Inter-fractional error and intra-fractional motion of prostate and dosimetry comparisons of patient position registrations with versus without fiducial markers during treatment with carbon-ion radiotherapy

A few reports have discussed the influence of inter-fractional position error and intra-fractional motion on dose distribution, particularly regarding a spread-out Bragg peak. We investigated inter-fractional and intra-fractional prostate position error by monitoring fiducial marker positions. In 2020, data from 15 patients with prostate cancer who received carbon-ion beam radiotherapy (CIRT) with gold markers were investigated. We checked marker positions before and during irradiation to calculate the inter-fractional positioning and intra-fractional movement and evaluated the CIRT dose distribution by adjusting the planning beam isocenter and clinical target volume (CTV) position. We compared the CTV dose coverages (CTV receiving 95% [V95%] or 98% [V98%] of the prescribed dose) between skeletal and fiducial matching irradiation on the treatment planning system. For inter-fractional error, the mean distance between the marker position in the planning images and that in a patient starting irradiation with skeletal matching was 1.49 ± 1.11 mm (95th percentile = 1.85 mm). The 95th percentile (maximum) values of the intra-fractional movement were 0.79 mm (2.31 mm), 1.17 mm (2.48 mm), 1.88 mm (4.01 mm), 1.23 mm (3.00 mm), and 2.09 mm (8.46 mm) along the lateral, inferior, superior, dorsal, and ventral axes, respectively. The mean V95% and V98% were 98.2% and 96.2% for the skeletal matching plan and 99.5% and 96.8% for the fiducial matching plan, respectively. Fiducial matching irradiation improved the CTV dose coverage compared with skeletal matching irradiation for CIRT for prostate cancer.

CT-guided Transgluteal Prostate Fiducial Marker Insertion for Localized Radiation Therapy

PURPOSE

To Evaluate the safety and technical success of transgluteal CT-guided fiducial marker implantation into the prostate as an alternative method to transperineal and transrectal approaches.

MATERIAL AND METHODS

We retrospectively identified all patients who had undergone CT-guided transgluteal fiducial marker insertion between 2020 and 2022. Four patients with confirmed prostate cancer were identified. One radiologist performed all procedures via a bilateral transgluteal approach under the guidance of real-time CT-fluoroscopy. Twenty cm long pre-waxed 18G guiding needles, preloaded with smooth gold fiducial markers, were used to implant markers. Technical success was defined as the successful placement of the fiducial markers into the planned positions.

RESULTS

The mean age of patients was 70 years. The mean procedure time was 19.25 (SD: 6.75) min, and the mean total dose length product (DLP) was 801.75 (SD: 291.17) mGycm, which is compatible with the 12 mSv estimated effective dose. All procedures were technically successful (100%). All patients tolerated the procedure and did not require any analgesia for pain, and there were no requests to stop or pause the procedure. Only one patient reported hematuria one day after the procedure, which required no treatment.

CONCLUSION

Transgluteal CT-guided fiducial marker implantation into the prostate is an alternative method to transperineal and transrectal approaches. In this technique, the risk of septic complications is minor, and general anesthesia is not required. Thus, transgluteal CT-guided marker insertion is a feasible and well-tolerated method for image-guided radiation therapy (IGRT) in patients with prostate cancer.

Factors related to fixedness after transbronchial fiducial marker placement for image-guided proton therapy: A retrospective study

BACKGROUND

The usefulness of transbronchially inserted gold fiducial markers has been reported in radiation therapy and proton therapy for mobile lesions, such as lung tumors. However, there is occasional dropout of inserted markers. This retrospective study investigated the factors related to dropout of markers inserted for image-guided proton therapy (IGPT).

METHODS

Between June 2013 and October 2021, 535 markers were inserted in 171 patients with lung tumors. We investigated whether marker dropout was affected by the location of marker insertion, distance between the marker and the chest wall (DMC), and difference in forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC). Marker dropout from the time of planning computed tomography (CT) to follow-up CT was also evaluated.

RESULTS

Of the 535 inserted markers, 417 were confirmed on planning CT and 356 on follow-up CT after IGPT. Multivariate analysis revealed that marker insertion into the upper lobe and FEV1/FVC ≥70% were factors associated with total marker dropout. Marker dropout between planning CT and follow-up CT was associated with DMC, FEV1/FVC ≥70%, and planning CT performed within 4 days of marker insertion.

CONCLUSIONS

Marker dropout can be minimized by inserting markers more peripherally, by considering the planned insertion location, and FEV1/FVC. Additionally, planning CT should be scheduled at least 5 days after marker insertion.

Impact of planning organ at risk volume margins and matching method on late gastrointestinal toxicity in moderately hypofractionated IMRT for locally advanced pancreatic ductal adenocarcinoma

BACKGROUND

This study examined the differences in late gastrointestinal (GI) toxicities in moderately hypofractionated intensity-modulated radiation therapy (IMRT) for locally advanced pancreatic ductal adenocarcinoma (LA-PDAC) by changing the planning organs at risk volume (PRV) margin and the target matching method and assessed the causes of adverse events.

METHODS

We examined 37 patients with LA-PDAC who underwent moderately hypofractionated IMRT between 2016 and 2020 at our institution; 23 patients were treated with wide PRV margins and soft tissue matching (Protocol A) and 14 with narrow PRV margins and fiducial marker matching (Protocol B). The GI toxicities, local control (LC) rate, and overall survival (OS) were assessed for each protocol. The initially planned and daily doses to the gross tumor volume (GTV), stomach, and duodenum, reproduced from cone-beam computed tomography, were evaluated.

RESULTS

The late GI toxicity rate of grades 3-4 was higher in Protocol B (42.9%) than in Protocol A (4.3%). Although the 2-year LC rates were significantly higher in Protocol B (90.0%) than in Protocol A (33.3%), no significant difference was observed in OS rates. In the initial plan, no deviations were found for the stomach and duodenum from the dose constraints in either protocol. In contrast, daily dose evaluation for the stomach to duodenal bulb revealed that the frequency of deviation of V3 Gy per session was 44.8% in Protocol B, which was significantly higher than the 24.3% in Protocol A.

CONCLUSIONS

Reducing PRV margins with fiducial marker matching increased GI toxicities in exchange for improved LC. Daily dose analysis indicated the trade-off between the GTV dose coverage and the irradiated doses to the GI. This study showed that even with strict matching methods, the PRV margin could not be reduced safely because of GI inter-fractional error, which is expected to be resolved with online adaptive radiotherapy.

Patient-specific respiratory motion management using lung tumors vs fiducial markers for real-time tumor-tracking stereotactic body radiotherapy

Background and purpose

In real-time lung tumor-tracking stereotactic body radiotherapy (SBRT), tracking accuracy is related to radiotherapy efficacy. This study aimed to evaluate the respiratory movement relationship between a lung tumor and a fiducial marker position in each direction using four-dimensional (4D) computed tomography (CT) images.

Materials and methods

A series of 31 patients with a fiducial marker for lung SBRT was retrospectively analyzed using 4DCT. In the upper (UG) and middle and lower lobe groups (MLG), the cross-correlation coefficients of respiratory movement between the lung tumor and fiducial marker position in four directions (anterior-posterior, left-right, superior-inferior [SI], and three-dimensional [3D]) were calculated for each gating window (≤1, ≤2, and ≤ 3 mm). Subsequently, the proportions of phase numbers in unplanned irradiation (with lung tumors outside the gating window and fiducial markers inside the gating window) were calculated for each gating window.

Results

In the SI and 3D directions, the cross-correlation coefficients were significantly different between UG (mean r = 0.59, 0.63, respectively) and MLG (mean r = 0.95, 0.97, respectively). In both the groups, the proportions of phase numbers in unplanned irradiation were 11 %, 28 %, and 63 % for the ≤ 1-, ≤2-, and ≤ 3-mm gating windows, respectively.

Conclusions

Compared with MLG, fiducial markers for UG have low cross-correlation coefficients between the lung tumor and the fiducial marker position. Using 4DCT to assess the risk of unplanned irradiation in a gating window setting and selecting a high cross-correlation coefficient fiducial marker in advance are important for accurate treatment using lung SBRT.

Statistical evaluation of the effectiveness of dual amplitude-gated stereotactic body radiotherapy using fiducial markers and lung volume

•

Approximately 30% of the fiducial markers demonstrated a low correlation on comparing lung volumes.

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Monitoring of lung volume can achieve stable tracking of lung tumors.

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Dual monitoring by employing the marker and lung volume may possibly avoid the deterioration of monitoring accuracy.

Background and purpose

The low tracking accuracy of lung stereotactic body radiotherapy (SBRT) risks reduced treatment efficacy. We used four-dimensional computed tomography (4DCT) images to determine the correlation between changes in fiducial marker positions and lung volume for lung tumors, and we evaluated the effectiveness of the combined use of these images in lung SBRT.

Materials and methods

Data of 30 patients who underwent fiducial marker placement were retrospectively analyzed. We calculated the motion amplitudes of the center of gravity coordinates of the lung tumor and fiducial markers in each phase and the ipsilateral, contralateral, and bilateral lung volumes using 4DCT. Moreover, we calculated the cross-correlation coefficient between the fiducial marker position and the lung volume changes waveform for the motion amplitude waveform of the lung tumor over three gating windows (all phases, ≤2 mm³, and ≤3 mm³).

Results

Compared with the lung volume, approximately 30 % of the fiducial markers demonstrated a low correlation with the lung tumor. In the ≤2 mm³ and ≤3 mm³ gating windows, the cross-correlation coefficients between the lung tumor and the optimal marker (r > 0.9: 83 % and 86 %) were significantly different for all fiducial markers (r > 0.9: 39 %, 53 %) and the ipsilateral (r > 0.9: 35 % and 40 %), contralateral (r > 0.9: 44 % and 41 %), and bilateral (r > 0.9: 39 % and 45 %) lung volumes.

Conclusions

Some of the fiducial markers showed a low correlation with the lung tumor. This study indicated that the combined use of lung volume monitoring can improve tracking accuracy.

Hepatocellular carcinoma effective stereotactic body radiotherapy using Gold Anchor and the Synchrony system: Two case reports and review of literature

BACKGROUND

Radiotherapy for hepatocellular carcinoma (HCC) is considered to have limited efficacy because of treatment intensity considering that the irradiated area includes the liver, which is highly radiosensitive. In this report, we present two cases in which tumor control by surgical resection, radiofrequency ablation, transcatheter arterial chemoembolization (TACE), and lenvatinib administration was difficult, but stereotactic body radiotherapy (SBRT) using the Synchrony system by Radixact™ and Gold Anchor^® (GA) was effective.

CASE SUMMARY

A 60-year-old man had a single 10-cm HCC in the right lobe. Viable lesions remained after TACE, and levels of alpha-fetoprotein and protein induced by vitamin K antagonists II (PIVKA-II) decreased and quickly re-elevated. We performed SBRT with GA. Three weeks after implantation, localized radiotherapy (SBRT; 40 Gy/5 fractions) was performed using the Synchrony system by Radixact™. Four weeks later, the viable lesion had disappeared, and the PIVKA-II levels decreased. A 77-year-old man had a single 12-cm HCC in the right lobe. The patient experienced recurrence after hepatectomy. Further recurrence occurred after TACE, and we performed SBRT with GA. Because of the proximity of the HCC to the gastrointestinal tract, localized radiotherapy (SBRT; 39 Gy/13 fractions) to the HCC was performed 3 wk after implantation using the Synchrony system by Radixact™. Four weeks later, the viable lesion had disappeared on computed tomography, and the PIVKA-Ⅱ levels decreased.

CONCLUSION

SBRT using the Synchrony system and GA can deliver a large dose accurately and safely, and could have a high therapeutic effect.

Robust and fast laparoscopic vision-based ultrasound probe tracking using a binary dot array marker

Laparoscopic vision-based ultrasound probe tracking systems have gained considerable attention in ultrasound-guided laparoscopic surgeries as replacements for external tracking systems (e.g. optical tracking and electromagnetic tracking systems), which increase cost and setting time, require additional operation space, and introduce new limitations. Most existing laparoscopic ultrasound (LUS) probe tracking systems rely on fiducial markers, which cannot easily realise fast and robust vision-based tracking in laparoscopic surgery owing to their design limitations. Therefore, we propose a novel binary dot array marker to realise a robust and fast LUS probe tracking system. The binary dot array marker comprises two dots (green and blue), which form multiple unique identification dot subarrays in the binary dot array. The binary dot array marker can be tracked when one of the identification dot subarrays is detected and identified; this novel design makes the binary dot array marker-based probe tracking system robust against occlusions during surgery. The evaluation results indicate that the proposed binary dot marker performs better in terms of robustness, computational efficiency, and tracking accuracy compared to the state-of-the-art fiducial markers used for vision-based probe tracking.

Development of an x-ray-opaque-marker system for quantitative phantom positioning in patient-specific quality assurance

PURPOSE

We developed an x-ray-opaque-marker (XOM) system with inserted fiducial markers for patient-specific quality assurance (QA) in CyberKnife (Accuray) and a general-purpose linear accelerator (linac). The XOM system can be easily inserted or removed from the existing patient-specific QA phantom. Our study aimed to assess the utility of the XOM system by evaluating the recognition accuracy of the phantom position error and estimating the dose perturbation around a marker.

METHODS

The recognition accuracy of the phantom position error was evaluated by comparing the known error values of the phantom position with the values measured by matching the images with target locating system (TLS; Accuray) and on-board imager (OBI; Varian). The dose perturbation was evaluated for 6 and 10 MV single-photon beams through experimental measurements and Monte Carlo simulations.

RESULTS

The root mean squares (RMSs) of the residual position errors for the recognition accuracy evaluation in translations were 0.07 mm with TLS and 0.30 mm with OBI, and those in rotations were 0.13° with TLS and 0.15° with OBI. The dose perturbation was observed within 1.5 mm for 6 MV and 2.0 mm for 10 MV from the marker.

CONCLUSIONS

Sufficient recognition accuracy of the phantom position error was achieved using our system. It is unnecessary to consider the dose perturbation in actual patient-specific QA. We concluded that the XOM system can be utilized to ensure quantitative and accurate phantom positioning in patient-specific QA with CyberKnife and a general-purpose linac.

Investigation of fiducial marker recognition possibility by water equivalent length in real-time tracking radiotherapy

Real-time tumor tracking radiotherapy (RTRT) systems typically use fiducial markers implanted near the tumor to track the target using X-ray fluoroscopy. Template pattern matching, used in tracking, is often used to automatically localize the fiducial markers. In radiotherapy of the liver, the thickness of the body that can recognize the fiducial markers must be clinically assessed. The purpose of this study was to quantify the recognition of fiducial markers according to body thickness in stereotactic body radiotherapy of the liver using clinical images obtained using SyncTraX FX4. The recognition scores of fiducial markers were examined in relation to water equivalent length (WEL), tube current, and each flat panel detector. The relationship between the contrast ratio of the fiducial marker and the background and the WEL was also investigated. The average recognition score was found to be less than 20 when the WEL was greater than 25 cm. The probability of successful tracking of image recognition was mostly smaller than 0.8 when the WEL was over 30 cm. The relationship between WEL and tube current did not significantly differ between 100 and 140 mA, but there was a significant difference (p < 0.05) for all other combinations. To ensure tracking of fiducial markers during SBRT, if the WEL representing body thickness is longer than 25 cm, the X-ray fluoroscopy arrangement should be determined based on the WEL.

Proof of concept of a multimodal intravital molecular imaging system for tumour transpathology investigation

Background

Transpathology highlights the interpretation of the underlying physiology behind molecular imaging. However, it remains challenging due to the discrepancies between in vivo and in vitro measurements and difficulties of precise co-registration between trans-scaled images. This study aims to develop a multimodal intravital molecular imaging (MIMI) system as a tool for in vivo tumour transpathology investigation.

Methods

The proposed MIMI system integrates high-resolution positron imaging, magnetic resonance imaging (MRI) and microscopic imaging on a dorsal skin window chamber on an athymic nude rat. The window chamber frame was designed to be compatible with multimodal imaging and its fiducial markers were customized for precise physical alignment among modalities. The co-registration accuracy was evaluated based on phantoms with thin catheters. For proof of concept, tumour models of the human colorectal adenocarcinoma cell line HT-29 were imaged. The tissue within the window chamber was sectioned, fixed and haematoxylin–eosin (HE) stained for comparison with multimodal in vivo imaging.

Results

The final MIMI system had a maximum field of view (FOV) of 18 mm × 18 mm. Using the fiducial markers and the tubing phantom, the co-registration errors are 0.18 ± 0.27 mm between MRI and positron imaging, 0.19 ± 0.22 mm between positron imaging and microscopic imaging and 0.15 ± 0.27 mm between MRI and microscopic imaging. A pilot test demonstrated that the MIMI system provides an integrative visualization of the tumour anatomy, vasculatures and metabolism of the in vivo tumour microenvironment, which was consistent with ex vivo pathology.

Conclusions

The established multimodal intravital imaging system provided a co-registered in vivo platform for trans-scale and transparent investigation of the underlying pathology behind imaging, which has the potential to enhance the translation of molecular imaging.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05574-y.

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.

Investigation of the clinical inter-observer bias in prostate fiducial marker image registration between CT and MR images

Background and purpose

Inter-modality image registration between computed tomography (CT) and magnetic resonance (MR) images is associated with systematic uncertainties and the magnitude of these uncertainties is not well documented. The purpose of this study was to investigate the potential uncertainty of gold fiducial marker (GFM) registration for localized prostate cancer and to estimate the inter-observer bias in a clinical setting.

Methods

Four experienced observers registered CT and MR images for 42 prostate cancer patients. Manual GFM identification was followed by a landmark-based registration. The absolute difference between observers in GFM identification and the displacement of the clinical target volume (CTV) was investigated. The CTV center of mass (CoM) vector displacements, DICE-index and Hausdorff distances for the observer registrations were compared against a clinical baseline registration. The time allocated for the manual registrations was compared.

Results

Absolute difference in GFM identification between observers ranged from 0.0 to 3.0 mm. The maximum CTV CoM displacement from the clinical baseline was 3.1 mm. Displacements larger than or equal to 1 mm, 2 mm and 3 mm were 46%, 18% and 4%, respectively. No statistically significant difference was detected between observers in terms of CTV displacement. Median DICE-index and Hausdorff distance for the CTV, with their respective ranges were 0.94 [0.70–1.00] and 2.5 mm [0.7–8.7].

Conclusions

Registration of CT and MR images using GFMs for localized prostate cancer patients was subject to inter-observer bias on an individual patient level. A CTV displacement as large as 3 mm occurred for individual patients. These results show that GFM registration in a clinical setting is associated with uncertainties, which motivates the removal of inter-modality registrations in the radiotherapy workflow and a transition to an MRI-only workflow for localized prostate cancer.

Endoscopic Ultrasound-Guided Fiducial Placement for Stereotactic Body Radiation Therapy in Pancreatic Malignancy

Stereotactic body radiation therapy (SBRT) is an important treatment option for pancreatic cancer, which is known to be one of the malignancies with the worst prognosis. However, the high radiation doses delivered during SBRT may cause damage to adjacent radiosensitive organs. To minimize such damage, fiducial markers are used for localization during SBRT for pancreatic cancer. The development of endoscopic ultrasound (EUS) has enabled fiducial markers to be inserted into the pancreas using an EUS fine-needle aspiration (FNA) needle, unlike in the past when percutaneous placement was generally performed. For successful EUS-guided fiducial marker placement, it is necessary for the fiducial markers to be loaded within the EUS-FNA needles to have a low probability of complications and a low migration risk, and to be stably observed in SBRT imaging. A systematic review has shown that the technical success rate of EUS-guided fiducial marker placement is 96.27%, whereas the fiducial marker migration and adverse event rates are 4.33% and 4.85%, respectively. Nonetheless, standardized techniques for fiducial marker placement and the characteristics of optimal fiducial markers have not yet been established. This review will introduce the characteristics (e.g., materials and shapes) of fiducial markers used in fiducial marker placement for pancreatic cancer and will discuss conventional techniques along with their success rates, difficulties, and adverse events.

Ultrasound-guided transrectal implantation of fiducial markers for image-guided radiotherapy of prostate cancer without local anesthesia: Patient-reported gastrointestinal-genitourinary system complications and pain

Purpose

The present study evaluates procedure-associated pain and side effects in the gastrointestinal-genitourinary system in patients with early-stage prostate cancer who were treated with image-guided radiotherapy (IGRT), accompanied by an ultrasound-guided transrectal implantation of fiducial markers, without local anesthesia.

Materials and Methods

A total of 46 patients who referred to our clinics between 2012 and 2017 with a diagnosis of early-stage prostate cancer were included in the study. Before undergoing radiotherapy, all patients were implanted with three intraprostatic fiducial markers through the ultrasound-guided transrectal approach without local anesthesia. The patients underwent radiotherapy after the clinical target volumes were established, in accordance with the respective risk groups, and localization of the markers was confirmed before each therapy session. The levels of procedure-associated pain and side effects were graded immediately after the procedure through the use of a patient-based scoring system.

Results

The faces pain scale - revised version was used for the measurement of the severity of procedure-associated pain. Of the total study sample, the facial expressions of 38 patients (35%) corresponded to level 0 in the study, seven (15%) to level 2, and a single patient (2%) to level 4. None of the facial expressions of the patients corresponded to levels 6, 8, or 10. The evaluation of procedure-related genitourinary and gastrointestinal system side effects indicated that nine patients (20%) experienced side effects, while no side effects were reported in 37 patients (80%). The reported side effects included rectal bleeding in two patients (4%), dysuria in three patients (6%), hematuria in five patients (11%), and frequent urination in five patients (11%). None of the patients experienced fever or hematospermia. All side effects were reported by the respondents as "a little," while only one patient answered positively to the question on the frequency of urination. Among the patients who answered "yes" and "a little" to the questions evaluating genitourinary and gastrointestinal system side effects, the severity of these events was reported as Grade 1, corresponding to mild adverse, in only 9 (20%) patients. None of the patients experienced a Grade 2 or higher severe adverse event. In the comparison of the severity of pain of the patients during the fiducial marker procedure without local anesthesia with the severity of pain during the biopsy, 24 patients (80%) reported "lower" levels of pain, while five patients (20%) reported "equal" levels of pain. None of the patients stated that they had experienced "more" pain.

Conclusion

IGRT accompanied by an ultrasound-guided implantation of fiducial markers without local anesthesia can be considered a safe method, given the associated acceptable levels of pain, low side effect profiles, and high prostate-specific antigen control rates.

The contribution of surgical clips for optimizing highly-conformal image-guided flank irradiation in pediatric renal tumors: A single center experience

BACKGROUND AND AIMS

Two-opposing photon beams are considered standard of care for flank irradiation in pediatric patients with renal tumors. Nowadays, Image-Guided Radiotherapy (IGRT) techniques allow high-precision dose delivery to complex flank target volumes taking into account postoperative organ shifts and tumor bed motion. This study examines the contribution of a lateral and superior surgical clip on flank target volume delineation intended for IGRT.

METHODS

Between 01-2015 and 09-2019, 30/162 newly-diagnosed pediatric patients with renal tumors, lateral/superior surgical clips (n = 30/30) and available 4D-CT-scans (n = 27/30), underwent postoperative flank irradiation. The lateral and superior clip, as respective markers for the lateral tumor extension and intrafraction motion, were analyzed. The positive and negative values depict the lateral/dorsal/cranial or the medial/ventral/caudal direction, respectively. Planning target volumes (PTV) were generated based on lateral clips (PTV_latclip), superior clips with 4D-CT technology (PTV_supclip), and both clips combined (PTV_combined), and compared to an approach without clips (PTV_noclip).

RESULTS

Indicated by clips, the mean lateral tumor bed extension along the posterior wall was 74° (range: 50°-93°), while mean intrafraction motion was +1.2 mm (range: -1.8/+4.8 mm), +0.6 mm (range: +0.6/+4.9 mm), -0.3 mm (range: -3.8/+0.7 mm) in craniocaudal, ventrodorsal, mediolateral direction, respectively. The median PTV_noclip (556 mL) was statistically different from the median PTV_latclip (454 mL, p = <0.01), median PTV_supclip (373 mL, p = <0.01) and median PTV_combined (348 mL p = <0.01).

CONCLUSION

In pediatric patients with renal tumors, surgical clips at the lateral and superior border of the tumor bed can optimize flank target volume delineation and, consequently, reduce the normal tissue volume receiving high-dose irradiation when IGRT techniques are applied.

Prospective evaluation of fiducial marker placement quality and toxicity in liver CyberKnife stereotactic body radiotherapy

Background

Evaluate morbidities and “quality” of fiducial marker placement in primary liver tumours (hepatocellular carcinoma [HCC]) for CyberKnife.

Materials and Methods

Thirty-six HCC with portal vein thrombosis (PVT) were evaluated for “quality” of fiducial placement, placement time, pain score, complications, recovery time and factors influencing placement.

Results

One hundred eight fiducials were placed in 36 patients. Fiducial placement radiation oncologist score was “good” in 24 (67%), “fair” in 4 (11%), and “poor” in 3(8%) patients. Concordance with radiologist score in “poor”, “fair”, and “good” score was 2/2 (100%), 4/5 (80%), and 24/27 (89%), respectively (p=0.001). Child-Pugh score (p=0.080), performance status (PS) (p=0.014) and accrued during “learning curve” (p=0.013) affected placement score. Mean placement time (p=0.055), recovery time (p=0.025) was longer and higher major complications (p=0.009) with poor PS. Liver segment involved (p=0.484) and the Barcelona Clinic Liver Cancer (BCLC) stage did not influence placement score. “Good” placement score was 30% in first cohort whereas 93% in last cohort (p=0.023). Time for placement was 42.2 and 14.3 minutes, respectively (p=0.069). Post-fiducial pain score 0–1 in 26 patients (72%) and pain score 3–4 was in 2 (6%). Five patients (14%) admitted in “day-care” (2 mild pneumothorax, 3 pain). Mortality in 1 patient (3%) admitted for hemothorax.

Conclusion

Fiducial placement is safe and in experienced hands, “quality” of placement is “good” in majority. Major complications and admission after fiducial placement are rare. Complications, fiducial placement time, recovery time is more during the “learning curve”. Poor Child-Pugh score, extensive liver involvement, poor PS have higher probability of complications.

Endoscopic ultrasound-guided fiducial marker placement in pancreatic cancer: A systematic review and meta-analysis

BACKGROUND

Pancreatic cancer (PC) mortality remains high despite advances in therapy. Combination chemoradiotherapy offers modest survival benefit over monotherapy with either. Fiducial markers serve as needed landmarks for image-guided radiotherapy (IGRT). Traditionally, these markers were placed surgically or percutaneously with limitations of each. Endoscopic ultrasound-guided placement overcomes these limitations.

AIM

To evaluate the safety, efficacy, and feasibility of endoscopic ultrasound (EUS)-guided fiducial placement for PC undergoing IGRT.

METHODS

Articles were searched in MEDLINE, PubMed, and Ovid journals. Pooling was conducted by fixed and random effects models. Heterogeneity was assessed using Cochran’s Q test based upon inverse variance weights.

RESULTS

Initial search identified 1024 reference articles for EUS-guided fiducial placement in PC. Of these, 261 relevant articles were reviewed. Data was extracted from 11 studies (n = 820) meeting inclusion criteria. Pooled proportion of successful placement was 96.27% (95%CI: 95.35-97.81) with fiducial migration rates low at 4.33% (95%CI: 2.45-6.71). Adverse event rates remained low, with overall pooled proportion of 4.85% (95%CI: 3.04-7.03).

CONCLUSION

EUS-guided placement of fiducial markers for IGRT of PC is safe, feasible, and efficacious. The ability to target deep structures under direct visualization while remaining minimally invasive are added benefits. Moreover, the ability to perform fine needle aspiration or celiac plexus neurolysis add value and increase patient-care efficiency. Whether EUS-guided fiducial placement improves outcomes in IGRT or offers any mortality benefits over traditional placement remains unknown and future studies are needed.

Endoscopic ultrasound-guided fiducial marker placement for neoadjuvant chemoradiation therapy for resectable pancreatic cancer

BACKGROUND

Preoperative neoadjuvant chemoradiation therapy (NACRT) is applied for resectable pancreatic cancer (RPC). To maximize the efficacy of NACRT, it is essential to ensure the accurate placement of fiducial markers for image-guided radiation. However, no standard method for delivering fiducial markers has been established to date, and the nature of RPC during NACRT remains unclear.

AIM

To determine the feasibility, safety and benefits of endoscopic ultrasound-guided (EUS) fiducial marker placement in patients with RPC.

METHODS

This was a prospective case series of 29 patients (mean age, 67.5 years; 62.1% male) with RPC referred to our facility for NACRT. Under EUS guidance, a single gold marker was placed into the tumor using either a 19- or 22-gauge fine-needle aspiration needle. The differences in daily marker positioning were measured by comparing simulation computed tomography and treatment computed tomography.

RESULTS

In all 29 patients (100%) who underwent EUS fiducial marker placement, fiducials were placed successfully with only minor, self-limiting bleeding during puncture observed in 2 patients (6.9%). NACRT was subsequently administered to all patients and completed in 28/29 (96.6%) cases, with one patient experiencing repeat cholangitis. Spontaneous migration of gold markers was observed in 1 patient. Twenty-four patients (82.8%) had surgery with 91.7% (22/24) R0 resection, and two patients experienced complete remission. No inflammatory changes around the marker were observed in the surgical specimen. The daily position of gold markers showed large positional changes, particularly in the superior-inferior direction. Moreover, tumor location was affected by food and fluid intake as well as bowel gas, which changes daily.

CONCLUSION

EUS fiducial marker placement following NACRT for RPC is feasible and safe. The RPC is mobile and is affected by not only aspiration, but also food and fluid intake and bowel condition.

A novel extraoral registration method for a dynamic navigation system guiding zygomatic implant placement in patients with maxillectomy defects

Zygomatic implants (ZIs) are used for the oral rehabilitation of patients with maxillectomy defects as an alternative to extensive bone grafting surgeries. New technologies such as computer-assisted navigation systems can improve the accuracy and safety of ZI placement. The intraoral anchorage of fiducial markers necessary for navigation registration is not possible in the case of a severe maxillary defect and lack of residual bone. This technical note presents a novel extraoral registration method for a dynamic navigation system guiding ZI placement in patients with maxillectomy defects. Titanium microscrews were inserted in the mastoid process, supraorbital ridge, and posterior zygomatic arch as registration markers. The mean fiducial registration error (FRE) was 0.53 ± 0.20 and the deviations between the planned and placed ZIs were 1.56 ± 0.54 mm (entry point), 1.87 ± 0.63 mm (exit point), and 2.52 ± 0.84° (angulation). The study results indicate that the placement of fiducial markers at extraoral sites can be used as a registration technique to overcome anatomical limitations in patients after maxillectomy, with a clinically acceptable registration accuracy.

Safety and efficacy of fiducial marker implantation for robotic stereotactic body radiation therapy with fiducial tracking

Purpose

The purpose of this study was to assess the feasibility, efficacy and toxicity of fiducial marker implantation and tracking in CyberKnife® stereotactic radiation therapy (SBRT) applied to extracranial locations.

Materials and method

This is a retrospective, single-centre, observational study to collect the data of all patients treated by stereotactic radiation therapy with fiducial marker tracking at extracranial locations, conducted between June 2014 and November 2017. Information regarding the implantation procedure, the types of toxicity related to marker implantation and the number of markers implanted/tracked during treatment were collected. Complication rates were evaluated using the CTCAE v4 [Common Terminology Criteria for Adverse Events] scale. The technical success rate was based on the ability to optimally track the tumor throughout all treatment fractions.

Results

Out of 2505 patients treated by stereotactic radiation therapy, 25% received treatment with fiducial marker tracking. The total number of implantation procedures was 616 and 1543 fiducial markers were implanted. The implantation-related complication rate was 3%, with 16 Grade 1 events and 4 Grade 2 events. The number of treated patients and the number of implanted markers has gradually increased since the technique was first implemented. The median treatment time was 27 min (range 10–76). 1295 fiducials were effectively tracked throughout all treatment fractions, corresponding to a technical success rate of 84%. The difference between the number of fiducials implanted and those tracked during treatment decreased significantly as the site’s experience increased.

Conclusion

Fiducial marker implantation and tracking is feasible, well-tolerated, and technically effective technique in SBRT for extracranial tumors.

Detectability and structural stability of a liquid fiducial marker in fresh ex vivo pancreas tumour resection specimens on CT and 3T MRI

PURPOSE

To test the detectability of a liquid fiducial marker injected into ex vivo pancreas tumour tissue on magnetic resonance imaging (MRI) and computed tomography (CT). Furthermore, its injection performance using different needle sizes and its structural stability after fixation in formaldehyde were investigated.

METHODS

Liquid fiducial markers with a volume of 20-100 µl were injected into freshly resected pancreas specimens of three patients with suspected adenocarcinoma. X‑ray guided injection was performed using different needle sizes (18 G, 22 G, 25 G). The specimens were scanned on MRI and CT with clinical protocols. The markers were segmented on CT by signal thresholding. Marker detectability in MRI was assessed in the registered segmentations. Marker volume on CT was compared to the injected volume as a measure of backflow.

RESULTS

Markers with a volume ≥20 µl were detected as hyperintensity on X‑ray and CT. On T₁- and T₂-weighted 3T MRI, marker sizes ranging from 20-100 µl were visible as hypointensity. Since most markers were non-spherical, MRI detectability was poor and their differentiation from hypointensities caused by air cavities or surgical clips was only feasible with a reference CT. Marker backflow was only observed when using an 18-G needle. A volume decrease of 6.6 ± 13.0% was observed after 24 h in formaldehyde and, with the exception of one instance, no wash-out occurred.

CONCLUSIONS

The liquid fiducial marker injected in ex vivo pancreatic resection specimen was visible as hyperintensity on kV X‑ray and CT and as hypointensity on MRI. The marker's size was stable in formaldehyde. A marker volume of ≥50 µL is recommended in clinically used MRI sequences. In vivo injection is expected to improve the markers sphericity due to persisting metabolism and thereby enhance detectability on MRI.

The use of tissue fiducial markers in improving the accuracy of post-prostatectomy radiotherapy

PURPOSE

The aim of this retrospective study was to investigate the use of a radiopaque tissue fiducial marker (TFM) in the treatment of prostate cancer patients who undergo post-prostatectomy radiotherapy (PPRT). TFM safety, its role and benefit in quantifying the set-up uncertainties in patients undergoing PPRT image-guided radiotherapy were assessed.

MATERIALS AND METHODS

A total of 45 consecutive PPRT patients underwent transperineal implantation of TFM at the level of vesicourethral anastomosis in the retrovesical tissue prior to intensity-modulated radiotherapy. Prostate bed motion was calculated by measuring the position of the TFM relative to the pelvic bony anatomy on daily cone-beam computed tomography. The stability and visibility of the TFM were assessed in the initial 10 patients.

RESULTS

No postoperative complications were recorded. A total of 3,500 images were analysed. The calculated prostate bed motion for bony landmark matching relative to TFM were 2.25 mm in the left-right, 5.89 mm in the superior-inferior, and 6.59 mm in the anterior-posterior directions. A significant 36% reduction in the mean volume of rectum receiving 70 Gy (rV70) was achieved for a uniform planning target volume (PTV) margin of 7 mm compared with the Australian and New Zealand Faculty of Radiation Oncology Genito-Urinary Group recommended PTV margin of 10 mm.

CONCLUSION

The use of TFM was safe and can potentially eliminate set-up errors associated with bony landmark matching, thereby allowing for tighter PTV margins and a consequent favourable reduction in dose delivered to the bladder and rectum, with potential improvements in toxicities.

National survey of fiducial marker insertion for prostate image guided radiotherapy

INTRODUCTION

In the United Kingdom fiducial marker IGRT is the second most common verification method employed in radical prostate radiotherapy yet little evidence exists to support centres introducing or developing this practice. We developed a survey to elicit current fiducial marker practices adopted in the UK, to recommend standardisation of practice.

METHODS

A 16 question survey was distributed across UK Radiotherapy centres via promotion at the British Uro-Oncology Group Conference, 2016. Included were questions relating to workforce planning, patient preparation, insertion procedure and verification methods. The survey was open from September 2016 to January 2017.

RESULTS

Results from 15 centres routinely inserting fiducial markers for prostate IGRT are presented. Eleven professional groups insert fiducial markers across the UK. Fourteen centres insert fiducial markers trans-rectally; one trans-perineally. Centres adopting a trans-rectal approach administer prophylactic ciprofloxacin as a single agent or combined with gentamicin or metronidazole; poor agreement between regimes presented. One centre has introduced targeted antibiotic prophylaxis. Five brands of fiducial markers are utilised nationally. Fourteen centres standardly insert three single fiducial markers, two common configurations emerged. Coupled fiducial markers are routinely implanted by one centre. All centres delay at least one week between fiducial marker insertion and planning CT; seven centres wait two weeks. The most common fiducial verification method is two-dimensional, paired kilo Voltage imaging.

CONCLUSION

Variation in fiducial marker practice across the UK is considerable. Standardisation is required to support centres and healthcare professionals developing this service. Seven recommendations, to unify practice, have been proposed based on survey results and literature.

Uncertainty in heart rate complexity metrics caused by R-peak perturbations

Heart rate complexity (HRC) is a proven metric for gaining insight into human stress and physiological deterioration. To calculate HRC, the detection of the exact instance of when the heart beats, the R-peak, is necessary. Electrocardiogram (ECG) signals can often be corrupted by environmental noise (e.g., from electromagnetic interference, movement artifacts), which can potentially alter the HRC measurement, producing erroneous inputs which feed into decision support models. Current literature has only investigated how HRC is affected by noise when R-peak detection errors occur (false positives and false negatives). However, the numerical methods used to calculate HRC are also sensitive to the specific location of the fiducial point of the R-peak. This raises many questions regarding how this fiducial point is altered by noise, the resulting impact on the measured HRC, and how we can account for noisy HRC measures as inputs into our decision models. This work uses Monte Carlo simulations to systematically add white and pink noise at different permutations of signal-to-noise ratios (SNRs), time segments, sampling rates, and HRC measurements to characterize the influence of noise on the HRC measure by altering the fiducial point of the R-peak. Using the generated information from these simulations provides improved decision processes for system design which address key concerns such as permutation entropy being a more precise, reliable, less biased, and more sensitive measurement for HRC than sample and approximate entropy.

Intrafraction esophageal motion in patients with clinical T1N0 esophageal cancer

Aim

To investigate the intrafraction movement of the esophagus using fiducial markers.

Background

Studies on intrafraction esophageal motion using the fiducial markers are scarce.

Materials and methods

We retrospectively analyzed patients with clinical T1N0 esophageal cancer who had received fiducial markers at our hospital between July 2007 and December 2013. Real-Time Position Management System to track the patient's respiration was used, and each patient underwent three-dimensional computed tomography of the resting expiratory and inspiratory level. We used the center of the marker to calculate the distance between the expiratory and inspiratory breath-holds, which were measured with the radiotherapy treatment planning system in three directions: left-right (LR), superior-inferior (SI), and anterior-posterior (AP). The movements at each site were compared with the Kruskal-Wallis analysis and Wilcoxon rank sum test with a Bonferroni correction.

Results

A total of 101 patients with 201 fiducial markers were included. The upper, middle and lower thoracic positions had 40, 77, and 84 markers, respectively. The mean absolute magnitudes of the shifts (standard deviation) were 0.18 (0.19) cm, 0.68 (0.46) cm, and 0.24 (0.24) cm in the LR, SI, and AP directions, respectively. From the cumulative frequency distribution, we assumed that 0.35 cm LR, 0.8 cm SI, and 0.3 cm AP in the upper; 0.5 cm LR, 1.55 cm SI, and 0.55 cm AP in the middle; and 0.75 cm LR, 1.9 cm SI, and 0.95 cm AP in the lower thoracic esophagus covered 95% of the cases.

Conclusions

The internal margin based on the site of esophagus was estimated.

The potential failure risk of the cone-beam computed tomography-based planning target volume margin definition for prostate image-guided radiotherapy based on a prospective single-institutional hybrid analysis

Background

The purpose of this study was to evaluate the impact of markerless on-board kilovoltage (kV) cone-beam computed tomography (CBCT)-based positioning uncertainty on determination of the planning target volume (PTV) margin by comparison with kV on-board imaging (OBI) with gold fiducial markers (FMs), and to validate a methodology for the evaluation of PTV margins for markerless kV-CBCT in prostate image-guided radiotherapy (IGRT).

Methods

A total of 1177 pre- and 1177 post-treatment kV-OBI and 1177 pre- and 206 post-treatment kV-CBCT images were analyzed in 25 patients who received prostate IGRT with daily localization by implanted FMs. Intrafractional motion of the prostate was evaluated between each pre- and post-treatment image with these two different techniques. The differences in prostate deviations and intrafractional motions between matching by FM in kV-OBI (OBI-FM) and matching by soft tissues in kV-CBCT (CBCT-ST) were compared by Bland-Altman limits of agreement. Compensated PTV margins were determined and compensated by references.

Results

Mean differences between OBI-FM and CBCT-ST in the anterior to posterior (AP), superior to inferior (SI), and left to right (LR) directions were − 0.43 ± 1.45, − 0.09 ± 1.65, and − 0.12 ± 0.80 mm, respectively, with R² = 0.85, 0.88, and 0.83, respectively. Intrafractional motions obtained from CBCT-ST were 0.00 ± 1.46, 0.02 ± 1.49, and 0.15 ± 0.64 mm, respectively, which were smaller than the results from OBI-FM, with 0.43 ± 1.90, 0.12 ± 1.98, and 0.26 ± 0.80 mm, respectively, with R² = 0.42, 0.33, and 0.16, respectively. Bland-Altman analysis showed a significant proportional bias. PTV margins of 1.5 mm, 1.4 mm, and 0.9 mm for CBCT-ST were calculated from the values of CBCT-ST, which were also smaller than the values of 3.15 mm, 3.66 mm, and 1.60 mm from OBI-FM. The practical PTV margin for CBCT-ST was compensated with the values from OBI-FM as 4.1 mm, 4.8 mm, and 2.2 mm.

Conclusions

PTV margins calculated from CBCT-ST might be underestimated compared to the true PTV margins. To determine a reliable CBCT-ST-based PTV margin, at least the systemic error Σ and the random error σ for on-line matching errors need to be investigated by supportive preliminary FM evaluation at least once.

Experimental study of beam distortion due to fiducial markers during salvage HIFU in the prostate

Background

Prostate cancer is frequently treated using external beam radiation therapy (EBRT). Prior to therapy, the prostate is commonly implanted with a small number of permanent fiducial markers used to monitor the position of the prostate during therapy. In the case of local cancer recurrence, high-intensity focused ultrasound (HIFU) provides a non-invasive salvage treatment option. However, the impact of the fiducial markers on HIFU treatment has not been thoroughly studied to date. The objective of this study was to experimentally investigate the effect of a single EBRT fiducial marker on the efficacy of HIFU treatment delivery using a tissue-mimicking material (TMM).

Methods

A TMM with the acoustic properties of the prostate was developed based on a polyacrylamide hydrogel containing bovine serum albumin. Each phantom was implanted with a cylindrical fiducial marker and then sonicated using a 3.3 MHz focused bowl HIFU transducer. Two sets of experiments were performed. In the first, a single lesion was created at different positions along either the anteroposterior or left-right axes relative to the marker. In the second, a larger ablation volume was created by raster scanning. The size and position of the ablated volume were assessed using a millimetre grid overlaid on the phantom.

Results

The impact of the marker on the position and size of the HIFU lesion was significant when the transducer focus was positioned within 7 mm anteriorly, 18 mm posteriorly or within 3 mm laterally of the marker. Beyond this, the generated lesion was not affected. When the focus was anterior to the marker, the lesion increased in size due to reflections. When the focus was posterior, the lesion decreased in size or was not present due to shadowing.

Conclusions

The presence of an EBRT fiducial marker may result in an undertreated region beyond the marker due to reduced energy arriving at the focus, and an overtreated region in front of the marker due to reflections. Depending on the position of the targeted regions and the distribution of the markers, both effects may be undesirable and reduce treatment efficacy. Further work is necessary to investigate whether these results indicate the necessity to reconsider patient selection and treatment planning for prostate salvage HIFU after failed EBRT.

Comparison of MRI sequences in ideal fiducial maker-based radiotherapy for prostate cancer

Aim

Prostate contouring using CT alone is difficult. To overcome the uncertainty, CT/MRI registration using a fiducial marker is generally performed. However, visualization of the marker itself can be difficult with MRI. This study aimed to determine the optimal MRI pulse sequence for defining the marker as well as the prostate outline among five sequences.

Materials and methods

A total of 21 consecutive patients with prostate cancer were enrolled. Two gold fiducial markers were placed before CT/MRI examination. We used the following five sequences: T1-weighted spin-echo (T1WI; TR/TE, 400-650/8 ms); T2-weighted fast spin-echo (T2WI; 4000/80); T2*-2D-weighted gradient echo (T2*2D; 700/18); T2*-3D-weighted gradient echo (T2*3D; TR/TE1/deltaTE, 37/14/7.3); and contrast-enhanced T1-weighted spin-echo (CE-T1WI; 400-650/8). Qualitative image analysis of the sequences was performed by three observers. These observers subjectively scored all images on a scale of 1-3 (1 = unclear, 2 = moderate, 3 = well visualized). A higher score indicated better visualization.

Results

T2WI was significantly superior to the other sequences in terms of prostate definition. T2*2D and T2*3D were strongly superior to the other sequences and were significantly superior in terms of fiducial marker definition.

Conclusions

T2*2D and T2*3D are superior to the other sequences for prostate contouring and marker identification. Therefore, we recommend initial T2*3D and T2*2D examinations.

The advantage of iron-containing fiducial markers placed with a thin needle for radiotherapy of liver cancer in terms of visualization on MRI: an initial experience of Gold Anchor

Radiotherapy for liver malignancy is increasing due to advances in radiotherapy technique. Visualization of the tumor as well as fiducial markers is essential. To see if improved visibility exists on computed tomography (CT) and magnetic resonance imaging (MRI), we evaluated an iron-containing fiducial marker. A patient with hepatocellular carcinoma and a patient with cholangiocarcinoma were enrolled. Pain caused by placement of marker and the best MRI sequence for visualization of both the fiducial marker as well as the liver tumor on MRI was evaluated. CT was obtained in 2.5-mm thickness, and MRIs were obtained in eight sequences (ie, T2-weighted image). 22G preloaded needles were used for marker placement in both patients; this caused little pain during placement under local anesthesia with xylocaine. No complication occurred in either patient. Both markers and tumors were well visualized by the same MRI sequence. The iron-containing fiducial marker is safe and useful for detecting fiducial markers in the liver and for registration using CT and MRI.

Is it essential to use fiducial markers during cone-beam CT-based radiotherapy for prostate cancer patients?

PURPOSE

To compare soft-tissue cone-beam computed tomography (CBCT-P) and fiducial marker (CBCT-FM)-based image guided radiotherapy in prostate cancer patients.

MATERIALS AND METHODS

Sixteen prostate cancer patients were treated with volumetric modulated arc therapy. Manual alignment using CBCT-P and CBCT-FM was performed for each patient. Couch shifts were calculated and compared between methods in the left-right (x), superior-inferior (y), and anterior-posterior (z) directions.

RESULTS

CBCT-P and CBCT-FM alignments were compared using 252 scans from the 16 patients. Mean displacement from zero was 2.4 ± 1.3, 1.7 ± 1.2, and 1.8 ± 1.1 mm for CBCT-P and 2.3 ± 1.3, 1.7 ± 1.1 and 1.8 ± 1.1 mm for CBCT-FM in the x, y and z directions, respectively. There was no difference in median displacement between CBCT-P and CBCT-FM; however, there was a significant positive correlation between CBCT-P- and CBCT-FM-based displacements in the x (r = 0.881; p < 0.001), y (r = 0.789; p < 0.001) and z (r = 0.856; p < 0.001) directions by linear regression analysis. Systematic deviations within each group were <1 mm; however, random and systematic errors were similar in the x and y directions but larger in the z direction.

CONCLUSION

Our study demonstrated that CBCT-FM was not superior to CBCT-P for image-guided radiotherapy in prostate cancer patients.

Fiducial-based registration with a touchable region model

PURPOSE

Image-guided surgery requires registration between an image coordinate system and an intraoperative coordinate system that is typically referenced to a tracking device. In fiducial-based registration methods, this is achieved by localizing points (fiducials) in each coordinate system. Often, both localizations are performed manually, first by picking a fiducial point in the image and then by using a hand-held tracked pointer to physically touch the corresponding fiducial on the patient. These manual procedures introduce localization error that is user-dependent and can significantly decrease registration accuracy. Thus, there is a need for a registration method that is tolerant of imprecise fiducial localization in the preoperative and intraoperative phases.

METHODS

We propose the iterative closest touchable point (ICTP) registration framework, which uses model-based localization and a touchable region model. This method consists of three stages: (1) fiducial marker localization in image space, using a fiducial marker model, (2) initial registration with paired-point registration, and (3) fine registration based on the iterative closest point method.

RESULTS

We perform phantom experiments with a fiducial marker design that is commonly used in neurosurgery. The results demonstrate that ICTP can provide accuracy improvements compared to the standard paired-point registration method that is widely used for surgical navigation and surgical robot systems, especially in cases where the surgeon introduces large localization errors.

CONCLUSIONS

The results demonstrate that the proposed method can reduce the effect of the surgeon's localization performance on the accuracy of registration, thereby producing more consistent and less user-dependent registration outcomes.

Feasibility study on image guided patient positioning for stereotactic body radiation therapy of liver malignancies guided by liver motion

Background

Fiducial markers are the superior method to compensate for interfractional motion in liver SBRT. However this method is invasive and thereby limits its application range. In this retrospective study, the compensation method for the interfractional motion using fiducial markers (gold standard) was compared to a new non-invasive approach, which does rely on the organ motion of the liver and the relative tumor position within this volume.

Methods

We analyzed six patients (3 m, 3f) treated with SBRT in 2014. After fiducial marker implantation, all patients received a treatment CT (free breathing, without abdominal compression) and a 4D-CT (consisting of 10 respiratory phases). For all patients the gross tumor volumes (GTVs), internal target volume (ITV), planning target volume (PTV), internal marker target volumes (IMTVs) and the internal liver target volume (ILTV) were delineated based on the CT and 4D-CT images. CBCT imaging was used for the standard treatment setup based on the fiducial markers. According to the patient coordinates the 3 translational compensation values (t_x, t_y, t_z) for the interfractional motion were calculated by matching the blurred fiducial markers with the corresponding IMTV structures. 4 observers were requested to recalculate the translational compensation values for each CBCT (31) based on the ILTV structures. The differences of the translational compensation values between the IMTV and ILTV approach were analyzed.

Results

The magnitude of the mean absolute 3D registration error with regard to the gold standard overall patients and observers was 0.50 cm ± 0.28 cm. Individual registration errors up to 1.3 cm were observed. There was no significant overall linear correlation between the respiratory motion and the registration error of the ILTV approach.

Conclusions

Two different methods to calculate the translational compensation values for interfractional motion in stereotactic liver therapy were evaluated. The registration accuracy of the ILTV approach is mainly limited by the non-rigid behavior of the liver and the individual registration experience of the observer. The ILTV approach lacks the accuracy that would be desired for stereotactic radiotherapy of the liver.

Intravascular Placement of Metallic Coils as Lung Tumor Markers for CyberKnife Stereotactic Radiation Therapy

Objective

To present our experience with placing endovascular coils in pulmonary arteries used as a fiducial marker for CyberKnife therapy and to describe the technical details and complications of the procedure.

Materials and Methods

Between June 2005 and September 2013, 163 patients with primary or secondary lung malignancies, referred for fiducial placement for stereotactic radiosurgery, were retrospectively reviewed. Fourteen patients (9 men, 5 women; mean age, 70 years) with a history of pneumonectomy (n = 3), lobectomy (n = 3) or with severe cardiopulmonary co-morbidity (n = 8) underwent coil (fiducial marker) placement. Pushable or detachable platinum micro coils (n = 49) 2-3 mm in size were inserted through coaxial microcatheters into a small distal pulmonary artery in the vicinity of the tumor under biplane angiography/fluoroscopy guidance.

Results

Forty nine coils with a median number of 3 coils per tumor were placed with a mean tumor-coil distance of 2.7 cm. Forty three (87.7%) of 49 coils were successfully used as fiducial markers. Two coils could not be used due to a larger tumor-coil distance (> 50 mm). Four coils were in an acceptable position but their non-coiling shape precluded tumor tracking for CyberKnife treatment. No major complications needing further medication other than nominal therapy, hospitalization more than one night or permanent adverse sequale were observed.

Conclusion

Endovascular placement of coil as a fiducial marker is safe and feasible during CyberKnife therapy, and might be an option for the patients in which percutaneous transthoracic fiducial placement might be risky.

Electron Tomography Methods for C. elegans

Methods for electron tomography of the nematode C. elegans are explained in detail, including a brief introduction to specimen preparation, methods for image collection, and a comparison of several general methods for producing dual-axis tomograms, with or without external fiducial reference objects. New electron tomograms highlight features in software for data display, annotation, and analysis. This chapter discusses the ultrastructural analysis of cells and tissues, rather than molecular studies.

Transarterial Fiducial Marker Placement for Image-guided Proton Therapy for Malignant Liver Tumors

PURPOSE

The aim of this study is to analyze the technical and clinical success rates and safety of transarterial fiducial marker placement for image-guided proton therapy for malignant liver tumors.

METHODS AND MATERIALS

Fifty-five patients underwent this procedure as an interventional treatment. Five patients had 2 tumors, and 4 tumors required 2 markers each, so the total number of procedures was 64. The 60 tumors consisted of 46 hepatocellular carcinomas and 14 liver metastases. Five-mm-long straight microcoils of 0.018 inches in diameter were used as fiducial markers and placed in appropriate positions for each tumor. We assessed the technical and clinical success rates of transarterial fiducial marker placement, as well as the complications associated with it. Technical success was defined as the successful delivery and placement of the fiducial coil, and clinical success was defined as the completion of proton therapy.

RESULTS

All 64 fiducial coils were successfully installed, so the technical success rate was 100 % (64/64). Fifty-four patients underwent proton therapy without coil migration. In one patient, proton therapy was not performed because of obstructive jaundice due to bile duct invasion by hepatocellular carcinoma. Thus, the clinical success rate was 98 % (54/55). Slight bleeding was observed in one case, but it was stopped immediately and then observed. None of the patients developed hepatic infarctions due to fiducial marker migration.

CONCLUSION

Transarterial fiducial marker placement appears to be a useful and safe procedure for proton therapy for malignant liver tumors.

High-precision alignment of electron tomography tilt series using markers formed in helium-ion microscope

Tungsten nanodots formed in a helium-ion microscope (HIM) provide a practical means of aligning markers of electron tomography tilt series with a high degree of precision. The nanodots were formed using a HIM equipped with a W(CO)6 gas injection system, enabling the precise placement of the nanodots at desired locations of a sample. Template matching was applied to the markers formed in the HIM to detect the positions automatically. The relation between the positions of the markers and the accuracy of the alignment was also determined in order to achieve precise alignment. The method was applied to the markers in order to reconstruct three-dimensional (3D) images of a rod-shaped specimen that contained a 65-nm-diameter via structure in a Cu/Low-k interconnect.

Safety and efficacy of ultrasound-guided fiducial marker implantation for CyberKnife radiation therapy

Objective

To evaluate the safety and technical success rate of an ultrasound-guided fiducial marker implantation in preparation for CyberKnife radiation therapy.

Materials and Methods

We retrospectively reviewed 270 percutaneous ultrasound-guided fiducial marker implantations in 77 patients, which were performed from June 2008 through March 2011. Of 270 implantations, 104 were implanted in metastatic lymph nodes, 96 were in the liver, 39 were in the pancreas, and 31 were in the prostate. During and after the implantation, major and minor procedure-related complications were documented. We defined technical success as the implantation enabling adequate treatment planning and CT simulation.

Results

The major and minor complication rates were 1% and 21%, respectively. One patient who had an implantation in the liver suffered severe abdominal pain, biloma, and pleural effusion, which were considered as major complication. Abdominal pain was the most common complication in 11 patients (14%). Among nine patients who had markers inserted in the prostate, one had transient hematuria for less than 24 hours, and the other experienced transient voiding difficulty. Of the 270 implantations, 261 were successful (97%). The reasons for unsuccessful implantations included migration of fiducial markers (five implantations, 2%) and failure to discriminate the fiducial markers (three implantations, 1%). Among the unsuccessful implantation cases, six patients required additional procedures (8%).

Conclusion

The symptomatic complications following ultrasound-guided percutaneous implantation of fiducial markers are relatively low. However, careful consideration of the relatively higher rate of migration and discrimination failure is needed when performing ultrasound-guided percutaneous implantations of fiducial markers.