Gold Markers Research Articles

Fiducial markers and their impact on ablation outcome for patients treated with MR-guided transurethral ablation (TULSA): a retrospective technical analysis

Objectives Fiducial markers improve accuracy in external beam radiation therapy (EBRT) for treatment of prostate cancer (PCa). However, many patients recur after EBRT necessitating additional treatment, such as MR-guided transurethral ultrasound ablation (TULSA). Residual markers may compromise TULSA through ultrasound field distortions and generation of local susceptibility artifacts. The objective was to investigate how markers affect the ablation outcome during clinical TULSA treatments. Subjects and methods A retrospective analysis was performed on nine patients with radiorecurrent PCa and residual markers who received TULSA. The MR susceptibility artifact was quantified as a function of marker type, size and orientation, in particular for thermometry. The spatial distribution of markers inside the prostate was recorded, and the resulting impact on the thermal dose was measured. The thermal dose measurements were directly compared to the residual enhancing prostatic tissue observed on the immediate and control post-TULSA contrast enhanced (CE) image. Results Successful thermal dose accumulation to the target boundary occurred for 14/20 (70%) of markers, confirmed with CE imaging. Gold markers situated simultaneously close to the urethra (≤12 mm) and far from the target boundary (≥13 mm) reduced the ultrasound depth of heating. Nitinol markers produced large, hypointense artifacts that disrupted thermometry and compromised treatment. Artifacts from gold markers were less pronounced, but when located near the target boundary, also affected treatment. Conclusion Marker composition, orientation and location inside the prostate can all potentially impact treatment outcome. Proper patient selection through detailed MRI screening is critical to ensure successful radiorecurrent PCa treatment outcomes with TULSA.

A comparative study of prostate PTV margins for patients using hydrogel spacer or rectal balloon in proton therapy.

To compare the planning target volume (PTV) margins needed for prostate patients who have used hydrogel spacer or rectal balloon during proton treatments. Total of 190 prostate patients treated with proton therapy during 2017 were selected for this study. Of these patients, 96 had hydrogel spacer injection and 94 patients had only rectal balloons insertion. All patients had implanted gold markers inside the prostate for daily target alignment. Post-treatment radigraphs were obtained to evaluate prostate intrafraction motion. The systematic and random components of patient setup residual error and prostate intrafraction motion error were obtained. PTV margins were calculated using the van Herk formula for both patient groups. For setup residual error, the mean values in the superior-inferior (SI) direction and the variances in the left-right (LR) direction were statistically different between the two groups. For intrafraction motion, there were significant differences of the mean values in the SI direction and of the variances in both LR and anterior-posterior (AP) directions. The population PTV margins for hydrogel spacer group were 2.6mm, 3.3mm, and 1.6mm in LR, SI, AP directions, respectively. For the rectal balloon group, the PTV margins were 2.1mm, 3.1mm, and 2.0mm in LR, SI, AP directions, respectively. Statistically significant differences were observed in the patient setup and prostate intrafraction motion errors of the two patient groups. However, under the current protocol of bladder preparation and daily marker-based x-ray image-guidance, population PTV margins were comparable between the two patient groups.

Determination of the CTV-PTV margin for prostate cancer radiotherapy depending on the prostate gland positioning control method

Abstract Objective: The objective of the study was to determine the correct CTV-PTV margin, depending on the method used to verify the PG position. In the study, 3 methods of CBCT image superimposition were assessed as based on the location of the prostate gland (CBCT images), a single gold marker, and pubic symphysis respectively. Materials and methods: The study group consisted of 30 patients undergoing irradiation therapy at the University Hospital in Zielona Góra. The therapy was delivered using the VMAT (Volumetric Modulated Arc Therapy) protocol. CBCT image-based superimposition (prostate-based alignment) was chosen as the reference method. The uncertainty of the PG positioning method was determined and the margin to be used was determined for the CBCT-based reference method. Then, changes in the position of the prostate gland relative to these determined using the single marker and pubic symphysis-based methods were determined. The CTV-PTV margin was calculated at the root of the sum of the squares for the doubled value of method uncertainty for the CBCT image-based alignment method and the value of the difference between the locations of planned and actual isocenters as determined using the method of interest and the CBCT-based alignment method for which the total number of differences accounted for 95% of all differences. Results: The CTV-PTV margins to be used when the prostate gland is positioned using the CBCT imaging, single marker, and pubic symphysis-based methods were determined. For the CBCT-based method, the following values were obtained for the Vrt, Lng, and Lat directions respectively: 0.43 cm, 0.48 cm, 0.29 cm. For the single marker-based method, the respective values were 0.7 cm, 0.88 cm, and 0.44 cm whereas for the pubic symphysis-based method these were 0.65 cm, 0.76 cm, and 0.46 cm. Conclusions: Regardless of the method, the smallest margin values were obtained for the lateral direction, with the CBCT-based method facilitating the smallest margins to be used. The largest margins were obtained using the single marker-based alignment method.

On-line range verification for proton beam therapy using spherical ionoacoustic waves with resonant frequency

In contrast to conventional X-ray therapy, proton beam therapy (PBT) can confine radiation doses to tumours because of the presence of the Bragg peak. However, the precision of the treatment is currently limited by the uncertainty in the beam range. Recently, a unique range verification methodology has been proposed based on simulation studies that exploit spherical ionoacoustic waves with resonant frequency (SPIREs). SPIREs are emitted from spherical gold markers in tumours initially introduced for accurate patient positioning when the proton beam is injected. These waves have a remarkable property: their amplitude is linearly correlated with the residual beam range at the marker position. Here, we present proof-of-principle experiments using short-pulsed proton beams at the clinical dose to demonstrate the feasibility of using SPIREs for beam-range verification with submillimetre accuracy. These results should substantially contribute to reducing the range uncertainty in future PBT applications.

The use of tumour markers in oesophageal cancer to quantify setup errors and baseline shifts during treatment

PurposeTo prospectively evaluate the feasibility of solid gold marker placement in oesophageal cancer patients and to quantify inter-fractional and intra-fractional (baseline shift) marker motion during radiation treatment. Radiotherapy target margins and matching strategies were investigated. Materials/methodsThirty-four markers were implanted by echo-endoscopy in 10 patients. Patients received a planning 4D CT, daily pre-treatment cone-beam CT (CBCT) and a post-treatment CBCT for at least five fractions. For fractions with both pre- and post-treatment CBCT, marker displacement between planning CT and pre-treatment CBCT (inter-fractional) and between pre-treatment and post-treatment CBCT (intra-fractional; only for fractions without rotational treatment couch correction) were calculated in left–right (LR), cranio-caudal (CC) and anterior-posterior (AP) direction after bony-anatomy and soft-tissue matching. Systematic/random setup errors were estimated; treatment margins were calculated. ResultsNo serious adverse events occurred. Twenty-three (67.6%) markers were visible during radiotherapy (n = 3 middle oesophagus, n = 16 distal oesophagus, n = 4 proximal stomach). Margins for inter-fractional displacement after bony-anatomy match depended on the localisation of the primary tumour and were 11.2 mm (LR), 16.4 mm (CC) and 8.2 mm (AP) for distal markers. Soft-tissue matching reduced the CC margin for these markers (16.4 mm to 10.5 mm). The mean intra-fractional shift of 12 distal markers was 0.4 mm (LR), 2.3 mm (CC) and 0.7 mm (AP). Inclusion of this shift resulted in treatment margins for distal markers of 12.8 mm (LR), 17.3 mm (CC) and 10.4 mm (AP) after bony-anatomy matching and 12.4 mm (LR), 11.4 mm (CC) and 9.7 mm (AP) after soft-tissue matching. ConclusionThis study demonstrated that the implantation of gold markers was safe, albeit less stable compared to other marker types. Inter-fractional motion was largest cranio-caudally for markers in the distal oesophagus, which was reduced after soft-tissue compared to bony-anatomy matching. The impact of intra-fractional baseline shifts on margin calculation was rather small.

PO-1697: Radiotherapy for prostate cancer: Effects of fiducial gold marker on diffusion-weighted MR imaging

PO-1697: Radiotherapy for prostate cancer: Effects of fiducial gold marker on diffusion-weighted MR imaging

A Multi-institutional Phase II Study of Dynamic Tumor Tracking SBRT for the Lung

The purpose of the present study was to evaluate safety and efficacy of dynamic tumor tracking stereotactic radiotherapy (DTT-SBRT) for lung cancer. The main eligibility criteria for the study were as follows: (1) primary or metastatic lung cancer with a diameter of 5 cm or less, and up to 3 lesions without any extra-pulmonary lesions; (2) ineligibility to standard surgery, or patient's refusal of surgery; (3) ECOG-PS of 0 to 2; and (4) respiratory motion of 10 mm or more. Spherical gold markers were inserted near the tumor using a bronchofiberscope. CTV was defined as the GTV, which was delineated on exhale CT images, plus 3-mm margins. PTV was determined CTV plus margins compensating errors related to positional variations between CTV and the fiducials, correlation models, and mechanical errors for tracking. The prescribed dose was 50 Gy in 4 fractions to PTV D95. A gimbal-mounted Linac was used for delivery of DTT-SBRT. Primary endpoint was 2-year local control rate. The sample size was determined as 48 to test the expected value of 90% with the threshold value of 80%, one-sided alpha of 0.15 and power of 80%. Toxicity was evaluated using the Common Terminology Criteria for Adverse Events, version 4.0. Forty-eight patients from 4 institutions were enrolled into the study between July 2015 and Jan 2018. The patient cohort consisted of 38 males and 10 females with a median age of 80 years (range, 49-90 years). Forty-two patients had primary non-small cell lung cancer, and 6 patients had metastatic lung tumors. The tumor diameter was 23.5 mm in median (range, 5-47 mm). DTT-SBRT was successfully delivered to 47 lesions in 47 patients. A median treatment time per fraction in DTT-SBRT was 28 min (range, 14-77 min). Amplitude of respiratory motion during the treatment was 13.7 mm in median (range, 4.5-28.1 mm). Abdominal wall motion in the remaining one patient was not well correlated with the tumor movement, to which the ITV method was applied. The median follow-up period was 32.3 months (range, 3.0-53.8 months) at the time of data cut-off. Local control rate at 2 years was 95.2% (lower limit of the one-sided 85% confidence interval, 90.3%). Overall survival and progression-free survival at 2 years were 79.2% and 75.0%, respectively. There was no Grade 4 or 5 toxicity. Grade 3 toxicity was observed in one patient (2%) with radiation pneumonitis. Regarding Grade 2 toxicities, radiation pneumonitis, dermatitis, rib fracture, and pleural effusion were observed in 3, 1, 2, and 1 patient, respectively. DTT-SBRT achieved excellent local control and low incidence of severe toxicities for lung tumors with substantial respiratory motion. To the best of our knowledge, the present study is the first phase 2 trial evaluating DTT-SBRT for the lung in a multi-institutional setting. (Funded by the Japan Agency for Medical Research and Development; and UMIN Clinical Trials Registry number, UMIN000016547).

Radiotherapy for prostate cancer: Effect of gold fiducial markers on diffusion-weighted magnetic resonance imaging.

There has been an increase in the use of gold fiducial markers to ensure precise radiotherapy delivery in prostate cancer patients. However, metal artifacts may affect the quality of subsequent imaging used to assess disease status following treatment. In this study, we evaluated the effect of gold fiducial markers on magnetic resonance imaging (MRI), particularly on diffusion-weighted imaging (DWI). Among 57 patients with prostate cancer, 21 patients in whom two gold markers were placed in the prostate tumor with abnormal signal intensity on DWI were evaluated. The effect of the markers on DWI was evaluated on a scale of 1-5, with a high score indicating clinical usefulness. Change inapparent diffusion coefficient (ADC; 10-3 mm2 /s) from before to after marker placement was also evaluated. The mean effect of the markers on DWI was 4.3 (standard deviation [SD] 1.3, range 2-5) points. The mean change in ADC was 0.045 (SD 0.041, range 0.025-0.089) × 10-3 mm2 /s. The gold fiducial markers demonstrated negligible effect on DWI quality. Therefore, gold markers do not affect MRI quality, particularly DWI, and may be used during follow-up in prostate cancer patients.

Prevention of Wrong-level Surgery in the Thoracic Spine: Preoperative Computer Tomography Fluoroscopy-guided Percutaneous Gold Fiducial Marker Placement in 57 Patients.

Retrospective review. The aim of this study was to evaluate the feasibility, safety,s and complications of computer tomography (CT) fluoroscopy-guided percutaneous transpedicular gold fiducial marker insertion to reduce incidence of wrong-level surgery in the thoracic spine. Intraoperative localization of the correct thoracic level can be challenging and time-consuming, especially in obese patients and patients with anatomical variations. In the literature there are very few studies containing low numbers of patients which assessed CT or CT fluoroscopy-guided fiducial marker placement of the thoracic spine. Description of this technique has been similarly scarce. All patients who underwent percutaneous CT fluoroscopy-guided gold fiducial marker placement of the thoracic spine were retrospectively reviewed. Indications for surgery included degenerative disc disease, infection, spinal metastasis, and intra- and extradural tumors. Gold fiducial markers were placed using a percutaneous CT fluoroscopy-guided transpedicular approach with local anesthesia. In addition, sex, age, body mass index (BMI), thoracic level, related pathology, and procedure-related complications were also recorded. A total of 57 patients (24 females, 33 males) were included. Mean age was 58.6 ± 15.5 years. No complications during CT fluoroscopy-guided gold fiducial marker placement were recorded. Intraoperative localization was successful in all patients. Mean BMI was 32.98 kg/m (range, 18.63-56.03 kg/m), and 63% of patients were obese (>30 kg/m). T7 (n = 11) was the most often marked vertebral body, followed by T10 (n = 10) and T6 (n = 7). The most cranial and most caudal levels marked were T2 and T12, respectively. Preoperative CT fluoroscopy-guided percutaneous gold fiducial marker placement is safe, feasible, and accurate. The resulting facilitated localization of the intended thoracic level of surgery can reduce the length of surgery and prevent wrong-level surgery. Further studies are needed to evaluate in the effect on exposure to radiation and quantify the difference in operating room time. 4.

CN7 Improved staff ergonomics and time efficiency using surface guided radiotherapy for prostate setup

The use of surface guided radiotherapy (SGRT) for prostate patients with internal gold markers was investigated in this study. The purpose was to investigate the effects on ergonomics for the oncology nurses using the SGRT system for initial patient setup. Also, the time efficiency was evaluated using an automatic couch shift function. A total of 40 prostate patients with gold markers were included, 20 patients using the SGRT system CatalystTM (C-rad Positioning AB, Uppsala, Sweden) for patient setup and 20 reference patients using tattoos’ and laser alignment. At the first treatment fraction, the lateral laser was used to control that the patient was centered on the couch for all patients. For the SGRT patients, a colour map was projected onto the patients’ skin for guidance of posture correction. The calculated couch shift was automatically applied using an auto-couch function. Daily orthogonal kV-images were used for final positioning of the internal gold markers. For comparison purposes, 184 fractions using SGRT, and 192 fractions using laser alignment was included. The staff ergonomics was evaluated using a questionnaire that was sent out to ten oncology nurses. The result from the questionnaire showed an improvement in the staff ergonomics. Working with the colour map reduced the amount of heavy lifting for patient adjustments. It was reported that the pain in the neck, shoulders, elbow and thumbs was decreased from all the participators. These ergonomic effects were evaluated during a relatively limited time, suggesting that long term use of SGRT could have a great impact on the staff ergonomics. For most treatment fractions, the SGRT system improved the time efficiency compared to laser alignment (Figure 1). However, during the first treatment fraction an increased setup time was observed (median 3 min) due to time for camera optimization and learning the SGRT system. The treatment staff experienced an ergonomic benefit using the colour map projected onto the patients’ skin. Shorter patient positioning times were observed using SGRT for most treatment sessions. The result of this study led to implementation of the SGRT workflow for all prostate patients with internal markers in our clinic.

Novel artifact-robust and highly visible zinc solid fiducial marker for kilovoltage x-ray image-guided radiation therapy.

To develop a novel biocompatible solid fiducial marker that prevents radiopaque imaging artifacts and also maintains high imaging contrast for kilovoltage x-ray image-guided radiation therapy. The fiducial marker was made of pure zinc. An in-house water-equivalent phantom was designed to evaluate artifacts and visibility under various simulated treatment scenarios. Image artifacts were quantitatively assessed in terms of the metal artifact index (MAI) on kilovoltage computed tomography (CT) and cone-beam CT (CBCT) scans. Marker visibility was evaluated on two types of kilovoltage planar x-ray images in terms of the contrast-to-background ratio (CBR). Comparisons with a conventional gold fiducial marker were conducted. The use of zinc rather than a gold marker mitigates imaging artifacts. The MAI near the zinc marker decreased by 76, 79, and 77 % in CT, and by 77 (81), 74 (80), and 79 (85) % in CBCT full-fan (half-fan) scans, when using one-, two-, and three-marker phantom settings, respectively. The high-contrast part of the zinc marker exhibited CBRs above 2.00 for 28/32 exposures under four (lung, tissue, low-density bone, and high-density bone) different simulation scenarios, making its visibility comparable to that of the gold marker (30/32 exposures with CBRs>2.00). We developed a biocompatible, artifact-robust, and highly visible solid zinc fiducial marker. Although further evaluation is needed in clinical settings, our findings suggest its feasibility and benefits for kilovoltage x-ray image-guided radiation therapy.

Direct measurement and correction of both megavoltage and kilovoltage scattered x-rays for orthogonal kilovoltage imaging subsystems with dual flat panel detectors.

PurposeTo measure the scattered x‐rays of megavoltage (MV) and kilovoltage (kV) beams (MV scatter and kV scatter, respectively) on the orthogonal kV imaging subsystems of Vero4DRT.MethodsImages containing MV‐ and kV‐scatter from another source only (i.e., MV‐ and kV‐scatter maps) were acquired for each investigated flat panel detector. The reference scatterer was a water‐equivalent cuboid phantom. The maps were acquired by changing one of the following parameters from the reference conditions while keeping the others fixed: field size: 10.0 × 10.0 cm2; dose rate: 400 MU/min; gantry and ring angles: 0°; kV collimator aperture size at isocenter: 10.0 × 10.0 cm2: tube voltage: 110 kV; and exposure: 0.8 mAs. The average pixel values of MV‐ and kV‐scatter (i.e., the MV‐ and kV‐scatter values) at the center of each map were calculated and normalized to the MV‐scatter value under the reference conditions (MV‐ and kV‐scatter value factor, respectively). In addition, an MV‐ and kV‐scatter correction experiment with intensity‐modulated beams was performed using a phantom with four gold markers (GMs). The ratios between the intensities of the GMs and those of their surroundings were calculated.ResultsThe measurements showed a strong dependency of the MV‐scatter on the field size and dose rate. The maximum MV‐scatter value factors were 2.0 at a field size of 15.0 × 15.0 cm2 and 2.5 at a dose rate of 500 MU/min. The maximum kV‐scatter value was 0.48 with a fully open kV collimator aperture. In the phantom experiment, the intensity ratios of kV images with MV‐ and kV‐scatter were decreased from the reference ones. After correction of kV‐scatter only, MV‐scatter only, and both MV‐ and kV‐scatter, the intensity ratios gradually improved.ConclusionsMV‐ and kV‐scatter could be corrected by subtracting the scatter maps from the projections, and the correction improved the intensity ratios of the GMs.

Implementation of Stereotactic Accelerated Partial Breast Irradiation Using Cyber-Knife \u2013 Technical Considerations and Early Experiences of a Phase II Clinical Study

To report the implementation, dosimetric results of and early experiences with stereotactic accelerated partial breast irradiation (SAPBI) following breast conserving surgery (BCS) for postmenopausal low-risk St I-II invasive breast cancer (IBC) patients. Between November 2018 and August 2019, 27 patients were registered in our phase II prospective study. SAPBI was performed with Cyber-Knife (CK) M6 machine, in 4 daily fractions of 6.25 Gy to a total dose of 25 Gy. Respiratory movements were followed with implanted gold markers and Synchrony system. Corrections for patient displacement and respiratory movement during treatment were performed with the robotic arm. Early side effects, cosmetic results, and dosimetric parameters were assessed. The average volume of the surgical cavity, clinical target volume (CTV), and planning target volume (PTV_EVAL) were 8.1 cm3 (range: 1.75–27.3 cm3), 55.3 cm3 (range: 26.2–103.5 cm3), and 75.7 cm3 (range: 40–135.4 cm3), respectively. The mean value of the PTV_eval/whole breast volume ratio was 0.09 (range: 0.04–0.19). No grade 2 or worst acute side-effect was detected. Grade 1 (G1) erythema occurred in 6 (22.2%) patients, while G1 oedema was reported by 3 (11.1%) cases. G1 pain was observed in 1 (3.4%) patient. Cosmetic result were excellent in 17 (62.9%) and good in 10 (37.1%) patients. SAPBI with CK is a suitable and practicable technique for the delivery of APBI after BCS for low-risk, St. I-II. IBC. Our early findings are encouraging, CK-SAPBI performed with four daily fractions is convenient and perfectly tolerated by the patients.

Fluence perturbation from fiducial markers due to edge-scattering measured with pixel sensors for 12C ion beams

Fiducial markers are nowadays a common tool for patient positioning verification before radiotherapy treatment. These markers should be visible on x-ray projection imaging, produce low streak artifacts on CTs and induce small dose perturbations due to edge-scattering effects during the ion-beam therapy treatment. In this study, the latter effect was investigated and the perturbations created by the markers were evaluated with a new measurement method using a tracker system composed of six CMOS pixel sensors. The present method enables the determination of the particle trajectory before and after the target. The experiments have been conducted at the Marburg Ion Beam Therapy Center with carbon ion beams and the measurement concept was validated by comparison with radiochromic films. This work shows that the new method is very efficient and precise to measure the perturbations due to fiducial markers with a tracker system. Three dimensional fluence distributions of all particle trajectories were reconstructed and the maximum cold spots due to the markers and their position along the beam axis were quantified. In this study, four small commercial markers with different geometries and materials (gold and carbon-coated ZrO2) were evaluated. The gold markers showed stronger perturbations than the lower density ones. However, it is important to consider that low density and low atomic number fiducial markers are not always visible on x-ray projections.

DLLME-μSPE extraction coupled to HPLC-ESI-MS/MS for the determination of F2α-IsoPs in human urine

Oxidative stress is a pathological condition characterized by an imbalance between body’s antioxidant defenses and oxidizing agents, resulting in damage of endogenous molecules. These products can be used as markers of oxidative conditions; in particular, isoprostanes (IsoPs) come from the reaction of arachidonic acid with reactive oxygen species (ROS) and are currently defined as gold markers of oxidative stress in urine. Our main goal was the development of a reliable analytical method for the determination and quantification of the IsoPs in human urine by dispersive Liquid–Liquid Micro Extraction (dLLME) coupled with micro Solid Phase Extraction (μSPE) clean-up and HPLC-MS/MS analysis. The selected compounds are present in very small concentration in urine, furthermore, due to relevant matrix effect, they are challenging for ESI-MS/MS analysis. This approach provided selectivity and sensitivity for 8-isoprotaglandine F2α (8-iso-PGF2α), the “gold” OS marker, together with the main isomers. dLLME extraction allowed a significant enrichment factor and μSPE clean-up provided the removal of ion-suppressing compounds from the sample resulting in low matrix effect. The chromatographic separation was also challenging as the target compounds possess very similar chemical characteristics, so experimental conditions were carefully tuned. The reported method represents a useful tool for the detection of IsoPs in urine taking advantage of the combination of dLLME extraction and μSPE clean-up; overall recoveries were above 50 % and matrix effects were ≤15 %, with LOQs ranging between 0.020 and 0.060 ng mL−1. The procedure is easy to use and rapid allowing the removal of interfering compounds and matrix effect maintaining a highly sensitive determination.

A novel gold marker to aid intraoperative localisation during spinal surgery!

Methods of pre-operative level marking for spinal surgery include fiducial implants, coil implants, spinal needle implant, methylene blue and cement injection. We describe a novel gold marker used for preoperative spinal marking and report our experience.The notes and scans of patients who had gold marker for preoperative spinal marking over the period from June 2016 to November 2018 were analysed.20 patients had preoperative spinal marking using the gold marker. The accuracy was 100% and there were no complications. Compared to injecting cement, we save over £700 per patient!

Fiducial markers visibility and artefacts in prostate cancer radiotherapy multi-modality imaging

BackgroundIn this study, a novel pelvic phantom was developed and used to assess the visibility and presence of artefacts from different types of commercial fiducial markers (FMs) on multi-modality imaging relevant to prostate cancer.Methods and materialsThe phantom was designed with 3D printed hollow cubes in the centre. These cubes were filled with gel to mimic the prostate gland and two parallel PVC rods were used to mimic bones in the pelvic region. Each cube was filled with gelatine and three unique FMs were positioned with a clinically-relevant spatial distribution. The FMs investigated were; Gold Marker (GM) CIVCO, GM RiverPoint, GM Gold Anchor (GA) line and ball shape, and polymer marker (PM) from CIVCO. The phantom was scanned using several imaging modalities typically used to image prostate cancer patients; MRI, CT, CBCT, planar kV-pair, ExacTrac, 6MV, 2.5MV and integrated EPID imaging. The visibility of the markers and any observed artefacts in the phantom were compared to in-vivo scans of prostate cancer patients with FMs.ResultsAll GMs were visible in volumetric scans, however, they also had the most visible artefacts on CT and CBCT scans, with the magnitude of artefacts increasing with FM size. PM FMs had the least visible artefacts in volumetric scans but they were not visible on portal images and had poor visibility on lateral kV images. The smallest diameter GMs (GA) were the most difficult GMs to identify on lateral kV images.ConclusionThe choice between different FMs is also dependent on the adopted IGRT strategy. PM was found to be superior to investigated gold markers in the most commonly used modalities in the management of prostate cancer; CT, CBCT and MRI imaging.

Quantification of Esophageal Tumor Motion and Investigation of Different Image-Guided Correction Strategies

PurposeTo accurately quantify esophageal tumor position variability and to optimize image guided correction strategies. Material and MethodsEsophageal cancer patients receiving chemoradiotherapy (41.4-50.4 Gy in 23-28 fractions combined with carboplatin plus paclitaxel) were included in a prospective cohort study (NCT02139488). Gold fiducial markers were inserted into the esophageal tumors during diagnostic endoscopic ultrasound. Four-dimensional (4D) planning computed tomography (CT) and daily 4D cone beam (CB) CT scans were acquired. Each CBCT was registered to the planning CT using different regions of interest (bone; 3D), and carina, diaphragm, clinical target volume (CTV), and fiducial markers (4D) for alignment and using the fiducial markers as the true tumor position. Subsequently, a planning target volume (PTV) margin accounting for residual uncertainties, including the average respiratory motion, was calculated for each of these registrations. ResultsFifty-six patients with tumors located in the proximal (n = 1), mid (n = 7), or distal esophagus (n = 25) or at the gastroesophageal junction (n = 23) were included. The average peak-to-peak respiratory tumor motion was 0.20, 0.92, and 0.34 cm on the planning CT in left–right (LR), cranial–caudal (CC), and anterior–posterior (AP) directions, respectively. The required PTV margin with average motion amplitude, depending on the correction strategy used for image guidance, ranged from 0.8 cm to 1.0 cm, 1.1 cm to 1.6 cm, and 0.7 cm to 0.9 cm in LR, CC, and AP direction, respectively. A registration based on the CTV resulted in the smallest PTV margins (0.8, 1.1, and 0.7 cm in LR, CC, and AP direction, respectively). For bone registration the calculated PTV margins were 1.0, 1.3, and 0.7 cm in LR, CC, and AP directions, respectively. The registration based on the diaphragm increased PTV margins. ConclusionsSubstantial and anisotropic position variability of esophageal tumors was observed during radiation therapy, and nonuniform margins should be considered. Cranial-caudal PTV margins need to be larger than those commonly used. Target positioning during image-guided radiotherapy could be improved with a CTV registration-based correction strategy.

Simulated multileaf collimator tracking for stereotactic liver radiotherapy guided by kilovoltage intrafraction monitoring: Dosimetric gain and target overdose trends

PurposeTo investigate the potential benefit of multileaf collimator (MLC) tracking guided by kilovoltage intrafraction monitoring (KIM) during stereotactic body radiotherapy (SBRT) in the liver, and to understand trends of target overdose with MLC tracking. MethodsSix liver SBRT patients with 2–3 implanted gold markers received SBRT delivered with volumetric modulated arc therapy (VMAT) in three fractions using daily cone-beam CT setup. The CTV-to-PTV margins were 5 mm in the axial plane and 10 mm in the cranio-caudal directions, and the plans were designed to give minimum target doses of 95% (CTV) and 67% (PTV). The three-dimensional marker trajectory estimated by post-treatment analysis of kV fluoroscopy images acquired throughout treatment delivery was assumed to represent the tumor motion. MLC tracking guided by real-time KIM was simulated. The reduction in CTV D95 (minimum dose to 95% of the clinical target volume) relative to the planned D95 (ΔD95) was compared between actual non-tracking and simulated MLC tracking treatments. ResultsMLC tracking maintained a high CTV dose coverage for all 18 fractions with ΔD95 (mean: 0.2 percentage points (pp), range: −1.7 to 1.9 pp) being significantly lower than for the actual non-tracking treatments (mean: 6.3 pp range: 0.6–16.0 pp) (p = 0.002). MLC tracking of large target motion perpendicular to the MLC leaves created dose artifacts with regions of overdose in the CTV. As a result, the mean dose in spherical volumes centered in the middle of the CTV was on average 2.4 pp (5 mm radius sphere) and 1.3 pp (15 mm radius sphere) higher than planned (p = 0.002). ConclusionsIntrafraction tumor motion can deteriorate the CTV dose of liver SBRT. The planned CTV dose coverage may be restored with KIM-guided MLC tracking. However, MLC tracking may have a tendency to create hotspots in the CTV.

A cone beam CT-based study on fiducial seed migration and planning target volume margin in prostate radiotherapy

AbstractAim:This study attempts to investigate fiducial marker (FM) migration and calculate the prostate planning target volume (PTV) margin considering the setup errors after translation corrections alone (T) and translation plus rotational corrections (T+R) and anatomy variation with respect to the corrected fiducial position, analysed on cone beam computed tomography (CBCT) images.Methods and materials:CBCT images from 25 patients are analysed for FM movements, setup error and anatomy variation with respect to the seed match positions. Systematic and random components of setup error and prostate movements are used to calculate the PTV margin for CBCT-based FM localisation in two scenarios, translation corrections only and translation plus rotational correction. MTNW887825 soft tissue gold markers (Civco, Orange City, FL, USA) were used with the department-specific immobilisation system and rectal and bladder filling protocols.Results:The average directional inter-marker distance variation is −0·05 ± 0·90 mm. The systematic setup errors for T+R are 0·40, 0·63 and 0·80 mm in right–left (RL), anterior–posterior (AP) and superior–inferior (SI), respectively. The corresponding values for T only are 0·54, 0·69 and 0·90 mm. The systematic prostate movement from T+R corrected FM positions are 0·65, 1·27 and 1·32 mm in the RL, AP and SI directions.Findings:Minimal FM movements are noted from the study. The PTV margins to incorporate the daily T+R corrected setup error and prostate deformation are found to be 2·5, 4·5 and 5·2 mm in the RL, AP and SI directions, respectively. The corresponding margins for T only corrected scenario are found to be 2·8, 4·8 and 5·7 mm.