. RESULTS: The Pearson coefficient of correlation for the patient position shifts using fiducial markers in MV vs. kV was (R2 = 0.95, 0.84, 0.81) in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. The correlation using soft-tissue matching was as follows: R2 = 0.90, 0.49, 0.51 in the LR, AP and SI directions. A Bland-Altman analysis showed no significant trends in the data. The percentage of shifts within a +/-3-mm tolerance (the clinical action level) was 99.7%, 95.5%, 91.3% for fiducial marker matching and 99.5%, 70.3%, 78.4% for soft-tissue matching. CONCLUSIONS: Cone-beam CT is an accurate and precise tool for image guidance. It provides an equivalent means of patient setup correction for prostate patients with implanted gold fiducial markers. Use of the additional information provided by the visualization of soft-tissue structures is an active area of research.     

基于EPID三维剂量验证系统的物理模型测试及临床应用的初步研究

目的 使用EPID三维剂量验证系统进行物理建模和物理参数优化,并行临床应用前的初步研究。方法 通过EPID采集3、5、10、15、20、25 cm的方野图像建立物理模型,比较在均匀水模体中系统重建的百分深度剂量、射野总散因子及10 cm深度处的离轴比曲线,优化物理模型参数。采用指型电离室和免冲洗胶片,在均匀模体和仿真人模体中测量单野、组合野及IMRT计划点剂量和平面剂量,并与系统重建结果比较。在仿真人模体和 10例不同部位IMRT计划中,比较系统重建和TPS计算的5%/3 mm、3%/3 mm标准下的γ通过率,并对临床病例进行靶区和OAR剂量体积分析。结果 对于单野、组合野以及IMRT计划,系统重建剂量和电离室测量及TPS计算的点剂量平均偏差分别<0.5%和2.0%;在均匀或仿真人模体中以及临床病例中其平面或三维剂量的5%/3 mm、3%/3 mm平均γ通过率均>95%;但临床病例中体现小体积的OAR有较大剂量偏差。结论 通过一系列临床应用前测试,明确了该三维剂量验证系统可有效应用于临床剂量验证,并有较好的临床应用价值。     

On-line aSi portal imaging of implanted fiducial markers for the reduction of interfraction error during conformal radiotherapy of prostate carcinoma

PURPOSE: An on-line system to ensure accuracy of daily setup and therapy of the prostate has been implemented with no equipment modification required. We report results and accuracy of patient setup using this system. METHODS AND MATERIALS: Radiopaque fiducial markers were implanted into the prostate before radiation therapy. Lateral digitally reconstructed radiographs (DRRs) were obtained from planning CT data. Before each treatment fraction, a lateral amorphous silicon (aSi) portal image was acquired and the position of the fiducial markers was compared to the DRRs using chamfer matching. Couch translation only was used to account for marker position displacements, followed by a second lateral portal image to verify isocenter position. Residual displacement data for the aSi and previous portal film systems were compared. RESULTS: This analysis includes a total of 239 portal images during treatment in 17 patients. Initial prostate center of mass (COM) displacements in the superior, inferior, anterior, and posterior directions were a maximum of 7 mm, 9 mm, 10 mm and 11 mm respectively. After identification and correction, prostate COM displacements were <3 mm in all directions. The therapists found it simple to match markers 88% of the time using this system. Treatment delivery times were in the order of 9 min for patients requiring isocenter adjustment and 6 min for those who did not. CONCLUSIONS: This system is technically possible to implement and use as part of an on-line correction protocol and does not require a longer than standard daily appointment time at our center with the current action limit of 3 mm. The system is commercially available and is more efficient and user-friendly than portal film analysis. It provides the opportunity to identify and accommodate interfraction organ motion and may also permit the use of smaller margins during conformal prostate radiotherapy. Further integration of the system such as remote table control would improve efficiency.     

Set-up variation of patients treated with radiotherapy to the prostate measured with an electronic portal imaging device

The set-up variation of 11 patients treated supine with radical radiotherapy for carcinoma of the prostate was measured with an electronic portal imaging device to determine the adequacy of set-up techniques and current margins, as well as the need for immobilization. During the treatments 172 images of the anterior fields and 159 images of the left-lateral fields were taken and the errors in treatment placement were measured by template matching. The variation in the superior-inferior direction was small, 1.4-1.6 mm (1 SD), while the medio-lateral variation was 2.8 mm (1 SD). The anterior-posterior variation was largest, 4.6 mm (1 SD) with an offset of 3.3 mm anterior. This anterior offset and large anterior-posterior variation suggests that set-up techniques were not optimal for this direction. The 1 cm margin used was adequate for set-up variation except in a small number of cases, which was mainly due to the anterior trend. Random (treatment-to-treatment) variations were small (1.1-2.3 mm; 1 SD), indicating that immobilization would result in only modest improvement in reproducibility for these supine patients.     

Long-term experience with transrectal and transperineal implantations of fiducial gold markers in the prostate for position verification in external beam radiotherapy; feasibility, toxicity and quality of life

Background and purpose

This study presents an overview of the experience with transrectal and transperineal implantations of fiducial markers for position verification in prostate radiotherapy, regarding the practical feasibility, procedure-related toxicity and influence on quality of life (QoL).

Material and methods

Since 2001, 914 patients scheduled for intensity-modulated radiotherapy (IMRT) have received gold markers in the prostate. The incidence of severe toxicity, defined by the CTCAE v3.0, was evaluated retrospectively. The influence on QoL was measured prospectively in 36 patients using a combination of three validated questionnaires: the Rand-36, the EORTC QLQ-C30(+3) and the prostate cancer-specific EORTC QLQ-PR25. Next, the incidence of marker migration was assessed.

Results

From 2001 to 2005, 402 patients received markers via the transrectal route. Two of these patients developed urosepsis (grade 3 toxicity). Since 2005, 512 patients received markers via the transperineal route. No grade 3 or 4 toxicity occurred in this group. No significant and clinically relevant differences were found in QoL between pre- and post-implant measures. In 5 patients marker migration led to discontinuation of the marker-based IMRT.

Conclusions

Clinical use of transperineal-implanted fiducial gold markers for position verification in external beam radiotherapy for prostate cancer is a feasible and safe procedure without influencing patients’ QoL.     

应用EPID代替胶片法对MLC的质控研究

目的 研究EPID代替胶片对加速器MLC的质控方法并探讨其在任意机架角度下的可行性。方法 采用RIT113软件对EPID影像和EBT3胶片影像数据进行分析。以EBT3胶片射野边缘50%等剂量曲线位置定义MLC叶片实际位置,在同一射野条件下EPID影像数据中找到MLC叶片实际位置所对应百分剂量值,从而完成EPID到EBT3胶片的替代过程。结果 加速器机架角0°时,以EBT3胶片确定的MLC叶片位置处EPID影像对应的期望百分剂量值为44%,最大MLC位置误差为0.12 mm。任意机架角度时,EPID影像数据通过与0°结果做距离一致性分析比对,半径为0.5 mm时所有像素点均通过。结论 采用EPID代替胶片对加速器MLC叶片到位质控方法可行,且其精度满足临床要求并适用于任意机架角的测量,具有广泛推广和借鉴意义。