Implantation Of Markers Research Articles

Interventional radiotherapy: CT-sim guided modern minimally invasive technique

The concept of interventional radiology was introduced in 1976 as a new diagnostic and therapeutic method, relying on image guidance, such as X-ray, ultrasound, computed tomography (CT), and magnetic resonance imaging. Its indications mainly include obstructive diseases, and to a lesser extent, malignant tumors. Radiotherapy (RT) plays a pivotal role in the comprehensive treatment of cancer. The advent of the CT simulator has significantly enhanced the precision of RT and improvement outcomes and accelerated the development of a series of diagnostic and RT modalities, including puncture biopsy, fiducial marker implantation, high-dose rate after-loading after-loading brachytherapy, and radioactive seed implantation. The innovative concept of image-guidance interventional RT, inspired by interventional radiology, extends the benefits to not only cancer diagnosis but also RT. The image-guidance interventional RT advances the field of RT by expanding its indications and connotation.

CT-Guided Fiducial Marker Implantation with Ultra-fine 25-Gauge Needle Prior to Proton Therapy for Liver Malignancies.

Proton therapy is highly effective for liver malignancies, and to increase its accuracy, placement of fiducial markers in the liver is preferred. We retrospectively evaluated the safety and feasibility of CT-guided fiducial marker implantation using ultra-fine 25-gauge needles before proton therapy for liver malignancies. Between May 2016 and April 2021, 334 cases were investigated. All of procedures were performed without anesthesia. Technical success was defined as the completion of implantation at the intended site. Tumor-markerdistance and possibility of synchronization between tumors and markers were evaluated and compared with Mann-Whitney U test. Complications were evaluated using the Common Terminology Criteria for Adverse Events, version 4.0. Technical success rate was 97.3%. Tumor-markerdistance was 19.1mm (median, range 0-96) in the group in which the implanted marker was synchronized with tumor (n = 315), while it was 34.5mm (median, range 6-94) in the group in which the implanted marker was not synchronized (n = 13) (p value = 0.011 < 0.05). The complication rate was 2.4%, 2 were classified as grade 4 and 5 as grade 1, and 1 as grade 2. There were no grade 3 or higher complications that seemed to be related to the procedure. CT-guided marker implantation using a 25-gauge needle achieved a satisfactory success rate with few complications and was useful for the image-guided and respiratory-synchronized proton therapy. LEVEL OF EVIDENCE 3: Local non-random sample.

Radiomic feature robustness in CT scans affected by fiducial marker induced streak artifacts for patients with hepatocellular carcinoma.

Stereotactic body radiation therapy for hepatocellular carcinoma necessitates the implantation of gold fiducial markers in the liver, resulting in artifacts on computed tomography (CT) scans, which affect radiomic feature values. This report aims to assess the effect of these artifacts on radiomic features and how removing CT slices affects radiomic features extracted from 3D regions of interest (ROI). First, the range variation in 38 tumor contours unaffected by artifacts was assessed after sequentially and randomly removing 25%, 50%, 75% of slices. Subsequently, the agreement of feature values before and after removing ROI slices containing artifacts from 186 patients' CT scans was assessed with Lin's concordance correlation coefficient (CCC) and a Wilcoxon signed-rank test. In artifact-free tumor volumes, at least 71% of features remain robust with up to 50% of slices removed, while 56% remains robust with up to 75% of slices removed. When comparing contours before and after removing slices containing artifacts, around a third of features in the tumor contour and surrounding area remain robust (CCC>0.9), compared to 44% in the healthy liver. Concerning the tumor, 13% (Gray Level Size Zone Matrix) to 61% (first order) of the features remain robust (CCC>0.9). Over 90% of features differ significantly as assessed by Wilcoxon signed-rank test, however. This study demonstrates that removing slices containing artifacts is a feasible solution for the CT fiducial problem in this patient population and provides insight into which features are affected.

Assessment of real-time US-CT/MR-guided percutaneous gold fiducial marker implementation in malignant hepatic tumors for stereotactic body radiation therapy

Backgrounds/Aims: This study explored the initial institutional experience of using gold fiducial markers for stereotactic body radiotherapy (SBRT) in treating malignant hepatic tumors using real-time ultrasound-computed tomography (CT)/magnetic resonance (MR) imaging fusion-guided percutaneous placement.Methods: From May 2021 to August 2023, 19 patients with 25 liver tumors that were invisible on pre-contrast CT received fiducial markers following these guidelines. Postprocedural scans were used to confirm their placement. We assessed technical and clinical success rates and monitored complications. The implantation of fiducial markers facilitating adequate treatment prior to SBRT, which was achieved in 96% of the cases (24 of 25 tumors), was considered technical success. Clinical success was the successful completion of SBRT without evidence of marker displacement and was achieved in 88% of cases (22 of 25 tumors). Complications included one major subcapsular hematoma and marker migration into the right atrium in two cases, which prevented SBRT.Results: Among the treated tumors, 20 of 24 (83.3%) showed a complete response, three of 24 (12.5%) remained stable, and one of 24 (4.2%) progressed during an average 11.7-month follow-up (range, 2-32 months).Conclusions: This study confirms that percutaneous gold fiducial marker placement using real-time CT/MR guidance is effective and safe for SBRT in hepatic tumors, but warns of marker migration risks, especially near the hepatic veins and in subcapsular locations. Using fewer markers than traditionally recommended-typically two per patient, the outcomes were still satisfactory, particularly given the increased risk of migration when markers were placed near major hepatic veins.

CRASH2p: Closed-loop Two Photon Imaging in Freely Moving Animals.

Direct measurement of neural activity in freely moving animals is essential for understanding how the brain controls and represents behaviors. Genetically encoded calcium indicators report neural activity as changes in fluorescence intensity, but brain motion confounds quantitative measurement of fluorescence. Translation, rotation, and deformation of the brain and the movements of intervening scattering or auto-fluorescent tissue all alter the amount of fluorescent light captured by a microscope. Compared to single-photon approaches, two photon microscopy is less sensitive to scattering and off-target fluorescence, but more sensitive to motion, and two photon imaging has always required anchoring the microscope to the brain. We developed a closed-loop resonant axial-scanning high-speed two photon (CRASH2p) microscope for real-time 3D motion correction in unrestrained animals, without implantation of reference markers. We complemented CRASH2p with a novel scanning strategy and a multi-stage registration pipeline. We performed volumetric ratiometrically corrected functional imaging in the CNS of freely moving Drosophila larvae and discovered previously unknown neural correlates of behavior.

Acute Toxicity in Moderate Hypofractionation Over Three Weeks for Localized Prostate Cancer Without Marker Implantation

Purpose: prospective observational study of patients with localized prostate cancer referred for radiotherapy using a hypofractionation scheme without marker implantation with the advantages offered by shorter treatments in lower-middle-income countries. Our objective was to establish the acute genitourinary and gastrointestinal toxicity using hypofractionation radiotherapy scheme of 15 fractions. Methods and Materials: From March to November 2022, patients with low- to intermediate-risk prostate cancer received 54 Gy in 15 fractions (3.6 Gy per fraction) for 3 weeks using VMAT without intraprostatic fiducial markers or a rectal hydrogel spacer. Were evaluated through rectal examination, prostate-specific antigen (PSA) levels, and diagnostic imaging such as computed tomography (CT), magnetic resonance imaging (MRI), bone scan, or positron emission tomography (PET/CT) with PSM, the cumulative incidence of late grade ≥2 genitourinary and gastrointestinal toxicities were analyzed. Results: Thirty-six patients were enrolled in this prospective observational study; all of them were treated with highly hypofractionated VMAT with intermediate to high risk. The follow-up period was 3 months for evaluated acute toxicity. In terms of genitourinary toxicity, 8% of patients experienced grade 2 toxicity, which included urinary frequency, urgency, and dysuria. There were no cases of grade 3 or higher genitourinary toxicity. Regarding gastrointestinal toxicity, 5% of patients experienced grade 2 toxicity, which included diarrhea and rectal bleeding. No grade 3 or higher gastrointestinal toxicity was observed. Conclusions: Highly hypofractionated VMAT delivering 54 Gy in 15 fractions for 3 weeks for prostate cancer without intraprostatic fiducial markers facilitated favorable oncological outcomes without severe complications. These findings support the feasibility and safety of this treatment option and highlight the potential advantages of hypofractionation, further studies are needed to confirm these findings and evaluate the long-term oncological outcomes of moderate hypofractionation for localized prostate cancer.

Recent advances in stem cells therapy: efficacy, ethics, safety concerns and future directions focusing on neurodegenerative disorders- a review

Neurodegeneration refers to the gradual loss of neurons and extensive changes occur in glial cells like tau inclusions in astrocytes and oligodendrocytes, α-synuclein inclusions in oligodendrocytes and SOD1 aggregates in astrocytes along with deterioration in the motor, cognition, learning, and behaviour. Common neurodegenerative disorders are Alzheimer’s Disease (AD), Parkinson’s Disease (PD), Amyotrophic Lateral Sclerosis (ALS), Huntington’s disease (HD), Spinocerebellar Ataxia (SCAs), and Supranuclear palsy are some common one. There is a lack of effective treatment for neurodegenerative diseases, and scientists are putting their efforts into developing therapies against them. Stem cell therapy has emerged as a hope for neurodegenerative disorders since it is not only the damaged neurons that might be replaced, but other neuromodulators and neuroprotectors are secreted. Stem cell terminal differentiation before implantation ensures the implantation of correct cells and molecular markers like carbonic anhydrase II, CNPase (2′,3′-cyclic nucleotide 3′-phosphohydrolase), myelin basic protein (MBP), and myelin oligodendrocyte glycoprotein ​(MOG) elucidate the differentiation. Secretion of various growth factors like epidermal growth factor (EGF), keratinocyte growth factor (KGF), vascular endothelial growth factor-α (VEGF-α), transforming growth factor (TGF) and macrophage inflammatory protein (MIP) supports cell survival, cell proliferation, blood vessel formation, axon regeneration, and neuroglial functional connection formation at the site of degeneration. Adverse effects of stem cell therapy, like teratogenicity and differentiation in different cells other than the desired one under the influence of microenvironment, are a few key concerns. Post-transplantation improved synaptic plasticity, apoptosis inhibition, and reduction in tau-phosphorylation and Amyloid beta (Aβ) production has been observed in Alzheimer’s patients.A large number of experimental, preclinical, and clinical studies have been conducted, and encouraging results have been obtained. The present review exhaustively discusses various kinds of stem cells, their usage in treating neurodegenerative disorders, limitations and challenges, and ethical issues related to stem cell therapy.

End-to-end validation of fiducial tracking accuracy in robotic radiosurgery using MRI-only simulation imaging.

Image-guided radiation-therapy (IGRT)-based robotic radiosurgery using magnetic resonance imaging (MRI)-only simulation could allow for improved target definition with highly conformal radiotherapy treatments. Fiducial marker (FM)-based alignment is used with robotic radiosurgery treatments of sites such as the prostate because it aids in accurate target localization. Synthetic CT (sCT) images are generated in the MRI-only workflow but FMs used for IGRT appear as signal voids in MRIs and do not appear in MR-generated sCTs, hindering the ability to use sCTs for fiducial-based IGRT. In this study we evaluate the fiducial tracking accuracy for a novel artificial fiducial insertion method in sCT images that allows for fiducial marker tracking in robotic radiosurgery, using MRI-only simulation imaging (MRI-only workflow). Artificial fiducial markers were inserted into sCT images at the site of the real marker implantation as visible in MRI. Two phantoms were used in this study. A custom anthropomorphic pelvis phantom was designed to validate the tracking accuracy for a variety of artificial fiducials in an MRI-only workflow. A head phantom containing a hidden target and orthogonal film pair inserts was used to perform end-to-end tests of artificial fiducial configurations inserted in sCT images. The setup and end-to-end targeting accuracy of the MRI-only workflow were compared to the computed tomography (CT)-based standard. Each phantom had six FMs implanted with a minimum spacing of 2cm. For each phantom a bulk-density sCT was generated, and artificial FMs were inserted at the implantation location. Several methods of FM insertion were tested including: (1) replacing HU with a fixed value (10000HU) (voxel-burned); (2) using a representative fiducial image derived from a linear combination of fiducial templates (composite-fiducial); (3) computationally simulating FM signal voids using a digital phantom containing FMs and inserting the corresponding signal void into sCT images (simulated-fiducial). All tests were performed on a CyberKnife system (Accuray, Sunnyvale, CA). Treatment plans and digital-reconstructed-radiographs were generated from the original CT and sCTs with embedded fiducials and used to align the phantom on the treatment couch. Differences in the initial phantom alignment (3D translations/rotations) and tracking parameters between CT-based plans and sCT-based plans were analyzed. End-to-end plans for both scenarios were generated and analyzed following our clinical protocol. For all plans, the fiducial tracking algorithm was able to identify the fiducial locations. The mean FM-extraction uncertainty for the composite and simulated FMs was below 48% for fiducials in both the anthropomorphic pelvis and end-to-end phantoms, which is below the 70% treatment uncertainty threshold. The total targeting error was within tolerance (<0.95mm) for end-to-end tests of sCT images with the composite and head-on simulated FMs (0.26, 0.44, and 0.35mm for the composite fiducial in sCT, head-on simulated fiducial in sCT, and fiducials in original CT, respectively. MRI-only simulation for robotic radiosurgery could potentially improve treatment accuracy and reduce planning margins. Our study has shown that using a composite-derived or simulated FM in conjunction with sCT images, MRI-only workflow can provide clinically acceptable setup accuracy in line with CT-based standards for FM-based robotic radiosurgery.

P033 - Infectious rates comparison of targeted transrectal biopsy of the prostate and fiducial marker implantation in patients undergoing image-guided radiation therapy.

P033 - Infectious rates comparison of targeted transrectal biopsy of the prostate and fiducial marker implantation in patients undergoing image-guided radiation therapy.

CyberKnife® stereotactic radiation therapy for stage I lung cancer and pulmonary oligometastases: is fiducial implantation still relevant?-a cohort study.

Few studies have investigated whether there is a difference in local control or overall survival rates following treatment with robotic stereotactic body radiation therapy (SBRT) with or without prior fiducial marker implantation. Our study aimed to investigate this in patients with primary or secondary lung tumors. A retrospective study was conducted at the Institut de Cancérologie de Lorraine of patients treated for primary lung cancer or pulmonary oligometastases with SBRT from January 2013 to July 2016. We included patients at least 18 years old who had stage I non-small cell lung cancer (NSCLC) or lung metastases and a follow-up of at least 1 month. A total of 294 patients were included. Tumors included 122 lung metastases, 89 stage I NSCLC, and 83 non-histologically confirmed lung lesions. The tracking methods were Synchrony® in 191 cases (119 gold seeds and 72 coils) and Xsight® Spine with 4D computed tomography in 103 cases. Median follow-up was 31.6 months [interquartile range (IQR), 18.1-50.2 months]. The two- and five-year probability of local control were respectively 92.22% [95% confidence interval (CI): 0.89-0.95] and 85.35% (95% CI: 0.79-0.99). The two- and five-year probability of overall survival were respectively 87.46% and 72.77% (P=0.586). Local control rates did not significantly differ between techniques at 2 and 5 years (P=0.685) (gold seeds, coils or Xsight® Spine) within tumors grouped by location, gross tumor volume (GTV) (respectively P=0.9, P=0.7, and P=0.4), planning target volume (PTV) (respectively P=0.4, P=0.9, and P=0.7), or PTV/GTV ratio (respectively P=0.6, P=0.6, and P=0.5). Metastasis-free survival and Overall survival rates did not significantly differ between techniques at 2 and 5 years (P=0.664 and P=0.586, respectively). There were no grade 4 or 5 toxicities and only one grade 3 pneumonitis and one grade 3 pneumothorax. Fiducial-less SBRT using Xsight® Spine is a safe alternative to Synchrony® using gold seeds or coils, with comparable local control and overall survival rates and a similar toxicity profile.

Endoscopically placed fiducial markers for image-guided radiotherapy in preoperative gastric cancer: Technical feasibility and potential benefit.

Background and study aims Fiducial markers have demonstrated clinical value in radiotherapy in several organs, but little is known about markers in the stomach. Here, we assess the technical feasibility of endoscopic placement of markers in gastric cancer patients and their potential benefit for image-guided radiotherapy (IGRT). Patients and methods In this prospective feasibility study, 14 gastric cancer patients underwent endoscopy-guided gold (all patients) and liquid (7 patients) marker placements distributed throughout the stomach. Technical feasibility, procedure duration, and potential complications were evaluated. Assessed benefit for IGRT comprised marker visibility on acquired imaging (3-4 computed tomography [CT] scans and 19-25 cone-beam CTs [CBCTs] per patient) and lack of migration. Marker visibility was compared per marker type and location (gastroesophageal junction (i.e., junction/cardia), corpus (corpus/antrum/fundus), and pylorus). Results Of the 93 marker implantation attempts, 59 were successful, i.e., marker in stomach wall and present during entire 5-week radiotherapy course (2-6 successfully placed markers per patient), with no significant difference (Fisher's exact test; P >0.05) in success rate between gold (39/66=59%) and liquid (20/27=74%). Average procedure duration was 24.4 min (range 16-38). No procedure-related complications were reported. All successfully placed markers were visible on all CTs, with 81% visible on ≥95% of CBCTs. Five markers were poorly visible (on <75% of CBCTs), possibly due to small marker volume and peristaltic motion since all five were liquid markers located in the corpus. No migration was observed. Conclusions Endoscopic placement of fiducial markers in the stomach is technically feasible and safe. Being well visible and positionally stable, markers provide a potential benefit for IGRT.

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

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. 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. The mean age of patients was 70years. 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 12mSv 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. 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.

PO-2197 Prostate inverse brachy boost - 10 Gy with implantation of gold markers – results and feasibility

PO-2197 Prostate inverse brachy boost - 10 Gy with implantation of gold markers – results and feasibility

Infection after prostatic transrectal fiducial marker implantation for image guided radiation therapy

PurposeThe aim of this retrospective study is to assess the risk of infection after transrectal ultrasound-guided fiducial marker insertion for image-guided radiotherapy of prostate cancer. Material and methodsBetween January 2016 and December 2020, 829 patients scheduled for intensity-modulated radiotherapy for prostate cancer had an intraprostatic fiducial marker transrectal implantation under ultrasound guidance by radiation-oncologists specialized in brachytherapy. Patients received standard oral prophylactic antibiotic with quinolone. If Gram negative bacteria resistant to quinolone were detected at the time of the prostate cancer biopsies, the antibioprophylaxis regimen was modified accordingly. The resistance to quinolone screening test was not repeated before fiducial marker insertion. Infectious complications were assessed with questionnaires at the time of CT-planning and medical record reviewed. Toxicity was evaluated according to CTCAE v5.0. ResultsThe median time between fiducial marker implantation and evaluation was 10 days (range: 0–165 days). Four patients (0.48%) developed urinary tract infection related to the procedure, mostly with Gram-negative bacteria resistant to quinolone (75%). Three had a grade 2 infection, and one patient experienced a grade 3 urosepsis. The quinolone-resistance status was known for two patients (one positive and one negative) and was unknown for the other two patients prior to fiducial marker implantation. ConclusionIntraprostatic transrectal fiducial marker implantation for image-guided radiotherapy is well tolerated with a low rate of infection. With such a low rate of infection, there is no need to repeat the search of Gram-negative bacteria resistant to quinolone before fiducial marker implantation if it was done at the time of prostate biopsies. Optimal antibioprophylaxis should be adapted to the known status of Gram-negative bacteria resistant to quinolone.

Effects of gold fiducial marker implantation on tumor control and toxicity in external beam radiotherapy of prostate cancer.

Evidence regarding the effects of fiducials in image-guided radiotherapy (IGRT) for tumor control and acute and late toxicity is sparse. Patients with primary low- and intermediate-risk prostate cancer, 40 with and 21 without gold fiducial markers (GFM), and treated between 2010 and 2015 were retrospectively included. The decision for or against GFM implantation took anaesthetic evaluation and patient choice into account. IGRT was performed using electronic portal imaging devices. The prescribed dose was 78 Gy, with 2 Gy per fraction. Biochemical no evidence of disease (bNED) failure was defined using the Phoenix criteria. Acute and late gastrointestinal (GI) and genitourinary toxicity (GU) were assessed using the Radiation Therapy Oncology Group criteria. Most patients did not receive GFM due to contraindications for anaesthesia or personal choice (60% and 25%). Regarding tumor control, no significant differences were found regarding bNED and overall and disease-specific survival (p = 0.61, p = 0.56, and p > 0.9999, respectively). No significant differences in acute and late GI (p = 0.16 and 0.64) and GU toxicity (p = 0.58 and 0.80) were observed. We were unable to detect significant benefits in bNED or in early or late GI and GU side effects after GFM implantation.

MRI-guided fiducial marker implantation as a method of tagging an ultrasound- and non-enhanced CT-invisible liver tumor before thermal ablation.

Some liver tumors are not visible on ultrasound or non-enhanced CT (NECT) which are main modalities used in image-guided ablations. This is a report of MR-guided implantation of fiducial marker to tag a neuroendocrine tumor metastasis in a patient with renal insufficiency precluding the use of contrast - enhanced CT during ablation. The marker was well visible on NECT which allowed for precise needle placement and complete ablation which was confirmed in 12-months follow-up.

Impact of fiducial markers placement on the delineation of target volumes in radiation therapy for oesophageal cancer: FIDUCOR study.

This prospective monocentric phase II study (FIDUCOR-study, NCT02526134) aimed to assess the impact of fiducial markers (FMs) implantation on conformal chemo-radiation therapy (CRT) planning in oesophageal carcinoma (EC) patients. Fifteen EC patients were enrolled in the study. Each patient underwent two simulation CT-scans before (CT1) and after (CT2) FMs implantation, in the same position. FMs (3 mm length gold markers, preloaded in a 22G needle) were implanted after sedation, under endoscopic ultrasound (EUS) and X-Ray guidance, and were placed at the tumor's extremities, and in the visible lymph nodes. Target delineation and treatment plan were both performed first on CT1 with the assistance of diagnosis CT, gastroscopy and EUS details, and second on CT2 using FMs and CT-data. The value of FMs implantation was assessed by the difference of growth-tumor-volume (GTV) and clinical-target-volume (CTV) between CT1-based and CT2-based delineation. A significant difference was defined as a ≥5 mm-difference on axial(x) or coronal(y) slices, a ≥10mm-difference on sagittal slices, or a ≥20%-difference in GTV. The impact on dose distribution in organs at risk (OAR) (lung, heart, liver) was also studied. Between 09/2014 and 12/2015, 15 patients could achieve fiducial procedures, without any complication. One FM migration occurred. We observed a significant modification of the GTV-dimension in 100% of the cases (15/15, 95%CI: [78.2;100.0]), mainly due to a difference in sagittal dimension with a mean variation of 11.2 mm and a difference&gt; 10 mm for 8/15 patients (53.3%). One patient had a significant isocenter displacement as high as 20 mm. The oesophagus tumor was not seen on the CT-scan in one patient due to its small size. One patient had a distant lymph node metastasis not visible on CT-scan. We observed no significant impact on OAR distribution. In our study, FMs-implantation under EUS had a positive impact on accurate volume definition in EC-patients (modification of GTV in 15/15 patients). Close cooperation between gastroenterologist and radiation oncologist has the potential to improve local treatment of oesophagealcarcinoma.

Feasibility Study of Removable Fiducial Marker Implantation with the Intelligent Navigation Bronchoscopy Technology in Robotic Radiosurgery System Tracking

<h3>Purpose/Objective(s)</h3> To investigate the feasibility of removable fiducial marker implantation with the intelligent navigation bronchoscopy technology in a frameless robotic radiosurgery system tracking. <h3>Materials/Methods</h3> CT scans of an inflatable anti-corruption pig lung were acquired, and two simulated tumor lesion sites were designed in the left and right lung lobes by intelligent navigation software, respectively. According to the principle of fiducial marker implantation, 24 removable fiducial markers were implanted around each simulated tumor lesion via bronchus after intelligent guiding. Simulating the end-expiratory state, the pig lung was scanned again to obtain CT images of the implanted removable fiducial markers and the number of successfully implanted fiducial markers was recorded. Six deliverable treatment plans were designed using the planning system, and then the pig lung plans were delivered based on the simulated respiratory movements. After the treatment, the implanted removable fiducial markers were retrieved through bronchoscopy, and the number of successful retrievals was recorded. The rigid body error and translation error were extracted and analyzed from the log file. <h3>Results</h3> No removed fiducial markers slipped and fell off during the experiment. 24 removable fiducial markers were successfully implanted under bronchoscopic intelligent magnetic navigation guidance, with a 100% implantation success rate (24/24) and 100% removable success rate (24/24). The fiducial marker tracking rate was 83.33% (20/24), with 4 fiducial markers being too far away from the simulated tumor location to be used during the tracking process. The data from the log file displayed that the mean rigid body error for 6 groups was 1.45 mm, the mean translation error was 1.78 mm. <h3>Conclusion</h3> The technology of bronchoscopy intelligent navigation and implantation of removable fiducial marker is feasible, and the tracking accuracy of the frameless robotic radiosurgery system can meet the clinical requirements, which has a good clinical application and teaching application prospect.

S2689 A Rare Case of SpaceOARTM Hydrogel-Induced Rectal Ulcer Leading to Hematochezia

Introduction: SpaceOAR hydrogel is a soft gel-like synthetic material that was FDA approved in 2015 for prostate cancer patients who are planning to undergo radiotherapy (RT). It is intended to position the anterior rectal wall away from the prostate during RT thereby reducing the dose of radiation delivered to the rectum and minimizing complications. We present a case of rectal ulcer after implantation of SpaceOAR prior to the patient receiving RT. Case Description/Methods: A 76-year-old male was diagnosed with prostate cancer- Gleason 3+4 and was planned for RT. He underwent implantation of spaceOAR hydrogel and gold fiducial markers before RT to minimize his risk of rectal toxicity. Approximately 10 days after placement, he started experiencing severe rectal pain and hematochezia. On physical exam his abdomen was benign, but a digital rectal exam showed bright red blood. Labs revealed normal hemoglobin of 16 g/dL. A computerized tomography (CT) scan without contrast was obtained showing the presence of hydrogel between the posterior margin of the prostate and the anterior wall of the low rectum with focal proctitis in that area of the rectum. Due to ongoing hematochezia, he was scheduled for a colonoscopy which confirmed CT findings of focal proctitis but also showed a large ulcer with overlying fibrotic tissue congruent with the site of his recent urological procedure. The tissue was friable and not amenable to biopsy. He was managed with a course of levofloxacin and given polyethylene glycol to avoid constipation. At a follow-up visit, he reported resolution of hematochezia and improvement in his rectal pain. He will proceed with the initiation of RT for prostate cancer. (Figure) Discussion: The SpaceOAR Hydrogel is designed to reduce rectal toxicity during RT for prostate cancer so a higher dose of radiation can be delivered to the prostate. There have been only a few cases of rectal ulcers after placement of the Hydrogel before the patient received RT. In most reported cases, the management was conservative. The mechanisms of injury are thought to be from infection, inflammation, or ischemia due to mechanical injury. We managed our patient with a course of antibiotics and laxatives resulting in improvement of his symptoms and he will proceed with RT as planned. This case is unique in that the patient developed symptoms only 10 days after implantation of SpaceOAR when all other documented cases took at least a few weeks to a few months.Figure 1.: A- Focal proctitis and large rectal ulcer in the anterior wall B- Friable tissue not amenable to biopsy C- CT scan showing hydrogel and focal proctitis.

A New Approach to Imaging and Rapid Microbiome Identification for Prostate Cancer Patients Undergoing Radiotherapy.

(1) Background: Little is known about the impact of urinary microflora, in particular, its effects on side effects after radiotherapy. The use of mass spectrometry identification method (MALDI) may bring a new look at the issue of the composition and significance of the urinary microbiome. This study aimed to use the mass spectrometry identification method (MALDI) to identify the microbiome of urine samples collected from 50 irradiated prostate cancer patients. (2) Methods: Blood and urine samples were collected before gold marker implantation, at the start and last day of radiotherapy, 1, 4 months after. Patients do not always collect the urine from the midstream; therefore, samples were collected from the first void and midstream in 12 patients for MALDI analysis; in the remaining 38 patients—from the midstream void for MALDI and biochemical analysis. (3) Results: Microorganisms were present in 140/181 urine samples. We found 33 different species 3G(−) and 30G(+). The most frequently isolated strains were: Staphylococcus haemolyticus, Staphylococcus epidermidis, Staphylococcus hominis, Enterococcus faecalis, and Micrococcus luteus. When comparing the type of urine samples, bacteria were more common in samples from the first-void urine than from the midstream one. The absence of bacteria was found in 12.2% of samples from the first-void urine and in 24.7% from the midstream. There was no difference in the total incidence of species between streams (p = 0.85). Before fiducial implantation, the total number of detected bacterial species was significantly higher in comparison to the end of radiotherapy (p = 0.038), indicating that the administered therapy resulted in depleting the local microbiome. One month after radiotherapy, an increase in the number of isolated bacteria was observed. The number of bacterial species in urine did not correlate with blood parameters. The presence of leukocytes (p = 0.013) and proteins (p = 0.004) in urine was related to a greater variety of bacteria found in urine specimens. (4) Conclusions: We obtained a similar spectrum of bacteria from the initial and middle urine streams. We also showed that there is a change in bacteria species affected by the treatment of prostate cancer patients, with both antibiotics before gold fiducial implantation and radiotherapy.