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.     

大剂量放疗联合经皮注射骨水泥椎体成形术治疗脊柱骨转移癌临床疗效观察

目的:观察大分割放射治疗联合经皮注射骨水泥椎体成形术(PVP)在脊椎骨转移瘤中的治疗效果。方法:骨转移疼痛患者52例,有明显疼痛椎体68个。以大分割放射治疗,分割剂量3Gy/次,或 4Gy/次,1次/d,5次/周。总剂量:DT 30Gy/10次,或 20Gy/5次;3天后应用PVP治疗脊柱转移性肿瘤52例共68个椎体,在CT引导下或X线电视监视下经皮穿刺至病变椎体后注入适量骨水泥(聚甲基丙烯酸甲酯,PMMA),观察放疗及PVP术后止痛效果、并发症及脊椎稳定性情况。结果:52例患者中,48例DT 30Gy/10次,4例20Gy/5次,52例穿刺全部成功。放疗及PVP术后,患者的疼痛均有不同程度缓解:疼痛完全缓解(CR)42例(54个椎体)、疼痛部分缓解(PR)9例(12个椎体)、轻度缓解(MR)1例(2个椎体)、疼痛无缓解(NR)0例。病变脊椎稳定性良好,术后影学检查显示38例49个病椎的肿瘤区域被PMMA完全均匀充填加固,另14例19个椎体大部分充填。放疗中、PVP术中及术后均无严重并发,随访3～６个月效果良好。结论:大分割放射治疗联合经皮注射骨水泥椎体成形术(PVP)治疗脊椎骨转移瘤缓解疼痛疗效好,并可加强病变椎体的稳定性。     

Head scatter factors for small MV photon fields. Part I: a comparison of phantom types and methodologies.

BACKGROUND AND PURPOSE: Small field dosimetry continues to be problematic for the planning and delivery of both circular stereotactic radiotherapy (SRT) fields and intensity modulated radiotherapy (IMRT) fields. Although the separation of head and phantom scatter is primarily of interest in IMRT fields, measurements can often been difficult. However, the set-up in fields formed by stereotactic collimators is more precise and total scatter and head scatter factors can be more easily measured. Phantom scatter factors calculated from these measurements can be extrapolated from the stereotactic situation to the IMRT one. However, the problem of measuring small field head scatter factors must be overcome first. In this work, different techniques were examined to measure small (4-1cm width) field head scatter factors and determine an optimum phantom and the simplest methodology to ensure set-up accuracy. METHODS AND MATERIALS: All measurements were carried out on the 6 MV beam of a Varian 600 CD. Different phantom diameters, depths and materials were compared and the effects of electron contamination in the lateral and forward directions assessed. Measurements were carried out in fields formed by stereotactic collimators (4-1.25 cm diameter) and in open fields defined by the movable linac collimators (4 x 4 to 1 x 1 cm(2)). RESULTS: A small plastic top, equal in thickness to the build-up depth and equal in diameter to that of an appropriate solid state detector, was found to be the most suitable phantom. This allows measurements in fields >or=1cm, with the detectors investigated. Small differences were found between results in open (standard collimator) fields and in those defined by the stereotactic collimators, but these were likely to be due to differences in beam fluence and in phantom scatter. CONCLUSION: The use of an appropriate small plastic top to measure head scatter factors shows that it is not necessary to preserve lateral electronic equilibrium, nor is electron contamination a problem. Monte Carlo modelling would be useful to investigate the differences further.     

恶性肿瘤立体定向放疗联合免疫治疗研究进展

手术、放疗及化疗是恶性肿瘤的三种传统治疗方式。随着医学的发展,免疫治疗逐渐走进人们的视野,并成为恶性肿瘤治疗的一支新兴力量。近年来的一些临床研究表明放疗联合免疫治疗可以增强机体抗肿瘤免疫,改善患者预后。立体定向放疗单次剂量大,精度高,相比常规放疗更能诱发远隔效应及机体抗肿瘤应答,与免疫治疗联合应用更具前景,这在一些临床研究中已经初步显现。然而,在实际临床应用中,并非所有类型的肿瘤都能在联合治疗时获益,有关联合治疗时的最佳放疗剂量与分割方式、放疗靶病灶的选择、免疫调节剂、安全性等问题尚不明确。本文旨在就恶性肿瘤立体定向放疗联合免疫治疗的进展、相关争议及未来研究方向进行综述。     

Commissioning an image-guided localization system for radiotherapy

PURPOSE: To describe the design and commissioning of a system for the treatment of classes of tumors that require highly accurate target localization during a course of fractionated external-beam therapy. This system uses image-guided localization techniques in the linac vault to position patients being treated for cranial tumors using stereotactic radiotherapy, conformal radiotherapy, and intensity-modulated radiation therapy techniques. Design constraints included flexibility in the use of treatment-planning software, accuracy and precision of repeat localization, limits on the time and human resources needed to use the system, and ease of use. METHODS AND MATERIALS: A commercially marketed, stereotactic radiotherapy system, based on a system designed at the University of Florida, Gainesville, was adapted for use at the University of Washington Medical Center. A stereo pair of cameras in the linac vault were used to detect the position and orientation of an array of fiducial markers that are attached to a patient's biteblock. The system was modified to allow the use of either a treatment-planning system designed for stereotactic treatments, or a general, three-dimensional radiation therapy planning program. Measurements of the precision and accuracy of the target localization, dose delivery, and patient positioning were made using a number of different jigs and devices. Procedures were developed for the safe and accurate clinical use of the system. RESULTS: The accuracy of the target localization is comparable to that of other treatment-planning systems. Gantry sag, which cannot be improved, was measured to be 1.7 mm, which had the effect of broadening the dose distribution, as confirmed by a comparison of measurement and calculation. The accuracy of positioning a target point in the radiation field was 1.0 +/- 0.2 mm. The calibration procedure using the room-based lasers had an accuracy of 0.76 mm, and using a floor-based radiosurgery system it was 0.73 mm. Target localization error in a phantom was 0.64 +/- 0.77 mm. Errors in positioning due to couch rotation error were reduced using the system. CONCLUSION: The system described has proven to have acceptable accuracy and precision for the clinical goals for which it was designed. It is robust in detecting errors, and it requires only a nominal increase in setup time and effort. Future work will focus on evaluating its suitability for use in the treatment of head-and-neck cancers not contained within the cranial vault.     

Coverage of anterior fossa in whole-brain irradiation

PURPOSE: Whole-brain irradiation is indispensable in the treatment of several brain tumors and requires coverage of the entire subarachnoid space. Retrospective studies have revealed frequent recurrences in the frontobasal fossa above the cribriform plate (CP). We sought to determine how accurately the latter could actually be identified on lateral radiographs such as those used for radiotherapy planning. METHODS AND MATERIALS: The CP was localized by five radiation oncologists and five radiologists on lateral radiographs of 30 human skulls from an anatomic collection. Reference radiographs were acquired under identical conditions except for lead markers pointing to the CP and the ethmoid cells. The targeting accuracy was analyzed. RESULTS: In 39% (n = 116), the location of the CP was correctly estimated within 2 mm. Mislocations of 2-5, 5-10, and >10 mm were noted in 34% (n = 102), 20% (n = 61), and 7% (n = 21), respectively. Neither specialty nor experience (years of training) exerted a significant influence on targeting accuracy. If the roofs of the ethmoid cells formed prominent bony edges, they were mistaken for the CP in 37%. CONCLUSION: Lateral radiographs provide insufficient information to locate the CP accurately in whole brain irradiation. Additionally, localization was significantly impaired by prominent ethmoid cells.     

From clinical target volume to biological target volume

The authors' experience with a point matching algorithm for image registration belonging to a commercially available software package for conformal radiotherapy, is reported. The algorithm IFS (Image Fusion System) permits the registration of two image data-sets in two different manners: by use of a stereotactic localization frame, dedicated to brain studies, and by means of point markers that may be internal anatomical landmarks or external fiducials fixed on the patient skin. Position errors were obtained by evaluating the stereotactic coordinates of seven sources detectable by Magnetic Resonance Imaging (MRI) and Computed Tomography (CT), for the first method. The comparison of the geometric centers of cylindrical rods enclosed in a second phantom was employed to evaluate the registration accuracy of the second algorithm. The mean differences in source identification between CT and MRI images are inferior to 1 mm with both techniques, if MRI distortion phenomenon and patient movements are excluded. The software utility of the IFS algorithm to draw, after fusion, a target ROI that is the synthesis of the two information modalities undergoing registration may be a useful tool for the optimization of a radiotherapy treatment planning.     

X线立体定向放射治疗29例体部恶性肿瘤近期疗效观察

目的　探讨立体定向放射治疗体部恶性肿瘤的近期疗效。方法　单用立体定向放射治疗者 ,每次 4 .0～6 .0GY ,治疗 6～ 1 0次 ;肺癌应用立体定向放疗作为追加剂量者 ,每次 3 .5～ 5 .0GY ,治疗 4～ 7次。结果　总有效率 68.9% ,5例死亡。结论　立体定向放射治疗体部恶性肿瘤可得到较理想的姑息甚至根治性疗效 ,可降低正常组织的损伤 ,大幅度提高肿瘤局部剂量     

人工椎体置换治疗脊柱转移性肿瘤

目的观察人工椎体置换治疗脊椎转移性肿瘤的疗效。方法采用无磁性的医用钛金属加工成可调式中空人工椎体,用于治疗脊椎转移性肿瘤12例。观察术后疼痛缓解和脊髓功能恢复情况及手术椎节的稳定性。结果随访6～34个月,平均11.5个月。脊髓功能障碍术后明显改善,尤以神经根性疼痛缓解迅速。X线摄片定期观察人工椎体稳定,椎间高度恢复良好。结论可调式中空人工椎体可撑开施术椎节,缓解神经压迫症状,并能提供即刻稳定,可用于治疗脊椎转移性肿瘤。     

Evaluation of image-guided helical tomotherapy for the retreatment of spinal metastasis

INTRODUCTION: Patients with vertebral metastasis that receive radiation therapy are typically treated to the spinal cord tolerance dose. As such, it is difficult to successfully deliver a second course of radiation therapy for patients with overlapping treatment volumes. In this study, an image-guided helical tomotherapy system was evaluated for the retreatment of previously irradiated vertebral metastasis. METHODS AND MATERIALS: Helical tomotherapy dose gradients and maximum cord doses were measured in a cylindrical phantom for geometric test cases with separations between the planning target volume (PTV) and the spinal cord organ at risk (OAR) of 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm. Megavoltage computed tomography (CT) images were examined for their ability to localize spinal anatomy for positioning purposes by repeat imaging of the cervical spine in an anthropomorphic phantom. In addition to the phantom studies, 8 patients with cord compressions that had received previous radiation therapy were retreated to a mean dose of 28 Gy using conventional fractionation. RESULTS AND DISCUSSION: Megavoltage CT images were capable of positioning an anthropomorphic phantom to within +/-1.2 mm (2sigma) superior-inferiorly and within +/-0.6 mm (2sigma) anterior-posteriorly and laterally. Dose gradients of 10% per mm were measured in phantom while PTV uniformity indices of less than 11% were maintained. The calculated maximum cord dose was 25% of the prescribed dose for a 10-mm PTV-to-OAR separation and 71% of the prescribed dose for a PTV-to-OAR separation of 2 mm. Eight patients total have been treated without radiation-induced myelopathy or any other adverse effects from treatment. CONCLUSIONS: A technique has been evaluated for the retreatment of vertebral metastasis using image-guided helical tomotherapy. Phantom and patient studies indicated that a tomotherapy system is capable of delivering dose gradients of 10% per mm and positioning the patient within 1.2 mm without the use of special stereotactic immobilization.     

体部恶性肿瘤的立体定向放射治疗(附21例近期疗效)

目的：报道立体定向放射治疗体部恶性肿瘤的近期疗效。方法：对原采用放射治疗的病变,如肺癌,分次立体定向放射作为追加剂量,每次５￣７Ｇｙ,共４￣７次;对原不适合放射治疗的病变,如胰腺癌,则单用立体定向放射治疗,每次５￣７Ｇｙ,共６￣７次。结果：总有效率为６６．７％,４例死亡。３例胰腺癌均于治疗后５￣６个月死于肿瘤未控。６例脊椎转移瘤疼痛症状均完全缓解。结论：立体定向放射治疗可得到良好的姑息甚至根治的疗     

A high-precision system for conformal intracranial radiotherapy

PURPOSE: Currently, optimally precise delivery of intracranial radiotherapy is possible with stereotactic radiosurgery and fractionated stereotactic radiotherapy. We report on an optimally precise optically guided system for three-dimensional (3D) conformal radiotherapy using multiple noncoplanar fixed fields. METHODS AND MATERIALS: The optically guided system detects infrared light emitting diodes (IRLEDs) attached to a custom bite plate linked to the patient's maxillary dentition. The IRLEDs are monitored by a commercially available stereo camera system, which is interfaced to a personal computer. An IRLED reference is established with the patient at the selected stereotactic isocenter, and the computer reports the patient's current position based on the location of the IRLEDs relative to this reference position. Using this readout from the computer, the patient may be dialed directly to the desired position in stereotactic space. The patient is localized on the first day and a reference file is established for 5 different couch positions. The patient's image data are then imported into a commercial convolution-based 3D radiotherapy planning system. The previously established isocenter and couch positions are then used as a template upon which to design a conformal 3D plan with maximum beam separation. RESULTS: The use of the optically guided system in conjunction with noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit a high degree of dose homogeneity and a steep dose gradient. To date, this approach has been used to treat 28 patients. CONCLUSION: Because IRLED technology improves the accuracy of patient localization relative to the linac isocenter and allows real-time monitoring of patient position, one can choose treatment-field margins that only account for beam penumbra and image resolution without adding margin to account for larger and poorly defined setup uncertainty. This approach enhances the normal tissue sparing, high degree of conformality, and homogeneity characteristics possible with 3D conformal radiotherapy.     

Doses dans les organes à risque en radiothérapie conformationnelle et en radiothérapie en conditions stéréotaxiques : os et moelle osseuse

In patients undergoing external radiation therapy, bone marrow and cortical bone structures are all often neglected as organs at risk. Still, from increased febrile neutropenia risk in patients undergoing chemoradiation for a pelvic tumour to increased risk of vertebral fracture when undergoing hypofractioned stereotactic radiotherapy of a spinal metastasis, adverse effects are frequent and sometimes serious. This literature review first defines the rules for contouring these structures, then the dose constraints currently recommended. This article focuses first on conventional irradiation or intensity modulation radiotherapy considering classical fractionation. Secondly, it focuses on stereotactic radiotherapy. The considered organs will be haematopoietic structures, and bone cortical structures. Current recommendations are summarised in a table.     

后程立体定向放射治疗体部恶性肿瘤

目的 :探讨后程立体定向放射治疗对体部恶性肿瘤的治疗价值。方法 :选择 80例体部恶性肿瘤 ,包括原发癌 6 3例 ,转移癌 17例。先给予常规外照射DT4 0～ 5 0Gy 4～ 5W ,休息 7～ 10d后 ,行后程立体定向放射治疗补量治疗 ,分次治疗方法为DT4～ 8Gy F ,隔日 1次 ,4～ 6次为 1个疗程 ,平均补量为DT30Gy(2 4～ 4 0Gy)。结果 :治疗后 3～ 6个月 ,CT及MRI复查示 :6 3例原发癌中 ,5 5例肿瘤缩小或消失 ,占 87% ;17例转移癌中有 14例肿块明显缩小 ,占 82 %。 73例患者KPS评分有提高 ,占91%。全部病例均未出现明显放疗并发症。结论 :立体定向放射治疗体部恶性肿瘤疗效肯定 ,后程立体定向放射治疗结合常规放疗对于改善患者预后是有益的。     

Noninvasive patient fixation for extracranial stereotactic radiotherapy.

PURPOSE: To evaluate the setup accuracy that can be achieved with a novel noninvasive patient fixation technique based on a body cast attached to a recently developed stereotactic body frame during fractionated extracranial stereotactic radiotherapy. METHODS AND MATERIALS: Thirty-one CT studies (> or = 20 slices, thickness: 3 mm) from 5 patients who were immobilized in a body cast attached to a stereotactic body frame for treatment of paramedullary tumors in the thoracic or lumbar spine were evaluated with respect to setup accuracy. The immobilization device consisted of a custom-made wrap-around body cast that extended from the neck to the thighs and a separate head mask, both made from Scotchcast. Each CT study was performed immediately before or after every second or third actual treatment fraction without repositioning the patient between CT and treatment. The stereotactic localization system was mounted and the isocenter as initially located stereotactically was marked with fiducials for each CT study. Deviation of the treated isocenter as compared to the planned position was measured in all three dimensions. RESULTS: The immobilization device can be easily handled, attached to and removed from the stereotactic frame and thus enables treatment of multiple patients with the same stereotactic frame each day. Mean patient movements of 1.6 mm+/-1.2 mm (laterolateral [LL]), 1.4 mm+/-1.0 mm (anterior-posterior [AP]), 2.3 mm+/-1.3 mm (transversal vectorial error [VE]) and < slice thickness = 3 mm (craniocaudal [CC]) were recorded for the targets in the thoracic spine and 1.4 mm+/-1.0 mm (LL), 1.2 mm+/-0.7 mm (AP), 1.8 mm+/-1.2 mm (VE), and < 3 mm (CC) for the lumbar spine. The worst case deviation was 3.9 mm for the first patient with the target in the thoracic spine (in the LL direction). Combining those numbers (mean transversal VE for both locations and maximum CC error of 3 mm), the mean three-dimensional vectorial patient movement and thus the mean overall accuracy can be safely estimated to be < or = 3.6 mm. CONCLUSION: The presented combination of a body cast and head mask system in a rigid stereotactic body frame ensures reliable noninvasive patient fixation for fractionated extracranial stereotactic radiotherapy and may enable dose escalation for less radioresponsive tumors that are near the spinal cord or otherwise critically located while minimizing the risk of late sequelae.     

Multifractionated image-guided and stereotactic intensity-modulated radiotherapy of paraspinal tumors: a preliminary report

PURPOSE: The use of image-guided and stereotactic intensity-modulated radiotherapy (IMRT) techniques have made the delivery of high-dose radiation to lesions within close proximity to the spinal cord feasible. This report presents clinical and physical data regarding the use of IMRT coupled with noninvasive body frames (stereotactic and image-guided) for multifractionated radiotherapy. METHODS AND MATERIALS: The Memorial Sloan-Kettering Cancer Center (Memorial) stereotactic body frame (MSBF) and Memorial body cradle (MBC) have been developed as noninvasive immobilizing devices for paraspinal IMRT using stereotactic (MSBF) and image-guided (MBC) techniques. Patients were either previously irradiated or prescribed doses beyond spinal cord tolerance (54 Gy in standard fractionation) and had unresectable gross disease involving the spinal canal. The planning target volume (PTV) was the gross tumor volume with a 1 cm margin. The PTV was not allowed to include the spinal cord contour. All treatment planning was performed using software developed within the institution. Isocenter verification was performed with an in-room computed tomography scan (MSBF) or electronic portal imaging devices, or both. Patients were followed up with serial magnetic resonance imaging every 3-4 months, and no patients were lost to follow-up. Kaplan-Meier statistics were used for analysis of clinical data. RESULTS: Both the MSBF and MBC were able to provide setup accuracy within 2 mm. With a median follow-up of 11 months, 35 patients (14 primary and 21 secondary malignancies) underwent treatment. The median dose previously received was 3000 cGy in 10 fractions. The median dose prescribed for these patients was 2000 cGy/5 fractions (2000-3000 cGy), which provided a median PTV V100 of 88%. In previously unirradiated patients, the median prescribed dose was 7000 cGy (5940-7000 cGy) with a median PTV V100 of 90%. The median Dmax to the cord was 34% and 68% for previously irradiated and never irradiated patients, respectively. More than 90% of patients experienced palliation from pain, weakness, or paresthesia; 75% and 81% of secondary and primary lesions, respectively, exhibited local control at the time of last follow-up. No cases of radiation-induced myelopathy or radiculopathy have thus far been encountered. CONCLUSIONS: Precision stereotactic and image-guided paraspinal IMRT allows the delivery of high doses of radiation in multiple fractions to tumors within close proximity to the spinal cord while respecting cord tolerance. Although preliminary, the clinical results are encouraging.     

Cone-beam computed tomography for on-line image guidance of lung stereotactic radiotherapy: localization, verification, and intrafraction tumor position

PURPOSE: Cone-beam computed tomography (CBCT) in-room imaging allows accurate inter- and intrafraction target localization in stereotactic body radiotherapy of lung tumors. METHODS AND MATERIALS: Image-guided stereotactic body radiotherapy was performed in 28 patients (89 fractions) with medically inoperable Stage T1-T2 non-small-cell lung carcinoma. The targets from the CBCT and planning data set (helical or four-dimensional CT) were matched on-line to determine the couch shift required for target localization. Matching based on the bony anatomy was also performed retrospectively. Verification of target localization was done using either megavoltage portal imaging or CBCT imaging; repeat CBCT imaging was used to assess the intrafraction tumor position. RESULTS: The mean three-dimensional tumor motion for patients with upper lesions (n = 21) and mid-lobe or lower lobe lesions (n = 7) was 4.2 and 6.7 mm, respectively. The mean difference between the target and bony anatomy matching using CBCT was 6.8 mm (SD, 4.9, maximum, 30.3); the difference exceeded 13.9 mm in 10% of the treatment fractions. The mean residual error after target localization using CBCT imaging was 1.9 mm (SD, 1.1, maximum, 4.4). The mean intrafraction tumor deviation was significantly greater (5.3 mm vs. 2.2 mm) when the interval between localization and repeat CBCT imaging (n = 8) exceeded 34 min. CONCLUSION: In-room volumetric imaging, such as CBCT, is essential for target localization accuracy in lung stereotactic body radiotherapy. Imaging that relies on bony anatomy as a surrogate of the target may provide erroneous results in both localization and verification.