An assessment of clinically optimal gold marker length and diameter for pelvic radiotherapy verification using an amorphous silicon flat panel electronic portal imaging device

Endoscopic Ultrasound Placement of Preloaded Fiducial Markers Shortens Procedure Time Compared to Back-Loaded Markers

BACKGROUND & AIMS

Fiducial markers are inert radiopaque gold or carbon markers implanted in or near pancreatic tumor to demarcate areas for image-guided radiation therapy. Endoscopic ultrasound (EUS) pre-loaded fiducial needles (PLNs) have been developed to circumvent technical issues associated with traditional back-loaded fiducials (BLNs). We performed a randomized controlled trial to compare procedure times in patients with pancreatic adenocarcinoma undergoing EUS-guided placement of BLNs vs PLNs.

METHODS

In a prospective study, 44 patients with pancreatic adenocarcinoma referred for fiducial marker placement at 2 tertiary care centers were assigned to groups that received PLNs (n = 22) or BLNs (n = 22); each group had the same proportion of patients with tumors of different locations (head or neck vs body or tail).The procedure was standardized among all endoscopists and placement of a minimum of 3 markers inside the tumor was defined as technical success. The times for procedure and fiducial placement were recorded, total number of fiducial markers used documented, and grade of procedure difficulty ranked by passing the needle or deploying the fiducials. Other recorded variables included tumor characteristics, fluoroscopy use, and the number of fiducials clearly seen by EUS and fluoroscopy. The primary aim was to compare the duration of EUS-guided fiducial insertion of BLNs vs PLNs.

RESULTS

The median placement time was significantly shorter in the PLN group (9 min) than the BLN group (16 min) (P < .001). However, the 44% reduction in time did not reach pre-specified levels (≥60%). Similar results were found after stratifying by tumor location. Deployment of BLNs was easier than deployment of PLNs (P = .03). There was no significant difference between groups in technical success, number of fiducials placed, EUS or fluoroscopic visualization, or adverse events. During simulation computed tomography and image-guided radiation therapy, there was no difference between groups in visualization of fiducials, migration rate, or accuracy of placement.

CONCLUSIONS

In a randomized controlled trial of 44 patients with pancreatic adenocarcinoma, we found EUS-guided placement of PLNs to require less time and produce similar results compared with BLNs. Further refinements in PLN delivery system are needed to increase the ease of deployment. Clinicaltrials.gov no: NCT02332863.

Daily On-Line Set-Up Correction in 3D-Conformal Radiotherapy: Is It Feasible?

Aims and background

The aim of this report was to investigate the feasibility in terms of treatment time prolongation of an on-line no-action level correction protocol, based on daily electronic portal image verification.

Methods and study design

The occupation of a linear accelerator (LINAC) delivering 3-D conformal treatments was monitored for two weeks (from Monday to Friday, 10 working days). An electronic portal image device I-View (Elekta, UK) was used for setup verification. Single-exposure portal images were acquired daily using the initial 8 monitor units delivered for each treatment field. Translational deviations of isocenter position larger than 5 mm or 7 mm, for radical or palliative treatments, respectively, were immediately corrected. In order to estimate the extra workload involved with the on-line protocol, the time required for isocenter check and table correction was specifically monitored.

Results

Forty-eight patients were treated. In all, 482 fractions had electronic portal images taken. Two hundred and forty-five setup corrections were made (50.8% of all fractions). The occupation of the LINAC lasted 106 h on the whole. Twelve h and 25 min (11.7% of LINAC occupation time) were spent for portal image verification and setup correction. On the average, 4.3 fractions per hour were carried out.

Conclusions

When used by trained therapists, ideally, portal imaging may be carried out before each fraction, requiring approximately 10% of LINAC occupation time.

Qualitative evaluation of fiducial markers for radiotherapy imaging

PURPOSE

To evaluate visibility, artifacts, and distortions of various commercial markers in magnetic resonance imaging (MRI), computer tomography (CT), and ultrasound imaging used for radiotherapy planning and treatment guidance.

METHODS

We compare 2 solid gold markers, 4 gold coils, and 1 polymer marker from 3 vendors. Imaging modalities used were 3-T and 1.5-T GE MRIs, Siemens Sequoia 512 Ultrasound, Phillips Big Bore CT, Varian Trilogy linear accelerator (cone-beam CT [CBCT], on-board imager kilovoltage [OBI-kV], electronic portal imaging device megavoltage [EPID-MV]), and Medtronic O-ARM CBCT. Markers were imaged in a 30 × 30 × 10 cm(3) custom bolus phantom. In one experiment, Surgilube was used around the markers to reduce air gaps. Images were saved in Digital Imaging and Communications in Medicine (DICOM) format and analyzed using an in-house software. Profiles across the markers were used for objective comparison of the markers' signals. The visibility and artifacts/distortions produced by each marker were assessed qualitatively and quantitatively.

RESULTS

All markers are visible in CT, CBCT, OBI-kV, and ultrasound. Gold markers below 0.75 mm in diameter are not visible in EPID-MV images. The larger the markers, the more CT and CBCT image artifacts there are, yet the degree of the artifact depends on scan parameters and the scanner itself. Visibility of gold coils of 0.75 mm diameter or larger is comparable across all imaging modalities studied. The polymer marker causes minimal artifacts in CT and CBCT but has poor visibility in EPID-MV. Gold coils of 0.5 mm exhibit poor visibility in MRI and EPID-MV due to their small size. Gold markers are more visible in 3-T T1 gradient-recalled echo than in 1.5-T T1 fast spin-echo, depending on the scan sequence. In this study, all markers are clearly visible on ultrasound.

CONCLUSION

All gold markers are visible in CT, CBCT, kV, and ultrasound; however, only the large diameter markers are visible in MV. When MR and EPID-MV imagers are used, the selection of fiducial markers is not straightforward. For hybrid kV/MV image-guided radiotherapy imaging, larger diameter markers are suggested. If using kV imaging alone, smaller sized markers may be used in smaller sized patients in order to reduce artifacts. Only larger diameter gold markers are visible across all imaging modalities.

Comparative analysis of traditional and coiled fiducials implanted during EUS for pancreatic cancer patients receiving stereotactic body radiation therapy

BACKGROUND

EUS-guided fiducial placement facilitates image-guided radiation therapy (IGRT).

OBJECTIVE

To compare 2 types of commercially available fiducials for technical success, complications, visibility, and migration.

DESIGN

Retrospective, single-center, comparative study.

SETTING

Tertiary-care medical center.

INTERVENTIONS

Traditional fiducials (TFs) (5-mm length, 0.8-mm diameter) and Visicoil fiducials (VFs) (10-mm length, 0.35-mm diameter) were compared. Fiducials were placed using linear 19-gauge (for TFs) or 22-gauge (for VFs) needles. A subjective visualization scoring system (0-2; 0 = not visible, 1 = barely visible, 2 = clearly visible) was used to assess visibility on CT. Fiducial migration was calculated as a change in interfiducial distance.

MAIN OUTCOME MEASUREMENTS

Technical success, complications, visibility, and migration of 2 types of fiducials.

RESULTS

Thirty-nine patients with locally advanced pancreatic cancer underwent EUS-guided placement of 103 fiducials (77 TFs, 26 VFs). The mean number of fiducials placed per patient was 2.66 (standard deviation 0.67) for the 19-gauge needle and 2.60 (standard deviation 0.70) for the 22-gauge needle (P = .83). No intra- or postprocedural complications were encountered. The median visibility score for TFs was significantly better than that for VFs, both when scores of 0 were and were not included (2.00, interquartile range [IQR] 2.00-2.00 vs 1.75, IQR 1.50-2.00, P = .009 and 2.00, IQR 2.00-2.00 vs 2.00, IQR 1.50-2.00, P < .0001, respectively). The mean migration was not significantly different between the 2 types of fiducials (0.8 mm [IQR 0.4-1.6 mm] for TFs vs 1.3 mm [IQR 0.6-1.5 mm] for VFs; P = .72).

LIMITATIONS

Retrospective, nonrandomized design.

CONCLUSIONS

Visibility was significantly better for TFs compared with VFs. The degree of fiducial migration was not significantly different for TFs and VFs. There was no significant difference in the mean number of fiducials placed, indicating a similar degree of technical difficulty for TF and VF deployment.

Investigation of dose perturbations and the radiographic visibility of potential fiducials for proton radiation therapy of the prostate

Image guidance using implanted fiducial markers is commonly used to ensure accurate and reproducible target positioning in radiation therapy for prostate cancer. The ideal fiducial marker is clearly visible in kV imaging, does not perturb the therapeutic dose in the target volume and does not cause any artifacts on the CT images used for treatment planning. As yet, ideal markers that fully meet all three of these criteria have not been reported. In this study, 12 fiducial markers were evaluated for their potential clinical utility in proton radiation therapy for prostate cancer. In order to identify the good candidates, each fiducial was imaged using a CT scanner as well as a kV imaging system. Additionally, the dose perturbation caused by each fiducial was quantified using radiochromic film and a clinical proton beam. Based on the results, three fiducials were identified as good candidates for use in proton radiotherapy of prostate cancer.

Validation des plans de radiothérapie conformationnelle avec modulation d'intensité avec les images portales

The goal of this study was to show the feasibility of step and shoot intensity-modulated radiation therapy pre-treatment quality control for patients using the electronic portal imaging device (iViewGT) fitted on a Sli+ linac (Elekta Oncology Systems, Crawley, UK) instead of radiographic films. Since the beginning of intensity-modulated radiation therapy treatments, the dosimetric quality control necessary before treating each new patient has been a time-consuming and therefore costly obligation. In order to fully develop this technique, it seems absolutely essential to reduce the cost of these controls, especially the linac time. Up to now, verification of the relative dosimetry field by field has been achieved by acquiring radiographic films in the isocenter plane and comparing them to the results of the XiO planning system (Computerized Medical Systems, Missouri, USA) using RIT113 v4.1 software (Radiological Imaging Technology, Colorado, USA). A qualitative and quantitative evaluation was realised for every field of every patient. A quick and simple procedure was put into place to be able to make the same verifications using portal images. This new technique is not a modification of the overall methodology of analysis. The results achieved by comparing the measurement with the electronic portal imaging device and the calculation with the treatment planning system were in line with those achieved with the films for all indicators we studied (isodoses, horizontal and vertical dose profiles and gamma index).

A feasibility study of using gold seeds as fiducial markers for bladder localization during radical radiotherapy

Target localization and verification of the treatment position is important for the accurate delivery of conformal radiotherapy. The bladder in particular is a deformable structure whose shape and position continually varies throughout a course of radiation treatment as a result of bladder filling. We report a novel technique of organ localization using gold seeds as fiducial markers that are implanted into the bladder using a specially adapted applicator that is passed through a rigid cystoscope. The seeds are readily apparent on electronic portal imaging taken at the time of radiotherapy and can thus act as a surrogate for bladder position. The feasibility and technical aspects of performing such a procedure on eight patients were assessed. In all of the patients, some of the seeds were visible on the planning CT scan and remained within the bladder wall throughout the course of radiotherapy treatment. The drop-out rate was minimized by the use of cystodiathermy at the site of seed insertion. It was possible to place the seeds in both areas of normal and diseased bladder tissue. The procedure was associated with minimal toxicity. This technique will form the basis for planning further studies on bladder localization.

Developments in electronic portal imaging systems

Verification of geometric accuracy at the time of treatment delivery has always been a necessary part of the radiotherapy process. Since the introduction of conformal and intensity-modulated radiotherapy, the consequences of patient positioning errors are more serious. Portal imaging has played a large part in fulfilling the need for improved geometric accuracy. This review examines how portal imaging has progressed through the development and evolution of electronic portal imaging devices (EPIDs). Changes in technology, including the current commercial systems, and how image quality has changed are presented. The clinical usage of EPIDs and the technological innovations being devised for further improvements in image quality and systems are considered.