Complications of Thoracic Computed Tomography–Guided Fiducial Placement for the Purpose of Stereotactic Body Radiation Therapy

Robust localization of poorly visible tumor in fiducial free stereotactic body radiation therapy

BACKGROUND AND PURPOSE

Effective respiratory motion management reduces healthy tissue toxicity and ensures sufficient dose delivery to lung cancer cells in pulmonary stereotactic body radiation therapy (SBRT) with high fractional doses. An articulated robotic arm paired with an X-ray imaging system is designed for real-time motion-tracking (RTMT) dose delivery. However, small tumors (<15 mm) or tumors at challenging locations may not be visible in the X-ray images, disqualifying patients with such tumors from RTMT dose delivery unless fiducials are implanted via an invasive procedure. To track these practically invisible lung tumors in SBRT, we hereby develop a deep learning-enabled template-free tracking framework, SAFE Track.

METHODS

SAFE Track is a fully supervised framework that trains a generalizable prior for template-free target localization. Two sub-stages are incorporated in SAFE Track, including the initial pretraining on two large-scale medical image datasets (DeepLesion and Node21) followed by fine-tuning on our in-house dataset. A two-stage detector, Faster R-CNN, with a backbone of ResNet50, was selected as our detection network. 94 patients (415 fractions; 40,348 total frames) with low tumor visibility who thus had implanted fiducials were included. The cohort is categorized by the longest dimension of the tumor (<10 mm, 10-15 mm and > 15 mm). The patients were split into training (n = 66) and testing (n = 28) sets. We simulated fiducial-free tumors by removing the fiducials from the X-ray images. We classified the patients into two groups - fiducial implanted inside tumors and implanted outside tumors. To ensure the rigor of our experiment design, we only conducted fiducial removal simulation in training patients and utilized patients with fiducial implanted outside of the tumors for testing. Commercial Xsight Lung Tracking (XLT) and a Deep Match were included for comparison.

RESULTS

SAFE Track achieves promising outcomes to as accurate as 1.23±1.32 mm 3D distance in testing patients with tumor size > 15 mm where Deep Match is at 4.75±1.67 mm and XLT is at 12.23±4.58 mm 3D distance. Even for the most challenging tumor size (<10 mm), SAFE Track maintains its robustness at 1.82 plus or minus 1.67 mm 3D distance, where Deep Match is at 5.32 plus or minus 2.32 mm, and XLT is at 24.83±12.95 mm 3D distance. Moreover, SAFE Track can detect some considerably challenging cases where the tumor is almost invisible or overlapped with dense anatomies.

CONCLUSION

SAFE Track is a robust, clinically compatible, fiducial-free, and template-free tracking framework that is applicable to patients with small tumors or tumors obscured by overlapped anatomies in SBRT.

Clinical implementation and patient-specific quality assurance solutions for real-time target tracking and dynamic delivery in Radixact synchrony

BACKGROUND

The installation and testing of the first Radixact with Synchrony system in Colombia marked a significant milestone in Latin America's medical landscape. There was a need to devise a robust quality assurance protocol to comprehensively evaluate both dose delivery and motion tracking accuracy. However, testing experiences under clinical conditions have not been extensively reported. Additionally, there are limited recommended measuring devices for Synchrony evaluation.

PURPOSE

To validate and implement an alternative setup for dynamic-PSQA while testing Synchrony's functionality under clinical scenarios, including real-patient motion traces, and to provide guidance to new centers undergoing clinical implementation of Helical Synchrony.

METHODS

This approach involves using the Iba miniPhantomR with strategically placed fiducial markers for configuring Gafchromic-films and array-based setups. When paired with the CIRS Dynamic Platform, this enables an innovative dynamic setup with trackable features for Synchrony delivery testing. Assessment scenarios, including compensation (M1S1) and no-motion compensation (M1S0), were evaluated using 2D-gamma pass rate analysis with multiple clinical gamma criteria. The Synchrony-Simulation feature was used to assess pre-treatment performance and capture the patient's target motion pattern. Synchrony for common clinical cases with patient's motion-traces was validated.

RESULTS

The results for M1S0 and M1S1 demonstrated consistency with previous studies evaluating Synchrony functionality. Analysis using different gamma criteria unveiled dosimetric differences and impacts across various motion ranges. The application of effective kV-dose subtraction for array-based methods is of upmost importance when evaluating dynamic-PSQA with stringent gamma-criteria. However, no significant kV-dose impact on EBT3-Film was detectable.

CONCLUSION

Two implemented configurations for dynamic-PSQA setups were validated and successfully integrated into our clinic. We addressed both the benefits and limitations of array-based and film-based methods. The functionality and limitations of Synchrony were evaluated using the proposed setups. The potential utility of Synchrony-Simulation, along with the proposed patient-case classification table, can offer valuable support for new users during the clinical implementation of Synchrony treatments.

Evaluation of a New Method for CyberKnife Treatment for Central Lung and Mediastinal Tumors by Tracheobronchial Tracking

BACKGROUND

CyberKnife treatment for central lung tumors and mediastinal tumors can be difficult to perform with marker less.

PURPOSE

We aimed to evaluate a novel tracheobronchial-based method (ie, tracheobronchial tracking) for the purpose of minimally invasive CyberKnife treatment for central lung and mediastinal tumors.

METHODS

Five verification plans were created using an in-house phantom. Each plan included five irradiation sessions. The reference plan irradiated and tracked the simulated tumor (using the target tracking volume, TTV). Trachea plans tracked the simulated tracheo-bronchus and irradiated the simulated tumor and included two types of subplans: correlated plans in which the displacement of the simulated tracheobronchial and the simulated tumor were correlated, and non-correlated plans in which these factors were not correlated. Moreover, 15 mm and 25 mm TTVs were evaluated for each plan. The sin waveform and the patient's respiratory waveform were prepared as the respiratory model. Evaluations were performed by calculating the dose difference between the radiophotoluminescent glass dosimeter (RPLD)-generated mean dose values (generated by the treatment planning system, TPS) and the actual absorbed RPLD dose. Statistical analyses were performed to evaluate findings for each plan. Correlation and prediction errors were calculated for each axis of each plan using log files to evaluate tracking accuracy.

RESULTS

Dose differences were statistically significant only in comparisons with the non-correlated plan. When evaluated using the sin waveform, the mean values for correlation and prediction errors in each axis and for all plans were less than 0.6 mm and 0.1 mm, respectively. In the same manner, they were less than 1.1 mm and 0.2 mm when evaluated using the patient's respiratory waveform.

CONCLUSION

Our newly-developed tracheobronchial tracking method would be useful in facilitating minimally invasive CyberKnife treatment in certain cases of central lung and mediastinal tumors.

Four-Dimensional Computed Tomography-Based Correlation of Respiratory Motion of Lung Tumors With Implanted Fiducials and an External Surrogate

Purpose

Our purpose was to assess the suitability of airway-implanted internal fiducial markers and an external surrogate of respiratory motion for motion management during radiation therapy of lung tumors.

Methods and Materials

We analyzed 4-dimensional computed tomography scans acquired during radiation therapy simulation for 28 patients with lung tumors who had anchored fiducial markers bronchoscopically implanted inside small airways in or near the tumor in a prospective trial. We used a linear mixed model to build population-based correlative models of tumor and surrogate motion. The first 24 of the 28 patients were used to build correlative models, and 4 of the 28 consecutive patients were excluded and used as an internal validation cohort. Of the 24 patients from the model building cohort, all were used for the models based on the internal fiducial. The external surrogate was completely visualized in 11 patients from the model building cohort, so only those were used for the models based on the external surrogate. Furthermore, we determined the predicted residual error sum of squares for our correlative models, which may serve as benchmarks for future research.

Results

The motion of the internal fiducials was significantly associated with the tumor motion in the anterior-posterior (P < .0001) and superior-inferior (SI) directions (P < .0001). We also observed a strong correlation of the external surrogate anterior-posterior motion to the tumor dominant SI motion (P < .0001). In the validation cohort, the internal fiducial SI motion was the only reliable predictor of lung tumor motion.

Conclusions

The internal fiducials appear to be more reliable predictors of lung tumor motion than the external surrogate. The suitability of such airway-implanted internal fiducial markers for advanced motion management techniques should be further investigated. Although the external surrogate seems to be less reliable, its wide availability and noninvasive application support its clinical utility, albeit the greater uncertainty will need to be compensated for.

A simulated comparison of lung tumor target verification using stereoscopic tomosynthesis or radiography

PURPOSE

Mobile lung tumors are increasingly being treated with ablative radiotherapy, for which precise motion management is essential. In-room stereoscopic radiography systems are able to guide ablative radiotherapy for stationary cranial lesions but not optimally for lung tumors unless fiducial markers are inserted. We propose augmenting stereoscopic radiographic systems with multiple small x-ray sources to provide the capability of imaging with stereoscopic, single frame tomosynthesis.

METHODS

In single frame tomosynthesis, nine x-ray sources are placed in a 3 × 3 configuration and energized simultaneously. The beams from these sources are collimated so that they converge on the tumor and then diverge to illuminate nine non-overlapping sectors on the detector. These nine sector images are averaged together and filtered to create the tomosynthesis effect. Single frame tomosynthesis is intended to be an alternative imaging mode for existing stereoscopic systems with a field of view that is three times smaller and a temporal resolution equal to the frame rate of the detector. We simulated stereoscopic tomosynthesis and radiography using Monte Carlo techniques on 60 patients with early-stage lung cancer from the NSCLC-Radiomics dataset. Two board-certified radiation oncologists reviewed these simulated images and rated them on a 4-point scale (1: tumor not visible; 2: tumor visible but inadequate for motion management; 3: tumor visible and adequate for motion management; 4: tumor visibility excellent). Each tumor was independently presented four times (two viewing angles from radiography and two viewing angles from tomosynthesis) in a blinded fashion over two reading sessions.

RESULTS

The fraction of tumors that were rated as adequate or excellent for motion management (scores 3 or 4) from at least one viewing angle was 53% using radiography and 90% using tomosynthesis. From both viewing angles, the corresponding fractions were 7% for radiography and 48% for tomosynthesis. Readers agreed exactly on 62% of images and within 1 point on 98% of images. The acquisition technique was estimated to be 75 mAs at 120 kVp per treatment fraction assuming one verification image per breath, approximately one order of magnitude less than a standard dose cone beam CT.

CONCLUSIONS

Stereoscopic tomosynthesis may provide a noninvasive, low dose, intrafraction motion verification technique for lung tumors treated by ablative radiotherapy. The system architecture is compatible with real-time video capture at 30 frames per second. Simulations suggest that most, but not all, lung tumors can be adequately visualized from at least one viewing angle.

Fiducial markers for stereotactic lung radiation therapy: review of the transthoracic, endovascular and endobronchial approaches

Stereotactic body radiation therapy is an alternative to surgery for early-stage, inoperable peripheral non-small cell lung cancer. As opposed to linear accelerator (linac)-based (e.g. gating) and free-breathing techniques, CyberKnife® with Synchrony® technology allows accurate radiation delivery by means of a real-time respiratory motion tracking system using, in most cases, metal fiducial markers (FMs) placed in the vicinity of the target. The aims of this review are as follows. First, to describe the safety and efficacy of the transthoracic, endovascular and endobronchial FM insertion techniques for peripheral pulmonary lesions (PPLs). Second, to analyse performance in terms of the migration and tracking rates of different FM types. Recent developments in FM tracking for central lesions will also be reviewed. In conclusion, for PPLs, the endobronchial approach provides a low rate of pneumothorax, offers the possibility of concurrent diagnostic sampling for both the PPL and the lymph nodes, and, finally, reduces the intervention time compared to other techniques. In this context, coil-tailed and coil-spring FMs have shown the lowest migration rate with a consequently high tracking rate.

Lobar Gross Endobronchial Disease Predicts for Overall Survival and Grade 5 Pulmonary Toxicity in Medically Inoperable Early Stage Non-Small Cell Lung Cancer Patients Treated With Stereotactic Body Radiation Therapy

PURPOSE

Stereotactic body radiation therapy (SBRT) is considered standard of care for medically inoperable early stage non-small cell lung cancer (ES-NSCLC). Central tumor location is a known risk factor for severe SBRT related toxicity. Bronchoscopy allows for visualization of the central airways prior to treatment. Five fraction SBRT approaches have been advocated to mitigate treatment induced toxicity. In this report, we examine the mature clinical outcomes of a diverse cohort of ES-NSCLC patients with both peripheral and central tumors treated with a conservative 5 fraction SBRT approach and evaluate the role of lobar gross endobronchial disease (LGED) in predicting overall survival and treatment-related death.

METHODS

Medically inoperable biopsy-proven, lymph node-negative ES-NSCLC patients were treated with SBRT. Bronchoscopy was completed prior to treatment in all centrally located cases. The Kaplan-Meier method was used to estimate overall survival (OS), local control (LC), regional control (RC), distant metastasis free survival (DMFS) and disease-free survival (DFS). Overall survival was stratified based on clinical stage, histology, tumor location and LGED. Toxicities were scored according to the National Cancer Institute Common Terminology Criteria for Adverse Events, Version 5.0.

RESULTS

From December 2010 to December 2015, 50 consecutive patients were treated uniformly with a 50 Gy in 5 fraction SBRT approach (tumor BED10 ≥ 100 Gy) and followed for a minimum of 5 years or until death. At a median follow up of 42 months for all patients, 3-year OS was 50%. Three-year OS did not statistically differ between stage I and stage II disease (51% vs. 47%; p=0.86), adenocarcinoma and squamous cell carcinoma (50% vs. 45%; p=0.68), or peripheral and central tumors (56% vs. 45%; p=0.46). Five central tumors were found to have LGED, and 3-year OS for this cohort was quite poor at 20%. Cox regression analysis identified LGED as a predictor of OS while controlling for age, stage and location (OR:4.536, p-value=0.038). Despite the relatively low dose delivered, treatment likely contributed to the death of 4 patients with central tumors. Lobar gross endobronchial disease was an independent predictor for grade 5 pulmonary toxicity (n=4, p=0.007). Specifically, 3 of the 5 patients with LGED developed fatal radiation-induced bronchial stricture. Three-year LC, RC, DMFS and DFS results for the group were similar to contemporary studies at 90%, 90%, 82% and 65%.

CONCLUSIONS

Central location of ES-NSCLC is a well-established predictor for severe SBRT-related toxicity. Here we identify LGED as a significant predictor of poor overall survival and grade 5 pulmonary toxicity. The relatively high rates of severe treatment-related toxicity seen in patients with central ES-NSCLC may be due in part to LGED. Underlying LGED may cause irreparable damage to the lobar airway, unmitigated by SBRT treatment thus increasing the risk of severe treatment-related toxicity. These findings should be verified in larger data sets. Future prospective central ES-NSCLC clinical trials should require staging bronchoscopy to identify LGED and further assess its clinical significance.

Risks and Benefits of Fiducial Marker Placement in Tumor Lesions for Robotic Radiosurgery: Technical Outcomes of 357 Implantations

Simple Summary

Robotic radiosurgery (RRS) allows for the accurate treatment of primary tumors or metastases with high single doses. However, organ motion during or between fractions can lead to imprecise irradiation. We sought to evaluate the risks and advantages of fiducial marker (FM) implantation regarding clinical complications, marker migration, and motion amplitude. Complications were most common in Synchrony^®-tracked lesions affected by respiratory motion, particularly lung lesions. Pneumothoraces and pulmonary bleeding were the most common complications. An increased complication rate was associated with concomitant biopsy sampling and FM implantation. Most FM migration observed in this study occurred after CT-guided placements and clinical FM insertions. The largest motion amplitudes were observed in hepatic and lower lung lobe lesions. This study highlights the benefits of marker implantation, especially in lesions with a large motion amplitude, including hepatic lesions and lesions of the lower lobe of the lung located >100.0 mm from the spine.

Abstract

Fiducial markers (FM) inserted into tumors increase the precision of irradiation during robotic radiosurgery (RRS). This retrospective study evaluated the clinical complications, marker migration, and motion amplitude of FM implantations by analyzing 288 cancer patients (58% men; 63.1 ± 13.0 years) who underwent 357 FM implantations prior to RRS with CyberKnife, between 2011 and 2019. Complications were classified according to the Society of Interventional Radiology (SIR) guidelines. The radial motion amplitude was calculated for tumors that moved with respiration. A total of 725 gold FM was inserted. SIR-rated complications occurred in 17.9% of all procedures. Most complications (32.0%, 62/194 implantations) were observed in Synchrony^®-tracked lesions affected by respiratory motion, particularly in pulmonary lesions (46.9% 52/111 implantations). Concurrent biopsy sampling was associated with a higher complication rate (p = 0.001). FM migration occurred in 3.6% after CT-guided and clinical FM implantations. The largest motion amplitudes were observed in hepatic (20.5 ± 11.0 mm) and lower lung lobe (15.4 ± 10.5 mm) lesions. This study increases the awareness of the risks of FM placement, especially in thoracic lesions affected by respiratory motion. Considering the maximum motion amplitude, FM placement remains essential in hepatic and lower lung lobe lesions located >100.0 mm from the spine.

Transthoracic placement of fiducials with ultrasound or electronic navigational bronchoscopy needle guidance by the interventional pulmonologist: A case series

Stereotactic body radiotherapy (SBRT) has become one of the main options for treatment of thoracic malignancies, leading to the need for more fiducial marker placement. We report cases where these fiducials were placed transthoracically by interventional pulmonologists using ultrasound (US) and electronic navigational bronchoscopy (ENB) needle guidance. Six cases were identified in the Cooper University Hospital medical records where such procedures were performed, alone or in combination with other interventions. All six patients underwent successful placement of fiducials. Concomitant bronchoscopic procedures were performed in four cases. All patients proceeded to SBRT without the need for further interventions. The overall retention rate of fiducials was 80%. No complications were noted. Fiducials' placement by interventional pulmonologists using US or ENB needle guidance is safe and effective, and may be combined with other procedures in a single setting.

Image-guided marking techniques in interventional radiology: A review of current evidence

Precise marking of lesions using image-guided techniques is essential, as imprecise targeting of a tumor can result in either insufficient excision/treatment with an increased risk of recurrence, or excessive removal of healthy tissue. Most frequent indications include localization of nonpalpable lesions before surgical resection (i.e., hook-wire localization of pulmonary nodules before video-assisted thoracoscopy) and definite marking of liver metastasis before neoadjuvant therapy. Other indications include marking of hepatocellular carcinomas that are not visible on ultrasound and unenhanced computed tomography before thermal ablation, of bone lesions before surgical excision, and of different visceral tumors before stereotactic radiotherapy. This review presents the different existing indications, assesses their usefulness, gives systematic details on the technique and lastly analyzes the current literature with emphasis on results and complications.

Comparison of technical success and safety of transbronchial versus percutaneous CT-guided fiducial placement for SBRT of lung tumors

OBJECTIVE

To evaluate the technical success and safety of transbronchial (bronchoscopic) fiducial placement compared to percutaneous CT-guided fiducial placement for stereotactic body radiotherapy (SBRT) of lung tumors.

MATERIALS AND METHODS

This IRB-approved, HIPAA-compliant retrospective study was performed at a single tertiary institution. Consecutive patients undergoing lung fiducial placement for purposes of guiding SBRT (CyberKnife®, Accuray, Inc.) between September 2005 to January 2013 were included in the study. Fiducial seeds were placed percutaneously with CT guidance or transbronchially with bronchoscopic guidance. We compared procedure-related complications (pneumothorax, chest tube placement), technical success (defined as implantation enabling adequate treatment planning with CT simulation) and migration rate. The need for repeat procedures and their mode was noted. Statistical analysis was performed using Fisher exact and Chi square probability tests.

RESULTS

Two hundred and forty-four patients with lung tumors and 272 fiducial seed placements were included in the study. Two hundred and twenty-one of the 272 (81.2%) fiducial markers were placed percutaneously and 51/272 (18.8%) were placed transbronchially. Pneumothorax was seen in 73/221 (33%) of percutaneously-placed fiducials and in 4/51 (7.8%) of transbronchial placements (p<0.001). No significant difference was seen in the rate of chest tube placement between the two groups: 20/221 (9%) of percutaneously placed fiducials and 2/51 (3.9%) of transbronchially placed fiducials (p=0.39). Fifteen of the 51 (29%) of fiducial placements with transbronchial approach were unsuccessful, as discovered at radiotherapy planning session, and required a repeat procedure. Nine of the 15 (60%) of repeat procedures were performed percutaneously, 5/15 (33%) were placed during repeat bronchoscopy, and 1/15 (7%) was placed at transesophageal endoscopic ultrasound. No repeat fiducial placements were required for patients who had the fiducials placed percutaneously (p<0.001), with a technical success rate of 100%.

CONCLUSION

Transbronchial fiducial marker placement has a significantly higher rate of failed seed placements requiring repeat procedures in comparison to percutaneous placement. Complication rate of pneumothorax requiring chest drain placement is similar between the two approaches.

Endobronchial coil spring fiducial markers for CyberKnife® stereotactic body radiation therapy

BACKGROUND AND OBJECTIVE

SBRT is an alternative treatment for early-stage inoperable lung cancer. Metallic FM allow to increase tumour tracking precision by CyberKnife®. Currently used techniques for FM placement have many limitations; transthoracic insertion has a high risk for pneumothorax, endovascular insertion requires expertise and dedicated angiography infrastructure and endobronchial linear-gold FM dislocate frequently. This is the first study to assess the safety and efficacy of cs-FM endobronchial insertion under fluoroscopy with or without R-EBUS assessment.

METHODS

We retrospectively evaluated all consecutive patients undergoing endobronchial cs-FM placement for at least one PPL <25 mm between 10.2015 and 12.2019. TBB of the PPL were performed in case of a typical R-EBUS signal. PPL tracking accuracy by CyberKnife, complications, cs-FM migration rate and procedure duration were analysed.

RESULTS

A total of 52 patients were treated during 55 procedures and 207 cs-FM were placed in 70 PPL. Tracking was successful for 65 of 70 (93%) PPL. R-EBUS was performed for 33 (47%) PPL and TBB for 9 (13%) PPL. Bronchospasm occurred once and any other complications were observed. Migration of cs-FM occurred in 16 of 207 (8%) cs-FM. Migration was more frequent when the target was in a previously irradiated area (P = 0.022). The median bronchoscopy duration was 31.5 min (n = 48 procedures).

CONCLUSION

Bronchoscopic cs-FM placement is a rapid and safe procedure. It is associated with a low migration rate and allows precise SBRT delivery. Previous irradiation of the PPL was associated with a higher migration rate.

RealDRR - Rendering of realistic digitally reconstructed radiographs using locally trained image-to-image translation

INTRODUCTION

Digitally reconstructed radiographs (DRRs) represent valuable patient-specific pre-treatment training data for tumor tracking algorithms. However, using current rendering methods, the similarity of the DRRs to real X-ray images is limited, requires time-consuming measurements and/or are computationally expensive. In this study we present RealDRR, a novel framework for highly realistic and computationally efficient DRR rendering.

MATERIALS AND METHODS

RealDRR consists of two components applied sequentially to render a DRR. First, a raytracer is applied for forward projection from 3D CT data to a 2D image. Second, a conditional Generative Adverserial Network (cGAN) is applied to translate the 2D forward projection to a realistic 2D DRR. The planning CT and CBCT projections from a CIRS thorax phantom and 6 radiotherapy patients (3 prostate, 3 brain) were split in training and test sets for evaluating the intra-patient, inter-patient and inter-anatomical region generalization performance of the trained framework. Several image similarity metrics, as well as a verification based on template matching, were used between the rendered DRRs and respective CBCT projections in the test sets, and results were compared to those of a current state-of-the-art DRR rendering method.

RESULTS

When trained on 800 CBCT projection images from two patients and tested on a third unseen patient from either anatomical region, RealDRR outperformed the current state-of-the-art with statistical significance on all metrics (two-sample t-test, p < 0.05). Once trained, the framework is able to render 100 highly realistic DRRs in under two minutes.

CONCLUSION

A novel framework for realistic and efficient DRR rendering was proposed. As the framework requires a reasonable amount of computational resources, the internal parameters can be tailored to imaging systems and protocols through on-site training on retrospective imaging data.

Endovascular Coils as Lung Tumor Fiducial Markers for Real-Time Tumor Tracking in Stereotactic Body Radiotherapy: Comparison of Complication Rates with Transthoracic Fiducial Marker Placement

PURPOSE

To evaluate safety of endovascular coil fiducial placement and compare complication rates with transthoracic fiducial placement in patients with peripheral early-stage lung cancer receiving fiducial markers for stereotactic body radiotherapy (SBRT).

MATERIALS AND METHODS

This retrospective study included consecutive patients who received endovascular coils (n = 416 patients, n = 1,335 coils) or transthoracic fiducials (n = 30 patients, n = 80 fiducials) for SBRT between August 2005 and January 2017. During the first 3 years of the study period, patients preferentially received cylindrical platinum fiducial markers by percutaneous transthoracic placement; only patients with contraindications received endovascular coils. Thereafter, patients received endovascular fiducials as the first-line procedure. Endovascular embolization coils were placed via the femoral vein into subsegmental pulmonary artery branches near the tumor. Complications were scored by SIR criteria.

RESULTS

The success rate of endovascular coil placement was 99.8%. One patient developed grade 2 hemoptysis requiring procedure discontinuation. Following placement, 1 patient (0.2%) developed grade 3 cardiac arrhythmia. A total of 36 patients (9%) developed grade 1 complications: mild hemoptysis (n = 4; 1%), small asymptomatic pulmonary infarction or hemorrhage (n = 30; 7%), hypoglycemia (n = 1; 0.2%), and vasovagal episode (n = 1; 0.2%). Following transthoracic marker placement, 4 patients (13%) developed a pneumothorax requiring hospital admission and chest tube (grade 2), 6 patients (20%) developed pneumothorax requiring no intervention (grade 1), 2 patients (7%) experienced asymptomatic pulmonary bleeding, and 1 patient (3%) developed persistent pain.

CONCLUSIONS

Endovascular coil fiducial placement for lung SBRT is associated with high procedural success rates and lower rates of clinically relevant complications than transthoracic marker placement.

Fiducial marker placement with electromagnetic navigation bronchoscopy: a subgroup analysis of the prospective, multicenter NAVIGATE study

BACKGROUND

Fiducial markers (FMs) help direct stereotactic body radiation therapy (SBRT) and localization for surgical resection in lung cancer management. We report the safety, accuracy, and practice patterns of FM placement utilizing electromagnetic navigation bronchoscopy (ENB).

METHODS

NAVIGATE is a global, prospective, multicenter, observational cohort study of ENB using the superDimension™ navigation system. This prospectively collected subgroup analysis presents the patient demographics, procedural characteristics, and 1-month outcomes in patients undergoing ENB-guided FM placement. Follow up through 24 months is ongoing.

RESULTS

Two-hundred fifty-eight patients from 21 centers in the United States were included. General anesthesia was used in 68.2%. Lesion location was confirmed by radial endobronchial ultrasound in 34.5% of procedures. The median ENB procedure time was 31.0 min. Concurrent lung lesion biopsy was conducted in 82.6% (213/258) of patients. A mean of 2.2 ± 1.7 FMs (median 1.0 FMs) were placed per patient and 99.2% were accurately positioned based on subjective operator assessment. Follow-up imaging showed that 94.1% (239/254) of markers remained in place. The procedure-related pneumothorax rate was 5.4% (14/258) overall and 3.1% (8/258) grade ⩾ 2 based on the Common Terminology Criteria for Adverse Events scale. The procedure-related grade ⩾ 4 respiratory failure rate was 1.6% (4/258). There were no bronchopulmonary hemorrhages.

CONCLUSION

ENB is an accurate and versatile tool to place FMs for SBRT and localization for surgical resection with low complication rates. The ability to perform a biopsy safely in the same procedure can also increase efficiency. The impact of practice pattern variations on therapeutic effectiveness requires further study.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02410837.

Longitudinal assessment of anchored transponder migration following lung stereotactic body radiation therapy

Purpose

To assess the long‐term stability of the anchored radiofrequency transponders and compare displacement rates with other commercially available lung fiducial markers. We also sought to describe late toxicity attributable to fiducial implantation or migration.

Materials and methods

The transponder cohort was comprised of 17 patients at our institution who enrolled in a multisite prospective clinical trial and underwent bronchoscopic implantation of three anchored transponders into small (2–2.5 mm) airways. We generated a comparison cohort of 34 patients by selecting patients from our institutional lung SBRT database and matching 2:1 based on the lobe containing tumor and proximity to the bronchial tree. Assessment of migration was performed by rigidly registering the most recent follow‐up CT scan to the simulation scan, and assessing whether the relative geometry of the fiducial markers had changed by more than 5 mm. Toxicity outcomes of interest were hemoptysis and pneumothorax.

Results

The median follow‐up of patients in the transponder cohort was 25.3 months and the median follow‐up in the comparison cohort was 21.7 months. When assessing the most recent CT, all fiducial markers were within 5 mm of their position at CT simulation in 11 (65%) patients in the transponder group as compared to 23 (68%) in the comparison group (P = 0.28). One case of hemoptysis was identified in the transponder cohort, and bronchoscopy confirmed bleeding from recurrent tumor; no cases of hemoptysis were noted in the comparison cohort. No case of pneumothorax was noted in either group.

Conclusion

No significant difference in the rates of fiducial marker retention and migration were noted when comparing patients who had anchored transponders placed into small airways and a 2:1 matched cohort of patients who had other commercially available lung fiducial markers placed. In both groups, no late or chronic toxicity appeared to be related to the implanted fiducial markers.

Long term safety and visibility of a novel liquid fiducial marker for use in image guided radiotherapy of non-small cell lung cancer

Safety and clinical feasibility of injecting a novel liquid fiducial marker for use in image guided radiotherapy in 15 patients with non-small cell lung cancer are reported. No major safety or toxicity issues were encountered. Markers present at start of radiotherapy remained visible in cone beam computed tomography and fluoroscopy images throughout the treatment course and on computed tomography images during follow-up (0-38 months). Marker volume reduction was seen until 9 months after treatment, after which no further marker breakdown was found. No post-treatment migration or marker related complications were found.

MR-guided Gated Stereotactic Radiation Therapy Delivery for Lung, Adrenal, and Pancreatic Tumors: A Geometric Analysis

PURPOSE

We implemented magnetic resonance-guided breath-hold stereotactic body radiation therapy in combination with visual feedback using the MRIdian system. Both accuracy of gated delivery and reproducibility of tumor positions were studied.

METHODS AND MATERIALS

Tumor tracking is realized through repeated magnetic resonance imaging in a single sagittal plane at 4 frames per second with deformable image registration. An in-room monitor allowed visualization of the tracked gross tumor volume (GTV) contour and the planning target volume (PTV) (GTV + 3 mm), which was the gating boundary. For each delivery, a predefined threshold-region of interest percentage (ROI%) allows a percentage of GTV area to be outside the gating boundary before a beam-hold is triggered. Accuracy of gated delivery and tumor position reproducibility during breath-holds was analyzed for 15 patients (87 fractions) with lung, adrenal, and pancreas tumors. For each fraction, we analyzed (1) reproducibility of system-tracked GTV centroid position within the PTV; (2) geometric coverage of GTV area within the PTV; (3) treatment duty cycle efficiency; (4) effects of threshold ROI% settings on treatment duty cycle efficiency and GTV area coverage; and (5) beam-off latency effect on mean GTV coverage.

RESULTS

For lung, adrenal, and pancreatic tumors, grouped 5th to 95th percentile distributions of GTV centroid positions in the dorsoventral direction, relative to PTV-center of mass (COM), were, respectively, -3.3 mm to 2.8 mm, -2.5 mm to 3.7 mm, and -4.4 mm to 2.9 mm. Corresponding distributions in the craniocaudal direction were -2.6 mm to 4.6 mm, -4.1 mm to 4.4 mm, and -4.4 mm to 4.5 mm, respectively. Mean GTV areas encompassed during beam-on for all fractions were 94.6%, 94.3%, and 95.3% for lung, adrenal, and pancreas tumors, respectively. Mean treatment duty cycle efficiency ranged from 67% to 87% for these tumors. Use of higher threshold-ROI% resulted in increased duty cycle efficiency, at the cost of a small decrease in GTV area coverage. The beam-off latency had a marginal impact on the GTV coverage.

CONCLUSIONS

Gated stereotactic body radiation therapy delivery during breath-hold, real-time magnetic resonance guidance resulted in at least 95% geometric GTV coverage in lung, adrenal, and pancreatic tumors.

Lung Cancer Biopsies

Image-guided percutaneous transthoracic needle biopsy (PTNB) is a well-established and minimally invasive technique for evaluating pulmonary nodules. Implementation of a national lung screening program and increased use of chest computed tomography have contributed to the frequent identification of indeterminate pulmonary nodules that may require tissue sampling. The advent of biomarker-driven lung cancer therapy has led to increased use of repeat PTNB after diagnosis. Percutaneous insertion of markers for preoperative localization of small nodules can aid in minimally invasive surgery and radiation treatment planning. This article discusses PTNB, patient selection, and biopsy technique, including minimizing and managing complications.

The impact of technology on the changing practice of lung SBRT

Stereotactic body radiotherapy (SBRT) for lung tumours has been gaining wide acceptance in lung cancer. Here, we review the technological evolution of SBRT delivery in lung cancer, from the first treatments using the stereotactic body frame in the 1990's to modern developments in image guidance and motion management. Finally, we discuss the impact of current technological approaches on the requirements for quality assurance as well as future technological developments.

Fiducial marker placement for stereotactic body radiation therapy via convex probe endobronchial ultrasound: a case series and review of literature

Convex probe endobronchial ultrasound (CP-EBUS) and stereotactic body radiotherapy (SBRT) are valuable tools in the diagnosis, staging, and treatment of thoracic malignancies. With widespread clinical adoption, novel uses of CP-EBUS beyond mediastinal diagnosis and staging continue to be discovered. SBRT is an attractive treatment strategy in early-stage lung cancer and oligo-metastatic disease of the chest when a surgical approach is either not feasible or desirable. Accurate application of SBRT is aided by the placement of radio-opaque fiducial markers (FM) to compensate for respiratory cycle movements. We describe eight patients with central thoracic lesions, either known or suspected to be malignant, who underwent EBUS bronchoscopy with lesion sampling and successful intralesional placement of modified FM via our technique, review the existing literature on this topic, and discuss the nuances of coding and billing aspects of FM placement.

Percutaneous thermal ablation for stage IA non-small cell lung cancer: long-term follow-up

Background

Surgical resection is the most effective curative therapy for non-small cell lung cancer (NSCLC). However, many patients are unable to tolerate resection secondary to poor reserve or comorbid disease. Radiofrequency ablation (RFA) and microwave ablation (MWA) are methods of percutaneous thermal ablation that can be used to treat medically inoperable patients with NSCLC. We present long-term outcomes following thermal ablation of stage IA NSCLC from a single center.

Methods

Patients with stage IA NSCLC and factors precluding resection who underwent RFA or MWA from July 2005 to September 2009 were studied. CT and PET-CT scans were performed at 3 and 6 month intervals, respectively, for first 24 months of follow-up. Factors associated with local progression (LP) and overall survival (OS) were analyzed.

Results

Twenty-one patients underwent 21 RFA and 4 MWA for a total of 25 ablations. Fifteen patients had T1a and six patients had T1b tumors. Mean follow-up was 42 months, median survival was 39 months, and OS at three years was 52%. There was no significant difference in median survival between T1a nodules and T1b nodules (36 vs. 39 months, P=0.29) or for RFA and MWA (36 vs. 50 months, P=0.80). Ten patients had LP (47.6%), at a median time of 35 months. There was no significant difference in LP between T1a and T1b tumors (22 vs. 35 months, P=0.94) or RFA and MWA (35 vs. 17 months, P=0.18). Median OS with LP was 32 months compared to 39 months without LP (P=0.68). Three patients underwent repeat ablations. Mean time to LP following repeat ablation was 14.75 months. One patient had two repeat ablations and was disease free at 40-month follow-up.

Conclusions

Thermal ablation effectively treated or controlled stage IA NSCLC in medically inoperable patients. Three-year OS exceeded 50%, and LP did not affect OS. Therefore, thermal ablation is a viable option for medically inoperable patients with early stage NSCLC.

Dosimetric validation of a magnetic resonance image gated radiotherapy system using a motion phantom and radiochromic film

PURPOSE

Magnetic resonance image (MRI) guided radiotherapy enables gating directly on the target position. We present an evaluation of an MRI-guided radiotherapy system's gating performance using an MRI-compatible respiratory motion phantom and radiochromic film. Our evaluation is geared toward validation of our institution's clinical gating protocol which involves planning to a target volume formed by expanding 5 mm about the gross tumor volume (GTV) and gating based on a 3 mm window about the GTV.

METHODS

The motion phantom consisted of a target rod containing high-contrast target inserts which moved in the superior-inferior direction inside a body structure containing background contrast material. The target rod was equipped with a radiochromic film insert. Treatment plans were generated for a 3 cm diameter spherical planning target volume, and delivered to the phantom at rest and in motion with and without gating. Both sinusoidal trajectories and tumor trajectories measured during MRI-guided treatments were used. Similarity of the gated dose distribution to the planned, motion-frozen, distribution was quantified using the gamma technique.

RESULTS

Without gating, gamma pass rates using 4%/3 mm criteria were 22-59% depending on motion trajectory. Using our clinical standard of repeated breath holds and a gating window of 3 mm with 10% target allowed outside the gating boundary, the gamma pass rate was 97.8% with 3%/3 mm gamma criteria. Using a 3 mm window and 10% allowed excursion, all of the patient tumor motion trajectories at actual speed resulting in at least 95% gamma pass rate at 4%/3 mm.

CONCLUSIONS

Our results suggest that the device can be used to compensate respiratory motion using a 3 mm gating margin and 10% allowed excursion results in conjunction with repeated breath holds. Full clinical validation requires a comprehensive evaluation of tracking performance in actual patient images, outside the scope of this study.

Electromagnetic Navigational Bronchoscopy for Peripheral Pulmonary Nodules

Electromagnetic navigational bronchoscopy is a useful addition to the array of modalities available to sample peripheral lung lesions. Its utility in diagnosing peripheral lesions has been steadily increasing since the Food and Drug Administration first approved it in 2004. The improvement can be attributed to continuous refinement in technology, increasing training and experience with the procedure, perhaps widespread availability of rapid onsite cytologic evaluation, and better patient selection. It may also be attributable to improvements of the technology and more available tools to perform biopsy of the peripheral lung.

Tumor track seeding: A new complication of fiducial marker insertion

In the United States, lung cancer is the leading cause of cancer-related death. Candidates for tumor ablation using CyberKnife® require fiducial placement in or near the target tumor to achieve precision. Placing these reference points may lead to complications including pneumothorax and/or hemorrhage. We report a new complication: the appearance of metastatic foci along the track of the fiducial marker. Since the marker was inserted by traversing the original primary tumor, we hypothesize that malignant cells were seeded along the track. In light of this new complication, current techniques for the insertion of fiducial markers should consider a peripheral approach when possible to avoid tracking of malignant cells.

A radiopaque polymer hydrogel used as a fiducial marker in gynecologic-cancer patients receiving brachytherapy

PURPOSE

We assessed a novel Food and Drug Administration-approved hydrogel, synthesized as absorbable iodinated particles, in gynecologic-cancer patients undergoing computed tomography (CT) or magnetic resonance (MR) based brachytherapy after external beam radiation.

METHODS AND MATERIALS

Nineteen patients underwent CT-guided (n = 13) or MR-guided (n = 6) brachytherapy for gynecologic cancers. Seventy-seven hydrogel injections were placed. The hydrogel material was injected into gross residual disease and/or key anatomic landmarks in amounts ranging from 0.1 to 0.4 mL. The visibility of the tracer was scored on CT and on MR images using a 5-point scoring scale. A Cohen's kappa statistic was calculated to assess interobserver agreement. To assess the unadjusted effects of baseline parameters on hydrogel visibility, we modeled visibility using a linear mixed-effect model.

RESULTS

Injections were without complication. The kappa statistic was 0.77 (95% confidence interval [CI], 0.68-0.87). The volume of hydrogel injected was significantly associated with visibility on both CT (p = 0.032) and magnetic resonance imaging (p = 0.016). We analyzed visibility by location, controlling for amount. A 0.1-cc increase in volume injected was associated with increases of 0.54 (95% CI = 0.05-1.03) in the CT visibility score and 0.83 (95% CI = 0.17-1.49) in the MR visibility score. Injection of 0.4 cc or more was required for unequivocal visibility on CT or MR. No statistically significant correlation was found between tumor type, tumor location, or anatomical location of injection and visibility on either CT or magnetic resonance imaging.

CONCLUSIONS

In this first report of an injectable radiopaque hydrogel, targets were visualized to assist with three-dimensional-based brachytherapy in gynecologic malignancies. This marker has potential for several applications, is easy to inject and visualize, and caused no acute complications.

Feasibility of markerless tumor tracking by sequential dual-energy fluoroscopy on a clinical tumor tracking system

A novel approach to dual-energy imaging for markerless tumor tracking was proposed consisting of sequential dual-energy fluoroscopy, omitting the need for fast-switching kV generators. The implementation of this approach on a clinical tumor tracking system and its efficacy is shown feasible through optimization of the imaging parameters.

Minimal Inter-Fractional Fiducial Migration during Image-Guided Lung Stereotactic Body Radiotherapy Using SuperLock Nitinol Coil Fiducial Markers

Objectives

Stereotactic body radiotherapy (SBRT) is being increasingly used for the treatment of patients with lung cancer or lung metastasis who are medically unfit to undergo resection. In order to improve accuracy and confidence in targeting tumors, many centers rely on fiducial implantation. We evaluated the migration of a novel fiducial marker specifically designed for lung tissue implanted via electromagnetic navigation bronchoscopy (ENB).

Methods

We retrospectively quantified the individual and group migrations of SuperLock nitinol coil fiducials for 15 patients receiving lung stereotactic body radiotherapy (SBRT), in order to evaluate the reliability of using these fiducials as a target surrogate for cases where tumors cannot be clearly delineated on cone beam CTs (CBCTs). For each fraction, we compared the individual and group migrations of the fiducials between the planning CT and the acquired CBCT. The group migration was defined as the distance between the centroids of the fiducial group and GTV.

Results

A total of 16 lung targets were included in our study for these 15 patients (one patient with two targets). Of 55 fiducials placed, we observed a 100% retention rate. The mean individual migration was 1.87 mm (range, 0.63–5.25 mm) with a standard deviation of 1.26 mm. The mean group migration was 1.94 mm (range, 0.03–6.19 mm) with a standard deviation of 1.45 mm. Overall, there was minimal change in the relative locations of the markers with respect to each other, as well as to the target.

Conclusions

We found that the SuperLock nitinol coil fiducial marker positions are stable throughout the radiation treatment, and can be used as a reliable surrogate to target, and to avoid geometric misses during gated treatments.

Electromagnetic Navigational Bronchoscopy: A Safe and Effective Method for Fiducial Marker Placement in Lung Cancer Patients

The emergence of Electromagnetic Navigational Bronchoscopy (ENB) as a diagnostic tool for small peripheral lung nodules has introduced a new method for delivery of fiducial markers. This technique has not been well studied in the literature. The purpose of our study was to evaluate the safety and effectiveness of ENB when used in fiducial marker placement. We reviewed all patients undergoing ENB fiducial placement between June 2010 and February 2014 (n = 64). These 64 patients had 68 lung lesions, in which we placed a total of 190 markers. Primary end points were marker retention and postoperative complications. The retention rate for the study was 82 per cent (n = 156). Upper lobe lesions had a 78 per cent retention rate and the middle/lower lobe lesions had an 89 per cent retention rate; the difference was not significant ( P = 0.126). Complications included hospital admissions, respiratory failure, and pneumothorax. The difference in complication rates between upper and middle/lower lobe markers was not significant. We found ENB to be a safe method for the placement of fiducial markers. We also found that placement of an average of three markers/lesion led to an adequate retention rate to allow for successful treatment of lung cancer in nonsurgical patients using lung-sparing stereotactic radiation.

Injectable Colloidal Gold for Use in Intrafractional 2D Image-Guided Radiation Therapy

In the western world, approximately 50% of all cancer patients receive radiotherapy alone or in combination with surgery or chemotherapy. Image-guided radiotherapy (IGRT) has in recent years been introduced to enhance precision of the delivery of radiation dose to tumor tissue. Fiducial markers are often inserted inside the tumor to improve IGRT precision and to enable monitoring of the tumor position during radiation therapy. In the present article, a liquid fiducial tissue marker is presented, which can be injected into tumor tissue using thin and flexible needles. The liquid fiducial has high radio-opacity, which allows for marker-based image guidance in 2D and 3D X-ray imaging during radiation therapy. This is achieved by surface-engineering gold nanoparticles to be highly compatible with a carbohydrate-based gelation matrix. The new fiducial marker is investigated in mice where they are highly biocompatible and stable after implantation. To investigate the clinical potential, a study is conducted in a canine cancer patient with spontaneous developed solid tumor in which the marker is successfully injected and used to align and image-guide radiation treatment of the canine patient. It is concluded that the new fiducial marker has highly interesting properties that warrant investigations in cancer patients.

Advantages of CyberKnife for inoperable stage I peripheral non-small-cell lung cancer compared to three-dimensional conformal radiotherapy

This study was conducted to compare the clinical curative effect and acute radiation lung reactions between CyberKnife (CK) and three-dimensional conformal radiotherapy (3DCRT) treatment for inoperable stage I peripheral non-small-cell lung cancer (NSCLC). We retrospectively analyzed 68 patients with inoperable stage I peripheral NSCLC between 2012 and 2013 in our institution. The CK patients were treated with 42-60 Gy in three fractions, while the 3DCRT patients were treated with a total of 60 Gy, at 2 Gy per fraction. The patients were followed up and the clinical outcome was evaluated according to the Response Evaluation Criteria in Solid Tumours. We assessed the presence of acute radiation pneumonitis and pulmonary function status by thoracic scan and pulmonary function tests following CK and 3DCRT treatment. The binary univariate logistic regression analysis demonstrated that treatment method and forced expiratory volume in 1 sec/forced vital capacity (FEV1/FVC) prior to treatment (pre-FEV1/FVC) were the main factors affecting the risk of radiation pneumonitis. The analysis of these factors through multivariate logistic regression method demonstrated that treatment method for grade 1 and 2 [odds ratio (OR)= 7.866 and 11.334, respectively) and pre-FEV1/FVC for grade 1, 2 and 3 (OR = 5.062, 11.498 and 15.042, respectively) were significant factors affecting the risk of radiation pneumonitis (P<0.05). The 68 patients were divided into two subgroups using the threshold of pre-FEV1/FVC selected by the receiver operating characteristic curve. There were significant differences between the 3DCRT and CK treatment in both the pre-FEV1/FVC <68% and ≥68% subgroups for radiation pneumonitis (P=0.023 and 0.002, respectively). There was no statistically significant change in FVC, FEV1 and carbon monoxide diffusion capacity (DCLO) in the CK group, whereas there was a decrease in DCLO in the 3DCRT group. The complete remission rate was 40 vs. 34.2% at 1 year in the CK and 3DCRT groups, respectively. In conclusion, in this cohort of patients with inoperable stage I peripheral NSCLC, CK appears to be a safe and superior alternative to conventionally fractionated radiotherapy.

Fiducial marker placement via conventional or electromagnetic navigation bronchoscopy (ENB): an interdisciplinary approach to the curative management of lung cancer

BACKGROUND AND AIMS

Conventional and electromagnetic navigation bronchoscopy (ENB) is generally used as a diagnostic tool in suspicious pulmonary nodules. The use of this technique for the placement of fiducial markers in patients with inoperable but early-stage lung cancer could present an innovative approach enabling risk-reduced therapy.

METHODS

We present seven clinical cases where conventional bronchoscopy and ENB were used as part of an experimental interdisciplinary approach to clinical management and therapy planning. In each case, we analyzed the clinical indication, endoscopic procedures and post-interventional outcome.

RESULTS

In six patients (three females, three males) with peripheral non-small cell lung cancer (NSCLC), stage cT1cN0cM0, surgery and conventional stereotactic radiation therapy was not possible because of end-stage chronic obstructive pulmonary disease. ENB was used for fiducial marker placement prior to cyberknife radiotherapy. No procedure-related complications were observed. Complete remission could be achieved in four cases, partial remission in two cases and no relevant complications induced by radiotherapy were observed. In one male patient, an endoluminal relapse in the right lower lobe was diagnosed following a right upper lobe resection for a NSCLC. The tumor could not be clearly identified by computerized tomography, so that the bronchoscopic placement of a fiducial marker in the tumor was performed in order to allow stereotactic radiochemotherapy, by which complete remission could be achieved.

CONCLUSION

Fiducial marker placement may be an interesting bronchoscopic technique in the interdisciplinary therapeutic approach to inoperable early-stage lung cancer. In the described cases, therapy planning was successful and no procedure-related complications were observed.

Injectable colloidal gold in a sucrose acetate isobutyrate gelating matrix with potential use in radiation therapy

External beam radiation therapy relies on the ability to deliver high radiation doses to tumor cells with minimal exposure to surrounding healthy tissue. Advanced irradiation techniques, including image-guided radiation therapy (IGRT), rely on the ability to locate tumors to optimize the therapeutic benefit of these techniques. Today, radiopaque fiducial tissue markers are placed in or around tumors, for example, in prostate cancer patients to enhance the precision of daily and/or real-time IGRT. A liquid injectable fiducial marker (nanogel) is developed based on PEGylated gold nanoparticles and sucrose acetate isobutyrate (SAIB) with improved properties compared to current solid fiducial markers. The developed nanogel is investigated in vitro and subsequently evaluated in vivo in immunocompetent NMRI mice. The nanogel shows high CT-contrast and excellent stability in vivo over a period of 12 weeks. The nanogel is found to be biocompatible and well tolerated. No induction of the inflammatory cytokines INF-γ, IL-6, or TNF-α is observed throughout the study period. The developed nanogel seems to be a safe injectable fiducial marker ideally suited for IGRT that may further enhance the effect of radiation.

Prospective evaluation of dual-energy imaging in patients undergoing image guided radiation therapy for lung cancer: initial clinical results

PURPOSE

A prospective feasibility study was conducted to investigate the utility of dual-energy (DE) imaging compared to conventional x-ray imaging for patients undergoing kV-based image guided radiation therapy (IGRT) for lung cancer.

METHODS AND MATERIALS

An institutional review board-approved feasibility study enrolled patients with lung cancer undergoing IGRT and was initiated in September 2011. During daily setup, 2 sequential respiration-gated x-ray images were obtained using an on-board imager. Imaging was composed of 1 standard x-ray image at 120 kVp (1 mAs) and a second image obtained at 60 kVp (4 mAs). Weighted logarithmic subtraction of the 2 images was performed offline to create a soft tissue-selective DE image. Conventional and DE images were evaluated by measuring relative contrast and contrast-to-noise ratios (CNR) and also by comparing spatial localization, using both approaches. Imaging dose was assessed using a calibrated ion chamber.

RESULTS

To date, 10 patients with stage IA to IIIA lung cancer were enrolled and 57 DE images were analyzed. DE subtraction resulted in complete suppression of overlying bone in all 57 DE images, with an average improvement in relative contrast of 4.7 ± 3.3 over that of 120 kVp x-ray images (P<.0002). The improvement in relative contrast with DE imaging was seen for both smaller (gross tumor volume [GTV] ≤5 cc) and larger tumors (GTV >5 cc), with average relative contrast improvement ratios of 3.4 ± 4.1 and 5.4 ± 3.6, respectively. Moreover, the GTV was reliably localized in 95% of the DE images versus 74% of the single energy (SE images, (P=.004). Mean skin dose per DE image set was 0.44 ± 0.03 mGy versus 0.43 ± 0.03 mGy, using conventional kV imaging parameters.

CONCLUSIONS

Initial results of this feasibility study suggest that DE thoracic imaging may enhance tumor localization in lung cancer patients receiving kV-based IGRT without increasing imaging dose.

Potential position errors using fiducial markers for gated image guided radiotherapy

BACKGROUND

Fiducials can be used as surrogate for target position during radiotherapy. However, fiducial motion could lead to potential position errors when using fiducials in four-dimensional computed tomography (4DCT) treatment planning and for gated image guided radiotherapy (IGRT).

MATERIAL AND METHODS

One gold marker (GM) and 5, 10 and 15 mm nickel-titanium (NiTi) stents were inserted in a moving phantom for the purpose of fiducial detection in 4DCT and gated IGRT. Fiducial position errors in 4DCT and BrainLAB's gated IGRT were defined as residuals between fiducial detection and the actual physical position at the instance of image acquisition.

RESULTS

Fiducials position errors correlate to speed, fiducial type and orientation during 4DCT acquisition. Lower detection accuracy was measured for the 5 mm NiTi-stent relative to the 10 and 15 mm NiTi stents and GM. Fiducials with orientation 45° relative to the scan direction showed a lower detection accuracy relative to parallel and perpendicular orientations. The standard deviation of position errors in 4DCT were up to 2.2 mm with a maximum deviation of 4.0 mm. Using BrainLAB's gated IGRT the fiducials were detected with a standard deviation of 0.6 mm and a maximum deviation of 1.9 mm. For gated IGRT no correlation to fiducial speed was found.

CONCLUSIONS

Clinical use of fiducials in combination with treatment planning on mid-ventilation CT phase for moving target should include margins up to 5.5 mm due to potential systematic position errors.

Real-time automatic fiducial marker tracking in low contrast cine-MV images

PURPOSE

To develop a real-time automatic method for tracking implanted radiographic markers in low-contrast cine-MV patient images used in image-guided radiation therapy (IGRT).

METHODS

Intrafraction motion tracking using radiotherapy beam-line MV images have gained some attention recently in IGRT because no additional imaging dose is introduced. However, MV images have much lower contrast than kV images, therefore a robust and automatic algorithm for marker detection in MV images is a prerequisite. Previous marker detection methods are all based on template matching or its derivatives. Template matching needs to match object shape that changes significantly for different implantation and projection angle. While these methods require a large number of templates to cover various situations, they are often forced to use a smaller number of templates to reduce the computation load because their methods all require exhaustive search in the region of interest. The authors solve this problem by synergetic use of modern but well-tested computer vision and artificial intelligence techniques; specifically the authors detect implanted markers utilizing discriminant analysis for initialization and use mean-shift feature space analysis for sequential tracking. This novel approach avoids exhaustive search by exploiting the temporal correlation between consecutive frames and makes it possible to perform more sophisticated detection at the beginning to improve the accuracy, followed by ultrafast sequential tracking after the initialization. The method was evaluated and validated using 1149 cine-MV images from two prostate IGRT patients and compared with manual marker detection results from six researchers. The average of the manual detection results is considered as the ground truth for comparisons.

RESULTS

The average root-mean-square errors of our real-time automatic tracking method from the ground truth are 1.9 and 2.1 pixels for the two patients (0.26 mm/pixel). The standard deviations of the results from the 6 researchers are 2.3 and 2.6 pixels. The proposed framework takes about 128 ms to detect four markers in the first MV images and about 23 ms to track these markers in each of the subsequent images.

CONCLUSIONS

The unified framework for tracking of multiple markers presented here can achieve marker detection accuracy similar to manual detection even in low-contrast cine-MV images. It can cope with shape deformations of fiducial markers at different gantry angles. The fast processing speed reduces the image processing portion of the system latency, therefore can improve the performance of real-time motion compensation.

Markerless EPID image guided dynamic multi-leaf collimator tracking for lung tumors

Compensation of target motion during the delivery of radiotherapy has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. We implement an online image guided therapy system based on soft tissue localization (STiL) of the target from electronic portal images and treatment aperture adaptation with a dynamic multi-leaf collimator (DMLC). The treatment aperture is moved synchronously and in real time with the tumor during the entire breathing cycle. The system is implemented and tested on a Varian TX clinical linear accelerator featuring an AS-1000 electronic portal imaging device (EPID) acquiring images at a frame rate of 12.86 Hz throughout the treatment. A position update cycle for the treatment aperture consists of four steps: in the first step at time t = t0 a frame is grabbed, in the second step the frame is processed with the STiL algorithm to get the tumor position at t = t0, in a third step the tumor position at t = ti + δt is predicted to overcome system latencies and in the fourth step, the DMLC control software calculates the required leaf motions and applies them at time t = ti + δt. The prediction model is trained before the start of the treatment with data representing the tumor motion. We analyze the system latency with a dynamic chest phantom (4D motion phantom, Washington University). We estimate the average planar position deviation between target and treatment aperture in a clinical setting by driving the phantom with several lung tumor trajectories (recorded from fiducial tracking during radiotherapy delivery to the lung). DMLC tracking for lung stereotactic body radiation therapy without fiducial markers was successfully demonstrated. The inherent system latency is found to be δt = (230 ± 11) ms for a MV portal image acquisition frame rate of 12.86 Hz. The root mean square deviation between tumor and aperture position is smaller than 1 mm. We demonstrate the feasibility of real-time markerless DMLC tracking with a standard LINAC-mounted (EPID).

Developments in stereotactic ablative radiotherapy for the treatment of early-stage lung cancer

SUMMARY Stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy, has emerged as an effective treatment for inoperable early-stage non-small-cell lung cancer. SABR differs from conventional radiotherapy by virtue of its tight spatial tolerances and use of oligofractionated radiation. The modern technique is characterized by management of tumor motion, image guidance before each fraction and specialized radiation delivery techniques. The result is a highly conformal target dose with a sharp gradient that spares normal tissues with great accuracy. This enables delivery of very potent (ablative) doses, causing more rapid and durable responses than traditional radiation therapy treatment regimens can achieve. The established techniques, new developments and ongoing questions related to SABR for early-stage non-small-cell lung cancer are reviewed herein.

Hybrid MV-kV 3D respiratory motion tracking during radiation therapy with low imaging dose

A novel real-time adaptive MV-kV imaging framework for image-guided radiation therapy is developed to reduce the thoracic and abdominal tumor targeting uncertainty caused by respiration-induced intrafraction motion with ultra-low patient imaging dose. In our method, continuous stereoscopic MV-kV imaging is used at the beginning of a radiation therapy delivery for several seconds to measure the implanted marker positions. After this stereoscopic imaging period, the kV imager is switched off except for the times when no fiducial marker is detected in the cine-MV images. The 3D time-varying marker positions are estimated by combining the MV 2D projection data and the motion correlations between directional components of marker motion established from the stereoscopic imaging period and updated afterwards; in particular, the most likely position is assumed to be the position on the projection line that has the shortest distance to the first principal component line segment constructed from previous trajectory points. An adaptive windowed auto-regressive prediction is utilized to predict the marker position a short time later (310 ms and 460 ms in this study) to allow for tracking system latency. To demonstrate the feasibility and evaluate the accuracy of the proposed method, computer simulations were performed for both arc and fixed-gantry deliveries using 66 h of retrospective tumor motion data from 42 patients treated for thoracic or abdominal cancers. The simulations reveal that using our hybrid approach, a smaller than 1.2 mm or 1.5 mm root-mean-square tracking error can be achieved at a system latency of 310 ms or 460 ms, respectively. Because the kV imaging is only used for a short period of time in our method, extra patient imaging dose can be reduced by an order of magnitude compared to continuous MV-kV imaging, while the clinical tumor targeting accuracy for thoracic or abdominal cancers is maintained. Furthermore, no additional hardware is required with the proposed method.