图像引导体部伽玛刀摆位误差及影响因素的临床研究

目的：分析图像引导体部伽玛刀治疗患者的分次间摆位误差及其影响因素。方法：对211例接受图像引导体部伽玛刀治疗的实体肿瘤患者的摆位误差数据进行回顾性分析。每例患者每分次治疗时,首次图像引导定位获得的摆位误差为校正前摆位误差,经自动治疗床误差校正后,再次图像引导摆位验证后获得的剩余摆位误差为校正后摆位误差。采集每例患者每个分次在左右、前后、头尾三个方向上的校正前和校正后的摆位误差,并计算其总体摆位误差。对211例患者共2838分次图像引导摆位验证数据进行统计分析,并探讨其相关影响因素。结果：在左右、前后、头尾方向上的校正前摆位误差及其总体摆位误差(均值±标准差)分别为(1.17±4.75)mm、(0.02±2.94)mm、(0.29±4.34)mm和(6.24±3.52)mm,相应的校正后摆位误差及其总体摆位误差分别为(0.13±0.93)mm、(－0.13±0.67)mm、(－0.06±0.51)mm、(1.07±0.67)mm。经图像引导校正后的剩余摆位误差明显减小,差异具有统计学意义(Ｐ＜0.01)。在总体摆位误差上仰卧位优于俯卧位(Ｐ＜0.05),而双上肢固定位置、腹带对总体摆位误差的影响无统计学意义(P＞0.05)。结论：基于KV级X射线立体平面成像技术的图像引导定位系统,与体部伽玛刀组合使用,升级为图像引导体部伽玛刀,极大地提高了体部伽玛刀的摆位验证精度,满足SBRT治疗的临床要求。     

Setup accuracy of stereoscopic X-ray positioning with automated correction for rotational errors in patients treated with conformal arc radiotherapy for prostate cancer

We evaluated setup accuracy of NovalisBody stereoscopic X-ray positioning with automated correction for rotational errors with the Robotics Tilt Module in patients treated with conformal arc radiotherapy for prostate cancer. The correction of rotational errors was shown to reduce random and systematic errors in all directions. (NovalisBody™ and Robotics Tilt Module™ are products of BrainLAB A.G., Heimstetten, Germany).     

Evaluation and optimization of an image-subtraction method for the analysis of the repositioning accuracy of female patients with breast cancer

To analyze the repositioning accuracy in female patients with breast carcinoma, two different setups of an image-subtraction system (Positioning System FIVE) were devised using different numbers and alignments of lasers. The applicability of the system was tested for repositioning of the breast in normal volunteers. Horizontal translations as well as breathing-related movements in the vertical direction were measured. The mean repositioning accuracy was found to be 2.9 mm for the first setup and 1.5 mm for a second, optimized setup. For this second setup, a gating function was implemented which evaluates the position of the breast twelve times per second. The simulation of a gated treatment showed that the breathing-related displacement of the breast can be reduced to 45-70% of the displacement without gating. This implies a significant improvement of the positioning accuracy.     

A randomized comparison of interfraction and intrafraction prostate motion with and without abdominal compression

BACKGROUND AND PURPOSE: To quantify inter- and intrafraction prostate motion in a standard VacLok (VL) immobilization device or in the BodyFix (BF) system incorporating a compression element which may reduce abdominal movement. MATERIALS AND METHODS: Thirty-two patients were randomly assigned to VL or BF. Interfraction prostate motion >3 mm was corrected pre-treatment. EPIs were taken daily at the start and end of the first and last treatment beams. Interfraction and intrafraction prostate motion were measured for centre of mass (COM) and individual markers. RESULTS: There were no significant differences in interfraction (p0.002) or intrafraction (p0.16) prostate motion with or without abdominal compression. Median intrafraction motion was slightly smaller than interfraction motion in the AP (7.0 mm vs. 7.6 mm) and SI direction (3.2 mm vs. 4.7 mm). The final image captured the maximal intrafraction displacement in only 40% of fractions. Our PTV incorporated >95% of total prostate motion. CONCLUSIONS: Intrafraction motion became the major source of error during radiotherapy after online correction of interfraction prostate motion. The addition of 120 mbar abdominal compression to custom pelvic immobilization influenced neither interfraction nor intrafraction prostate motion.     

Clinical use of stereoscopic X-ray positioning of patients treated with conformal radiotherapy for prostate cancer

PURPOSE: To evaluate accuracy and time requirements of a stereoscopic X-ray-based positioning system in patients receiving conformal radiotherapy to the prostate. METHODS AND MATERIALS: Setup errors of the isocenter with regard to the bony pelvis were measured by means of orthogonal verification films and compared to conventional positioning (using skin drawings and lasers) and infrared marker (IR) based positioning in each of 261 treatments. In each direction, the random error represents the standard deviation and the systematic error the absolute value of the mean position. Time measurements were done in 75 treatments. RESULTS: Random errors with the X-ray positioning system in the anteroposterior (AP), lateral, and longitudinal direction were (average +/- 1 standard deviation) 2 +/- 0.6 mm, 1.7 +/- 0.6 mm, and 2.4 +/- 0.7 mm. The corresponding values of conventional as well as IR positioning were significantly higher (p < 0.01). Systematic errors for X-ray positioning were 1.1 +/- 1.2 mm AP, 0.6 +/- 0.5 mm laterally, and 1.5 +/- 1.6 mm longitudinally. Conventional and IR marker-based positioning showed significantly larger systematic errors AP and laterally, but longitudinally, the difference was not significant. Depending on the axis looked at, errors of >or=5 mm occurred in 2%-14% of treatments after X-ray positioning, 13%-29% using IR markers, and 28%-53% with conventional positioning. Total linac time for one treatment session was 14 min 51 s +/- 4 min 18 s, half of which was used for the X-ray-assisted positioning procedure. CONCLUSION: X-ray-assisted patient positioning significantly improves setup accuracy, at the cost of an increased treatment time.     

An investigation of a video-based patient repositioning technique

PURPOSE: We have investigated a video-based patient repositioning technique designed to use skin features for radiotherapy repositioning. We investigated the feasibility of the clinical application of this system by quantitative evaluation of performance characteristics of the methodology. METHODS AND MATERIALS: Multiple regions of interest (ROI) were specified in the field of view of video cameras. We used a normalized correlation pattern-matching algorithm to compute the translations of each ROI pattern in a target image. These translations were compared against trial translations using a quadratic cost function for an optimization process in which the patient rotation and translational parameters were calculated. RESULTS: A hierarchical search technique achieved high-speed (compute correlation for 128 x 128 ROI in 512 x 512 target image within 0.005 s) and subpixel spatial accuracy (as high as 0.2 pixel). By treating the observed translations as movements of points on the surfaces of a hypothetical cube, we were able to estimate accurately the actual translations and rotations of the test phantoms used in our experiments to less than 1 mm and 0.2 degrees with a standard deviation of 0.3 mm and 0.5 degrees respectively. For human volunteer cases, we estimated the translations and rotations to have an accuracy of 2 mm and 1.2 degrees. CONCLUSION: A personal computer-based video system is suitable for routine patient setup of fractionated conformal radiotherapy. It is expected to achieve high-precision repositioning of the skin surface with high efficiency.     

The accuracy of frameless stereotactic intracranial radiosurgery

Purpose

To determine the accuracy of frameless stereotactic radiosurgery using the BrainLAB ExacTrac system and robotic couch by measuring the individual contributions such as the accuracy of the imaging and couch correction system, the linkage between this system and the linac isocenter and the possible intrafraction motion of the patient in the frameless mask.

Materials and methods

An Alderson head phantom with hidden marker was randomly positioned 31 times. Automated 6D couch shifts were performed according to ExacTrac and the deviation with respect to the linac isocenter was measured using the hidden marker. ExacTrac-based set-up was performed for 46 patients undergoing hypofractionated stereotactic radiotherapy for 135 fractions, followed by verification X-rays. Forty-three of these patients received post-treatment X-ray verification for 79 fractions to determine the intrafraction motion.

Results

The hidden target test revealed a systematic error of 1.5 mm in one direction, which was corrected after replacement of the system calibration phantom. The accuracy of the ExacTrac positioning is approximately 0.3 mm in each direction, 1 standard deviation. The intrafraction motion was 0.35 ± 0.21 mm, maximum 1.15 mm.

Conclusion

Intrafraction motion in the BrainLAB frameless mask is very small. Users are strongly advised to perform an independent verification of the ExacTrac isocenter in order to avoid systematic deviations.     

Assessment of a daily online implanted fiducial marker‐guided prostate radiotherapy process

The aims of this study were to investigate whether intrafraction prostate motion can affect the accuracy of online prostate positioning using implanted fiducial markers and to determine the effect of prostate rotations on the accuracy of the software‐predicted set‐up correction shifts. Eleven patients were treated with implanted prostate fiducial markers and online set‐up corrections. Orthogonal electronic portal images were acquired to determine couch shifts before treatment. Verification images were also acquired during treatment to assess whether intrafraction motion had occurred. A limitation of the online image registration software is that it does not allow for in‐plane prostate rotations (evident on lateral portal images) when aligning marker positions. The accuracy of couch shifts was assessed by repeating the registration measurements with separate software that incorporates full in‐plane prostate rotations. Additional treatment time required for online positioning was also measured. For the patient group, the overall postalignment systematic prostate errors were less than 1.5 mm (1 standard deviation) in all directions (range 0.2–3.9 mm). The random prostate errors ranged from 0.8 to 3.3 mm (1 standard deviation). One patient exhibited intrafraction prostate motion, resulting in a postalignment prostate set‐up error of more than 10 mm for one fraction. In 14 of 35 fractions, the postalignment prostate set‐up error was greater than 5 mm in the anterior–posterior direction for this patient. Maximum prostate rotations measured from the lateral images varied from 2° to 20° for the patients. The differences between set‐up shifts determined by the online software without in‐plane rotations to align markers, and with rotations applied, was less than 1 mm (root mean square), with a maximum difference of 4.1 mm. Intrafraction prostate motion was found to reduce the effectiveness of the online set‐up for one of the patients. A larger study is required to determine the magnitude of this problem for the patient population. The inability in the current software to incorporate in‐plane prostate rotations is a limitation that should not introduce large errors, provided that the treatment isocentre is positioned near the centre of the prostate.     

Intrafraction variations in linac-based image-guided radiosurgery of intracranial lesions

PurposeThis study investigated image-guided patient positioning during frameless, mask-based, single-fraction stereotactic radiosurgery of intracranial lesions and intrafractional translational and rotational variations in patient positions.Patients and methodsA non-invasive head and neck thermoplastic mask was used for immobilization. The Exactrac/Novalis Body system (BrainLAB AG, Germany) was used for kV X-ray imaging guided positioning. Intrafraction displacement data, obtained by imaging after each new table position, were evaluated.ResultsThere were 269 radiosurgery treatments performed on 190 patients and a total of 967 setups within different angles. The first measured error after each table rotation (mean 2.6) was evaluated (698 measurements). Intrafraction translational errors were (1 standard deviation [SD]) on average 0.8, 0.8, and 0.7 mm for the left–right, superior–inferior, and anterior–posterior directions, respectively, with a mean 3D-vector of 1.0 mm (SD 0.9 mm) and a range from –5 mm to +5 mm. On average, 12%, 3%, and 1% of the translational deviations exceeded 1, 2, and 3 mm, respectively, in the three directions.ConclusionThe range of intrafraction patient motion in frameless image-guided stereotactic radiosurgery is often not fully mapped by pre- and post-treatment imaging. In the current study, intrafraction motion was assessed by performing measurements at several time points during the course of stereotactic radiosurgery. It was determined that 12% of the intrafraction values in the three dimensions are above 1 mm, the usual safety margin applied in stereotactic radiosurgery.     

Interfractional and intrafractional accuracy during radiotherapy of gynecologic carcinomas: a comprehensive evaluation using the ExacTrac system

PURPOSE: To evaluate positioning uncertainties with an infrared body marker-based positioning system (ExacTrac) compared with conventional laser positioning in patients treated for gynecologic carcinomas, and to investigate patient movement during therapy. MATERIALS AND METHODS: Ten patients were positioned both with a conventional laser system and with the ExacTrac system. Positioning accuracy was evaluated using repeated electronic portal images. Average displacements and overall, systematic, and random errors were calculated and compared for the two positioning methods. Further, inter- and intrafractional patient movement including time trends in positioning displacements, respiratory amplitudes, and breathing frequencies were analyzed by online documentation of body marker movement with the ExacTrac system. RESULTS: Average displacements ranged between -3.6 and 6.7 mm for the three coordinates. Mean systematic and random errors ranged from 1.6 to 3.7 mm and 2.2 to 3.7 mm, respectively, with no significant differences between conventional and ExacTrac positioning (p > 0.07). The main breathing direction was from dorsocaudal to anterocranial in 9 of 10 patients. The mean 3D breathing amplitude in the pelvis was 2.4 mm (0.49-6.96 mm). Significant interfractional and intrafractional time trends were observed concerning breathing amplitudes and positioning displacements. CONCLUSIONS: The observed displacements did not vary significantly between the two evaluated positioning systems. The analysis of registered body marker positions revealed a wide variation in respiratory frequencies, breathing amplitudes, and patient displacements with interfractional and intrafractional time trends. Systems that allow the measurement of each patient's motion characteristics are a necessary requirement for all efforts at individually tailored radiation therapy.     

Clinical feasibility study for the use of implanted gold seeds in the prostate as reliable positioning markers during megavoltage irradiation.

BACKGROUND AND PURPOSE: The aim of this study was to assess the feasibility of using gold seed implants in the prostate for position verification, using an a-Si flat panel imager as a detector during megavoltage irradiation of prostate carcinoma. This is a study to guarantee positioning accuracy in intensity-modulated radiotherapy. METHODS AND MATERIALS: Ten patients with localized prostate carcinoma (T2-3) received between one and three fiducial gold markers in the prostate. All patients were treated with 3-D conformal radiotherapy with an anterior-posterior (AP) and two lateral wedge fields. The acute gastrointestinal (GI) and genitourinary (GU) toxicities were scored using common toxicity criteria scales (CTC). Using three consecutive CT scans and portal images obtained during the treatment we have studied the occurrence of any change in prostate shape (deformation), seed migration and the magnitude of translations and rotations of the prostate. RESULTS: We observed no acute major complications for prostate irradiation regarding the seed implantation. The maximum acute GU toxicity grade 2 (dysuria and frequency) was observed in seven patients during the treatment. The maximum grade 2 (diarrhoea) was scored in two patients regarding the acute GI toxicities. No significant prostate deformation could be detected in the consecutive CT scans. It appeared that the distances between the markers only slightly changed during treatment (S.D. 0.5 mm). Random prostate translations were (1 S.D.) 2.1, 3.2 and 2.2 mm in the lateral (LR), AP and cranial-caudal (CC) directions, respectively, whereas systematic translations were 3.3, 4.8 and 3.5 mm in the LR, AP and CC directions, respectively. Random prostate rotations were (1 S.D.) 3.6, 1.7 and 1.9 degrees around the LR, AP and CC axis, respectively, whereas systematic rotations were 4.7, 2.0 and 2.7 degrees around the LR, AP and CC axis, respectively. CONCLUSIONS: We found that the fiducial gold seeds are a safe and appropriate device to verify and correct the position of prostate during megavoltage irradiation. The amount of seed migration and prostate deformation is far below our present tumour delineation accuracy.     

Benefits of six degrees of freedom for optically driven patient set-up correction in SBRT

To quantify the advantages of a 6 degrees of freedom (dof) versus the conventional 3- or 4-dof correction modality for stereotactic body radiation therapy (SBRT) treatments. Eighty-five patients were fitted with 5-7 infra-red passive markers for optical localization. Data, acquired during the treatment, were analyzed retrospectively to simulate and evaluate the best approach for correcting patient misalignments. After the implementation of each correction, the new position of the target (tumor's center of mass) was estimated by means of a dedicated stereotactic algorithm. The Euclidean distance between the corrected and the planned location of target point was calculated and compared to the initial mismatching. Initial and after correction median+/-quartile displacements affecting external control points were 3.74+/-2.55 mm (initial), 2.45+/-0.91 mm (3-dof), 2.37+/-0.95 mm (4-dof), and 2.03+/-1.47 mm (6-dof). The benefit of a six-parameter adjustment was particularly evident when evaluating the results relative to the target position before and after the re-alignment. In this context, the Euclidean distance between the planned and the current target point turned to 0.82+/-1.12 mm (median+/-quartile values) after the roto-translation versus the initial displacement of 2.98+/-2.32 mm. No statistical improvements were found after 3- and 4-dof correction (2.73+/-1.22 mm and 2.60+/-1.31 mm, respectively). Angular errors were 0.09+/-0.93 degrees (mean+/-std). Pitch rotation in abdomen site showed the most relevant deviation, being -0.46+/-1.27 degrees with a peak value of 5.46 degrees . Translational misalignments were -0.68+/-2.60 mm (mean+/-std) with the maximum value of 12 mm along the cranio-caudal direction. We conclude that positioning system platforms featuring 6-dof are preferred for high precision radiation therapy. Data are in line with previous results relative to other sites and represent a relevant record in the framework of SBRT.     

Repositioning accuracy of fractionated stereotactic irradiation: assessment of isocentre alignment for different dental fixations by using sequential CT scanning.

BACKGROUND AND PURPOSE: To quantify the accuracy and reproducibility of patient repositioning in fractionated stereotactic conformal radiotherapy (SCRT) using dental fixations in conjunction with a stereotactic head mask. PATIENTS AND METHODS: One hundred and fourteen verification CT scans were performed on 57 patients in order to check set-up alignment. The first scan was done immediately after the first treatment. Twelve patients were checked for alignment accuracy with weekly CT scans over a period of 3-6 weeks, all others had 1-2 scans. Two different dental fixations were used in combination with a non-invasive mask system: an upper jaw support (35 patients) and a customised bite-block (17 patients). Five patients were treated with no additional fixation. Co-registration to the planning CT was used to assess alignment of the isocentre to the reference markers. Additionally, the intra-operator variability of image co-registration was assessed. RESULTS: There was a significant improvement of the overall alignment in using the bite-block instead of the upper jaw support (P<0.001). The mean deviation was for the bite-block 2.2+/-1.1 mm (1 SD), for the upper jaw support 3.3+/-1.8 mm and 3.7+/-2.8 mm for the mask alone. Overall isocentre deviations independent of the method of fixation were 2.8 mm (1.7 mm, 1 SD). Displacements in CC direction were significantly less for the bite-block compared to the upper jaw support (P=0.03). The addition of an upper jaw support significantly reduced lateral rotations compared to the mask system alone (P=0.03). The intra-operator variability of image co-registration was 1.59+/-0.49 mm (1 SD). CONCLUSION: The reproducibility of patient positioning using a re-locatable head mask system combined with a bite-block is within the reported range for similar devices and is preferable to a simple upper jaw support. In order to further reduce the margin for the planning target volume an intra-oral dental fixation is recommended.     

On-line set-up corrections during radiotherapy of patients with gynecologic tumors

PURPOSE: Positioning of patients with gynecologic tumors for radiotherapy has proven to be relatively inaccurate. To improve the accuracy and reduce the margins from clinical target volume (CTV) to planning target volume (PTV), on-line set-up corrections were investigated. METHODS AND MATERIALS: Anterior-posterior portal images of 14 patients were acquired using the first six monitor units (MU) of each irradiation fraction. The set-up deviation was established by matching three user-defined landmarks in portal and simulator image. If the two-dimensional deviation exceeded 4 mm, the table position was corrected. A second portal image was acquired using 30 MU of the remaining dose. This image was analyzed off-line using a semiautomatic contour match to obtain the final set-up accuracy. To verify the landmark match accuracy, the contour match was retrospectively performed on the six MU images as well. RESULTS: The standard deviation (SD) of the distribution of systematic set-up deviations after correction was < 1 mm in left-right and cranio-caudal directions. The average random deviation was < 2 mm in these directions (1 SD). Before correction, all standard deviations were 2 to 3 mm. The landmark match procedure was sufficiently accurate and added on average 3 min to the treatment time. The application of on-line corrections justifies a CTV-to-PTV margin reduction to about 5 mm. CONCLUSIONS: On-line set-up corrections significantly improve the positioning accuracy. The procedure increases treatment time but might be used effectively in combination with off-line corrections.     

体表铅点标记辅助iSCOUT图像引导定位系统在乳腺癌术后调强放疗应用研究

目的 探究体表铅点标记辅助iSCOUT图像引导定位系统在乳腺癌调强放疗摆位误差监测及校正的应用价值,并计算PTV外放边界为临床提供参考。方法 选取2019年间福建医科大学附属协和医院行乳腺癌改良根治术后调强放疗的 25例患者,利用体表铅点标记辅助iSCOUT系统基于金标配准算法进行图像引导定位,分别记录3个平移方向左右(x)、头脚(y)和腹背(z)的初始摆位误差以及图像引导校正后的残余误差统计分析,进一步比较图像引导校正前后误差对计划剂量的影响,最后计算合理的计划靶体积(PTV)外放边界。结果 25例患者在体表铅点标记辅助iSCOUT图像引导定位下进行150次摆位验证,x、y、z轴向残余摆位误差绝对值分别为(1.53±0.96)、(1.30±0.99)、(1.34±0.92)mm,均小于初始误差值的(2.63±2.12)、(2.41±2.45)、(3.07±2.77)mm (P<0.001)。残余误差导致的剂量偏差百分比也比初始误差的小,在PTV的D98%、D2%、Dmax,心脏 Dmax、健侧乳腺 Dmax、患侧肺及双肺 Dmean等具有显著差异,与原计划偏差百分比分别由2.18%、3.19%、10.66%、8.75%、48.21%、10.50%、3.66%降低到0.38%、0.23%、2.31%、0.04%、13.78%、6.35%、0.41%(P<0.05)。图像引导后PTV外放边界估算得x、y、z轴向外放边界分别为1.87、1.75、1.69mm。结论 体表铅点标记辅助iSCOUT图像引导定位系统在乳腺癌放疗体位验证及校正中的应用具有可行性和应用价值,且为临床PTV外放边界提供新的参考。     

Initial clinical experience with infrared-reflecting skin markers in the positioning of patients treated by conformal radiotherapy for prostate cancer

PURPOSE: To evaluate an infrared (IR) marker-based positioning system in patients receiving conformal radiotherapy for prostate cancer. METHODS AND MATERIALS: During 553 treatments, the ability of the IR system to automatically position the isocenter was recorded. Setup errors were measured by means of orthogonal verification films and compared to conventional positioning (using skin drawings and lasers) in 184 treatments. RESULTS: The standard deviation of anteroposterior (AP) and lateral setup errors was significantly reduced with IR marker positioning compared to conventional: 2 vs. 4.8 mm AP (p < 0.01) and 1.6 vs. 3.5 mm laterally (p < 0.01). Longitudinally, the difference was not significant (3.5 vs. 3.0 mm). Systematic errors were on the average smaller AP and laterally for the IR method: 4.1 vs. 7.8 mm AP (p = 0.01) and 3.1 vs. 5.6 mm lateral (p = 0.07). Longitudinally, the IR system resulted in somewhat larger systematic errors: 5.0 vs. 3.4 mm for conventional positioning (p = 0.03). The use of an off-line correction protocol, based on the average deviation measured over the first four fractions, allowed virtual elimination of systematic errors. Inability of the IR system to correctly locate the markers, leading to an executional failure, occurred in 21% of 553 fractions. CONCLUSION: IR marker-assisted patient positioning significantly improves setup accuracy along the AP and lateral axes. Executional failures need to be reduced.     

Development of a four-dimensional image-guided radiotherapy system with a gimbaled X-ray head

PURPOSE: To develop and evaluate a new four-dimensional image-guided radiotherapy system, which enables precise setup, real-time tumor tracking, and pursuit irradiation. METHODS AND MATERIALS: The system has an innovative gimbaled X-ray head that enables small-angle (+/-2.4 degrees ) rotations (pan and tilt) along the two orthogonal gimbals. This design provides for both accurate beam positioning at the isocenter by actively compensating for mechanical distortion and quick pursuit of the target. The X-ray head is composed of an ultralight C-band linear accelerator and a multileaf collimator. The gimbaled X-ray head is mounted on a rigid O-ring structure with an on-board imaging subsystem composed of two sets of kilovoltage X-ray tubes and flat panel detectors, which provides a pair of radiographs, cone beam computed tomography images useful for image guided setup, and real-time fluoroscopic monitoring for pursuit irradiation. RESULTS: The root mean square accuracy of the static beam positioning was 0.1 mm for 360 degrees of O-ring rotation. The dynamic beam response and positioning accuracy was +/-0.6 mm for a 0.75 Hz, 40-mm stroke and +/-0.4 mm for a 2.0 Hz, 8-mm stroke. The quality of the images was encouraging for using the tomography-based setup. Fluoroscopic images were sufficient for monitoring and tracking lung tumors. CONCLUSIONS: Key functions and capabilities of our new system are very promising for precise image-guided setup and for tracking and pursuit irradiation of a moving target.     

千伏级锥形束断层扫描在鼻咽癌适形调强放射治疗中的初步应用

背景与目的:调强放射治疗(intensity-modulated radiotherapy, IMRT)由于剂量分布较常规放疗更符合鼻咽癌病灶与临近解剖结构对剂量的复杂要求而逐渐被临床采用.但IMRT对摆位精确度及其验证的要求高.千伏级锥形束断层扫描(kilo-volt cone-beam computed tomography, kV-CBCT)是新出现的实时图像引导技术,本研究旨在评价kV-CBCT图像引导技术在鼻咽癌调强放射治疗摆位修正中的应用价值.方法:应用kV-CBCT于放疗实施前对22例鼻咽癌患者进行扫描,并在线将重建的容积图像与计划CT扫描图像匹配,调整床位后给予放疗.对患者数据离线后进行分析,计算摆位误差以及计划靶体积(planning target volume, PTV)边界.结果:22例患者共754次kV-CBCT扫描中,首次kV-CBCT(调整前)扫描共505次,其中摆位偏差在左右、头足和前后3个方向误差≤2 mm的检测次数分别为386(76.4%)、384(76.0%)和433(85.7%);调整床位后(调整后)扫描共106次,其中在3个方向摆位偏差≤2 mm的检测次数分别为:103 (97.2%)、103 (97.2%)和106 (100%);治疗后扫描共143次,3个方向误差≤2 mm的检测次数分别为125(87.4%)、124(86.7%)和129(90.0%).患者摆位的系统和随机误差调整前在X、Y、Z轴分别为(-0.7±1.6)mm、(-0.7 1.8)mm和(-0.3±1.7)mm,调整后分别为(-0.4±0.8)mm、(0.3±0.8)mm和(0.0±0.7)mm,治疗后分别为(0.2±1.2)mm、(0.3±1.3)mm和(0.1±1.1)mm.在调整前、后PTV最大边界分别为4.0 mm和2.1 mm.结论:kV-CBCT图像引导放射治疗在鼻咽癌IMRT中可以提高等中心摆位精度,检测并调整摆位误差,有效减小照射野边界.     

Frame Slippage Verification in Stereotactic Radiosurgery

Purpose: To develop a method for detecting frame slippage in stereotactic radiosurgery by interactively matching in three dimensions Digitally Reconstructed Radiographs (DRRs) to portal images.Methods and Materials: DRRs are superimposed over orthogonal edge-detected portal image pairs obtained prior to treatment. By interactively manipulating the CT data in three dimensions (rotations and translations) new DRRs are generated and overlaid with the orthogonal portal images. This method of matching is able to account for ambiguities due to rotations and translations outside of the imaging plane. The matching procedure is performed with anatomical structures, and is used in tandem with a fiducial marker array attached to the stereotactic frame. The method is evaluated using portal images simulated from patient CT data and then tested using a radiographic head phantom.Results: For simulation tests a mean radial alignment error of 0.82 mm was obtained with the 3D matching method compared to a mean error of 3.52 mm when using conventional matching techniques. For the head phantom tests the mean alignment displacement error for each of the stereotactic coordinates was found to be Δx = 0.95 mm, Δy = 1.06 mm, Δz = 0.99 mm, with a mean error radial of 1.94 mm (SD = 0.61 mm).Conclusion: Results indicate that the accuracy of the system is appropriate for stereotactic radiosurgery, and is therefore an effective tool for verification of frame slippage.