Evaluation of a software for automatic delineation of the mammary gland and organs at risk in patients treated for breast cancer in lateral position

Purpose of the studyThe purpose of this study was to assess the potential for improvement of routine breast and organs at risk contouring in patients treated in the lateral decubitus position using Workflow Box™ (Mirada Medical™, UK) automatic contouring software.Materials and methodsAutomatic contouring of the breast by this software is currently based on an atlas created from isodoses representing 95% of the prescribed dose in a population of patients previously treated at institut Curie. Forty cases of breast cancer (20 right breasts and 20 left breasts) were contoured by three radiation oncologists specialized in breast cancer, allowing the creation of a new atlas in the automatic contouring software. This study assessed the quality of contouring in 20 patients (ten right breasts and ten left breasts) by comparing manual contouring performed by the expert radiation oncologists (reference) with those generated by the old and new atlases developed at Institut Curie. The accuracy of contouring was assessed by overlap volume and the associated standard deviations.ResultsBreast contouring based on the new atlas and by radiation oncologists presented a mean overlap of 0.80 ± 0.09 for the right breast and 0.81 ± 0.06 for the left breast. By comparing volumes of interest contoured by radiation oncologists and those obtained from the old atlas, mean overlap volumes were 0.75 ± 0.08 and 0.74 ± 0.13 for the right and left breasts, respectively. Twenty cases (ten right breasts and ten left breasts) used to create the new atlas were also reprocessed by this same atlas in order to assess the quality of automatic contouring of the breast when the case was already known to the software. The mean overlap volume in this case was 0.84 ± 0.08 for the right breast and 0.83 ± 0.06 for the left breast. Finally, after automatic contouring of organs at risk by means of the new atlas, the mean overlap volume was 0.87 ± 0.04 for the heart and 0.93 for each lung (±0.05 for the right lung and ± 0.04 for the left lung).ConclusionWorkflow Box™ automatic contouring software, based on our new atlas provides reliable and clinically relevant organs at risk and breast contouring. The contours proposed by the software from the new atlas were better than those obtained with the previous atlas based on 95% isodoses obtained from old treatment plans. This software has therefore become more efficient, justifying its use in routine clinical practice for breast cancer contouring in patients treated in the lateral decubitus position. Investigations are currently underway to develop a fully automated process to ensure reliable, robust and operator-independent contouring and breast cancer treatment dosimetry in the lateral decubitus position. Promising preliminary results have already been obtained.     

Consensus on Contouring Primary Breast Tumors on MRI in the Setting of Neoadjuvant Partial Breast Irradiation in Trials

PurposeOur purpose was to present and evaluate expert consensus on contouring primary breast tumors on magnetic resonance imaging (MRI) in the setting of neoadjuvant partial breast irradiation in trials.Methods and MaterialsExpert consensus on contouring guidelines for target definition of primary breast tumors on contrast-enhanced MRI in trials was developed by an international team of experienced breast radiation oncologists and a dedicated breast radiologist during 3 meetings. At the first meeting, draft guidelines were developed through discussing and contouring 2 cases. At the second meeting 6 breast radiation oncologists delineated gross tumor volume (GTV) in 10 patients with early-stage breast cancer (cT1N0) according to draft guidelines. GTV was expanded isotropically (20 mm) to generate clinical target volume (CTV), excluding skin and chest wall. Delineations were reviewed for disagreement and guidelines were clarified accordingly. At the third meeting 5 radiation oncologists redelineated 6 cases using consensus-based guidelines. Interobserver variation of GTV and CTV was assessed using generalized conformity index (CI). CI was calculated as the sum of volumes each pair of observers agreed upon, divided by the sum of encompassing volumes for each pair of observers.ResultsFor the 2 delineation sessions combined, mean GTV ranged between 0.19 and 2.44 cm³, CI for GTV ranged between 0.28 and 0.77, and CI for CTV between 0.77 and 0.94. The largest interobserver variation in GTV delineations was observed in cases with extended tumor spiculae, blood vessels near or markers within the tumor, or with increased enhancement of glandular breast tissue. Consensus-based guidelines stated to delineate all visible tumors on contrast enhanced–MRI scan 1 to 2 minutes after contrast injection and if a marker was inserted in the tumor to include this.ConclusionsExpert-based consensus on contouring primary breast tumors on MRI in trials has been reached. This resulted in low interobserver variation for CTV in the context of a uniform 20 mm GTV to CTV expansion margin.     

Evaluation of a delineation software for cardiac atlas-based autosegmentation: An example of the use of artificial intelligence in modern radiotherapy

PurposeThe primary objective of this work was to implement and evaluate a cardiac atlas-based autosegmentation technique based on the “Workflow Box” software (Mirada Medical, Oxford UK), in order to delineate cardiac substructures according to European Society of Therapeutic Radiation Oncology (ESTRO) guidelines; review and comparison with other cardiac atlas-based autosegmentation algorithms published to date.Materials and MethodsOf an atlas of data set from 20 breast cancer patients’ CT scans with recontoured cardiac substructures creation according to the ESTRO guidelines. Performance evaluation on a validation data set consisting of 20 others CT scans acquired in the same treatment position: cardiac substructure were automatically contoured by the Mirada system, using the implemented cardiac atlas, and simultaneously manually contoured by a radiation oncologist. The Dice similarity coefficient was used to evaluate the concordance level between the manual and the automatic segmentations.ResultsDice similarity coefficient value was 0.95 for the whole heart and 0.80 for the four cardiac chambers. Average Dice similarity coefficient value for the left ventricle walls was 0.50, ranging between 0.34 for the apical wall and 0.70 for the lateral wall. Compared to manual contours, autosegmented substructure volumes were significantly smaller, with the exception of the left ventricle. Coronary artery segmentation was unsuccessful. Performances were overall similar to other published cardiac atlas-based autosegmentation algorithms.ConclusionThe evaluated cardiac atlas-based autosegmentation technique, using the Mirada software, demonstrated acceptable performance for cardiac cavities delineation. However, algorithm improvement is still needed in order to develop efficient and trusted cardiac autosegmentation working tools for daily practice.     

Évaluation d’un logiciel pour la délinéation automatique des organes à risques et des volumes cibles ganglionnaires chez des patientes prises en charge pour un cancer du sein

Purpose

Intensity-modulated radiotherapy needs the strict delineation of target volumes as well as organs at risk and the time used for this procedure is long. The purpose of this study was to evaluate the Workflow Box system (Mirada Medical, UK) for automatic delineation and segmentation for everyday use of organs at risk and lymph nodes delineation in patients treated for early stage breast cancer.

Auto-segmentation of low-risk clinical target volume for head and neck radiation therapy

PurposeTo investigate atlas-based auto-segmentation methods to improve the quality of the delineation of low-risk clinical target volumes (CTVs) of unilateral tonsil cancers.Method and MaterialsSixteen patients received intensity modulated radiation therapy for left tonsil tumors. These patients were treated by a total of 8 oncologists, who delineated all contours manually on the planning CT image. We chose 6 of the patients as atlas cases and used atlas-based auto-segmentation to map each the atlas CTV to the other 10 patients (test patients). For each test patient, the final contour was produced by combining the 6 individual segmentations from the atlases using the simultaneous truth and performance level estimation algorithm. In addition, for each test patient, we identified a single atlas that produced deformed contours best matching the physician's manual contours. The auto-segmented contours were compared with the physician's manual contours using the slice-wise Hausdorff distance (HD), the slice-wise Dice similarity coefficient (DSC), and a total volume overlap index.ResultsNo single atlas consistently produced good results for all 10 test cases. The multiatlas segmentation achieved a good agreement between auto-segmented contours and manual contours, with a median slice-wise HD of 7.4 ± 1.0 mm, median slice-wise DSC of 80.2% ± 5.9%, and total volume overlap of 77.8% ± 3.3% over the 10 test cases. For radiation oncologists who contoured both the test case and one of the atlas cases, the best atlas for a test case had almost always been contoured by the oncologist who had contoured that test case, indicating that individual physician's practice dominated in target delineation and was an important factor in optimal atlas selection.ConclusionsMultiatlas segmentation may improve the quality of CTV delineation in clinical practice for unilateral tonsil cancers. We also showed that individual physician's practice was an important factor in selecting the optimal atlas for atlas-based auto-segmentation.     

ECOG-ACRIN Guideline for Contouring and Treatment of Early Stage Anal Cancer Using IMRT/IGRT

PurposePrevious anal cancer guidelines delineate target volumes similarly for all patients with squamous cell carcinoma of the anal canal and/or perianal skin (SCCA), regardless of disease stage. The purpose of this guideline is to provide customized radiation treatment recommendations for early stage (T1-2 N0 M0) anal cancer treated with intensity modulated and image guided radiation therapy (RT).Methods and MaterialsA contouring atlas and radiation treatment recommendations for the ongoing, randomized phase II trial of deintensified chemoradiation for early stage SCCA (EA2182) was created by an expert panel of radiation oncologists. A literature search was conducted to update and expand these recommendations into a guideline for routine clinical use.ResultsFor the majority of cases, we recommend treatment in the supine, frog leg position with the use of a customized immobilization device and daily image guided RT to ensure optimal bone and soft tissue alignment. Vaginal dilators can be used daily during RT to maximize genitalia sparing. We recommend use of a 10-mm margin on the gross tumor plus including the anal complex to create the primary clinical target volume. To define the elective lymph node clinical target volume, we recommend starting with a 7-mm expansion on blood vessels, but then further refining these volumes based on the anatomic location. A 5- to 10-mm planning target volume (PTV) margin is suggested based on institutional setup and patient-specific factors. When using a simultaneous integrated boost technique, a dose of 50.4 Gy to primary PTV and 42 Gy to lymph node PTV, both delivered over 28 fractions, with chemotherapy is appropriate for early stage anal cancer.ConclusionsThis guideline provides anatomic, clinical, and technical instructions to guide radiation oncologists in the planning and delivery of intensity modulated and image guided RT for early stage SCCA.     

A contouring guide for head and neck cancers with perineural invasion

PurposePerineural invasion (PNI) is a frequent pathological finding in head and neck cancers. When adjuvant radiation to cranial nerves at risk in head and neck cancers with PNI is considered, there is a need for consensus on which nerves are at risk and how to contour these nerves. This contouring guide attempts to address this need.Methods and materialsRepresentative patient diagnostic computed tomographic (CT) scans with contrast of the neck were used to create example contours. The cranial nerves V_2, V₃, VII, and XII, and sample primary tumor sites were initially delineated using the Varian Eclipse planning system by 5 radiation oncologists. All of the images were then reviewed with a diagnostic radiologist to establish consensus for delineating the cranial nerves.ResultsWe provided detailed contouring and planning guidelines on a CT atlas, with figures to help illustrate internerve connections, based on clinical experience, literature-based patterns of failure, and established anatomic connections between cranial nerves. Tumor bed, cranial nerve, and elective target volumes are depicted.ConclusionsThese planning guidelines and atlas provide anatomic, clinical, and technical recommendations for guiding radiation oncologists in the planning and delivery of intensity modulated radiation therapy for head and neck cancer with PNI.     

Target volume delineation variation in radiotherapy for early stage rectal cancer in the Netherlands

Purpose

The aim of this study was to measure and improve the quality of target volume delineation by means of national consensus on target volume definition in early-stage rectal cancer.

Methods and materials

The CTV’s for eight patients were delineated by 11 radiation oncologists in 10 institutes according to local guidelines (phase 1). After observer variation analysis a workshop was organized to establish delineation guidelines and a digital atlas, with which the same observers re-delineated the dataset (phase 2). Variation in volume, most caudal and cranial slice and local surface distance variation were analyzed.

Results

The average delineated CTV volume decreased from 620 to 460 cc (p < 0.001) in phase 2. Variation in the caudal CTV border was reduced significantly from 1.8 to 1.2 cm SD (p = 0.01), while it remained 0.7 cm SD for the cranial border. The local surface distance variation (cm SD) reduced from 1.02 to 0.74 for anterior, 0.63 to 0.54 for lateral, 0.33 to 0.25 for posterior and 1.22 to 0.46 for the sphincter region, respectively.

Conclusions

The large variation in target volume delineation could significantly be reduced by use of consensus guidelines and a digital delineation atlas. Despite the significant reduction there is still a need for further improvement.     

影响乳腺癌调强适形放射治疗全乳临床靶区确定的因素

背景与目的:调强适形放射治疗(intensity-modulatedradiotherapy,IMRT)在乳腺癌保留乳房治疗中显示了较好的剂量学优势和发展前景,其中靶区的确定是IMRT最关键的环节,决定了放射治疗计划和实施的准确性,但目前仍缺乏乳腺癌全乳临床靶体积(clinicaltargetvolume,CTV)确定与勾画的规范。本研究分析不同医师勾画全乳CTV的差异,以合理地确定乳腺癌IMRT中的全乳CTV。方法:由4名放射治疗医师与1名放射诊断医师分别在6例患者中勾画全乳CTV及相应的参考CTV,分析其体积差异,计算共有体积与最大体积之比R值,测量各医师勾画CTVs在不同方向与参考CTV比较的最大边距差异,以各医师勾画CTV为基础设计切线野并测量其射野中心肺厚度(centrallungdistance,CLD)。结果:2例乳腺腺体密度较低的患者体积差异最大,其R值仅为0.660和0.651,其余4例患者的R值分别是0.735、0.752及0.799、0.769,又以有乳腺边界体表标记患者的R值较大;与参考CTV相比,6例患者中各放疗医师勾画的CTVs在前界、后界、上界、下界和内界、外界最大边距的差异分别是0、(1.2±3.4)mm、(1.5±2.1)mm、(0.7±4.1)mm、(0.6±3.3)mm、(0.8±0.8)mm,各患者中差异部位以乳腺腋尾组织边界与无银夹标记的瘤床边界最为明显;以各医师勾画CTVs设计切线野的CLD平均值在4例患者中均超过2cm。结论:不同医师勾画全乳CTV差异的主要来源是患者本身乳腺腺体密度的个体化差异以及各医师对乳腺腋尾腺体边界、瘤床范围和保护肺组织限度的认识不一。     

Variability in target volume delineation on CT scans of the breast

To determine the intra- and interobserver variation in delineation of the target volume of breast tumors on computed tomography (CT) scans in order to perform conformal radiotherapy.

The clinical target volume (CTV) of the breast was delineated in CT slices by four radiation oncologists on our clinically used delineation system. The palpable glandular breast tissue was marked with a lead wire on 6 patients before CT scanning, whereas 4 patients were scanned without a lead wire. The CTV was drawn by each observer on three separate occasions. Planning target volumes (PTVs) were constructed by expanding the CTV by 7 mm in each direction, except toward the skin. The deviation in the PTV extent from the average extent was quantified in each orthogonal direction for each patient to find a possible directional dependence in the observer variations. In addition, the standard deviation of the intra- and interobserver variation in the PTV volume was quantified. For each patient, the common volumes delineated by all observers and the smallest volume encompassing all PTVs were also calculated.

The patient-averaged deviations in PTV extent were larger in the posterior (42 mm), cranial (28 mm), and medial (24 mm) directions than in the anterior (6 mm), caudal (15 mm), and lateral (8 mm) directions. The mean intraobserver variation in volume percentage (5.5%, 1 SD) was much smaller than the interobserver variation (17.5%, 1 SD). The average ratio between the common and encompassing volume for the four observers separately was 0.82, 0.74, 0.82, and 0.80. A much lower combined average ratio of 0.43 was found because of the large interobserver variations. For the observer who placed the lead wire, the intraobserver variation in volume was decreased by a factor of 4 on scans made with a lead wire in comparison to scans made without a lead wire. For the other observers, no improvement was seen. Based on these results, an improved delineation protocol was designed.

Intra- and especially interobserver variation in the delineation of breast target volume on CT scans can be rather large. A detailed delineation protocol making use of CT scans with lead wires placed on the skin around the palpable breast by the delineating observer reduces the intraobserver variation. To reduce the interobserver variation, better imaging techniques and pathology studies relating glandular breast tissue to imaging may be needed to provide more information on the extent of the clinical target volume.     

The Learning Curve and Inter-Observer Variability in Contouring the Hippocampus under the Hippocampal Sparing Guidelines of Radiation Therapy Oncology Group 0933

Hippocampal-sparing brain radiotherapy (HS-BRT) in cancer patients results in preservation of neurocognitive function after brain RT which can contribute to patients’ quality of life (QoL). The crucial element in HS-BRT treatment planning is appropriate contouring of the hippocampus. Ten doctors delineated the left and right hippocampus (LH and RH, respectively) on 10 patients’ virtual axial images of brain CT fused with T1-enhanced MRI (1 mm) according to the RTOG 0933 atlas recommendations. Variations in the spatial localization of the structure were described in three directions: right–left (X), cranio-caudal (Y), and forward–backward (Z). Discrepancies concerned three-dimensional localization, shape, volume and size of the hippocampus. The largest differences were observed in the first three delineated cases which were characterized by larger hippocampal volumes than the remaining seven cases. The volumes of LH of more than half of hippocampus contours were marginally bigger than those of RH. Most differences in delineation of the hippocampus were observed in the area of the posterior horn of the lateral ventricle. Conversely, a large number of hippocampal contours overlapped near the brainstem and the anterior horn of the lateral ventricle. The most problematic area of hippocampal contouring is the posterior horn of the lateral ventricle. Training in the manual contouring of the hippocampus during HS-BRT treatment planning under the supervision of experienced radiation oncologists is necessary to achieve optimal outcomes. This would result in superior outcomes of HS-BRT treatment and improvement in QoL of patients compared to without HS-BRT procedure. Correct delineation of the hippocampus is problematic. This study demonstrates difficulties in HS-BRT treatment planning and highlights critical points during hippocampus delineation.     

Evaluating cardiac substructure radiation exposure in breast rotational intensity modulated radiation therapy: Effects of cancer laterality,fractionation and deep inspiration breath-hold

PurposeRotational intensity-modulated radiation therapy currently has a growing role in breast cancer radiation therapy, since this radiation technique reduces cardiac radiation exposure while homogeneously covering target volumes. This study aims to evaluate radiation exposure of cardiac substructures across a broad spectrum of breast cancer cases differing by cancer laterality, fractionation regimen and addition of deep-inspiration breath hold.Materials and methodsCardiac substructures were delineated following guidelines endorsed by the European Society for Radiotherapy and Oncology (ESTRO) for forty-four breast cancer patients having undergone conserving surgery and adjuvant rotational intensity-modulated radiation therapy. Target volumes consisted of the whole breast with a boost, axillary and internal mammary nodes. Patients were treated using free-breathing technique for left-sided or right-sided, normofractionated or hypofractionated helical tomotherapy or volumetric modulated arc therapy, or using deep-inspiration breath hold for left-sided normofractionated volumetric modulated arc therapy. Mean and maximum doses to cardiac substructures were retrieved. Correlations were performed between mean- and maximum radiation doses to cardiac substructures.ResultsLeft-sided and right-sided irradiations were associated with different cardiac substructure exposure patterns despite comparable mean heart dose: 7.21 Gy for left-sided normofractionated regimen, 6.28 Gy for right-sided normofractionated regimen. Deep-inspiration breath hold reduced mean doses to almost all cardiac substructures for left-sided irradiation, but did not decrease maximum doses to coronary arteries. Correlations between mean- and maximum doses to cardiac substructures were usually moderate, but stronger for right-sided irradiation.ConclusionDespite comparable mean heart dose, cardiac substructure radiation exposure patterns with rotational intensity-modulated radiation therapy strongly depend on the breast side, which could trigger clinically different long-term cardiotoxicity events. Deep-inspiration breath hold improves cardiac substructure dosimetry. Mean- and maximum heart dose could probably not be used as surrogate markers for precise cardiac substructure evaluation. In a near future, clinical practice and cardiotoxicity studies could possibly gain by considering cardiac substructure in a more systematic manner, possibly relying on cardiac autosegmentation algorithms.     

Target volume delineation for partial breast radiotherapy planning: clinical characteristics associated with low interobserver concordance

PURPOSE: To examine variability in target volume delineation for partial breast radiotherapy planning and evaluate characteristics associated with low interobserver concordance. METHODS AND MATERIALS: Thirty patients who underwent planning CT for adjuvant breast radiotherapy formed the study cohort. Using a standardized scale to score seroma clarity and consensus contouring guidelines, three radiation oncologists independently graded seroma clarity and delineated seroma volumes for each case. Seroma geometric center coordinates, maximum diameters in three axes, and volumes were recorded. Conformity index (CI), the ratio of overlapping volume and encompassing delineated volume, was calculated for each case. Cases with CI 相似文献   

Evaluation of variability in seroma delineation between clinical specialist radiation therapist and radiation oncologist for adjuvant breast irradiation

PurposeBreast cancer is managed by a multidisciplinary team with a goal for the timely provision of high quality care. Given radiation oncologist (RO) time constraints, an opportunity arises for task delegation of breast seroma target delineation to an advanced practice clinical specialist radiation therapist (CSRT) with clinical and technical expertise to facilitate treatment planning. To explore this further, we quantitatively evaluated the variability in post-surgical seroma delineation between the CSRT and ROs.MethodsSpecialized site specific training was provided to the CSRT, who, with 7 ROs, independently contoured the seroma and graded its clarity, using the cavity visualization score (CVS), for 20 patients with clinical stage Tis-2N0 breast tumors. The conformity indices were analyzed for all possible pairs of delineations. The estimated “true” seroma contour was derived from the RO contours using the simultaneous truth and performance level estimation algorithm. Generalized kappa coefficient and center of mass metrics were used to examine the performance level of the CSRT in seroma delineations.ResultsThe CVS of the CSRT correlated well with the mean RO-group CVS, (Spearman ρ = 0.87, P < .05). The mean seroma conformity index for the RO group was 0.61 and 0.65 for the CSRT; a strong correlation was observed between the RO and CSRT conformity indices (Spearman ρ = 0.95, P < .05). Almost perfect agreement levels were observed between the CSRT contours and the STAPLE RO consensus contours, with an overall kappa statistic of 0.81 (P < .0001). The average center of mass shift between the CSRT and RO consensus contour was 1.69 ± 1.13 mm.ConclusionsFollowing specialized education and training, the CSRT delineated seroma targets clinically comparable with those of the radiation oncologists in women with early breast tumors suitable for accelerated partial breast or whole breast radiotherapy following lumpectomy. This study provides support for potential task delegation of breast seroma delineation to the CSRT in our current multidisciplinary environment. Further study is needed to assess the impact of this role expansion on radiotherapy system efficiency.     

Harmonization of practices between radiotherapy centres in the Nord and Pas-de-Calais regions (France): A three-year evaluation

Purpose

The delineation of volumes of interest can be a source of significant interobserver variability. The purpose of this study was to improve the homogeneity of delineation between oncologist-radiotherapists in the territorial departments of Nord and Pas-de-Calais (France) through discussions of clinical cases and the adoption of common published reference documents.

The delineation of target volumes for radiotherapy of lung cancer patients

Purpose

Differences in the delineation of the gross target volume (GTV) and planning target volume (PTV) in patients with non-small-cell lung cancer are considerable. The focus of this work is on the analysis of observer-related reasons while controlling for other variables.

Methods

In three consecutive patients, eighteen physicians from fourteen different departments delineated the GTV and PTV in CT-slices using a detailed instruction for target delineation. Differences in the volumes, the delineated anatomic lymph node compartments and differences in every delineated pixel of the contoured volumes in the CT-slices (pixel-by-pixel-analysis) were evaluated for different groups: ten radiation oncologists from ten departments (ROs), four haematologic oncologists and chest physicians from four departments (HOs) and five radiation oncologists from one department (RO1D).

Results

Agreement (overlap ? 70% of the contoured pixels) for the GTV and PTV delineation was found in 16.3% and 23.7% (ROs), 30.4% and 38.6% (HOs) and 32.8% and 35.9% (RO1D), respectively.

Conclusion

A large interobserver variability in the PTV and much more in the GTV delineation were observed in spite of a detailed instruction for delineation. The variability was smallest for group ROID where due to repeated discussions and uniform teaching a better agreement was achieved.     

Gastric lymph node contouring atlas: A tool to aid in clinical target volume definition in 3-dimensional treatment planning for gastric cancer

Purpose: To develop a contouring atlas of the gastric lymph node stations to be used in defining and planning clinical target volumes in 3-dimensional treatment planning for gastric cancers.Methods and Materials: Four physicians, including 2 radiation oncologists, a diagnostic radiologist, and a surgical oncologist specialized in gastric cancer, convened over the course of multiple meetings. Four patients were identified as representative cases, including 3 gastric cancer patients treated with differing surgical approaches (total gastrectomy, Ivor-Lewis esophagogastrectomy, and distal gastrectomy) and 1 patient with intact gastric anatomy. Radiographic delineation of lymph node stations was established for each case to highlight differences between intact anatomy and different postoperative anatomy.Results: Consensus was achieved among physicians in order to create a computed tomographic-based contouring atlas of gastric lymph node stations. Detailed radiographic lymph node station delineation for both intact gastric anatomy and post-surgical anatomy are discussed.Conclusions: This report serves as a template for the delineation of gastric lymph node stations to aid in the definition of elective clinical target volumes to be used in conformal treatment planning.