Generalized Conformity Index Research Articles

Interobserver variability of clinical target volume delineation in patients undergoing breast-conserving surgery without surgical clips: a pilot study on preoperative magnetic resonance simulation

BackgroundIn patients undergoing breast-conserving therapy without surgical clip implantation, the accuracy of tumor bed identification and the consistency of clinical target volume (CTV) delineation under computed tomography (CT) simulation remain suboptimal. This study aimed to investigate the feasibility of implementing preoperative magnetic resonance (MR) simulation on delineations by assessing interobserver variability (IOV).MethodsPreoperative MR and postoperative CT simulations were performed in patients who underwent breast-conserving surgery with no surgical clips implanted. Custom immobilization pads were used to ensure the same supine position. Three radiation oncologists independently delineated the CTV of tumor bed on the images acquired from MR and CT simulation registration and CT simulation alone. Cavity visualization score (CVS) was assigned to each patient based on the clarity of the tumor bed on CT simulation images. IOV was indicated by generalized conformity index (CIgen), denoted as CIgen−CT and CIgen−MR/CT, and the distance between the centroid of mass (dCOM), denoted as dCOMCT and dCOMMR/CT. The variation of IOV in different CVS subgroups was analyzed.ResultsA total of 10 patients were enrolled in this study. The median and interquartile range (IQR) of maximum pathological diameter of the tumors in all patients were 1.55 (0.80–1.92) cm. No statistical significance was found between the volumes of CTVs on CT simulation and on MR/CT simulation registration images (p = 0.387). CIgen−MR/CT was significantly larger than CIgen−CT (p = 0.005). dCOMMR/CT was significantly smaller than dCOMCT (p = 0.037). The median and IQR of CVS in all patients were 2.34 (2.00–3.08). The difference of CIgen between CIgen−MR/CT and CIgen−CT was larger in the low CVS group (p = 0.016). The difference of dCOM showed a decreasing trend when CVS was lower, although it did not reach statistical significance (p = 0.095).ConclusionsFor patients who underwent breast-conserving surgery without surgical clip implantation, the use of preoperative MR simulation in delineating the CTV of tumor bed decreased the IOV among observers. The consistency of tumor bed identification was improved especially in cases where the margins of tumor bed were challenging to visualize on CT simulation images. The study findings offer potential benefits in reducing local recurrence and minimizing tissue irritation in the surrounding areas. Future investigation in a larger patient cohort to validate our results is warranted.

Inter-observer variation in gross tumour volume delineation of oesophageal cancer on MR, CT and PET/CT.

The aim of our study was to assess the inter-observer variability in delineation of the gross tumour volume (GTV) of oesophageal cancer on magnetic resonance (MR) in comparison to computed tomography (CT) and positron emission tomography and CT (PET/CT). Twenty-three consecutive patients with oesophageal cancer treated with chemo-radiotherapy were enrolled. All patients had PET/CT and MR imaging in treatment position. Five observers independently delineated the GTV on CT alone, MR alone, CT with co-registered MR, PET/CT alone and MR with co-registered PET/CT. Volumes of GTV were measured per patient and imaging modality. Inter-observer agreement, expressed in generalized conformity index (CIgen), volumetric conformity index (VCI), planar conformity index (PCI) and inter-delineation distance (IDD) were calculated per patient and imaging modality. Linear mixed models were used for statistical analysis. GTV volume was significantly lower on MR (33.03 cm3) compared to CT (37.1 cm3; p = 0.002) and on PET/CT MR (35.2 cm3; p = 0.018) compared to PET/CT (39.1 cm3). The CIgen was lowest on CT (0.56) and highest on PET/CT MR (0.67). The difference in CIgen between MR (0.61) and CT was borderline significant (p = 0.048). The VCI was significantly higher on MR (0.71; p = 0.007) and on CT MR (0.71; p = 0.004) compared to CT (0.67). The PCI was significantly higher on CT MR (0.67; p = 0.031) compared to CT (0.64). The largest differences were observed in the cranio-caudal direction. The highest inter-observer agreement was found for PET/CT MR and the lowest for CT. MR could reduce the difference in delineation between observers and provide additional information about the local extent of the tumour.

Artificial intelligence-generated targets and inter-observer variation in online adaptive radiotherapy of bladder cancer

Background and purposeDaily target re-delineation in online adaptive radiotherapy (oART) introduces uncertainty. The aim of this study was to evaluate artificial intelligence (AI) generated contours and inter-observer target variation among radiotherapy technicians in cone-beam CT (CBCT) guided oART of bladder cancer. Materials and methodsFor each of 10 consecutive patients treated with oART for bladder cancer, one CBCT was randomly selected and retrospectively included. The bladder (CTV-T) was AI-segmented (CTV-TAI). Seven radiotherapy technicians independently reviewed and edited CTV-TAI, generating CTV-TADP. Contours were benchmarked against a ground truth contour (CTV-TGT) delineated blindly from scratch. CTV-TADP and CTV-TAI were compared to CTV-TGT using volume, dice similarity coefficient, and bidirectional local distance. Dose coverage (D99%>95 %) of CTV-TGT was evaluated for treatment plans optimized for CTV-TAI and CTV-TADP with clinical margins. Inter-observer variation among CTV-TADP was assessed using coefficient of variation and generalized conformity index. ResultsCTV-TGT ranged from 48.7 cm3 to 211.6 cm3. The median [range] volume difference was 4.5 [−17.8, 42.4] cm3 for CTV-TADP and −15.5 [−54.2, 4.3] cm3 for CTV-TAI, compared to CTV-TGT. Corresponding dice similarity coefficients were 0.87 [0.71, 0.95] and 0.84 [0.64, 0.95]. CTV-TGT was adequately covered in 68/70 plans optimized on CTV-TADP and in 6/10 plans optimized on CTV-TAI with clinical margins. The median [range] coefficient of variation was 0.08 [0.05, 0.11] and generalized conformity index was 0.78 [0.71, 0.88] among CTV-TADP. ConclusionsTarget re-delineation in CBCT-guided oART of bladder cancer demonstrated non-isotropic inter-observer variation. Manual adjustment of AI-generated contours was necessary to cover ground truth targets.

Target Re-Delineation in Daily Online Adaptive Radiotherapy of Bladder Cancer: AI vs. Adapters

The purpose was to assess the quality of artificial intelligence (AI) generated targets in cone-beam CT (CBCT) guided online adaptive radiotherapy (oART) of bladder cancer and compare it to corresponding contours edited by adapters (radiotherapy technicians performing oART routinely). Furthermore, to assess the inter-observer delineation variation in daily target re-delineation in oART of bladder cancer. Ten consecutive patients treated with oART for muscle-invasive bladder cancer from Feb 2020 to Feb 2021 were retrospectively included. One CBCT randomly selected from each of the 10 clinical treatment courses was exported to an emulator, where delineations and oART simulations were carried out. The bladder was automatically segmented (clinical target volume (CTV)) using AI. Seven adapters independently reviewed and, if necessary, manually edited the AI-generated structure. A ground truth structure was first delineated blindly by a senior oncologist, then reviewed by an oART experienced medical physicist, and finally edited to a consensus structure. Planning CT and MR images with reference delineations were available during all simulations and delineations. The AI-generated and adapter-edited CTVs were compared to ground truth using dice similarity coefficient (DSC) and volume difference. The inter-observer variation in adapter-edited CTVs was assessed using coefficient of variation (CV) and the generalized conformity index (CIgen). Cigen was calculated as the ratio of the sum of all overlapping volumes between pairs of observers and the sum of all overlapping and non-overlapping volumes between the same pairs. Nine CTVs (7 adapter-edited, 1 AI-generated, 1 ground truth) were generated per patient. Patient cases included three male and seven females; three had catheter. The ground truth volume ranged from 51.5 to 221.6 cc. The median volume difference compared to ground truth was -4.5 (range, -17.8 - 42.4) cc and -15.5 (range, -54.2 - 4.3) cc for adapter-edited and AI-generated structures, respectively. Corresponding DSC values were 0.87 (range, 0.71 - 0.95) and 0.84 (range, 0.64 - 0.95). The AI-generated CTV was smaller than ground truth for all patients except one and smaller than all adapter-edited CTVs. The largest differences among adapter-edited CTVs were observed in cranial, caudal and posterior directions. The median CV was 0.08 (range, 0.05-0.11) and Cigen was 0.78 (range, 0.71-0.88). Target re-delineations in daily CBCT-based oART of bladder cancer demonstrated small inter-observer variation. Manual adjustment of AI-generated structures resulted in improved accuracy in target delineation compared to ground truth. Efforts to reduce the inter-observer variation, e.g., physician support during the initial fractions and review by a second adapter, have been implemented clinically.

Interobserver variation in clinical target volume (CTV) delineation for stereotactic radiotherapy to non-spinal bone metastases in prostate cancer: CT, MRI and PET/CT fusion

Background and purposeThe use of SBRT for the treatment of oligometastatic prostate cancer is increasing rapidly. While consensus guidelines are available for non-spinal bone metastases practice continues to vary widely. The aim of this study is to look at inter-observer variability in the contouring of prostate cancer non-spinal bone metastases with different imaging modalities. Materials and methods15 metastases from 13 patients treated at our centre were selected. 4 observers independently contoured clinical target volumes (CTV) on planning CT alone, planning CT with MRI fusion, planning CT with PET-CT fusion and planning CT with both MRI and PET-CT fusion combined. The mean inter-observer agreement on each modality was compared by measuring the delineated volume, generalized conformity index (CIgen), and the distance of the centre of mass (dCOM), calculated per metastasis and imaging modality. ResultsMean CTV volume delineated on planning CT with MRI and PET-CT fusion combined was significantly larger compared to other imaging modalities (p = 0.0001). CIgen showed marked variation between modalities with the highest agreement between planning CT + PET-CT (mean CIgen 0.55, range 0.32–0.73) and planning CT + MRI + PET-CT (mean CIgen 0.59, range 0.34–0.73). dCOM showed small variations between imaging modalities but a significantly shorter distance found on planning CT + PET-CT when compared with planning CT + PET-CT + MRI combined (p = 0.03). ConclusionsHighest consistency in CTV delineation between observers was seen with planning CT + PET-CT and planning CT + PET-CT + MRI combined.

Deep learning-based segmentation of the thorax in mouse micro-CT scans

For image-guided small animal irradiations, the whole workflow of imaging, organ contouring, irradiation planning, and delivery is typically performed in a single session requiring continuous administration of anaesthetic agents. Automating contouring leads to a faster workflow, which limits exposure to anaesthesia and thereby, reducing its impact on experimental results and on animal wellbeing. Here, we trained the 2D and 3D U-Net architectures of no-new-Net (nnU-Net) for autocontouring of the thorax in mouse micro-CT images. We trained the models only on native CTs and evaluated their performance using an independent testing dataset (i.e., native CTs not included in the training and validation). Unlike previous studies, we also tested the model performance on an external dataset (i.e., contrast-enhanced CTs) to see how well they predict on CTs completely different from what they were trained on. We also assessed the interobserver variability using the generalized conformity index (hbox {CI}_{mathrm{gen}}) among three observers, providing a stronger human baseline for evaluating automated contours than previous studies. Lastly, we showed the benefit on the contouring time compared to manual contouring. The results show that 3D models of nnU-Net achieve superior segmentation accuracy and are more robust to unseen data than 2D models. For all target organs, the mean surface distance (MSD) and the Hausdorff distance (95p HD) of the best performing model for this task (nnU-Net 3d_fullres) are within 0.16 mm and 0.60 mm, respectively. These values are below the minimum required contouring accuracy of 1 mm for small animal irradiations, and improve significantly upon state-of-the-art 2D U-Net-based AIMOS method. Moreover, the conformity indices of the 3d_fullres model also compare favourably to the interobserver variability for all target organs, whereas the 2D models perform poorly in this regard. Importantly, the 3d_fullres model offers 98% reduction in contouring time.

The Impact of Different Simulation Modalities on Target Volume Delineation in Breast-Conserving Radiotherapy.

PurposeIn the management of breast-conserving radiotherapy, computed tomography (CT) simulation is now commonly used to identify tumor bed while has difficulties defining precisely. We aimed to evaluate the impact of magnetic resonance (MR) and CT simulation on defining the postoperative tumor bed for breast-conserving radiotherapy in patients without the aid of surgical clips.MethodsFrom August 2018 to March 2019, twenty patients with T1-2N0M0 breast cancer at our institution were enrolled. All the patients underwent breast-conserving surgery without implantation of surgical clips and were prepared to receive radiotherapy. CT and MR images were acquired on the same day for each patient. Three radiation oncologists independently assigned cavity visualization score (CVS) and delineated the tumor bed based on first the CT then the MR images. Interobserver variability was assessed by volumes, generalized conformity index (CIgen) and the distance between the centers of mass (dCOM). Differences in mean values for parameters were tested by paired t-test or one-way analysis of variance, as appropriate.ResultsFirst, the mean volumes of tumor bed derived from MR were 22%, 27% and 21% smaller than those based on CT images for each observer. In addition, the mean CIgen was significantly superior, and dCOM was smaller for MR than for CT images (CIgen: 0.59 vs 0.52, P= 0.008; dCOM: 1.30 cm vs 1.39 cm, P= 0.095). Moreover, the mean CVS was 3.23±1.34 and 2.43±0.92 for MR and CT images, respectively (P= 0.035). Last, a positive association was observed between the CVS and CIgen for both modalities (P< 0.01).ConclusionCompared to CT, MR can improve the visualization of changes in the postoperative tumor bed. In addition, MR can yield a more precise definition of the tumor bed and improve the consistency of tumor bed contouring in patients without surgical clips.

DE-MR simulation imaging for prone radiotherapy after breast-conserving surgery: assessing its application in lumpectomy cavity delineation based on deformable image registration

BackgroundThe application of delayed-enhancement magnetic resonance (DE-MR) simulation imaging in lumpectomy cavity (LC) delineation for prone radiotherapy in patients with an invisible seroma or a low seroma clarity score (SCS) after breast-conserving surgery (BCS) based on deformable image registration (DIR) was assessed.MethodsTwenty-six patients who were suitable for radiotherapy in prone positions after BCS were enrolled, and both computed tomography (CT) and DE-MR simulation scans were acquired. The LC delineated based on titanium surgical clips on CT images was denoted as LCCT. The LC delineated based on the signal of cavity boundaries on fat-suppressed T2-weighted imaging (T2WI) and multiphase delayed-enhancement T1-weighted imaging (DE-T1WI), which was performed at 2 min, 5 min and 10 min postinjection, were denoted as LCT2, LC2T1, LC5T1 and LC10T1, respectively. Afterwards, DIR was performed to compare the volumes and locations of the LCs with MIM software. The generalized conformity index (CIgen) of inter (intra) observer (Inter-CIgen and Intra-CIgen) was also used to explore the inter(intra) observer variation for LC delineation on each image modality.ResultsLCCT–LC10T1 provided the best conformal index (CI) and degree of inclusion (DI), increasing by 2.08% and 4.48% compared to LCCT–LCT2, 11.36% and 2.94% for LCCT–LC2T1, and 8.89% and 7.69% for LC5T1–LCCT, respectively. The center of mass (COM) of LCCT–LC10T1 decreased by 17.86%, 6.12% and 13.21% compared with that of LCCT–LCT2, LCCT–LC2T1 and LCCT–LC5T1, respectively. The agreement of LC delineation was strongest for 10th min DE-TIWI (coefficient of variation, COV = 2.30%, Inter-CIgen = 87.06%, Intra-CIgen = 92.64%).ConclusionFor patients with a low SCS (SCS ≤ 2) after BCS, it is feasible to contour the LC based on prone DE-MR simulation images. Furthermore, the LC derived from prone DE-T1WI at 10 min was found to be most similar to that derived from prone CT simulation scans using titanium surgical clips regardless of the volume and location of the LC. Inter (intra) variability was minimal for the delineation of the LC based on 10th min DE-TIWI.

Development and evaluation of a manual segmentation protocol for deep grey matter in multiple sclerosis: Towards accelerated semi-automated references

BackgroundDeep grey matter (dGM) structures, particularly the thalamus, are clinically relevant in multiple sclerosis (MS). However, segmentation of dGM in MS is challenging; labeled MS-specific reference sets are needed for objective evaluation and training of new methods. ObjectivesThis study aimed to (i) create a standardized protocol for manual delineations of dGM; (ii) evaluate the reliability of the protocol with multiple raters; and (iii) evaluate the accuracy of a fast-semi-automated segmentation approach (FASTSURF). MethodsA standardized manual segmentation protocol for caudate nucleus, putamen, and thalamus was created, and applied by three raters on multi-center 3D T1-weighted MRI scans of 23 MS patients and 12 controls. Intra- and inter-rater agreement was assessed through intra-class correlation coefficient (ICC); spatial overlap through Jaccard Index (JI) and generalized conformity index (CIgen). From sparse delineations, FASTSURF reconstructed full segmentations; accuracy was assessed both volumetrically and spatially. ResultsAll structures showed excellent agreement on expert manual outlines: intra-rater JI > 0.83; inter-rater ICC ≥ 0.76 and CIgen ≥ 0.74. FASTSURF reproduced manual references excellently, with ICC ≥ 0.97 and JI ≥ 0.92. ConclusionsThe manual dGM segmentation protocol showed excellent reproducibility within and between raters. Moreover, combined with FASTSURF a reliable reference set of dGM segmentations can be produced with lower workload.

Comparison of Magnetic Resonance Imaging and Computed Tomography–Based Volume Delineation of Lumpectomy Cavity Without Surgical Clips in Breast-Conserving Radiotherapy

First, to compare magnetic resonance (MR) imaging and computed tomography (CT) -based definition of lumpectomy cavity in patients without surgical clips. Second, to quantify consistency of MR and CT-based lumpectomy cavity delineation for breast-conserving radiotherapy. Between August 2018 and March 2019, twenty patients with T1-2N0M0 breast cancer at our institution were enrolled in this study. All the patients had been treated by breast-conserving surgery without implantation of surgical clips, and prepared to receive radiotherapy. MR and CT images were required in the same day for each patient. Three radiation oncologists independently assigned cavity visualization score (CVS), and delineated the lumpectomy cavity based on CT then on MR images with a 14-day interval for each patient. Interobserver variability was assessed by volumes, generalized conformity index (CIgen) and the distance between the centers of mass (dCOM). Differences in means were tested by the paired sample t-test or One-way analysis of variance, as appropriate. The median age of included patients was 48 years old (range, 33-73). Mean volumes of lumpectomy cavity derived from MR were 22%, 27% and 21% smaller than those based on CT images for each radiation oncologist. And mean CVS was 2.43±0.92 and 3.23±1.34 for CT and MR scans (P = 0.035). In addition, mean CIgen was significantly superior and dCOM was closer for MR when compared to CT (CIgen: 0.59 vs 0.52, P = 0.008; dCOM: 1.30 cm vs 1.39 cm, P = 0.095). In the subgroup with a CVS≥3, the mean dCOM was also obviously larger obtained from CT than those from the MR images (1.35 cm vs 1.19 cm, P = 0.048). A positive association was observed between CVS and CIgen for CT and MR, while CVS was negatively correlated with dCOM for MR images (both P <0.001). In the present study, when compared to CT, MR was able to improve the visualization of postoperative lumpectomy cavity changes. In addition, MR yielded a more precise definition of lumpectomy cavity and improved the consistency of lumpectomy cavity delineation in patients without the aid of surgical clips.

Hybrid TRUS/CT with optical tracking for target delineation in image-guided adaptive brachytherapy for cervical cancer

ObjectiveTo prospectively compare the interobserver variability of combined transrectal ultrasound (TRUS)/computed tomography (CT)- vs. CT only- vs. magnetic resonance imaging (MRI) only-based contouring of the high-risk clinical target volume (CTVHR) in image-guided adaptive brachytherapy (IGABT) for locally advanced cervical cancer (LACC).MethodsFive patients with LACC (FIGO stages IIb–IVa) treated with radiochemotherapy and IGABT were included. CT, TRUS, and T2-weighted MRI images were performed after brachytherapy applicator insertion. 3D-TRUS image acquisition was performed with a customized ultrasound stepper device and software. Automatic applicator reconstruction using optical tracking was performed in the TRUS dataset and TRUS and CT images were fused with rigid image registration with the applicator as reference structure. The CTVHR (based on the GEC-ESTRO recommendations) was contoured by five investigators on the three modalities (CTVHR_CT, CTVHR_TRUS-CT, and CTVHR_MRI). A consensus reference CTVHR_MRI (MRIref) was defined for each patient. Descriptive statistics and overlap measures were calculated using RTslicer (SlicerRT Community and Percutaneous Surgery Laboratory, Queen’s University, Canada), comparing contours of every observer with one another and with the MRIref.ResultsThe interobserver coefficient of variation was 0.18 ± 0.05 for CT, 0.10 ± 0.04 for TRUS-CT, and 0.07 ± 0.03 for MRI. Interobserver concordance in relation to the MRIref expressed by the generalized conformity index was 0.75 ± 0.04 for MRI, 0.51 ± 0.10 for TRUS-CT, and 0.48 ± 0.06 for CT. The mean CTVHR_CT volume of all observers was 71% larger than the MRIref volume, whereas the mean CTVHR_TRUS-CT volume was 15% larger.ConclusionHybrid TRUS-CT as an imaging modality for contouring the CTVHR in IGABT for LACC is feasible and reproducible among multiple observers. TRUS-CT substantially reduces overestimation of the CTVHR volume of CT alone while maintaining similar interobserver variability.

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.

Reduced inter-observer and intra-observer delineation variation in esophageal cancer radiotherapy by use of fiducial markers

Objective: Delineation variation of esophageal tumors remains a large source of geometric uncertainty. In the present study, we investigated the inter- and intra-observer variation in esophageal gross tumor volume (GTV) delineation and the impact of endoscopically implanted fiducial markers on these variations.Material/Methods: Ten esophageal cancer patients with at least two markers endoscopically implanted at the cranial and caudal tumor borders and visible on the planning computed tomography (pCT) were included in this study. Five dedicated gastrointestinal radiation oncologists independently delineated GTVs on the pCT without markers and with markers. The GTV was first delineated on pCTs where markers were digitally removed and next on the original pCT with markers. Both delineation series were executed twice to determine intra-observer variation. For both the inter- and intra-observer analyses, the generalized conformity index (CIgen), and the standard deviation (SD) of the distances between delineated surfaces (i.e., overall, longitudinal, and radial SDs) were calculated. Linear mixed-effect models were used to compare the without and with markers series (α = 0.05).Results: Both the inter- and intra-observer CIgen were significantly larger in the series with markers than in the series without markers (p < .001). For the series without markers vs. with markers, the inter-observer overall SD, longitudinal SD, and radial SD was 0.63 cm vs. 0.22 cm, 1.44 cm vs. 0.42 cm, and 0.26 cm vs. 0.18 cm, respectively (p < .05); moreover, the intra-observer overall SD, longitudinal SD, and radial SD was 0.45 cm vs. 0.26 cm, 1.10 cm vs. 0.41 cm, and 0.22 cm vs. 0.15 cm, respectively (p < .05).Conclusion: The presence of markers at the cranial and caudal tumor borders significantly reduced both inter- and intra-observer GTV delineation variation, especially in the longitudinal direction. Our results endorse the use of markers in GTV delineation for esophageal cancer patients.

Inter-rater agreement in glioma segmentations on longitudinal MRI.

BackgroundTumor segmentation of glioma on MRI is a technique to monitor, quantify and report disease progression. Manual MRI segmentation is the gold standard but very labor intensive. At present the quality of this gold standard is not known for different stages of the disease, and prior work has mainly focused on treatment-naive glioblastoma. In this paper we studied the inter-rater agreement of manual MRI segmentation of glioblastoma and WHO grade II-III glioma for novices and experts at three stages of disease. We also studied the impact of inter-observer variation on extent of resection and growth rate.MethodsIn 20 patients with WHO grade IV glioblastoma and 20 patients with WHO grade II-III glioma (defined as non-glioblastoma) both the enhancing and non-enhancing tumor elements were segmented on MRI, using specialized software, by four novices and four experts before surgery, after surgery and at time of tumor progression. We used the generalized conformity index (GCI) and the intra-class correlation coefficient (ICC) of tumor volume as main outcome measures for inter-rater agreement.ResultsFor glioblastoma, segmentations by experts and novices were comparable. The inter-rater agreement of enhancing tumor elements was excellent before surgery (GCI 0.79, ICC 0.99) poor after surgery (GCI 0.32, ICC 0.92), and good at progression (GCI 0.65, ICC 0.91). For non-glioblastoma, the inter-rater agreement was generally higher between experts than between novices. The inter-rater agreement was excellent between experts before surgery (GCI 0.77, ICC 0.92), was reasonable after surgery (GCI 0.48, ICC 0.84), and good at progression (GCI 0.60, ICC 0.80). The inter-rater agreement was good between novices before surgery (GCI 0.66, ICC 0.73), was poor after surgery (GCI 0.33, ICC 0.55), and poor at progression (GCI 0.36, ICC 0.73). Further analysis showed that the lower inter-rater agreement of segmentation on postoperative MRI could only partly be explained by the smaller volumes and fragmentation of residual tumor. The median interquartile range of extent of resection between raters was 8.3% and of growth rate was 0.22 mm/year.ConclusionManual tumor segmentations on MRI have reasonable agreement for use in spatial and volumetric analysis. Agreement in spatial overlap is of concern with segmentation after surgery for glioblastoma and with segmentation of non-glioblastoma by non-experts.

Gross tumour delineation on computed tomography and positron emission tomography-computed tomography in oesophageal cancer: A nationwide study

Background and purposeAccurate delineation of the primary tumour is vital to the success of radiotherapy and even more important for successful boost strategies, aiming for improved local control in oesophageal cancer patients. Therefore, the aim was to assess delineation variability of the gross tumour volume (GTV) between CT and combined PET-CT in oesophageal cancer patients in a multi-institutional study. Materials and methodsTwenty observers from 14 institutes delineated the primary tumour of 6 cases on CT and PET-CT fusion. The delineated volumes, generalized conformity index (CIgen) and standard deviation (SD) in position of the most cranial/caudal slice over the observers were evaluated. For the central delineated region, perpendicular distance between median surface GTV and each individual GTV was evaluated as in-slice SD. ResultsAfter addition of PET, mean GTVs were significantly smaller in 3 cases and larger in 1 case. No difference in CIgen was observed (average 0.67 on CT, 0.69 on PET-CT). On CT cranial-caudal delineation variation ranged between 0.2 and 1.5 cm SD versus 0.2 and 1.3 cm SD on PET-CT. After addition of PET, the cranial and caudal variation was significantly reduced in 1 and 2 cases, respectively. The in-slice SD was on average 0.16 cm in both phases. ConclusionIn some cases considerable GTV delineation variability was observed at the cranial-caudal border. PET significantly influenced the delineated volume in four out of six cases, however its impact on observer variation was limited.

Inter-observer variation of hippocampus delineation in hippocampal avoidance prophylactic cranial irradiation.

Hippocampal avoidance prophylactic cranial irradiation (HA-PCI) techniques have been developed to reduce radiation damage to the hippocampus. An inter-observer hippocampus delineation analysis was performed and the influence of the delineation variability on dose to the hippocampus was studied. For five patients, seven observers delineated both hippocampi on brain MRI. The intra-class correlation (ICC) with absolute agreement and the generalized conformity index (CIgen) were computed. Median surfaces over all observers' delineations were created for each patient and regional outlining differences were analysed. HA-PCI dose plans were made from the median surfaces and we investigated whether dose constraints in the hippocampus could be met for all delineations. The ICC for the left and right hippocampus was 0.56 and 0.69, respectively, while the CIgen ranged from 0.55 to 0.70. The posterior and anterior-medial hippocampal regions had most variation with SDs ranging from approximately 1 to 2.5mm. The mean dose (Dmean) constraint was met for all delineations, but for the dose received by 1% of the hippocampal volume (D1%) violations were observed. The relatively low ICC and CIgen indicate that delineation variability among observers for both left and right hippocampus was large. The posterior and anterior-medial border have the largest delineation inaccuracy. The hippocampus Dmean constraint was not violated.

Large Interobserver Variation in the International MR-LINAC Oropharyngeal Carcinoma Delineation Study

Generally, a (contrast-enhanced) CT is used for delineation of oropharyngeal carcinomas (OPC’s). MRI however, has a superior soft tissue contrast. Adding MR images to the planning CT, might result in a reduced interobserver variation. MR-guided radiotherapy is in its infancy but will be the standard in the near future. Therefore, we want to determine the variation in target delineation for oropharyngeal cancer (OPC) by international experts using MR as a single delineation modality in order to develop guidelines for delineating OPC’s on MR images Twentyfour radiation oncologists from 7 centers affiliated with the MR-linac Consortium were asked to delineate the gross tumor volume (GTV) and the clinical target volume (CTV) of the primary tumor for 4 OPC cases. Observers were given a brief clinical history, a physical examination report and the T1-, T1- plus Gadolinium and T2- weighted MR images . Target contours were delineated according to experts’ institutional guidelines. The absolute and encompassing volumes, the generalized conformity index and median surface distances were then calculated from the voxel count maps of each case. Furthermore, the data were analyzed with the Simultaneous Truth and Performance Level Estimation (STAPLE) algorithm. The median years of experience for the participating radiation oncologists was 5 years (range 0-15 years). The mean absolute volumes of the GTVs of case 1, case 2, case 3 and case 4 were 6.5 ml (range: 3.9-9.9 ml), 8.6 ml (range 1.9-22.1 ml), 32.6 ml (range: 17.3-64.4 ml) and 20.3 ml (range 7.8-33.6 ml), respectively. The conformity indices for the GTV of the primary tumor were 0.6, 0.38, 0.5 and 0.59 for case 1, case 2, case 3 and case 4, respectively. The mean absolute volumes of the CTVs of case 1, case 2, case 3 and case 4 were 37.0 ml (range: 9.9 - 76.6 ml), 41.4 ml (range 19.7 - 108.5 ml), 113.8 ml (range: 48.5 - 254.7 ml) and 77.4 ml (range 22.7 - 140.6 ml), respectively. The conformity indices for the CTV of the primary tumor were 0.52, 0.46, 0.49 and 0.56 for case 1, case 2, case 3 and case 4 respectively. The STAPLE algorithm largely covers the median GTV voxel density. The interobserver variation of target volumes delineation of OPC patient based on MR is large. For the GTV, volume differences up to a factor of 10 were observed. For the CTV, differences up to of factor of 8 were observed.This demonstrates the need for international MR delineation guidelines for oropharyngeal cancer patients treated using MR-guided radiotherapy.

Inter-observer agreement in GTV delineation of bone metastases on CT and impact of MR imaging: A multicenter study

Background and purposeThe use of Stereotactic Body Radiotherapy (SBRT) for bone metastases is increasing rapidly. Therefore, knowledge of the inter-observer differences in tumor volume delineation is essential to guarantee precise dose delivery. The aim of this study is to compare inter-observer agreement in bone metastases delineated on different imaging modalities. Material and methodsTwenty consecutive patients with bone metastases treated with SBRT were selected. All patients received CT and MR imaging in treatment position prior to SBRT. Five observers from three institutions independently delineated gross tumor volume (GTV) on CT alone, CT with co-registered MRI and MRI alone. Four contours per imaging modality per patient were available, as one set of contours was shared by 2 observers. Inter-observer agreement, expressed in generalized conformity index [CIgen], volumes of contours and contours center of mass (COM) were calculated per patient and imaging modality. ResultsMean GTV delineated on MR (45.9±52.0cm3) was significantly larger compared to CT–MR (40.2±49.4cm3) and CT (34.8±41.8cm3). A considerable variation in CIgen was found on CT (mean 0.46, range 0.15–0.75) and CT–MRI (mean 0.54, range 0.17–0.71). The highest agreement was found on MRI (mean 0.56, range 0.20–0.77). The largest variations of COM were found in anterior–posterior direction for all imaging modalities. ConclusionsLarge inter-observer variation in GTV delineation exists for CT, CT–MRI and MRI. MRI-based GTV delineation resulted in larger volumes and highest consistency between observers.

Addition of MRI for CT-based pancreatic tumor delineation: a feasibility study

Purpose: To assess the effect of additional magnetic resonance imaging (MRI) alongside the planning computed tomography (CT) scan on target volume delineation in pancreatic cancer patients.Material and methods: Eight observers (radiation oncologists) from six institutions delineated the gross tumor volume (GTV) on 3DCT, and internal GTV (iGTV) on 4DCT of four pancreatic cancer patients, while MRI was available in a second window (CT + MRI). Variations in volume, generalized conformity index (CIgen), and overall observer variation, expressed as standard deviation (SD) of the distances between delineated surfaces, were analyzed. CIgen is a measure of overlap of the delineated iGTVs (1 = full overlap, 0 = no overlap). Results were compared with those from an earlier study that assessed the interobserver variation by the same observers on the same patients on CT without MRI (CT-only).Results: The maximum ratios between delineated volumes within a patient were 6.1 and 22.4 for the GTV (3DCT) and iGTV (4DCT), respectively. The average (root-mean-square) overall observer variations were SD = 0.41 cm (GTV) and SD = 0.73 cm (iGTV). The mean CIgen was 0.36 for GTV and 0.37 for iGTV. When compared to the iGTV delineated on CT-only, the mean volumes of the iGTV on CT + MRI were significantly smaller (32%, Wilcoxon signed-rank, p < .0005). The median volumes of the iGTV on CT + MRI were included for 97% and 92% in the median volumes of the iGTV on CT. Furthermore, CT + MRI showed smaller overall observer variations (root-mean-square SD = 0.59 cm) in six out of eight delineated structures compared to CT-only (root-mean-square SD = 0.72 cm). However, large local observer variations remained close to biliary stents and pathological lymph nodes, indicating issues with instructions and instruction compliance.Conclusions: The availability of MRI images during target delineation of pancreatic cancer on 3DCT and 4DCT resulted in smaller target volumes and reduced the interobserver variation in six out of eight delineated structures.

Considerable interobserver variation in delineation of pancreatic cancer on 3DCT and 4DCT: a multi-institutional study

BackgroundThe delineation of pancreatic tumors on CT is challenging. In this study, we quantified the interobserver variation for pancreatic tumor delineation on 3DCT as well as on 4DCT.MethodsEight observers (radiation oncologists) from six institutions delineated pancreatic tumors of four patients with (borderline) resectable pancreatic cancer. The study consisted of two stages. In the 3DCT-stage, the gross tumor volume (GTV) was delineated on a contrast-enhanced scan. In the 4DCT-stage, the internal GTV (iGTV) was delineated, accounting for the respiratory motion. We calculated the volumes of the (i)GTV, the overlap of the delineated volumes (expressed as generalized conformity index: CIgen), the local observer variation (local standard deviation: SD) and the overall observer variation (overall SD). We compared these results between GTVs and iGTVs. Additionally, observers were asked to fill out a questionnaire concerning the difficulty of the delineation and their experience in delineating pancreatic tumors.ResultsThe ratios of the largest to the smallest delineated GTV and iGTV within the same patient were 6.8 and 16.5, respectively. As the iGTV incorporates the GTV during all respiratory phases, the mean volumes of the iGTV (40.07 cm3) were larger than those of the GTV (29.91 cm3). For all patients, CIgen was larger for the iGTV than for the GTV. The mean overall observer variation (root-mean-square of all local SDs over four patients) was 0.63 cm and 0.80 cm for GTV and iGTV, respectively. The largest local observer variations were seen close to biliary stents and suspicious pathological enlarged lymph nodes, as some observers included them and some did not. This variation was more pronounced for the iGTV than for the GTV. The observers rated the 3DCT-stage and 4DCT-stage equally difficult and treated on average three to four pancreatic cancer patients per year.ConclusionsA considerable interobserver variation in delineation of pancreatic tumors was observed. This variation was larger for 4D than for 3D delineation. The largest local observer variation was found around biliary stents and suspicious pathological enlarged lymph nodes.