Margin Expansion Research Articles

Research on the impact of trade barriers on the binary marginal of enterprise exports: India's anti-dumping of China

ABSTRACT This paper derives a theoretical model of the impact of anti-dumping barriers on enterprise exports under the framework of heterogeneous firm trade theory and evaluates the trade-damaging effect of India's anti-dumping against China. The results show that the export volume and the number of export enterprises involved in anti-dumping cases show a downward trend after the anti-dumping is imposed. After controlling for heterogeneity, anti-dumping does not reduce the exports of incumbent enterprises. Anti-dumping mainly affects the exports of Chinese enterprises through the expansion margin, and has a small impact on the intensification margin. This research provides references for improving international trade development.

Oncological and Surgical Outcomes of Oncoplastic Reduction Mammoplasty: A Single-centre Retrospective Study.

Breast-conserving surgery is the preferred treatment for early-stage breast cancer but can often result in unsatisfactory cosmetic outcomes. Oncoplastic surgery aims to improve both oncologic and aesthetic outcomes by combining local excision with plastic surgery techniques. Using breast reduction techniques in breast cancer treatment has been shown to allow for wider margins of excision, leading to enhanced oncological safety and reduced recurrence rates without causing significant asymmetry. This study aimed to analyze the surgical and oncological outcomes of a large cohort of patients undergoing oncoplastic reduction mammoplasty (ORM). A retrospective analysis of postoperative surgical and oncological outcomes of all patients who underwent ORM at a single center between January 2018 and December 2023 was performed. Preoperative patient characteristics, operative and post-operative outcomes were recorded and analyzed. A total of 67 patients that underwent oncologic breast reduction were included in the final analysis - representing a total of 71 ORM, with a mean (SD) age of 53.1 (10.5) years and a mean (SD) BMI of 28.8 (5.9) kg/m2 A superomedial pedicle-based technique was the most frequently used (36.6%), followed by inferior pedicle-based technique (28.1%). A complication rate of 18.3% on the ipsilateral side was observed. Salvage surgery was necessary in five cases (7.0%) due to positive margins - with one patient (1.4%) requiring margin expansion surgery and four (5.6%) a completion mastectomy. This monocentric retrospective study shows that ORM is safe, with a complication rate on par with conventional breast reduction and offers satisfactory oncological outcomes.

Dynamics of Daily Glioblastoma Evolution During Chemoradiation Therapy on the 0.35T Magnetic Resonance Imaging-Linear Accelerator

Glioblastoma changes during chemoradiation therapy are inferred from magnetic resonance imaging (MRI) before and after treatment but are rarely investigated due to logistics of frequent MRI. Using a combination MRI-linear accelerator (MRI-linac), we evaluated changes during daily chemoradiation therapy. Patients with glioblastoma were prospectively imaged daily during chemoradiation therapy on 0.35T MRI-linac and at 3 timepoints with and without contrast on standalone high-field MRI. Tumor or edema (lesion) and resection cavity dynamics throughout treatment were analyzed and compared with standalone T1 postcontrast (T1+C) and T2 volumes. Of 36 patients included in this analysis, 8 had cavity only, 12 had lesion only, and 16 had both cavity and lesion. Of these, 64% had lesion growth and 46% had cavity shrinkage during treatment on MRI-linac scans. The average MRI-linac migration distance was 1.3 cm (range, 0-4.1 cm) for lesion and 0.6 cm (range, 0.1-2.1 cm) for cavity. Standalone versus MRI-linac volumes correlated strongly with R2 values: 0.991 (T2 vs MRI-linac cavity), 0.972 (T1+C vs MRI-linac cavity), and 0.973 (T2 vs MRI-linac lesion). There was a moderate correlation between T1+C and MRI-linac lesion (R2 = 0.609), despite noncontrast MRI-linac inability to separate contrast enhancement from surrounding nonenhancing tumor and edema. From pretreatment to posttreatment in patients with all available scans (n = 35), T1+C and MRI-linac lesions changed together-shrank (n = 6), grew (n = 12), or unchanged (n = 8)-in 26 (74%) patients. Another 9 patients (26%) had growth on MRI-linac, although the T1+C component shrank. In no patient did T1+C lesion grow while MRI-linac lesion shrank. Anatomic changes are seen in patients with glioblastoma imaged daily on MRI-linac throughout the chemoradiation therapy course. As surgical resection cavities shrink, margins may be reduced to save normal brain. Patients with unresected or growing lesions may require margin expansions to cover changes. Limited volume glioblastoma boost trials could consider triggered gadolinium contrast administration for evaluation of adaptive radiation therapy when lesion growth is seen on noncontrast MRI-linac.

Surgically targeted radiation therapy versus stereotactic radiation therapy: A dosimetric comparison for brain metastasis resection cavities

BackgroundSurgically targeted radiation therapy (STaRT) with Cesium-131 seeds embedded in a collagen tile is a promising treatment for recurrent brain metastasis. In this study, the biological effective doses (BED) for normal and target tissues from STaRT plans were compared with those of external beam radiotherapy (EBRT) modalities. MethodsNine patients (n=9) with 12 resection cavities (RCs) who underwent STaRT (cumulative physical dose of 60 Gy to a depth of 5 mm from the RC edge) were replanned with CyberKnife® (CK), Gamma Knife® (GK), and intensity modulated proton therapy (IMPT) using an SRT approach (30 Gy in 5 fractions). Statistical significance comparing D95% and D90% in BED10Gy (BED10Gy95% and BED10Gy90%) and to RC + 0 to + 5 mm expansion margins, and parameters associated with radiation necrosis risk (V83Gy, V103Gy, V123Gy and V243Gy) to the normal brain were evaluated by a Wilcoxon-signed rank test. ResultsFor RC+0 mm, median BED10Gy90% for STaRT (90.1 Gy10, range: 64.1-140.9 Gy10) was significantly higher than CK (74.3 Gy10, range:59.3-80.4 Gy10, p=0.04), GK (69.4 Gy10, range: 59.8-77.1 Gy10, p=0.005), and IMPT (49.3 Gy10, range: 49.0-49.7 Gy10, p=0.003), respectively. However, for the RC+5 mm, the median BED10Gy90% for STaRT (34.1 Gy10, range: 22.2-59.7 Gy10) was significantly lower than CK (44.3 Gy10, range: 37.8-52.4 Gy10), and IMPT (46.6 Gy10, range: 45.1-48.5 Gy10), respectively but not significantly different from GK (34.1 Gy10, range: 22.8-47.0 Gy10). The median V243Gy was significantly higher in CK (11.7 cc, range: 4.7-20.1 cc), GK(6.2 cc, range: 2.3-11.9 cc) and IMPT (19.9 cc, range: 11.1-36.6 cc) compared to STaRT (1.1 cc, range: 0.0-7.8 cc) (p<0.01). ConclusionThis comparative analysis suggests the STaRT approach may treat recurrent brain tumors effectively via delivery of higher radiation doses with equivalent or greater BED up to at least 3 mm from the RC edge as compared to EBRT approaches.

AkzoNobel delivers continued volume growth and margin expansion

AkzoNobel delivers continued volume growth and margin expansion

Digital economy and China's agricultural exports: based on trade cost and market competition effect

PurposeThe purpose of this study is to explore the effect and mechanism of the digital economy’s influence on the binary margin of agricultural exports.Design/methodology/approachBased on the theoretical analysis of the mechanism of the digital economy’s influence on the binary margin of agricultural exports, this study empirically examines the effect and mechanism of the digital economy’s influence on the binary margin of agricultural exports based on China’s customs export data from 2011 to 2016.FindingsThe relevant findings are threefold. (1) The digital economy significantly improves the binary margin of agricultural exports, and its effect on the intensive margin is stronger than that on the expansive margin. After the expansive margin is subdivided, the effects on the three sub-variables of the expansive margin are in the following order: old products exported to new markets > new products exported to old markets > new products exported to new markets. (2) The heterogeneity analysis reveals that the digital economy has a stronger role in promoting the binary margin of exports for enterprises in the eastern region, high-income countries as the destination of exports and state-owned enterprises. (3) Mechanism analysis shows that the digital economy promotes the binary margin of agricultural exports by reducing trade costs and intensifying market competition.Originality/valueFirst, in terms of research perspective, although there are some studies on the impact of the digital economy on export trade in existing literature, the research objects mainly focus on manufacturing enterprises. In fact, agricultural trade is susceptible to natural conditions and seasonal factors, and countries may impose more SPS measures and TBT measures on agricultural trade due to risk considerations. The relationship between the digital economy and agricultural trade also has its own characteristics, but there are few research studies in this area. At present, only Liu and Gao (2022), based on the data of total imports and exports of different agricultural products from 2004 to 2018, have established a vector auto-regressive model to empirically analyse the heterogeneous dynamic impact of the digital economy on the trade volume of agricultural products. In addition, Ma and Guo (2023) conducted an empirical test on the total effect, regional heterogeneity and threshold effect of the digital economy on agricultural export trade based on China’s provincial panel data from 2011 to 2020. Therefore, under the new circumstances of continuous integration of digital technology and agriculture, this study interprets the impact effect and mechanism of the digital economy on the binary margin of agricultural exports from the perspective of the digital economy, providing new research perspectives and approaches for promoting the growth of agricultural exports. Second, in terms of theoretical analysis, the above studies have not been fully analysed in terms of the specific mechanism of the impact of the digital economy on agricultural exports. Based on the positive and negative characteristics of agricultural trade, this study introduces two kinds of roles into the theoretical analysis framework to comprehensively determine the trade impact effect of the digital economy. Third, in terms of research design, this study empirically examines the impact of the digital economy on the binary margin of agricultural products, passing a series of robustness tests and investigating the mediating roles of trade cost and market competition effects, producing an empirical basis for China to leverage the digital economy to promote the binary margin of agricultural exports.

A Small Power Margin and Bandwidth Expansion Allow Data Transmission during Rainfall despite Large Attenuation: Application to GeoSurf Satellite Constellations at mm–Waves

The traditional approach of considering the probability distribution of rain attenuation leads to provide very large power margin (overdesign) in data channels. We have extended a method which, with a small power margin, bandwidth expansion and variable symbol rate, avoids overdesign and can transfer the same data volume as if the link were in clear–sky conditions. It is characterized only by the link mean efficiency, suitably defined. It is useful only if: (a) data must be up– and downloaded when it is raining; (b) real–time communication is not required. We have applied it to the links of GeoSurf satellite constellations (in which, at any latitude of ground stations, propagation paths are at the local zenith) by simulating rain attenuation time series at 80 GHz (mm–wave)–the new frontier of satellite frequencies–with the Synthetic Storm Technique, from rain–rate time series recorded on–site, at sites located in different climatic regions. The power margin to be implemented at 80 GHz ranges from 2.0 dB to 7.4 dB–well within the current technology–regardless the instantaneous rain attenuation. The clear–sky bandwidth is expanded 1.75 to 2.80 times, a factor not large per se, but it may challenge current technology if the clear–sky bandwidth is already large.

Evaluating AI-generated CBCT-based synthetic CT images for target delineation in palliative treatments of pelvic bone metastasis at conventional C-arm linacs

PurposeOne-table treatments with treatment imaging, preparation and delivery occurring at one treatment couch, could increase patients’ comfort and throughput for palliative treatments. On regular C-arm linacs, however, cone-beam CT (CBCT) imaging quality is currently insufficient. Therefore, our goal was to assess the suitability of AI-generated CBCT based synthetic CT (sCT) images for target delineation and treatment planning for palliative radiotherapy. Materials and methodsCBCTs and planning CT-scans of 22 female patients with pelvic bone metastasis were included. For each CBCT, a corresponding sCT image was generated by a deep learning model in ADMIRE 3.38.0. Radiation oncologists delineated 23 target volumes (TV) on the sCTs (TVsCT) and scored their delineation confidence. The delineations were transferred to planning CTs and manually adjusted if needed to yield gold standard target volumes (TVclin). TVsCT were geometrically compared to TVclin using Dice coefficient (DC) and Hausdorff Distance (HD). The dosimetric impact of TVsCT inaccuracies was evaluated for VMAT plans with different PTV margins. ResultsRadiation oncologists scored the sCT quality as sufficient for 13/23 TVsCT (median: DC = 0.9, HD = 11 mm) and insufficient for 10/23 TVsCT (median: DC = 0.7, HD = 34 mm). For the sufficient category, remaining inaccuracies could be compensated by +1 to +4 mm additional margin to achieve coverage of V95% > 95% and V95% > 98%, respectively in 12/13 TVsCT. ConclusionThe evaluated sCT quality allowed for accurate delineation for most targets. sCTs with insufficient quality could be identified accurately upfront. A moderate PTV margin expansion could address remaining delineation inaccuracies. Therefore, these findings support further exploration of CBCT based one-table treatments on C-arm linacs.

The influence of anisotropy on the clinical target volume of brain tumor patients

Objective. Current radiotherapy guidelines for glioma target volume definition recommend a uniform margin expansion from the gross tumor volume (GTV) to the clinical target volume (CTV), assuming uniform infiltration in the invaded brain tissue. However, glioma cells migrate preferentially along white matter tracts, suggesting that white matter directionality should be considered in an anisotropic CTV expansion. We investigate two models of anisotropic CTV expansion and evaluate their clinical feasibility. Approach. To incorporate white matter directionality into the CTV, a diffusion tensor imaging (DTI) atlas is used. The DTI atlas consists of water diffusion tensors that are first spatially transformed into local tumor resistance tensors, also known as metric tensors, and secondly fed to a CTV expansion algorithm to generate anisotropic CTVs. Two models of spatial transformation are considered in the first step. The first model assumes that tumor cells experience reduced resistance parallel to the white matter fibers. The second model assumes that the anisotropy of tumor cell resistance is proportional to the anisotropy observed in DTI, with an ‘anisotropy weighting parameter’ controlling the proportionality. The models are evaluated in a cohort of ten brain tumor patients. Main results. To evaluate the sensitivity of the model, a library of model-generated CTVs was computed by varying the resistance and anisotropy parameters. Our results indicate that the resistance coefficient had the most significant effect on the global shape of the CTV expansion by redistributing the target volume from potentially less involved gray matter to white matter tissue. In addition, the anisotropy weighting parameter proved useful in locally increasing CTV expansion in regions characterized by strong tissue directionality, such as near the corpus callosum. Significance. By incorporating anisotropy into the CTV expansion, this study is a step toward an interactive CTV definition that can assist physicians in incorporating neuroanatomy into a clinically optimized CTV.

RADT-32. USING NEUROANATOMICAL SUBSITE TO PREDICT PATTERNS OF GLIOBLASTOMA INFILTRATION: POTENTIAL FOR INDIVIDUALISING RADIATION THERAPY TARGET VOLUME DELINEATION OF THE PARIETAL AND POSTERIOR FRONTAL REGIONS

Abstract BACKGROUND Radiation therapy(IMRT) protocols for glioblastoma utilize isotropic margin expansion around neurosurgical cavities/residual contrast enhancing(T1gd) disease. However pathways of infiltration may be associated with white matter tract(WMT) involvement varying between neuroanatomical subsites. Posterior frontoparietal tumours involving posterior cingulate region (PostCing) may have extensive infiltration centrally. This study aims to quantify the PostCing infiltration pathway/relapse sites. METHODS Consecutive patients managed for GBMwt with IMRT between 1/2016-6/2022 were classified into 15 neuroanatomical subsites. Tumour segmentation on T1-gadolinium-enhanced(T1gd) and T2-weighted(T2) sequences was performed at diagnosis/relapse. Subsites of Frontal Lobe (Posterior) and Parietal Lobe (Superior/Posterior/Lateral) were identified. On both sequences involvement of adjacent/distant regions (cingulate gyrus, cingulum, splenium, ventricular trigone, parahippocampal-hippocampal gyrus) were identified; as were major WMT: cingulum-parahippocampal formation(CING-PHG), and arcuate fasciculus–inferior longitudinal fasciculus(AF-ILF). Survival was analysed in relation to pattern of infiltration and site of relapse. RESULTS Of 348 patients with glioblastoma, fifty-five(16%) involved PostCing region. Pre-IMRT features included near-total resection in 25%; impaired ECOG 2-3 in 47%; and 58% MGMT-methylated. Parietal lobe tumours(67%) were predominantly posterior(42%) with only 7% lateral parietal. WMT involvement was evident in 94% with T1gd(62%), and T2 alone(33%) abnormality. Infiltration to distal sites of cingulum/splenium/PHG was frequent and predictable; correlating to cingulum pathway involvement in 70% of patients. Median RFS and OS was 13.2 months(95%CI: 11.8-14.8) and 16.6 months(95%CI:14.8-18.5) respectively. Distant relapse was evident in 53% of relapses. In the forty-four Stupp60Gy patients, distant relapse occurred later and was associated with improved overall survival(p = 0.02). No difference in RFS(p = 0.82) or OS(p = 0.31) was noted if tract involvement was either T1gd or T2 alone abnormality. CONCLUSION For glioblastoma in posterior cingulate region, the infiltration and relapse pathways followed white matter tracts in a predictable distribution with high rate of distant disease at diagnosis and relapse. IMRT potentially may be individualised for neuroanatomical subsite and non-isotropic target volume expansion.

Toward an improved assessment of dose conformity in radiotherapy.

Evaluation of dose conformity is important to ensure minimum dose to normal tissue and sufficient dose coverage of the planning target volume (PTV). The existing conformity indices depend on the PTV volume and do not differentiate between two different scenarios: overdosing normal tissue and underdosing PTV. In this study, we introduce a novel index to assess conformity of dose distributions in radiotherapy. The suggested conformity index is defined by the ratio of the volume representing actual "non-conformity" of the planned dose and the volume representing acceptable "non-conformity." The latter volume is produced by expanding the PTV. If both the average distance ( ) between the reference isodose surface and planning target volume and arbitrarily selected PTV expansion margin ( ) are much smaller than the size of the PTV, approximately equals the ratio . In this work, was utilized to analyze 90 cases of brain metastases treated with stereotactic radiation therapy (SRS) and 102 cases of lung cancer treated with stereotactic body radiation therapy (SBRT). For =0.1cm, all considered SRS treatment plans were characterized by while 2 out of 102 SBRT plans had . The average values of for SRS and SBRT plans were 0.31 and 0.43, respectively. For =0.2cm, all studied treatment plans had , and the average values of for SRS and SBRT plans were 0.15 and 0.25, respectively. The suggested conformity index varies less with PTV volume than the RTOG and Riet-Paddick indices frequently used for evaluation of dose conformity. In addition, can be expressed as a sum of two terms which describe "over-coverage" and "under-coverage" of the treatment target. The results confirm that can be used for evaluation of dose conformity in SRS and SBRT.

Oncoplastic Breast Reduction: A Systematic Review of Postoperative Complications.

Breast-conserving therapy with oncoplastic reduction is a useful strategy for partial mastectomy defect reconstruction. The most recently published systematic review of oncoplastic breast reduction outcomes from 2015 showed wound dehiscence in 4.3%, hematoma in 0.9%, infection in 2.8%, and nipple necrosis in 0.9% of patients. We performed a systematic review of oncoplastic breast reduction literature, comparing outcomes and complication rates reported over the past 8 years. Studies describing the use of oncoplastic breast reduction and discussion of postoperative complications were included. The primary outcome assessed was the postoperative complication rate; secondary outcomes analyzed were rates of margin expansion, completion mastectomy, and delays in adjuvant therapy due to complications. Nine articles met inclusion criteria, resulting in 1715 oncoplastic breast reduction patients. The mean rate of hematoma was 3%, nipple necrosis was 2%, dehiscence was 4%, infection was 3%, and seroma was 2%. The need for re-excision of margins occurred in 8% of patients, and completion mastectomy in 2%. Finally, delay in adjuvant treatment due to a postoperative complication occurred in 4% of patients. Oncoplastic breast reduction is an excellent option for many patients undergoing breast-conserving therapy; however, postoperative complications can delay adjuvant radiation therapy. Results of this systematic literature review over the past 8 years showed a slight increase in complication rate compared to the most recent systematic review from 2015. With increased popularity and surgeon familiarity, oncoplastic breast reduction remains a viable option for reconstruction of partial mastectomy defects despite a slight increase in complication rate.

Dynamic Fluctuation Measurement and Factor Decomposition of China’s Export Growth to Japan and South Korea in the Context of COVID-19

In the context of the COVID-19, it is very significant to explore the dynamic fluctuation of China’s export growth to the international market and examine the causes of this fluctuation in a multi-dimensional way. The dynamic fluctuation level is measured in the short and medium-long cycle respectively based on monthly data. Factor decomposition of the dynamic fluctuation is made from the growth effect, the structure effect and the competitiveness effect by the improved CMS model, which results show that the growth effect has decreased first and then increased; The structure effects include market structure effects and commodity structure effects, and the former effect basically fluctuates around the X-axis while there is a negative commodity structure effect; There are different specific competitiveness effects on 21 categories of goods. China should rely on the RCEP agreement to strengthen and stabilize trade cooperation other countries, and strengthen its core position in the industry chain and value chain in the Asia Pacific region. The current paper creatively introduce the trade expansion margin including the ternary margin and product structure into the CMS model, explaining the internal relationship between the trade expansion margin analysis at the product- market level and the CMS analysis at the overall level; meanwhile, this paper analyses the dynamic fluctuation structure of China’s export growth to Japan and South Korea through a CMS factor decomposition from the perspective of technological structure and factor ladder, and studies the source and dynamic distribution evolution of this growth pattern.

A Comprehensive Deep Learning Framework for Automatic Target Volumes Segmentation in Post-Operative Stereotactic Partial Breast Irradiation (S-PBI)

In S-PBI, accurate delineation of post-surgical tumor bed volume (TBV) and clinical target volume (CTV) are crucial tasks to achieve effective radiotherapy outcomes. However, manual contouring is labor intensive, time consuming, and largely relies on the experience of clinicians. We aimed to propose a deep learning (DL) approach which mimics physicians' contouring practice to accurately segment target volumes in post-operative breast CT images. Our approach incorporated domain knowledge into a 3D U-Net based DL model for breast target volumes (TBV and CTV) delineation. Our TBV segmentation approach was inspired by the marker-guidance procedure in manual delineation, where the visual clues provided by the markers assist physicians in defining TBV. For this purpose, a distance-transformation coupled with a Gaussian filter was adopted to convert markers' locations on the CT images to saliency maps. Subsequently, the CT images and the corresponding saliency maps formed a two-channel input for the segmentation model. For CTV segmentation, TBV was incorporated as an input in addition to the CT images, guiding the model to encode the location-related image features. The architecture allowed the network to emulate the oncologist's manual delineation where CTV is derived from TBV via a margin expansion, followed by correcting the extensions for anatomical barriers of tumor invasion (e.g., skin, chest wall). We retrospectively collected 175 prone CT images from 35 post-operative breast cancer patients who received 5-fraction partial breast irradiation (PBI) regimen on a Co-60 prone based S-PBI unit. The 35 patients were randomly split into 25, 5, and 5 for model training, validation, and testing respectively. We evaluated the performance of the developed DL model on the testing dataset by comparing the predicted volumes with the manually delineated contours (ground truth) using Dice similarity coefficient (DSC), 95th percentile Hausdorff distance (HD95), and average symmetric surface distance (ASD). For TBV segmentation, our model achieved mean (standard deviation) of 0.76 (±2.7), 6.76 (±1.83) mm, and 1.9 (±0.66) mm for DSC, HD95, and ASD respectively. For CTV segmentation, our model achieved 0.94 (±0.02), 2.46 (±0.5) mm, and 0.53 (±0.14) mm for DSC, HD95, and ASD respectively. The proposed auto-segmentation approach generated TBV and CTV masks in ∼11 seconds per CT volume, implying significantly improved efficiency compared to manual contouring. We developed a comprehensive DL framework mimicking clinical contouring practice for auto-segmentation of target volumes in S-PBI. The results demonstrated high levels of agreement between the predicted contours and physicians' manual contours. The approach is promising for improving the efficiency and accuracy of the on-line treatment planning workflow, such as adaptive based S-PBI.

Influence of Eyes Movement on Lens Dose during MR-Guided Radiotherapy for Brain Tumor

Modern radiotherapy techniques achieve highly conformal target doses while avoiding organs at risk such as lens. The magnitude of eyes movement and its influence on lens dose is unclear. The lens dose is relevant for cataract formation. This study aims to evaluate the movement-range of lens and its influence on dose distribution during MR-guided radiotherapy for brain cancer patients. Fifty patients with brain cancer who were treated with MR-guided radiotherapy on 1.5 T MR-Linac were included in this study. All patients underwent a pre-treatment MRI and post-treatment MRI for each fraction. The eyes and lens were delineated on each MR image by a radiation oncologist. The reference treatment plans based original CT were recalculated on each MRI by "adapt to position" workflow. Then, we created planning risk volume (PRV) for lens by adding population margin and reoptimized the reference plans to evaluate the dose changes for lens. Inter-fraction and intrafraction variability for eyes and lens were evaluated with the Dice similarity coefficient (DSC), the Hausdorff distance (HD) and mean distance to agreement (MDA). Differences in daily dose (Dmax and Dmean) for eyes and lens were assessed. A total of 300 MR images were analyzed in this study. The eyes motion was observed (minimum DSC: 0.57; maximum HD: 10.53; maximum MDA: 3.13). And the obvious lens motion also was found (minimum DSC: 0.01; maximum HD: 10.78; maximum MDA: 5.68). The maximum dose changes for eyes were up to 34.1% and the mean dose changes were up to 18.1%. The maximum dose changes for lens were up to 97.9% and the mean dose changes for eyes were up to 89%. When the reoptimized plans were generated by PRV lens, the dose changes were decreased nearly to 0. Eyes movements in all radiotherapy fractions result in higher lens doses and potentially increase cataract formation rate. Adding margin expansions in treatment planning, to account for eyes motion, is the feasible approach to limit lens dose.

Planning Target Volume Margin Quantification of Retroperitoneal Tumors Using Robotic Stereotactic Body Radiotherapy with Spine Tracking

Stereotactic body radiotherapy treatment (SBRT) is an effective modality for treating primary and oligometastatic malignant lesions. Appropriate planning target volume (PTV) margins are essential when delivering SBRT to maximize target prescription coverage while minimizing dose to surrounding organs-at-risk. Spine tracking uses boney spinal anatomy as a surrogate for tumor localization during treatment delivery on robotic linear accelerator platforms that employ intrafraction kV x-ray imaging. The aim of this study was to quantify the PTV margin needed when spine tracking was used for tumor localization when treating retroperitoneal metastatic lesions with robotic SBRT. A single institution chart review was performed and identified 16 patients with retroperitoneal tumors treated stereotactically over 19 courses in 103 fractions. Daily cone-beam computed tomography (CBCT) images that were registered based on tumor position at the time of treatment were analyzed. Rigid registrations were re-performed aligning the position of the spine on the CBCT relative to its position on the planning CT. Shifts from the treatment position were recorded and per-patient mean shifts and standard deviations were calculated. Van Herk's margin recipe was used to determine the additional PTV margin required if spine tracking was used instead of soft tissue alignment. Patient tumors were stratified and compared based on proximity to the vertebral column (≤1 cm vs >1 cm) and location within the retroperitoneum (superior vs inferior to the renal artery). Student's t-test was used to compare statistical differences of shifts based on location. The additional margins calculated by van Herk's margin recipe to adequately cover the target volumes within the 95% isodose surface for 90% of the entire patient cohort in the vertical, longitudinal, and lateral directions were 2.7, 2.8, and 2.8 mm, respectively. When tumors were stratified by proximity to the vertebral column, average longitudinal (p<0.001) and total shifts (p<0.001) were statistically significant. Isometric PTV expansions of 3, 4, and 5 mm would have encompassed 55%, 76%, and 86% of the maximum total shifts for lesions >1 cm from the vertebral column versus 94%, 100%, and 100% for lesions ≤1 cm. When stratified by location within the retroperitoneum, isometric PTV expansions of 3, 4, and 5 mm would have encompassed 82%, 94%, and 100% of the maximum total shifts for lesions superior to the renal artery versus 78%, 94%, and 98% for lesions inferior to the renal artery. When treating retroperitoneal tumors with robotic SBRT, a minimum isometric margin expansion between 3 to 5 mm when creating the PTV is recommended if spine tracking is used for intrafraction tumor localization. Target volumes adjacent to the vertebral column may have PTV margins decreased to ≤4 mm without compromising target coverage.

Heatmaps to Assess Tumor Motion Probability with MRcine in Head and Neck Cancer

Intrafraction motion affects tumor position during radiation for head and neck cancers (HNC) and can be assessed using magnetic resonance cine (MR-cine). Heatmaps - visual representation of patient specific temporal tumor location akin to internal target volume (ITV) - were analyzed to demonstrate the variation of population-based motion margins in primary oropharyngeal (OP) and laryngeal/hypopharyngeal (LH) sites with the goal to provide insights towards personalized margins. MR-cine were performed for LH and OP HNC patients as part of simulation protocol. Images (900-1500 slices) were acquired across 3-5 minutes per patient. Gross target volumes were propagated on T1 contrast sagittal sequence using deformable image registration then adjusted manually. Tumor locations were integrated across all frames and displayed as heatmaps representing location probability. To determine individualized motion, a baseline contour representing average tumor rest position was expanded both isotropically and directionally in 1 mm increments in a novel analysis to define the contribution of each increment on target coverage. To assess directional dependence, displacements from rest position were evaluated in 4 planes from centroid: (A) 12 o'clock (OC) to 6OC (capturing volumetric shift in a portion of superior, posterior and inferior directions), B) 3OC-9OC, C) 6OC-12OC, D) 9OC-3OC. Histograms demonstrating the proportion of scan time the tumor was within expansions were generated, with expansion margins for 25%-95% coverage analyzed by patient. Wilcoxon-rank-sum test was performed to compare motion by site. Motion was evaluated in 66 patients (LH n = 27, OP n = 39). In LH, a median (med) isometric expansion of 8.5mm to achieve 95% target was required, with large variations observed for minimum (min): 2.8mm and maximum (max):23.5mm. Smaller differences were observed for OP with med of 5.3mm, (min:1.9mm, max:14.6mm). At 75%, 50% and 25% coverage, expansions for LH (med: 4.8 min: 1.9 max: 17.3; med: 3.8 min: 1.2 max: 12.9; med: 3.3, min: 0.6, max: 9.3) were not significantly different than OP (med: 3.8, min: 1.7, max: 10.9; med: 3.1 min: 1.3, max: 9.4; med: 2.1, min: 0.7, max: 8.4), suggesting larger but infrequent shifts in LH. Directional tumor displacement varied widely (Table 1), and by site and points describing the need for personalized margins. Current literature as well as the analysis in this study indicate a wide range of motion - both in magnitude and duty cycle - between and within HN sub-sites not captured on CT simulation. Moving forward, motion based heatmaps based on MR-cine may serve as visualization tool for ITV contouring or to generate personalized motion margins.

Set-up errors of the neck are underestimated using the overall registration frame of head and neck in IMRT for NPC.

There is no standardized registration frame of cone beam CT (CBCT) in intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). The overall registration frame that covers the whole head and neck is the most commonly used CBCT registration frame for NPC patients in IMRT. To compare the set-up errors using different registration frames of CBCT for NPC to assess the set-up errors for different region of the commonly used clinical overall registration frame. 294 CBCT images of 59 NPC patients were collected. Four registration frames were used for matching. The set-up errors were obtained using an automatic matching algorithm and then compared. The expansion margin from the clinical target volume (CTV) to the planned target volume (PTV) in the four groups was also calculated. The average range of the isocenter translation and rotation errors of four registration frames are 0.89∼2.41 mm and 0.49∼1.53°, respectively, which results in a significant difference in the set-up errors (p < 0.05). The set-up errors obtained from the overall frame are smaller than those obtained from the head, upper neck, and lower neck frames. The margin ranges of the overall, head, upper neck, and lower neck frames in three translation directions are 1.49∼2.39 mm, 1.92∼2.45 mm, 1.86∼3.54 mm and 3.02∼4.78 mm, respectively. The expansion margins calculated from the overall frame are not enough, especially for the lower neck. Set-up errors of the neck are underestimated by the overall registration frame. Thus, it is important to improve the position immobilization of the neck, especially the lower neck. The margin of the target volume of the head and neck region should be expanded separately if circumstances permit.

Evaluating the geometric and dosimetric impact of applying anisotropic CTV to PTV margins in image-guided post-prostatectomy radiation therapy.

Guidelines for clinical target volume (CTV) to planning target volume (PTV) margins in post-prostatectomy radiation therapy (PPRT) are varied and often not clearly defined. Assessment of appropriateness of margins is commonly measured on prevalence of geographic miss. Cone-beam CT (CBCT) images (n = 92) for 10 PPRT patients were incorporated to provide on-treatment information on the appropriateness of six different CTV expansion margins in terms of geographic miss and change in dose-volume statistics for CTV, rectum and bladder. Uniform margins included 10 mm, 5 mm, 10 mm + 5 mm posteriorly and 5 mm + 3 mm posteriorly. In addition, two anisotropic margins were evaluated by separating the superior and inferior portions of the CTV before expansion. Treatment plans were created for each PTV retrospectively. The frequency of geographic miss was the smallest for the large uniform expansions but resulted in the highest organ-at-risk (OAR) doses. Geographic miss in the smaller uniform and anisotropic PTVs was more prevalent but commonly to a small volume < 1% of CTV. When averaged over all CBCT fractions, V95% dose for all CTV margins remained > 99%. The anisotropic expansions generated smaller irradiated target volumes and consequently saw up to 7.3% reduction in bladder dose when compared with similar uniform expansion margins. Supplementing the incidence of geographic miss with dosimetric information on target coverage and OAR doses provides more informed assessment of the appropriateness of different CTV expansion margins. Our study extends the evaluation of anisotropic margins for PPRT.

Evaluation of Interfraction Setup Uncertainty of Patients With Glioblastoma Wearing TTFields (Tumor Treating Fields) During Radiation Therapy

Tumor treating fields (TTFields) with concurrent radiation therapy (RT) might improve the outcome of patients with newly diagnosed glioblastoma. Several trials, including that conducted in our center, have allowed patients to wear TTFields during RT. We aimed to evaluate the setup uncertainty introduced by TTFields and calculate the planning target volume (PTV) margin for clinical reference. We collected and analyzed 201 cone beam computed tomography images of 22 patients in our center. Patients with or without TTFields were divided into the control and TTFields groups. We evaluated the setup errors in 6 degrees of freedom and 3 degrees of freedom and the magnitudes in the 3-dimensional vectors. An estimated PTV margin for patients requiring nonimaging-guided RT was recommended. A significant difference was observed in the longitudinal axis between the TTFields and control groups (P < .05). These results were consistent with that of the intragroup comparison of the TTFields group. The position error of the longitudinal axis (from head to feet) was -0.51 ± 2.05 mm in the TTFields group. Wearing TTFields during RT increased the uncertainty, especially in the longitudinal axis, with a system error of 1.40 mm and a random error of 1.28 mm. Daily image guided RT for TTFields patients seems necessary. However, the recommended expansion margin of the PTV is 5 mm for patients requiring nonimage-guided RT to enhance the safety and efficacy of treatment.