SI Direction Research Articles

Enhanced structural stability of Si electrode employing TiNi/Si pillars with oriented Li diffusion pathway

As the anode materials of Li-ion batteries, pillar-shaped TiNi/Si particles fabricated by employing electrochemical etching of (100) Si wafers and TiNi alloy coating, were investigated for their structural and electrochemical properties. The most suitable porous wafer for producing Si pillars was obtained at a current density of 2.5 mA/cm2 during etching. The deposited TiNi alloy film consisted of a crystallized austenitic (B2) phase capable of inducing phase transformation through annealing at 500°C. Particularly, by coating with the inactive materials, only the (100) plane of single crystalline Si was exposed during the initial charging process to restrict Li ion movement exclusively along the <100>Si direction. The TiNi/Si electrode exhibited a lower capacity compared to the Si electrode but demonstrated improved cycling performance. It showed a charge capacity of 1110 mAh/g at 0.1 C with an initial efficiency of 77 % and maintained a capacity retention of 49 % (543 mAh/g) up to 100 cycles. After the initial cycle, Si electrodes exposed to various lithium insertion directions exhibited severe structural damage such as cracking and particle pulverization, whereas TiNi/Si electrodes demonstrated enhanced structural stability due to surface coating and restricted reaction pathway.

Rate of polyethylene wear correlates with earlier glenoid implant failure in anatomic total shoulder arthroplasty with cemented all-polyethylene glenoid components

BackgroundGlenoid component loosening is the most common cause of anatomic total shoulder arthroplasty failure, and osteolysis is a common intraoperative and radiographic finding associated with these failed arthroplasties. While preclinical testing can estimate failure mode and wear rates in the laboratory, there is limited in vivo data measuring polyethylene wear rate and location. MethodsUsing an institutional review board–approved total joint arthroplasty retrieval collection, 56 cemented all-polyethylene glenoid components from eleven different manufacturers were analyzed for in vivo dimensional change. We used the differential thickness measurement between the anteroposterior and superoinferior axes of each radially symmetrical implant to determine the dimensional change along that axis. A physiologic wear vector was determined for each retrieved device. ResultsThe implants had a median dimensional change of 0.13 mm/year (range 0.01-1.01mm/year) and the 25th and 75th percentiles were 0.060 and 0.22 mm/year, respectively. The average time to revision of devices with <0.1mm/year of wear was 140.9 months, while the averages for devices between 0.1-0.2mm/year and ≥0.2mm/year were 80.7 and 54.0 months, respectively. Devices with ≥0.2mm/year of wear had significantly shorter time to revision than those with <0.1mm/year (P = .0006). The devices had a similar material loss distribution in both superior-inferior and anterior-posterior directions, with 29 (52%) devices having a greater material loss in the superior-inferior distribution and the remaining 27 (48%) devices in the anterior-posterior axis. The physiologic wear vector had a mean of 47.3 degrees, with a relatively even distribution across all angles, suggesting that glenoid component loosening can occur along multiple axes. ConclusionWe conclude that polyethylene wear is a contributing factor for early failure of cemented all-polyethylene glenoid implants and that anatomic total shoulder arthroplasty may benefit from advances in polyethylene processing. We also suggest that in vitro testing of new polymers and designs should incorporate motion vectors beyond the traditional IS rocking horse test.

Prostate size, source configuration, and dosimetry dynamics of stranded 125I seed implants

PURPOSETo quantify changes in prostate size and seed movement over time after transperineal implantation of stranded 125I seeds, and to determine their impact on prostate dosimetry. METHODSCT and MR (T2, balanced steady-state free precession) image triplets were acquired on days 0, 3, 10, and 30 for a cohort of 20 patients and registered automatically. Prostate contours were drawn on MR-T2 images; seeds were found and matched in successive CT images. Prostate volume and dimensions, seed movements, and prostate dose metrics V200, V150, V100 and D90 were calculated, and their dynamic behaviors quantified in an operationally defined prostate coordinate system. RESULTSCohort-averaged reductions in prostate A-P dimension (∼8%) and L-R dimension (∼5%) inferred from seed movements agreed with those obtained from contour measurements, whereas prostate volume and S-I dimension (implant direction) reductions inferred from seed movements were overestimated by about 30%. Average overall seed movement was 4.8 ± 3.0 mm, of which the only identifiable systematic component was resolution of prostate edema. Cohort-averaged ratios of prostate V200, V150, V100, and D90 on day 30 relative to day 0 were 1.67, 1.33, 1.02, and 1.08, respectively. CONCLUSIONSPostimplant prostate size reduction in the SI (implant) direction cannot reliably be inferred from stranded seed movements. Apart from large-scale migration, residual seed movements relative to the prostate after accounting for edema resolution appear to be random. Prostate V100 and D90 changes 30 days post implant are modest, whereas those for V150 and V200 are substantial.

Reduction of cone-beam CT artifacts in a robotic CBCT device using saddle trajectories with integrated infrared tracking.

Cone beam computed tomography (CBCT) is widely used in many medical fields. However, conventional CBCT circular scans suffer from cone beam (CB) artifacts that limit the quality and reliability of the reconstructed images due to incomplete data. Saddle trajectories in theory might be able to improve the CBCT image quality by providing a larger region with complete data. Therefore, we investigated the feasibility and performance of saddle trajectory CBCT scans and compared them to circular trajectoryscans. We performed circular and saddle trajectory scans using a novel robotic CBCT scanner (Mobile ImagingRing (IRm); medPhoton, Salzburg, Austria). For the saddle trajectory, the gantry executed yaw motion up to using motorized wheels driving on the floor. An infrared (IR) tracking device with reflective markers was used for online geometric calibration correction (mainly floor unevenness). All images were reconstructed using penalized least-squares minimization with the conjugate gradient algorithm from RTK with voxel size. A disk phantom and an Alderson phantom were scanned to assess the image quality. Results were correlated with the local incompleteness value represented by , which was calculated at each voxel as a function of the source trajectory and the voxel's 3D coordinates. We assessed the magnitude of CB artifacts using the full width half maximum (FWHM) of each disk profile in the axial center of the reconstructed images. Spatial resolution was also quantified by the modulation transfer function at 10% (MTF10). When using the saddle trajectory, the region without CB artifacts was increased from 43 to 190mm in the SI direction compared to the circular trajectory. This region coincided with low values for . When was larger than 0.02, we found there was a linear relationship between the FWHM and . For the saddle, IR tracking allowed the increase of MTF10 from 0.37 to 0.98 lp/mm. We achieved saddle trajectory CBCT scans with a novel CBCT system combined with IR tracking. The results show that the saddle trajectory provides a larger region with reliable reconstruction compared to the circular trajectory. The proposed method can be used to evaluate other non-circulartrajectories.

Markerless dynamic tumor tracking (MDTT) radiotherapy using diaphragm as a surrogate for liver targets.

To assess the feasibility of using the diaphragm as a surrogate for liver targets during MDTT. Diaphragm as surrogate for markers: a dome-shaped phantom with implanted markers was fabricated and underwent dual-orthogonal fluoroscopy sequences on the Vero4DRT linac. Ten patients participated in an IRB-approved, feasibility study to assess the MDTT workflow. All images were analyzed using an in-house program to back-project the diaphragm/markers position to the isocenter plane. ExacTrac imager log files were analyzed. Diaphragm as tracking structure for MDTT: The phantom "diaphragm" was contoured as a markerless tracking structure (MTS) and exported to Vero4DRT/ExacTrac. A single field plan was delivered to the phantom film plane under static and MDTT conditions. In the patient study, the diaphragm tracking structure was contoured on CT breath-hold-exhale datasets. The MDTT workflow was applied until just prior to MV beam-on. Diaphragm as surrogate for markers: phantom data confirmed the in-house 3D back-projection program was functioning as intended. In patients, the diaphragm/marker relative positions had a mean±RMS difference of 0.70±0.89, 1.08±1.26, and 0.96±1.06mm in ML, SI, and AP directions. Diaphragm as tracking structure for MDTT: Building a respiratory-correlation model using the diaphragm as surrogate for the implanted markers was successful in phantom/patients. During the tracking verification imaging step, the phantom mean±SD difference between the image-detected and predicted "diaphragm" position was 0.52±0.18mm. The 2D film gamma (2%/2mm) comparison (static to MDTT deliveries) was 98.2%. In patients, the mean difference between the image-detected and predicted diaphragm position was 2.02±0.92mm. The planning target margin contribution from MDTT diaphragm tracking is 2.2, 5.0, and 4.7mm in the ML, SI, and AP directions. In phantom/patients, the diaphragm motion correlated well with markers' motion and could be used as a surrogate. MDTT workflows using the diaphragm as the MTS is feasible using the Vero4DRT linac and could replace the need for implanted markers for liver radiotherapy.

Optimal Fractionation and Timing of Weekly Cone-Beam CT in Daily Surface-Guided Radiotherapy for Breast Cancer

SGRT has been demonstrated as a promising supplement to CBCT in adjuvant breast cancer radiotherapy, but a rational combination mode is lacking in clinical practice. The aim of this study was to explore this mode and investigate its impact on setup and dose accuracy. Both daily SGRT and weekly CBCT images were acquired for 23 breast cancer patients receiving conventional fractionated radiotherapy after lumpectomy. Based on the scanning frequencies and time intervals of CBCT, sixteen modes were acquired by randomly selecting one (CBCT1), two (CBCTij), three (CBCTijk), four (CBCTijkl), and five (CBCT12345) images from the patient's off-line CBCT images for fusion with SGRT. Due to TPS system limitations, the 6D SGRT setup errors were transformed into 3D deviations in the translational directions, and the CTV-PTV margins, the dose coverage (V95%) of PTV and CTV, and the OAR doses (the ipsilateral lung's V5, V10, V20, and Dmean, the contralateral breast's V3 and Dmean, and the heart's Dmean and Dmax) were calculated based on the 3D deviations with different regions of interest (ROIs). Dose correlations between these modalities were investigated using Pearson and Spearman's methods. For the ipsilateral breast ROI, the larger SGRT errors in the AP direction and higher target doses were found in all modes compared to the whole breast ROI (P < 0.05). In the ipsilateral ROI, the CTV-PTV margins decreased as CBCT frequencies increased, reaching approximately 5 mm for CBCTijkl and CBCT12345. The decline of Σ (systematic errors) was greater than the decline of σ (random errors), and it contributed more to the decline of margins. For the same frequency, the CBCT time intervals had essentially little influence on the errors and margins. Compared with other directions, the margins in the SI direction were the largest for all modes except for CBCT124 and CBCT125. The target dose correlations between all modes increased with increasing CBCT time intervals, decreased and then increased with increasing CBCT frequencies, with the turning point observed at week 5 of CBCT participation. The dose deviations in CBCT123, CBCT124, CBCT125, CBCTijkl, and CBCT12345 were minimal and not significantly different (P > 0.05). There was excellent agreement in CBCT124 vs. CBCT1234, and (CBCTijkl, CBCT12345) vs. CBCT125 in determining the classification for the percentage of PTV deviation (Kappa = 0.775-0.901). The frequencies and time intervals of CBCT had little effect on the OAR doses. For all modes, there were strong correlations (R > 0.9) in the OAR doses between different modes, except for the ipsilateral lung's V20 and Dmean (R = 0.734-0.987). Based on weekly CBCT, these modes with the ipsilateral breast ROI and a combination of daily SGRT and CBCT frequencies of ≥ 3 were recommended, and the CBCT was required at weeks 1 and 2. Considering the additional radiation, time consumption, and expensive cost of CBCT, modes CBCT124 and CBCT125 could replace the modes with higher CBCT frequencies.

CBCT Guided Interfraction Absolute Displacement and Setup Error Assessment during Breast Prone Radiotherapy

To calculate interfraction absolute displacement/shift and setup error using cone beam computed tomography (CBCT) during breast prone radiotherapy. Fifty-nine patients undergoing prone whole breast-irradiation after breast-conserving surgery (BCS) were studied as part of an institutional review board- approved prospective trial. Setup precision was monitored using a daily online CBCT. Translational shifts in 3 axes (AP: anterior posterior; LR: left right; and SI: superior inferior) and 3 rotations (pitch, roll, and rtn) after CBCT were analyzed for 1062 treatment fractions. The random and systematic setup errors (SE) were calculated and were analyzed for time trends during the course of radiotherapy. For absolute inter-fractional shifts, the numbers of fractions exceeding 10 mm in the AP, LR, and SI directions were 6.5%, 17.42% and 8.92%, respectively; 0%, 0% and 1.31% fractions exceeded 3°for pitch, roll, and Rtn, respectively. The population systematic errors were 1.89/2.91/1.98 mm in AP/SI/LR directions, while the random error were 2.72/3.99/3.31 mm. In pitch, roll, rtn rotations, the population systematic error were 0.64°/0.49°/0.46°, and 0.89°/0.90°/0.93° for the random error. Without correction these would correspond to a clinical to planning target volume margin of 6.64/10.08/7.26 mm in AP/SI/LR directions and 2.22°/1.79°/1.8° in pitch, roll, rtn rotations. The magnitude of inter-fraction motion was not correlated with patient treatment time accept in AP direction (P = 0.000). SE was larger in prone position in breast cancer patients, attributable mostly to random errors, which emphasize the need for on-line imaging guidance in breast prone radiotherapy. 10mm margins would adequately cover the target volume and account for setup errors in the absence of IGRT.

Intrafraction Dosimetric Evaluation of Biology-Guided Radiotherapy to a Target Under Respiratory Motion

To evaluate the reproducibility and variability of biology-guided radiotherapy (BgRT) treatments using a large anthropomorphic phantom modeling the motion amplitude of a lung tumor. RefleXion X1 is equipped with two opposing 90 degrees PET detector arcs to capture the radionuclide emissions and direct the 6MV Linac to treat the lesions in real time. A custom-built phantom filled with a liquid [¹⁸F]Fluorodeoxyglucose (FDG) solution was used. Fillable target and OAR structures were 3D printed and attached to motion stages. The GTV = CTV was matched to the spherical 22 mm diameter target, and the PTV was a 5 mm expansion from the CTV volume. The Biology Tracking Zone (BTZ) was generated after adding 5 mm margin to the motion extent of the CTV. The OAR was a large C-shape annulus (emulating a heart) that was approximately 3 cm from the target. The 3D independent motion trajectory of the target was designed to mimic lung motion: range of +5.8 mm to -4.9 mm in LR, range of +14.4 mm to -11.3 mm in SI, and range of +5.2 mm to -5.1 mm in AP directions. The OAR motion waveform used a 1D sinusoidal pattern with a 5 mm amplitude in SI direction. The target and the OAR were filled with 40 kBq/mL while the background had 5 kBq/mL FDG. A BgRT Modeling (imaging-only) PET acquisition was performed using RefleXion X1 and used to generate a 4-fraction BgRT treatment plan prescribing 10 Gy/fraction to PTV. For each delivery, target, OAR and background were filled with the same FDG concentrations as in the BgRT Modeling PET planning scan. Dosimetry to the target and OAR were both measured using an ion-chamber (Exradin A14SL) and film in the coronal plane through the center of the GTV for all 4 fractions. The mean activity concentration within the (BTZ) was 7.4 ± 0.8 kBq/mL. The calculated signal-to-noise ratio metric (Normalized Target Signal) within the BTZ was 4.0 ± 0.3. Total treatment times were all less than 35 minutes (34.3 ± 0.2). Prescription dose coverage to the CTV for all 4 fractions was 100%. Ion chamber measurements in the CTV were -1.6 ± 1.3% relative to the planned dose over the active area of the ion-chamber. Minimum and maximum doses to the CTV, measured on film, were -7.7 ± 2.2% and 1.3 ± 1.4%, calculated relative to the planned dose distribution, respectively. The OAR maximum point dose measured on film was -8.7 ± 2.9%, calculated relative to the maximum OAR dose predicted on the bounded dose-volume histogram. Based on this initial study, accurate and reproducible dosimetry can be achieved for targets under respiratory motion using biology-guided radiotherapy over the course of a complete course of treatment. Further studies are needed to evaluate the intrafraction dosimetry of BgRT delivery under various motion models and tumor sizes.

Reducing the margin in prostate radiotherapy: optimizing radiotherapy with a general-purpose linear accelerator using an in-house position monitoring system.

To study the feasibility of optimizing the Clinical Target Volume to Planning Target Volume (CTV-PTV) margin in prostate radiotherapy(RT) with a general-purpose linear accelerator using an in-house developed position monitoring system, SeedTracker. A cohort of 30 patients having definitive prostate radiotherapy treated within an ethics-approved prospective trial was considered for this study. The intrafraction prostate motion and the position deviations were measured using SeedTracker system during each treatment fraction. Using this data the CTV-PTV margin required to cover 90% of the patients with a minimum of 95% of the prescription dose to CTV was calculated using van Herk's formula. The margin calculations were performed for treatment scenarios both with and without applying the position corrections for observed position deviations. The feasibility of margin reduction with real-time monitoring was studied by assessing the delivered dose that incorporates the actual target position during treatment delivery and comparing it with the planned dose. This assessment was performed for plans generated with reduced CTV-PTV margin in the range of 7mm-3mm. With real-time monitoring and position corrections applied the margin of 2.0mm, 2.1mm and 2.1mm in LR, AP and SI directions were required to meet the criteria of 90% population to receive 95% of the dose prescription to CTV. Without position corrections applied for observed position deviations a margin of 3.1mm, 4.0mm and 3.0mm was required in LR, AP and SI directions to meet the same criteria. A mean ± SD reduction of 0.5 ± 1.8% and 3 ± 7% of V60 for the rectum and bladder can be achieved for every 1mm reduction of PTV margin. With position corrections applied, the CTV D99 can be delivered within -0.2 ± 0.3 Gy of the planned dose for plans with a 3mm margin. Without applying corrections for position deviations the CTV D99 was reduced by a maximum of 1.1 ± 1.1 Gy for the 3mm margin plan and there was a statistically significant difference between planned and delivered dose for 3mm and 4mm margin plans. This study demonstrates the feasibility of reducing the margin in prostate radiotherapy with SeedTracker system without compromising the dose delivery accuracy to CTV while reducing dose to critical structures.

Deep learning enables MV-based real-time image guided radiation therapy for prostate cancer patients

Objective. Using MV images for real-time image guided radiation therapy (IGRT) is ideal as it does not require additional imaging equipment, adds no additional imaging dose and provides motion data in the treatment beam frame of reference. However, accurate tracking using MV images is challenging due to low contrast and modulated fields. Here, a novel real-time marker tracking system based on a convolutional neural network (CNN) classifier was developed and evaluated on retrospectively acquired patient data for MV-based IGRT for prostate cancer patients. Approach. MV images, acquired from 29 volumetric modulated arc therapy (VMAT) prostate cancer patients treated in a multi-institutional clinical trial, were used to train and evaluate a CNN-based marker tracking system. The CNN was trained using labelled MV images from 9 prostate cancer patients (35 fractions) with implanted markers. CNN performance was evaluated on an independent cohort of unseen MV images from 20 patients (78 fractions), using a Precision–Recall curve (PRC), area under the PRC plot (AUC) and sensitivity and specificity. The accuracy of the tracking system was evaluated on the same unseen dataset and quantified by calculating mean absolute (±1 SD) and [1st, 99th] percentiles of the geometric tracking error in treatment beam co-ordinates using manual identification as the ground truth. Main results. The CNN had an AUC of 0.99, sensitivity of 98.31% and specificity of 99.87%. The mean absolute geometric tracking error was 0.30 ± 0.27 and 0.35 ± 0.31 mm in the lateral and superior–inferior directions of the MV images, respectively. The [1st, 99th] percentiles of the error were [−1.03, 0.90] and [−1.12, 1.12] mm in the lateral and SI directions, respectively. Significance. The high classification performance on unseen MV images demonstrates the CNN can successfully identify implanted prostate markers. Furthermore, the sub-millimetre accuracy and precision of the marker tracking system demonstrates potential for adaptation to real-time applications.

Long-term experience in quality assurance of on-rail computed tomography systems for image-guided radiotherapy using in-house multifunctional phantoms

To report the long-term quality assurance (QA) experience of an on-rail computed tomography (CT) system for image-guided radiotherapy using an in-house phantom. An on-rail CT system combining the Elekta Synergy and Canon Aquilion LB was used. The treatment couch was shared by the linear accelerators and CT, and the couch was rotated by 180° when using the on-rail-CT system to ensure that the CT direction was toward the head. All QA analyses were performed by radiation technologists on CBCT or on-rail CT images of the in-house phantom. The CBCT center accuracy from the linac laser, couch rotational accuracy (CBCT center vs. on-rail CT center), horizontal accuracy by CT gantry shift, and remote couch shift accuracy were evaluated. This study reported the QA status of the system during the period 2014-2021. The absolute mean accuracy of couch rotation was 0.4 ± 0.28mm, 0.44 ± 0.36mm, and 0.37 ± 0.27mm in the SI, RL, and AP directions, respectively. Horizontal and remote movement accuracies of the treatment couch were also within 0.5mm of the absolute mean value. A decrease in the accuracy of couch rotation was also observed due to aging deterioration of related parts caused by the frequent use of couch rotation. The three-dimensional accuracy of on-rail CT systems derived mainly from treatment couches can be maintained within 0.5mm with appropriate accuracy assurance for at least > 8years.

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

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. 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≤3mm). 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. 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. 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.

Quantifying 6D tumor motion and calculating PTV margins during liver stereotactic radiotherapy with fiducial tracking

Our study aims to estimate intra-fraction six-dimensional (6D) tumor motion with rotational correction and the related correlations between motions of different degrees of freedom (DoF), as well as quantify sufficient anisotropic clinical target volume (CTV) to planning target volume (PTV) margins during stereotactic body radiotherapy (SBRT) of liver cancer with fiducial tracking technique. A cohort of 12 patients who were implanted with 3 or 4 golden markers were included in this study, and 495 orthogonal kilovoltage (kV) pairs of images acquired during the first fraction were used to extract the spacial position of each golden marker. Translational and rotational motions of tumor were calculated based on the marker coordinates by using an iterative closest point (ICP) algorithm. Moreover, the Pearson product-moment correlation coefficients (r) were applied to quantify the correlations between motions with different degrees of freedom (DoFs). The population mean displacement ( ), systematic error (Σ) and random error (σ) were obtained to calculate PTV margins based on published recipes. The mean translational variability of tumors were 0.56, 1.24 and 3.38mm in the left-right (LR, X), anterior-posterior (AP, Y), and superior-inferior (SI, Z) directions, respectively. The average rotational angles θ X , θ Y and θ Z around the three coordinate axes were 0.88, 1.24 and 1.12, respectively. (|r|>0.4) was obtainted between Y -Z , Y - θ Z , Z -θ Z and θ X - θ Y . The PTV margins calculated based on 13 published recipes in X, Y, and Z directions were 1.08, 2.26 and 5.42mm, and the 95% confidence interval (CI) of them were (0.88,1.28), (1.99,2.53) and (4.78,6.05), respectively. The maximum translational motion was in SI direction, and the largest correlation coefficient of Y-Z was obtained. We recommend margins of 2, 3 and 7mm in LR, AP and SI directions, respectively.

Planning Margins Determined by Inter Fractional Errors for Patients with Hepatocarcinoma—A Real-World Practice

<h3>Purpose/Objective(s)</h3> With the progress of radiation techniques, radiotherapy is increasingly widely used in the treatment of hepatocarcinoma. Previous studies showed high radio-sensitivity and frequently motion of hepatobiliary zone. Although the application of magnetic resonance simulation (MR) and four-dimensional computed tomography (4D-CT) help us to clearly the gross tumor volume (GTV), accurate calculation of set-up margin is required to define the clinical to planning target volume margin. This study aimed at calculate the suitable margin between clinical target volume (CTV) and planning target volume (PTV) after the evaluation of the set-up errors using cone beam computed tomography (CBCT). <h3>Materials/Methods</h3> Patients aged 18-85 years old with pathologically diagnosed as primary hepatocarcinoma, Eastern Cooperative Oncology Group performance score ≤ 3 points, accepted the radiation recommendation by multi-disciplinary team, with only one tumor located in liver will be enrolled. Both 4D-CT and MR simulations were delivered to determine GTV. CTV was GTV plus a 5 mm margin in liver and GTV plus a 10mm margin along vessels if tumor embolus were included. PTV was CTV plus a 5mm margin. All the patients received image guided intensity modulated radiotherapy with conventional fractionation. CBCT was prescribed daily at the first week and then 2-3 times at every following week. Patients whose tumor could not be clearly classified in CBCT will be excluded. CBCT The setup errors in translational directions were recorded based on the image registration between the CBCT and the free breath CT images at simulation as reference images. Mean value and standard deviations (∑) of each patient were obtained. After that, we calculated the margin between CTV and PTV by a formula MPTV=2.5∑+0.7σ (σ means rootmeansquare of ∑). <h3>Results</h3> From November 2020 to April 2021, 35 patients fulfilled the criteria. The median age of these patients were 65 years old. The median value of GTV and PTV were 512.91 ml (45.09-1987.56 ml) and 1074.77ml (221.09-3028.40 ml), respectively. The median body mass index (BMI)was 23.98. The median CBCT times was 8 (5-12). After alignments by one senior radiation oncologist and one senior radiation therapist, we analyzed 284 sets of CBCT images. M±SD shifts in translational were 0.04±0.25 mm (LR), 0.05±0.51 mm (AP), and 0.06±0.26 mm (SI), respectively. Accordingly, the margins in LR, SI and AP directions were 5 mm, 6 mm and 10 mm, respectively. For patients whose BMI <24, the margins in LR, SI and AP directions were 4 mm, 5 mm and 12 mm. For patients whose BMI ≥24, the corresponding margins should be 6 mm,7 mm and 10 mm, respectively. <h3>Conclusion</h3> For patients with hepatocarcinoma, the setup errors were different in LR, SI and AP directions. We recommended that the margins from CTV to PTV should be 5mm, 6mm and 10 mm in LR, SI and AP directions. For patients with BMI≥24, larger margins in LR and SI directions are needed.

Variability of Inter-Fraction Target Motion during Hypofractionated Lung Radiation Therapy

<h3>Purpose/Objective(s)</h3> Pre-treatment 4D-CTs are used in planning for motion management of lung RT. The target excursion (E) at the time of planning may differ between planning and treatment. Additionally, the tumor excursion can change between fraction deliveries. The objective of this study is to investigate patterns of excursion variability (∆E) during hypofractionated radiotherapy (HRT) and the clinical factors that correlate with ∆E. <h3>Materials/Methods</h3> 41 patients with primary or metastatic lung tumors underwent HRT. For each patient, planning was performed on 4D-CT imaging. Patients underwent daily pre- and post- treatment 4D-CBCT for setup conformation and motion assessment. Respiration-induced excursion (E) was quantified in the planning 4D-CT, and in each daily excursion 4D-CBCT. All excursion values were measured in 3 dimensions: AP, LR, and SI. ∆E was calculated as the difference between daily 4D-CBCT excursion values and the planning 4D-CT excursion value. The clinical statistics and excursion statistics were evaluated for all fractions. Finally, Pearson correlation was performed to associate clinical factors with ∆E. <h3>Results</h3> 377 4D-CBCTs were analyzed. ∆E was largest in the SI direction, with ∆E_avg in the SI, LR, and AP directions being 0.16, 0.05, and 0.08 cm respectively. Only 7.1% of all 4D-CBCT's displayed ∆E ≥ 4mm. The average age of patients with ∆E ≥ 4mm was 58.63 y/o, and that of patients with ∆E<4mm was 71.73 y/o (P<0.001). The average baseline weight of patients with ∆E ≥ 4mm and ∆E<4mm were 84.94 kg and 72.82 kg respectively (P<0.001). 71.1% of males and 28.9% of females gave ∆E ≥ 4mm (P=0.003). 58.3% of tumors with ∆E ≥ 4mm were in the right lower lobe (RLL) and 20.8% of tumors with ∆E ≥ 4mm were in the left lower lobe (LLL) (P<0.001). An average AP planning excursion of 0.34cm gave ∆E<4mm and that of 0.53 cm gave ∆E ≥ 4mm (P =0.008). The average Charlson Comorbidity Index (CCI) was 3.58 for tumors with ∆E<4mm, and 5.17 for tumors with ∆E ≥ 4mm (P=0.004). Pearson correlation between the left and right lungs didn't yield statistically significant results (P=0.76). <h3>Conclusion</h3> Large ∆E seems predictable, with ∆E ≥ 4mm seen more in young patients with higher baseline weight, male gender, tumors in the lower lobes, and with large 4D-CT excursion displayed in the AP direction. There was no correlation found between ∆E and right versus left lung. Additionally, CCI did not correlate with excursion variability. Finally, the largest degree of ∆E is displayed in the SI direction.

Surface Imaging-Guided Adaptive Radiotherapy (ART): Imaging Protocol and Verification for Inter- and Intra-Fractional Motion Managements

<h3>Purpose/Objective(s)</h3> CBCT-guided adaptive radiotherapy (CT-ART) has proven to account for inter-fractional anatomic changes. However, no commercial solution for intra-fractional respiratory motion management existed in CT-ART. Therefore, we investigated intra-fractional motion-managed treatment strategies in CT-ART (or Image-guided RT: IGRT) using optical surface imaging combined with <i>in-situ</i> CBCTs. <h3>Materials/Methods</h3> Eight of ten cancer patients with mobile lower lung or upper abdominal malignancies have completed CT-ART (or IGRT) using Ethos radiotherapy in an IRB-approved clinical trial (phase I). Four of the eight patients underwent additional MR simulations, including cine MRIs, to estimate the tumor/abdominal skin motion correlation. In CT-ART, a pre-configured gating window (±2 mm in vertical position) on surface imaging was used for manually triggering intra-fractional CBCT and treatment beam irradiation in breath-hold (six patients for exhalation and two patients for inhalation). A donut-shaped imaging-surrogate on patient's abdomen was used to localize Region of Interest (ROI) of the abdomen on CBCTs. Two inter-fractional CBCTs at exhalation and inhalation in each fraction were acquired to verify the tumor/imaging-surrogate motions range. Intra-fractional CBCTs were used to quantify the residual motion of the tumor/imaging-surrogate within the pre-configured gating window. Tumor motion was measured by tracking the position of a tumor centroid. <h3>Results</h3> The pre-configured gating window on surface imaging was confirmed based on the correlation of the tumor and abdominal skin motions using cine MRIs. Thirty-six pairs of inter-fractional CBCTs and 100 intra-fractional CBCTs from 36 fractions were analyzed (13 fractions for IGRT and 23 for ART). In the motion range study from the inter-fractional CBCTs, the values of mean ± std were 17.3 ± 12.0 mm in the SI direction for the tumors and 16.6 ± 7.9 mm in the AP direction for the imaging-surrogate, respectively. The residual motion of the imaging-surrogate from intra-fractional CBCTs was 2.5 ± 2.1 mm for SI, 2.3 ± 2.0 mm for RL, and 2.1 ± 2.3 mm for AP directions. The residual motion of the tumors was 2.4 ± 3.1 mm for SI, 2.3 ± 2.3 mm for RL, and 2.2 ± 2.0 mm for AP directions. Trends in the residual motion during the course of treatment fractions and over time through delivery were stable. Inter-fractional residual motions of the tumors were 2.3 ± 0.8 mm for SI, 2.3 ± 0.6 mm for RL, and 2.2 ± 0.7 mm for AP directions. Intra-fractional residual motions of the tumors were 2.4 ± 0.9 mm for SI, 2.4 ± 0.7 mm for RL, and 3.2 ± 1.3 mm for AP. <h3>Conclusion</h3> We demonstrated the inter- and intra-fractional motion-managed treatment strategies in CBCT-guided ART using surface imaging. Since the residual motion of the tumors was comparable to that of the imaging-surrogate within clinical PTV margins (5 mm) but a bit larger than the pre-configured gating window, additional caution is needed with intra-fractional motion management in CT-ART using the optical surface imaging.

On the Si content prediction for submerged arc welded metal via Calphad technique: a brief discussion

The slag-metal and gas-slag-metal equilibrium models have been employed via the Calphad technique to predict Si content in submerged arc welded metal. The investigated fluxes possess a wide range of basicity indices at full coverage with acidic, neutral, and basic fluxes. It is revealed that the gas-slag-metal equilibrium model offers better prediction accuracy for Si content than the slag-metal equilibrium model since the flux O potential is underestimated by the slag-metal equilibrium model. Especially, the gas-slag-metal equilibrium model is capable of predicting the transfer direction of Si between flux and weld metal, as well as Si content in submerged arc welded metal even when no SiO2 is contained in the initial flux. Additionally, the kinetic factors that influence the transfer behavior of Si have been evaluated to interpret the deviation between measured Si content and the value predicted from the equilibrium model. At last, we have proposed the limitations of the equilibrium models, as well as the models to be further developed with respect to improving the prediction accuracy.

Demonstration of quasi-real-time intrafractional motion in esophageal cancer radiotherapy provided by ExacTrac X-ray snap verification.

To investigate the following hypotheses: (1) ExacTrac X-ray Snap Verification (ET-SV) is an alternative to CBCT for positioning patients with esophageal carcinoma (EC), (2) ET-SV can detect displacement in EC patients during radiotherapy (RT) and (3) EC patients can be feasibly monitored in quasi-real-time with ET-SV during RT. Anthropomorphic phantoms and 13 patients were included in this study. CBCT and ET-SV were both implemented before treatment delivery to detect displacement, and their correction results were compared. For the patient tests, positional correction in 3 translational directions and the yaw direction were applied using the ET-SV correction results. The residual error was detected immediately using ET-SV. Finally, to acquire the intrafractional motion, ET-SV was implemented when the gantry was at 0°, 90°, 180° and 270°, respectively. In phantom tests, the maximum value of the difference in displacement between the CBCT and ET systems was 1.16 mm for translation and 0.31° for yaw. According to Bland-Altman analysis of the patient test results, 5% (5/98), 5% (5/98), 5% (5/98), and 4% (4/98) of points were beyond the upper and lower limits of agreement in the AP, SI, LR and yaw directions, respectively. The mean residual error was -0.482 mm, 1.215 mm, 1.0 mm, -0.487°, 0.105°, and 0.003° in the AP, SI, LR, pitch, roll and yaw directions, respectively. The intrafractional displacement ranged from -0.21 mm to 0 mm for translation and from -0.63° to 0.21° for rotation. The mean total translational error for intrafractional motion increased from 0.47 mm to 1.14 mm during the treatment. The accuracy of ET-SV for EC RT positional correction is comparable to that of CBCT. Thus, Quasi-real-time intrafractional monitoring can be used to detect EC patient displacement during radiotherapy.

Improvements and validation of particle channeling model in GEANT4

In this work several modifications to the default GEANT4 channeling model are provided and the results are validated against experimental data. The channeling model in GEANT4 10.3 version comes with physical process wrapper classes instead of cross section biasing operations which are used in the version 11.0. Initial simulations have shown that inaccurate energy losses of channeled particles are simulated with the original GEANT4 11.0 channeling model. In order to correct this, the cross section biasing operations were changed with the wrapper classes and the energy loss of channeled particles was compared to experimental results. The energy loss of protons and deuterons was evaluated and validated along the 〈100〉, 〈110〉 and 〈111〉 directions of Si, Ge and GaAs in the energy region 1–20 MeV. The difference between the simulated and the experimental stopping powers was less than 10 % in most cases. Higher deviations (up to ∼ 20 %) were observed in the low energy region, below 4 MeV. The overall good agreement with the experimental results shows that the modified model is able to accurately predict stopping powers in channeling conditions for protons and deuterons. Another modification to the model was the inclusion of the condition of critical channeling angle. The simulations have shown that the simulated critical angle is in good agreement with the theoretical one. Also, the comparison of different particle step size limitations during the simulations has shown that the channeling process is particularly sensitive to simulation conditions such as beam spread, sample rotation, lattice quality etc. The modified model is being further developed and the possibility of RBS/C spectra simulation is investigated.

The study of channeling parameters of protons along axial and planar directions of Si

In this work, the channeling parameters, the ratio of channeling to random stopping power, and the mean channeling distance, of protons along the 〈100〉, 〈110〉, {100} and {110} directions of Si were studied in terms of the atomic potential of channels. The channeling parameters were deduced using the simulation of the channeling Rutherford backscattering spectra based on the exponential dechanneling function. The best simulation parameters were set using the Levenberg- Marquardt algorithm. The RBS/C spectra were taken in energy interval 1400–2200 keV, using a Si wafer. Considering the deduced parameters along the 〈100〉, 〈110〉, {100} and {110} directions in terms of the atomic potential of channels and using the data along the 〈111〉 and {111} channels reported in the literature, the channeling behavior of protons along the 〈111〉 and {111} direction was explained concerning the shallow and deep potentials. Finally, the mean channeling distance along the {111} channel was estimated.