Accuracy of single-session extracranial radiotherapy for simple shaped lung tumor or metastasis using fast 3-D CT treatment planning

BACKGROUND: This study is situated in the area of measuring set-up accuracy and time periods of single-session extracranial radiotherapy (SSRT) for simple-shaped targets (e.g., spherical or rotational symmetrical) definitively located in the peripheral lung. METHODS AND MATERIALS: After adaptation of the stereotactic body frame, the patient has to remain in the vacuum pillow during planning computed tomography (CT), fast three-dimensional (3-D) treatment planning, and direct irradiation after verification. Fast preplanning is performed by using virtual simulation software to accelerate the method. RESULTS: In our new procedure, SSRT is applied in approximately 1.5 h. The mean setup accuracy vector was 2.4+/-0.7 mm in the range of 1.34 to 4 mm. Mean intrafractional patient movement in the stereotactic body frame before and after radiation was 0.70 mm+/-0.5 mm and 0.76+/-0.76 mm in the range of 0 to 2.8 mm. Mean time period steps were measured at (1) planning CT with 3-D treatment planning: 76+/-12 min; (2) irradiation and verification: 33+/-7 min; and (3) complete procedure duration: 109+/-11 min (range, 89-169). CONCLUSIONS: The main difference between the positioning technique of SSRT and that of conventional extracranial radiosurgery is the tighter patient fixation, which guarantees minimal patient movement. The main advantages are procedure acceleration and omission of CT simulation. SSRT is a preliminary stage of real-time treatment.     

The TALON removable head frame system for stereotactic radiosurgery/radiotherapy: measurement of the repositioning accuracy

PURPOSE: To present the TALON removable head frame system as an immobilization device for single-fraction intensity-modulated stereotactic radiosurgery (IMRS) and fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT); and to evaluate the repositioning accuracy by measurement of anatomic landmark coordinates in repeated computed tomography (CT) examinations. METHODS AND MATERIALS: Nine patients treated by fractionated stereotactic intensity-modulated radiotherapy underwent repeated CTs during their treatment courses. We evaluated anatomic landmark coordinates in a total of 26 repeat CT data sets and respective x, y, and z shifts relative to their positions in the nine treatment-planning reference CTs. An iterative optimization algorithm was employed using a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomic landmark measurements relative to the original image set. This allowed for the calculation of the x, y, and z components of translation of the target isocenter for each repeat CT. In addition to absolute target isocenter translation, the magnitude (sum vector) of isocenter motion and the patient/target rotation about the three principal axes were calculated. RESULTS: Anatomic landmark analysis over a treatment course of 6 weeks revealed a mean target isocenter translation of 0.95 +/- 0.55, 0.58 +/- 0.46, and 0.51 +/- 0.38 mm in x, y, and z directions, respectively. The mean magnitude of isocenter translation was 1.38 +/- 0.48 mm. The 95% confidence interval ([CI], mean translation plus two standard deviations) for repeated isocenter setup accuracy over the 6-week period was 2.34 mm. Average rotations about the x, y, and z axes were 0.41 +/- 0.36, 0.29 +/- 0.25, and 0.18 +/- 0.15 degrees, respectively. Analysis of the accuracy of the first repeated setup control, representative of single-fraction stereotactic radiosurgery situations, resulted in a mean target isocenter translation in the x, y, and z directions of 0.52 +/- 0.38, 0.56 +/- 0.30, and 0.46 +/- 0.25 mm, respectively. The mean magnitude of isocenter translation was 0.99 +/- 0.28 mm. The 95% confidence interval for these radiosurgery situations was 1.55 mm. Average rotations at first repeated setup control about the x, y, and z axes were 0.24 +/- 0.19, 0.19 +/- 0.17, and 0.19 +/- 0.12 degrees, respectively. CONCLUSION: The TALON relocatable head frame was seen to be well suited for immobilization and repositioning of single-fraction stereotactic radiosurgery treatments. Because of its unique removable design, the system was also seen to provide excellent repeat immobilization and alignment for fractionated stereotactic applications. The exceptional accuracy for the single-fraction stereotactic radiosurgical application of the system was seen to deteriorate only slightly over a 6-week fractionated stereotactic treatment course.     

CT image fusion as a tool for measuring in 3D the setup errors during conformal radiotherapy for prostate cancer

AIMS AND BACKGROUND: The importance of optimal daily patient positioning has been stressed in order to ensure treatment reproducibility and gain in accuracy and precision. We report our data on the 3D setup uncertainty during radiation therapy for prostate cancer using the CT image fusion technique. METHODS: Ten consecutive patients scheduled for radiation therapy for prostate cancer underwent 5 prone position CT scans using an individualized immobilization cast. These different setups were analyzed using the image fusion module of the ERGO 3D-Line Medical System (Milan, Italy) treatment planning system. The isocenter and the body marker displacements were measured. RESULTS: The 3D isocenter dislocations were quantified: systematic error was sigma(3D) = 3.9 mm, whereas random error was sigma(3D) = 1 mm. The mean of the minimum displacements was 0.2 +/- 1 mm showing that the immobilization device used allows an accurate setup to be obtained. Single direction errors were also measured showing systematic errors, sigma(AP), = 2.6 mm, sigma(LL) = 0.6 mm, SigmaSI = 3 mm in the anterior-posterior, latero-lateral, superior-inferior direction, respectively. Related random errors were sigma(AP), = 1 mm, sigma(LL) = 0.6 mm, sigma(SI) = 1.2 mm. In terms of accuracy, our uncertainties are similar to those reported in the literature. CONCLUSIONS: By applying the CT image fusion technique, a 3D study on setup accuracy was performed. We demonstrated that the use of an individualized immobilization system for prostate treatment is adequate to obtain good setup accuracy, as long as a high-quality positioning control method, such as the stereoscopic X-ray-based positioning system, is used.     

Reducing set-up uncertainty in the Elekta Stereotactic Body Frame using Stealthstation software

The Elekta Stereotactic Body Frame (SBF) is a device which allows extracranial targets to be localized and irradiated in a stereotactic coordinate system. Errors of positioning of the body relative to the frame are indirectly estimated by image fusion of multiple CT scans. A novel repositioning methodology, based on neurosurgical Stealth technology, is presented whereby accurate patient repositioning is directly confirmed before treatment delivery. Repositioning was performed on four extracranial stereotactic radiosurgery patients and a radiotherapy simulation phantom. The setup error was quantitatively measured by fiducial localization. A confirmatory CT scan was performed and the resulting image set registered to the initial scan to quantify shifts in the GTV isocenter. Alignment confirmation using Stealth took between 5 and 10 minutes. For the phantom studies, a reproducibly of 0.6 mm accuracy of phantom-to-SBF alignment was measured. The results on four actual patients showed setup errors of 1.5 mm or less. Using the Stealth Station process, rapid confirmation of alignment on the treatment table is possible.     

头颈肿瘤立体定向分次照射靶区定位的误差分析

背景与目的:明确靶区定位的精确度是立体定向分次照射质量保证的基本要求。本文主要分析头颈肿瘤立体定向分次照射(fractionatedstereotacticradiotherapy,FSRT)中机械等中心、CT定位、治疗摆位以及CT图像误差等可能引起的靶区定位误差。方法:使用立体定向治疗计划系统、靶点模拟器、头部定位框架检查各个治疗阶段靶区定位的误差。设置任意5个参考点,使用靶点模拟器检查CT定位误差;选取7个不同机器臂架/治疗床角度,定期用胶片检验使用的PhilipsSL-18直线加速器等中心误差大小;用验证片检查治疗摆位误差;对自制模体行CT扫描,分析CT图像伪影可能引起的图像误差。结果:CT定位误差约为(1.5±0.4)mm;在检查的不同机器臂架/治疗床角度中机械等中心最大误差为(1.0±0.6)mm;患者摆位的距离误差为(1.0±0.3)mm;整个治疗过程中靶区定位误差约为(2.1±0.8)mm。结论:立体定向分次照射中需要综合考虑各个阶段中可能对治疗靶区定位产生的影响,误差分析结果可用来确定治疗的计划靶区。     

Repositioning accuracy of a commercially available double-vacuum whole body immobilization system for stereotactic body radiation therapy

We evaluated the repositioning accuracy of a commercially available stereotactic whole body immobilization system (BodyFIX, Medical Intelligence, Schwabmuenchen, Germany) in 36 patients treated by hypofractionated stereotactic body radiation therapy. CT data were acquired for positional control of patient and tumor before each fraction of the treatment course. Those control CT datasets were compared with the original treatment planning CT simulation and analyzed with respect to positional misalignment of bony patient anatomy, and the respective position of the treated small lung or liver lesions. We assessed the stereotactic coordinates of distinct bony anatomical landmarks in the original CT and each control dataset. In addition, the target isocenter was recorded in the planning CT simulation dataset. An iterative optimization algorithm was implemented, utilizing a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomical landmark measurements relative to the original treatment planning CT data set. This allowed for the calculation of the x, y and z-components of translation of the patient's body and the target's center-of-mass for each control CT study, as well as rotation about the principal room axes in the respective CT data sets. In addition to absolute patient/target translation, the total magnitude vector of patient and target misalignment was calculated. A clinical assessment determined whether or not the assigned planning target volume safety margins would have provided the desired target coverage. To this end, each control CT study was co-registered with the original treatment planning study using immobilization system related fiducial markers, and the computed isodose calculation was superimposed. In 109 control setup CT scans available for comparison with their respective treatment planning CT simulation study (2-5 per patient, median 3), anatomical landmark analysis revealed a mean bony landmark translation of -0.4 +/- 3.9 (mean +/- SD), -0.1 +/- 1.6 and 0.3 +/- 3.6 mm in x, y and z-directions, respectively. Bony landmark setup deviations along one or more principal axis larger than 5 mm were observed in 32 control CT studies (29.4%). Body rotations about the x-, y- and z-axis were 0.9 +/- 0.7, 0.8 +/- 0.7 and 1.8 +/- 1.6 degrees, respectively. Assuming a rigid body relationship of target and bony anatomy, the mean computed absolute target translation was 2.9 +/- 3.3, 2.3 +/- 2.5 and 3.2 +/- 2.7 mm in x, y and z-directions, respectively. The median and mean magnitude vector of target isocenter displacement was computed to be 4.9 mm, and 5.7 +/- 3.7 mm. Clinical assessment of PTV/target volume coverage revealed 72 (66.1%), 23 (21.1%), and 14 (12.8%), of excellent (100% isodose coverage), good (>90% isodose coverage), and poor GTV/isodose alignment quality (less than 90% isodose coverage to some aspect of the GTV), respectively. Loss of target volume dose coverage was correlated with translations >5 mm along one or more axes (p<0.0001), rotations >3 degrees about the z-axis (p=0.0007) and body mass index >30 (p<0.0001). The analyzed BodyFIX whole body immobilization system performed favorably compared with other stereotactic body immobilization systems for which peer-reviewed repositioning data exist. While the measured variability in patient and target setup provided clinically acceptable setup accuracy in the vast majority of cases, larger setup deviations were occasional observed. Such deviations constitute a potential for partial target underdosing warranting, in our opinion, a pre-delivery positional assessment procedure (e.g., pre-treatment control CT scan).     

Reproducibility of organ position using voluntary breath-hold method with spirometer for extracranial stereotactic radiotherapy

PURPOSE: To evaluate in healthy volunteers the reproducibility of organ position using a voluntary breath-hold method with a spirometer and the feasibility of this method for extracranial stereotactic radiotherapy in a clinical setting. METHODS AND MATERIALS: For this study, 5 healthy volunteers were enrolled. After training sessions, they held their breath at the end-inspiration and the end-expiration phase under spirometer-based monitoring. Computed tomography (CT) scans were performed twice at each respiratory phase, with a 10-min interval, on 2 separate days. The total number of CT scans was four at each respiratory phase. After CT volume data were transferred to a three-dimensional treatment-planning system, digitally reconstructed radiographs (DRRs) were calculated for anterior-posterior and left-right beams. Verification was performed with DRRs relative to the diaphragm position, bony landmarks, and the isocenter in each healthy volunteer at each respiratory phase. To evaluate intrafraction reproducibility, we measured the distance between diaphragm position and bony landmarks. To evaluate interfraction reproducibility, we measured the distance between diaphragm position and the isocenter. Reproducibility and setup error were defined as the average value of the differences between each DRR with regard to the first DRR. RESULTS: Intrafraction reproducibility of the caudal-cranial direction was 4.0 +/- 3.5 mm at the end-inspiration phase and 2.2 +/- 2.0 mm at the end-expiration phase. Interfraction reproducibility of the caudal-cranial direction was 5.1 +/- 4.8 mm at the end-inspiration phase and 2.1 +/- 1.8 mm at the end-expiration phase. The end-expiration phase was more stable than the end-inspiration phase. CONCLUSIONS: The voluntary breath-hold method with a spirometer is feasible, with relatively good reproducibility. We are encouraged about the use of this technique clinically for extracranial stereotactic radiotherapy.     

A dosimetric analysis of respiration-gated radiotherapy in patients with stage III lung cancer

Background

The purpose of the study was the clinical implementation of a kV cone beam CT (CBCT) for setup correction in radiotherapy.

Patients and methods

For evaluation of the setup correction workflow, six tumor patients (lung cancer, sacral chordoma, head-and-neck and paraspinal tumor, and two prostate cancer patients) were selected. All patients were treated with fractionated stereotactic radiotherapy, five of them with intensity modulated radiotherapy (IMRT). For patient fixation, a scotch cast body frame or a vacuum pillow, each in combination with a scotch cast head mask, were used. The imaging equipment, consisting of an x-ray tube and a flat panel imager (FPI), was attached to a Siemens linear accelerator according to the in-line approach, i.e. with the imaging beam mounted opposite to the treatment beam sharing the same isocenter. For dose delivery, the treatment beam has to traverse the FPI which is mounted in the accessory tray below the multi-leaf collimator. For each patient, a predefined number of imaging projections over a range of at least 200 degrees were acquired. The fast reconstruction of the 3D-CBCT dataset was done with an implementation of the Feldkamp-David-Kress (FDK) algorithm. For the registration of the treatment planning CT with the acquired CBCT, an automatic mutual information matcher and manual matching was used.

Results and discussion

Bony landmarks were easily detected and the table shifts for correction of setup deviations could be automatically calculated in all cases. The image quality was sufficient for a visual comparison of the desired target point with the isocenter visible on the CBCT. Soft tissue contrast was problematic for the prostate of an obese patient, but good in the lung tumor case. The detected maximum setup deviation was 3 mm for patients fixated with the body frame, and 6 mm for patients positioned in the vacuum pillow. Using an action level of 2 mm translational error, a target point correction was carried out in 4 cases. The additional workload of the described workflow compared to a normal treatment fraction led to an extra time of about 10–12 minutes, which can be further reduced by streamlining the different steps.

Conclusion

The cone beam CT attached to a LINAC allows the acquisition of a CT scan of the patient in treatment position directly before treatment. Its image quality is sufficient for determining target point correction vectors. With the presented workflow, a target point correction within a clinically reasonable time frame is possible. This increases the treatment precision, and potentially the complex patient fixation techniques will become dispensable.     

Ultrasound-guided extracranial radiosurgery: technique and application

PURPOSE: Stereotactic radiosurgery is an effective treatment modality for many intracranial lesions, but target mobility limits its utility for extracranial applications. We have developed a new technique for extracranial radiosurgery based on optically guided three-dimensional ultrasound (3DUS). The 3DUS system provides the ability to image the target volume and critical structures in real time and determine any misregistration of the target volume with the linear accelerator. In this paper, we describe the system and its initial clinical application in the treatment of localized metastatic disease. METHODS AND MATERIALS: The extracranial stereotactic system consists of an ultrasound unit that is optically tracked and registered with the linear accelerator coordinate system. After an initial patient positioning based on computed tomographic (CT) simulation, stereotactic ultrasound images are acquired and correlated with the CT-based treatment plan to determine any soft-tissue shifts between the time of the planning CT and the actual treatment. Optical tracking is used to correct any patient offsets that are revealed by the real-time imaging. RESULTS: Preclinical testing revealed that the ultrasound-based stereotactic navigation system is accurate to within 1.5 mm in comparison with an absolute coordinate phantom. Between March 2001 and March 2002, the system was used to deliver extracranial radiosurgery to 17 metastatic lesions in 16 patients. Treatments were delivered in 1 or 2 fractions, with an average fractional dose of 16 Gy (range 12.5-24 Gy) delivered to the 80% isodose surface. Before each fraction, the target misalignment from isocenter was determined using the 3DUS system and the misalignments averaged over all patients were anteroposterior = 4.8 mm, lateral = 3.6 mm, axial = 2.1 mm, and average total 3D displacement = 7.4 mm (range = 0-21.0 mm). After correcting patient misalignment, each plan was delivered as planned using 6-11 noncoplanar fields. No acute complications were reported. CONCLUSIONS: A system for high-precision radiosurgical treatment of metastatic tumors has been developed, tested, and applied clinically. Optical tracking of the ultrasound probe provides real-time tracking of the patient anatomy and allows computation of the target displacement before treatment delivery. The patient treatments reported here suggest the feasibility and safety of the technique.     

CT image-guided intensity-modulated therapy for paraspinal tumors using stereotactic immobilization

PURPOSE: To design and implement a noninvasive stereotactic immobilization technique with daily CT image-guided positioning to treat patients with paraspinal lesions accurately and to quantify the systematic and random patient setup errors occurring with this method. METHODS AND MATERIALS: A stereotactic body frame (SBF) was developed for "rigid" immobilization of paraspinal patients. The inherent accuracy of this system for stereotactic CT-guided treatment was evaluated with phantom studies. Seven patients with thoracic and lumbar spine lesions were immobilized with the SBF and positioned for 33 treatment fractions using daily CT scans. For all 7 patients, the daily setup errors, as assessed from the daily CT scans, were corrected at each treatment fraction. A retrospective analysis was also performed to assess what the impact on patient treatment would have been without the CT-based corrections (i.e., if patient setup had been performed only with the SBF). RESULTS: The average magnitude of systematic and random errors from uncorrected patient setups using the SBF was approximately 2 mm and 1.5 mm (1 SD), respectively. For fixed phantom targets, the system accuracy for the SBF localization and treatment was shown to be within 1 mm (1 SD) in any direction. Dose-volume histograms incorporating these uncertainties for an intensity-modulated radiotherapy plan for lumbar spine lesions were generated, and the effects on the dose-volume histograms were studied. CONCLUSION: We demonstrated a very accurate and precise method of patient immobilization and treatment delivery based on a noninvasive SBF and daily image guidance for paraspinal lesions. The SBF provides excellent immobilization for paraspinal targets, with setup accuracy better than 2 mm (1 SD). However, for highly conformal paraspinal treatments, uncorrected systematic and random errors of 2 mm in magnitude can result in a significantly greater (>100%) dose to the spinal cord than planned, even though the planned target coverage may not change substantially. With daily CT guidance using the SBF, we showed that the maximal spinal cord dose is ensured to be within 10-15% of the planned value.     

A modified relocatable stereotactic frame for irradiation of eye melanoma: design and evaluation of treatment accuracy

PURPOSE: To describe a reliable, patient-friendly relocatable stereotactic frame for irradiation of eye melanoma and to evaluate the repositioning accuracy of the stereotactic treatment. METHODS AND MATERIALS: An extra construction with a blinking light and a camera is attached to a noninvasive relocatable Gill-Thomas-Cosman stereotactic frame. The position of the blinking light is in front of the unaffected eye and can be adjusted to achieve an optimal position for irradiation. The position of the diseased eye is monitored with a small camera. A planning CT scan is performed with the affected eye in treatment position and is matched with an MR scan to improve the accuracy of the delineation of the tumor. Both the translation and rotation of the affected eye are calculated by comparing the planning CT scan with a control CT scan, performed after the radiation therapy is completed. RESULTS: Nineteen irradiated eye melanoma patients were analyzed. All patients received 5 fractions of 10 Gy within 5 days. The depth-confirmation helmet measurements of the day-to-day treatment position of the skull within the Gill-Thomas-Cosman frame were analyzed in the anteroposterior, lateral, and vertical directions and were 0.1 +/- 0.3, 0.0 +/- 0.2, and 0.2 +/- 0.2 mm (mean +/- SD), respectively. The average translations of the eye on the planning and control CT scan were 0.1 +/- 0.3 mm, 0.1 +/- 0.4, and 0.1 +/- 0.5 mm, respectively. The median rotation of the diseased eye was 8.3 degrees. CONCLUSIONS: The described Rotterdam eye fixation system turned out to be a feasible, reliable, and patient-friendly system.     

Image localization for frameless stereotactic radiotherapy

Purpose: Infrared light-emitting diodes (IRLEDs) have been used for optic-guided stereotactic radiotherapy localization at the University of Florida since 1995. The current paradigm requires stereotactic head ring placement for the patient’s first fraction. The stereotactic coordinates and treatment plan are determined relative to this head ring. The IRLEDs are attached to the patient via a maxillary bite plate, and the position of the IRLEDs relative to linac isocenter is saved to file. These positions are then recalled for each subsequent treatment to position the patient for fractionated therapy. The purpose of this article was to report a method of predicting the desired IRLED locations without need for the invasive head ring.

Methods and Materials: To achieve the goal of frameless optic-guided radiotherapy, a method is required for direct localization of the IRLED positions from a CT scan. Because it is difficult to localize the exact point of light emission from a CT scan of an IRLED, a new bite plate was designed that contains eight aluminum fiducial markers along with the six IRLEDs. After a calibration procedure to establish the spatial relationship of the IRLEDs to the aluminum fiducial markers, the stereotactic coordinates of the IRLED light emission points are determined by localizing the aluminum fiducial markers in a stereotactic CT scan.

Results: To test the accuracy of direct CT determination of the IRLED positions, phantom tests were performed. The average accuracy of isocenter localization using the IRLED bite plate was 0.65 ± 0.17 mm for these phantom tests. In addition, the optic-guided system has a unique compatibility with the stereotactic head ring. Therefore, the isocentric localization capability was clinically tested using the stereotactic head ring as the absolute standard. The ongoing clinical trial has shown the frameless system to provide a patient localization accuracy of 1.11 ± 0.3 mm compared with the head ring.

Conclusion: Optic-guided radiotherapy using IRLEDs provides a mechanism through which setup accuracy may be improved over conventional techniques. To date, this optic-guided therapy has been used only as a hybrid system that requires use of the stereotactic head ring for the first fraction. This has limited its use in the routine clinical setting. Computation of the desired IRLED positions eliminates the need for the invasive head ring for the first fraction. This allows application of optic-guided therapy to a larger cohort of patients, and also facilitates the initiation of extracranial optic-guided radiotherapy.     

Geometric accuracy of field alignment in fractionated stereotactic conformal radiotherapy of brain tumors

PURPOSE: To assess the accuracy of field alignment in patients undergoing three-dimensional (3D) conformal radiotherapy of brain tumors, and to evaluate the impact on the definition of planning target volume and control procedures. METHODS AND MATERIALS: Geometric accuracy was analyzed in 20 patients undergoing fractionated stereotactic conformal radiotherapy for brain tumors. Rigid head fixation was achieved by using cast material. Transfer of stereotactic coordinates was performed by an external positioning device. The accuracy during treatment planning was quantitatively assessed by using repeated computed tomography (CT) examinations in treatment position (reproducibility of isocenter). Linear discrepancies were measured between treatment plan and CT examination. In addition, for each patient, a series of 20 verifications were taken in orthogonal projections. Linear discrepancies were measured between first and all subsequent verifications (accuracy during treatment delivery). RESULTS: For the total group of patients, the distribution of deviations during treatment setup showed mean values between -0.3-1.2 mm, with standard deviations (SD) of 1.3-2.0 mm. During treatment delivery, the distribution of deviations revealed mean values between 0.7-0.8 mm, with SDs of 0.5-0.6 mm, respectively. For all patients, deviations for the transition to the treatment machine were similar to deviations during subsequent treatment delivery, with 95% of all absolute deviations between less than 2.8 and 4.6 mm. CONCLUSION: Random fluctuations of field displacements during treatment planning and delivery prevail. Therefore, our quantitative data should be considered when prescribing the safety margins of the planning target volume. Repeated CT examination are useful to detect operator errors and large random or systematic deviations before start of treatment. Control procedures during treatment delivery appear to be of limited importance. In addition, our findings should help to determine "cut-off points" for corrective actions in stereotactic conformal radiotherapy of brain tumors.     

Reduction of radiation pneumonitis by V20-constraints in breast cancer

Background

To assess the accuracy of fractionated stereotactic radiotherapy (FSRT) using a stereotactic mask fixation system.

Patients and Methods

Sixteen patients treated with FSRT were involved in the study. A commercial stereotactic mask fixation system (BrainLAB AG) was used for patient immobilization. Serial CT scans obtained before and during FSRT were used to assess the accuracy of patient immobilization by comparing the isocenter position. Daily portal imaging were acquired to establish day to day patient position variation. Displacement errors along the different directions were calculated as combination of systematic and random errors.

Results

The mean isocenter displacements based on localization and verification CT imaging were 0.1 mm (SD 0.3 mm) in the lateral direction, 0.1 mm (SD 0.4 mm) in the anteroposterior, and 0.3 mm (SD 0.4 mm) in craniocaudal direction. The mean 3D displacement was 0.5 mm (SD 0.4 mm), being maximum 1.4 mm. No significant differences were found during the treatment (P = 0.4). The overall isocenter displacement as calculated by 456 anterior and lateral portal images were 0.3 mm (SD 0.9 mm) in the mediolateral direction, -0.2 mm (SD 1 mm) in the anteroposterior direction, and 0.2 mm (SD 1.1 mm) in the craniocaudal direction. The largest displacement of 2.7 mm was seen in the cranio-caudal direction, with 95% of displacements < 2 mm in any direction.

Conclusions

The results indicate that the setup error of the presented mask system evaluated by CT verification scans and portal imaging are minimal. Reproducibility of the isocenter position is in the best range of positioning reproducibility reported for other stereotactic systems.     

Cone-beam computed tomography in hypofractionated stereotactic radiotherapy for brain metastases

ABSTRACT: BACKGROUND: To assess interfraction translational and rotational setup errors, in patients treated with image-guided hypofractionated stereotactic radiotherapy, immobilized by a thermoplastic mask and a bite-block and positioned using stereotactic coordinates. METHODS: 37 patients with 47 brain metastases were treated with hypofractionated stererotactic radiotherapy. All patients were immobilized with a combination of a thermoplastic mask and a bite-block fixed to a stereotactic frame support. Daily cone-beam CT scans were acquired for every patient before the treatment session and were matched online with planning CT images, for 3D image registration. The mean value and standard deviation of all translational (X,Y,Z) and rotational errors (thetax, thetay, thetaz) were calculated for the matching results of bone matching algorithm. RESULTS: A total of 194 CBCT scans were analyzed. Mean +/- standard deviation of translational errors (X, Y, Z) were respectively 0.5 +/- 1.6 mm (range -5.7 and 5.9 mm) in X; 0.4 +/- 2.7 mm (range -8.2 and 12.1 mm) in Y; 0.4 +/- 1.9 mm (range -7.0 and 14 mm) in Z; median and 90th percentile were respectively within 0.5 mm and 2.4 mm in X, 0.3 mm and 3.2 mm in Y, 0.3 mm and 2.2 mm in Z. Mean +/- standard deviation of rotational errors (thetax, thetay, thetaz) were respectively 0.0 degrees +/- 1.3 degrees (thetax) (range -6.0 degrees and 3.1 degrees); -0.1 degrees +/- 1.1 degrees (thetay) (range -3.0 degrees and 2.4 degrees); -0.6 degrees +/- 1.4 degrees (thetaz) (range -5.0 degrees and 3.3 degrees). Median and 90th percentile of rotational errors were respectively within 0.1 degrees and 1.4 degrees (thetax), 0.0 degrees and 1.2 degrees (thetay), 0.0 degrees and 0.9 degrees (thetaz). Mean +/- SD of 3D vector was 3.1 +/- 2.1 mm (range 0.3 and 14.9 mm); median and 90th percentile of 3D vector was within 2.7 mm and 5.1 mm. CONCLUSIONS: Hypofractionated stereotactic radiotherapy have the significant limitation of uncertainty in interfraction repeatability of the patient setup; image-guided radiotherapy using cone-beam computed tomography improves the accuracy of the treatment delivery reducing setup uncertainty, giving the possibility of 3-dimensional anatomic informations in the treatment position.     

Isocenter accuracy in frameless stereotactic radiotherapy using implanted fiducials

PURPOSE: The stereotactic radiotherapy (SRT) system verifies isocenter accuracy in patient space. In this study, we evaluate isocenter accuracy in frameless SRT using implanted cranial gold markers. MATERIALS AND METHODS: We performed frameless SRT on 43 intracranial tumor patients between August 1997 and December 2000. The treatment technique was determined by the tumor shape and volume, and by the location of critical organs. The coordinates of anterior-posterior and lateral port film were inputted to ISOLOC software, which calculated (1) the couch moves translation distance required to bring the target point to the isocenter, and (2) the intermarker distance comparisons between the CT study and the treatment machine films. We evaluated the isocenter deviation based on the error between orthogonal film target coordinates and isocenter coordinates. RESULTS: The mean treatment isocenter deviations (x, y, z) were -0.03, 0.14, and -0.04 mm, respectively. The systematic component isocenter standard deviations were 0.28, 0.31, and 0.35 mm (1 SD), respectively, and the random component isocenter standard deviations were 0.53, 0.52, and 0.50 mm (1 SD), respectively. CONCLUSIONS: The isocenter accuracy in the frameless SRT-implanted fiducial system is highly reliable and is comparable to that of other stereotactic radiosurgery systems.     

Investigations of a minimally invasive method for treatment of spinal malignancies with LINAC stereotactic radiation therapy: accuracy and animal studies

PURPOSE: A new method for stereotactic irradiation of spinal malignancies is presented, with evaluations of the theoretic and practical limitations of localization accuracy and the implementation of the method in swine. MATERIALS AND METHODS: In a percutaneous procedure, a minimum of three small (1.7-mm-diameter) titanium markers are permanently affixed to a vertebra. Markers are localized on biplanar radiographs while isocenter positions are determined on CT. An external fiducial frame defines a three-dimensional coordinate system through the patient. Radiographs coupled with a rigid body rotation algorithm account for daily differences in patient position. Phantom studies were used to verify theoretic uncertainty calculations from a simulation program. A swine model was used to evaluate the difficulty and duration of the implant technique, the suitability of the vertebral process as an implant site, vertebral motion due to normal respiration, and the ability to target one vertebra with markers in an adjacent vertebra. RESULTS: Theoretic accuracy studies confirmed that localization accuracy is a function of marker separation. Phantom studies involving 296 measurements showed that individual implants could be localized within +/-0.25 mm. The largest targeting error observed in 3,600 measurements of 100 implant configurations was 1.17 mm. The implant procedure took 5-10 minutes per site. No significant migration of implants was observed up to 35 days postimplantation, and respiratory motion had no detectable influence on vertebral position. Adjacent vertebrae may be useful for targeting one another with a small sacrifice in localization accuracy. CONCLUSIONS: The use of implanted markers for localization of spinal malignancies has potential for applications in stereotactic radiotherapy. Phantom measurements suggest that localization accuracy similar to intracranial stereotactic radiotherapy techniques is achievable. Swine studies suggest that the implant technique is expedient and feasible for tumor targeting purposes.     

Image-guided and intensity-modulated radiosurgery for patients with spinal metastasis

BACKGROUND: Radiosurgery can deliver a single, large radiation dose to a localized tumor using a stereotactic approach and hence, requires accurate and precise delivery of radiation to the target. Of the extracranial organ targets, the spine is considered a suitable site for radiosurgery, because there is minimal or no breathing-related organ movement. The authors studied spinal radiosurgery in patients with spinal metastases to determine its accuracy and precision. METHODS: The spinal radiosurgery program was based on an image-guided and intensity-modulated, shaped-beam radiosurgical unit. It is equipped with micromultileaf collimators for beam shaping and radiation intensity modulation and with a noninvasive, frameless positioning device that uses infrared, passive marker technology together with corroborative image fusion of the digitally reconstructed image from computed tomography (CT) simulation and orthogonal X-ray imagery at the treatment position. These images were compared with the port films that were taken at the time of treatment to determine the accuracy of the isocenter position. Clinical feasibility was tested in 10 patients who had spinal metastasis with or without spinal cord compression. The patients were treated with fractionated external beam radiotherapy followed by single-dose radiosurgery as a boost (6-8 grays) to the most involved portion of the spine or to the site of spinal cord compression. RESULTS: The accuracy for the isocenter was within 1.36 mm +/- 0.11 mm, as measured by image fusion of the digitally reconstructed image from CT simulation and the port film. Clinically, the majority of patients had prompt pain relief within 2-4 weeks of treatment. Complete and partial recovery of motor function also was achieved in patients with spinal cord compression. The radiation dose to the spinal cord was minimal. The maximum dose of radiation to the anterior edge of the spinal cord within a transverse section, on average, was 50% of the prescribed dose. There was no acute radiation toxicity detected clinically during the mean follow-up of 6 months. CONCLUSIONS: Image-guided, shaped-beam spinal radiosurgery is accurate and precise. Rapid clinical improvement of pain and neurologic function also may be achieved. The results indicate the potential of spinal radiosurgery in the treatment of patients with spinal metastasis, especially those with solitary sites of spine involvement, to increase the prospects of long-term palliation.     

Is a Single Respiratory Correlated 4D-CT Study Sufficient for Evaluation of Breathing Motion?

PURPOSE: Respiratory correlated computed tomography has been shown to be effective for evaluation of breathing-induced motion of pulmonary tumors. This study investigated whether a single four-dimensional CT study (4D-CT) is representative and sufficient for treatment planning in stereotactic body radiotherapy (SBRT). METHODS AND MATERIALS: Four repeated helical 4D-CT studies were acquired every 10 min for 10 patients with 14 pulmonary metastases. Patients remained immobilized in a stereotactic body frame (SBF) for 30 min; abdominal compression was applied to seven patients. Using amplitude based sorting, eight phases equally distributed over the breathing cycle were reconstructed for each 4D-CT study. Tumor position was defined in a total of 406 CT series and variability of breathing motion and mean tumor position were evaluated. RESULTS: Peak-to-peak tumor motion was 9.9 mm +/- 6.8 mm (mean +/- standard deviation) and 9.0 mm +/- 7.4 mm at time point 0 min (t(0)) and t(30), respectively. In one patient with poor pulmonary function, continuous increase of breathing motion from 17.4 mm at t(0) to 28.3 mm at t(30) was seen. In five and two lesions, respectively, a drift of the mean tumor position greater than 3 mm and 5 mm was observed. A borderline significance was calculated for larger tumor position variability in midventilation phases compared with peak-ventilation phases of the breathing cycle (p = 0.08). CONCLUSION: Treatment planning based on a single 4D-CT study is reliable for the majority of patients. Increased intrafractional uncertainties were seen for patients with poor pulmonary function and with tumors located in the lower lobe.     

Cone-beam CT based image-guidance for extracranial stereotactic radiotherapy of intrapulmonary tumors

Cone-beam CT (CB-CT) based image-guidance was evaluated for extracranial stereotactic radiotherapy of intrapulmonary tumors. A total of 21 patients (25 lesions: prim. NSCLC n = 6; pulmonary metastases n = 19) were treated with stereotactic radiotherapy (1 to 8 fractions). Prior to every fraction a CB-CT was acquired in treatment position, errors between planned and actual tumor position were measured and corrected. Intra- and inter-observer variability of manual evaluation of tumor position error was investigated and this manual method was compared with automatic image registration. Based on CB-CTs from 66 fractions the discrepancy (3-D vector) between planned and actual tumor position was 7.7 mm +/-1.3 mm. Tumor position error relative to the bony anatomy was 5.3 mm +/-1.2 mm, the correlation between bony anatomy and tumor position was poor. Intra-observer and inter-observer variability of manual evaluation of tumor position error was 0.9 mm +/-0.8 mm and 2.3 mm +/-1.1 mm, respectively. Automatic image registration showed highly reproducible results (<1 mm). However, compared with manual registration a systematic error was found in direction of predominant tumor breathing motion (2.5 mm vs 1.4 mm). Image-guidance using CB-CT was validated for high precision radiotherapy of intrapulmonary tumors. It was shown that both the planning reference and the verification image study have to consider tumor breathing motion.