Highlights • A guideline for quality control of cone-beam computed tomography is now complete. • The guideline describes objective tests for radiation output and image quality. • The tests are valid ...for all kinds of cone-beam computed tomography systems. • Test frequencies and action levels were consensed by EFOMP, ESTRO and IAEA.
Purpose
For the cancer in the head and neck (HaN), radiotherapy (RT) represents an important treatment modality. Segmentation of organs‐at‐risk (OARs) is the starting point of RT planning, however, ...existing approaches are focused on either computed tomography (CT) or magnetic resonance (MR) images, while multimodal segmentation has not been thoroughly explored yet. We present a dataset of CT and MR images of the same patients with curated reference HaN OAR segmentations for an objective evaluation of segmentation methods.
Acquisition and validation methods
The cohort consists of HaN images of 56 patients that underwent both CT and T1‐weighted MR imaging for image‐guided RT. For each patient, reference segmentations of up to 30 OARs were obtained by experts performing manual pixel‐wise image annotation. By maintaining the distribution of patient age and gender, and annotation type, the patients were randomly split into training Set 1 (42 cases or 75%) and test Set 2 (14 cases or 25%). Baseline auto‐segmentation results are also provided by training the publicly available deep nnU‐Net architecture on Set 1, and evaluating its performance on Set 2.
Data format and usage notes
The data are publicly available through an open‐access repository under the name HaN‐Seg: The Head and Neck Organ‐at‐Risk CT & MR Segmentation Dataset. Images and reference segmentations are stored in the NRRD file format, where the OAR filenames correspond to the nomenclature recommended by the American Association of Physicists in Medicine, and OAR and demographics information is stored in separate comma‐separated value files.
Potential applications
The HaN‐Seg: The Head and Neck Organ‐at‐Risk CT & MR Segmentation Challenge is launched in parallel with the dataset release to promote the development of automated techniques for OAR segmentation in the HaN. Other potential applications include out‐of‐challenge algorithm development and benchmarking, as well as external validation of the developed algorithms.
Background
Accurate and consistent contouring of organs‐at‐risk (OARs) from medical images is a key step of radiotherapy (RT) cancer treatment planning. Most contouring approaches rely on computed ...tomography (CT) images, but the integration of complementary magnetic resonance (MR) modality is highly recommended, especially from the perspective of OAR contouring, synthetic CT and MR image generation for MR‐only RT, and MR‐guided RT. Although MR has been recognized as valuable for contouring OARs in the head and neck (HaN) region, the accuracy and consistency of the resulting contours have not been yet objectively evaluated.
Purpose
To analyze the interobserver and intermodality variability in contouring OARs in the HaN region, performed by observers with different level of experience from CT and MR images of the same patients.
Methods
In the final cohort of 27 CT and MR images of the same patients, contours of up to 31 OARs were obtained by a radiation oncology resident (junior observer, JO) and a board‐certified radiation oncologist (senior observer, SO). The resulting contours were then evaluated in terms of interobserver variability, characterized as the agreement among different observers (JO and SO) when contouring OARs in a selected modality (CT or MR), and intermodality variability, characterized as the agreement among different modalities (CT and MR) when OARs were contoured by a selected observer (JO or SO), both by the Dice coefficient (DC) and 95‐percentile Hausdorff distance (HD 95$_{95}$).
Results
The mean (±standard deviation) interobserver variability was 69.0 ± 20.2% and 5.1 ± 4.1 mm, while the mean intermodality variability was 61.6 ± 19.0% and 6.1 ± 4.3 mm in terms of DC and HD 95$_{95}$, respectively, across all OARs. Statistically significant differences were only found for specific OARs. The performed MR to CT image registration resulted in a mean target registration error of 1.7 ± 0.5 mm, which was considered as valid for the analysis of intermodality variability.
Conclusions
The contouring variability was, in general, similar for both image modalities, and experience did not considerably affect the contouring performance. However, the results indicate that an OAR is difficult to contour regardless of whether it is contoured in the CT or MR image, and that observer experience may be an important factor for OARs that are deemed difficult to contour. Several of the differences in the resulting variability can be also attributed to adherence to guidelines, especially for OARs with poor visibility or without distinctive boundaries in either CT or MR images. Although considerable contouring differences were observed for specific OARs, it can be concluded that almost all OARs can be contoured with a similar degree of variability in either the CT or MR modality, which works in favor of MR images from the perspective of MR‐only and MR‐guided RT.
•Hippocampal (HC) sparing RT for nasopharyngeal cancer (NPC) is feasible and safe.•Lower HC dose translates to significantly lower probability of memory decline.•The cognitive well-being in NPC ...patients should be paramount in RT planning.
Radiation-induced damage to the hippocampi can cause cognitive decline. International recommendations for nasopharyngeal cancer (NPC) radiotherapy (RT) lack specific guidelines for protecting the hippocampi. Our study evaluates if hippocampi-sparing (HS) RT in NPC ensures target coverage and meets recommended dose limits for other at-risk organs.
In a systematic literature review, we compared hippocampal D40% in conventional and HS RT plans. In an in silico dosimetric study, conventional and HS-VMAT plans were created for each patient, following international recommendations for OAR delineation, dose prioritization and acceptance criteria. We assessed the impact on neurocognitive function using a previously published normal tissue complication probability (NTCP) model.
In four previous studies (n = 79), researchers reduced D40% hippocampal radiation doses in HS plans compared to conventional RT on average from 24.9 Gy to 12.6 Gy.
Among 12 NPC patients included in this in silico study, statistically significant differences between HS and conventional VMAT plans were observed in hippocampal EQD2 Dmax (23.8 vs. 46.4 Gy), Dmin (3.8 vs. 4.6 Gy), Dmean (8.1 vs. 15.1 Gy), and D40% (8.3 vs. 15.8 Gy). PTV coverage and OAR doses were similar, with less homogeneous PTV coverage in HS plans (p = 0.038). This translated to a lower probability of memory decline in HS plans (interquartile range 15.8–29.6 %) compared to conventional plans (33.8–81.1 %) based on the NTCP model (p = 0.002).
Sparing the hippocampus in NPC RT is safe and feasible. Given the life expectancy of many NPC patients, their cognitive well-being must be paramount in radiotherapy planning.
A model of vesicle electrodeformation is described which obtains a parametrized vesicle shape by minimizing the sum of the membrane bending energy and the energy due to the electric field. Both the ...vesicle membrane and the aqueous media inside and outside the vesicle are treated as leaky dielectrics, and the vesicle itself is modeled as a nearly spherical shape enclosed within a thin membrane. It is demonstrated (a) that the model achieves a good quantitative agreement with the experimentally determined prolate-to-oblate transition frequencies in the kilohertz range and (b) that the model can explain a phase diagram of shapes of giant phospholipid vesicles with respect to two parameters: the frequency of the applied alternating current electric field and the ratio of the electrical conductivities of the aqueous media inside and outside the vesicle, explored in a recent paper (S. Aranda et al., Biophys J 95:L19-L21, 2008). A possible use of the frequency-dependent shape transitions of phospholipid vesicles in conductometry of microliter samples is discussed.
To devise a secondary cross-check for the software used in the quality control (QC) of the isocenter wobble during the collimator, couch and gantry rotation.
Monthly QC of the radiation isocenter ...wobble is performed with 3 slit-like fields spaced 120° apart, exposing cassettes with phosphor imaging plates, which are scanned using Kodak ACR-2000 tabletop computed radiography system. The ensuing DICOM images are analyzed both with Pipspro 4.4 (Standard Imaging, Middleton, WI, USA) and Pylinac 2.0.1 (James Kerns, https://pypi.python.org/pypi/pylinac) starshot module. The diameter of the circle which touches the projections at the point of intersection is taken as an estimate of the isocenter wobble.
Preliminary results obtained on data for a single treatment machine show an agreement which is below our expectations. The means (±standard deviations) for the difference of values obtained by the two methods are −0.014 mm (±0.268 mm) for the collimator, −0.162 mm (±0.229 mm) for the couch, and −0.064 mm (±0.180 mm) for the gantry.
The results show that at least one of the programs is performing sub-optimally. As a next step, we intend to test both systems with a set of synthetic images with varying ”wobble“. Our intention is to establish Pylinac as a primary standard, as it is an open-source solution, the correctness of which can be verified independently by analyzing the source code, and test the proprietary ”black-box“ solutions against it.
Lung cancer patients are often in poor physical condition, and a shorter treatment time would reduce their discomfort. Dynamic conformal arc therapy (DCAT) offers a shorter treatment time than ...conventional 3D conformal radiotherapy (3D CRT) and is usually available even in departments without inverse planning possibilities. We examined its suitability as a treatment modality for lung cancer patients.
On a cohort of 35 lung cancer patients, relevant dosimetric parameters were compared in respective DCAT and 3D CRT treatment plans. Radiochromic film dosimetry in an anthropomorphic phantom was used to compare both DCAT and 3D CRT dose distributions against their planned counterparts.
In comparison with their 3D CRT counterparts, DCAT plans equal or exceed the agreement between the calculated dose and the dose measured using film dosimetry. In dosimetric comparison, DCAT performed significantly better than 3D CRT in dose conformity to PTV and the number of monitor units used per plan, and significantly worse in dose homogeneity, mean lung dose and lung volume exposed to 5 Gy or more (V5Gy). No significant difference was found in the V20Gy value to lung, dose to 1 cm
of spinal cord, and the mean dose to oesophagus. Improvements in V20Gy and V5Gy were found to be negatively correlated. DCAT plans differ from 3D CRT by exhibiting a moderate negative correlation between target volume sphericity and dose homogeneity.
With respect to the agreement between the planned and the irradiated dose distribution, DCAT appears at least as reliable as 3D CRT. In specific conditions concerning the patient anatomy and treatment prescription, DCAT may yield more favourable dosimetric parameters. On average, however, conventional 3D CRT usually obtains better dosimetric parameters. We can thus only recommend DCAT as a complementary technique to the conventional 3D CRT.
Partitioning of fatty acids into phospholipid membranes is studied on giant unilamellar vesicles (GUVs) utilizing phase-contrast microscopy. With use of a micropipet, an individual GUV is transferred ...from a vesicle suspension in a mixed glucose/sucrose solution into an isomolar glycerol solution with a small amount of oleic acid added. Oleic acid molecules intercalate into the phospholipid membrane and thus increase the membrane area, while glycerol permeates into the vesicle interior and thus via osmotic inflation causes an increase of the vesicle volume. The conditions are chosen at which a vesicle swells as a sphere. At sufficiently low oleic acid concentrations, when the critical membrane strain is reached, the membrane bursts and part of vesicle content is ejected, upon which the membrane reseals and the swelling commences again. The radius of the vesicle before and after the burst is determined at different concentrations of oleic acid in suspension. The results of our experiments show that the oleic acid partitioning increases when the membrane strain is increased. The observed behavior is interpreted on the basis of a tension-dependent intercalation of oleic acid into the membrane.
A recently described technique Estes and Mayer, Biochim. Biophys. Acta 1712 (2005) 152–160 for the preparation of giant unilamellar vesicles (GUVs) in solutions with high ionic strength is examined. ...By observing a series of osmotic swellings followed by vesicle bursts upon a micropipette transfer of a single POPC GUV from a sucrose solution into an iso-osmolar glycerol solution, a value for the permeability of POPC membrane for glycerol,
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