Geometric and dosimetric evaluations of atlas-based segmentation methods of MR images in the head and neck region

Owing to its excellent soft-tissue contrast, magnetic resonance (MR) imaging has found an increased application in radiation therapy (RT). By harnessing these properties for treatment planning, automated segmentation methods can alleviate the manual workload burden to the clinical workflow. We investigated atlas-based segmentation methods of organs at risk (OARs) in the head and neck (H&N) region using one approach that selected the most similar atlas from a library of segmented images and two multi-atlas approaches. The latter were based on weighted majority voting and an iterative atlas-fusion approach called STEPS. We built the atlas library from pre-treatment T1-weighted MR images of 12 patients with manual contours of the parotids, spinal cord and mandible, delineated by a clinician. Following a leave-one-out cross-validation strategy, we measured the geometric accuracy by calculating Dice similarity coefficients (DSC), standard and 95% Hausdorff distances (HD and HD95), and the mean surface distance (MSD), whereby the manual contours served as the gold standard. To benchmark the algorithm, we determined the inter-observer variability (IOV) between three observers. To investigate the dosimetric effect of segmentation inaccuracies, we implemented an auto-planning strategy within the treatment planning system Monaco (Elekta AB, Stockholm, Sweden). For each set of auto-segmented OARs, we generated a plan for a 9-beam step and shoot intensity modulated RT treatment, designed according to our institution's clinical H&N protocol. Superimposing the dose distributions on the gold standard OARs, we calculated dose differences to OARs caused by delineation differences between auto-segmented and gold standard OARs. We investigated the correlations between geometric and dosimetric differences. The mean DSC was larger than 0.8 and the mean MSD smaller than 2 mm for the multi-atlas approaches, resulting in a geometric accuracy comparable to previously published results and within the range of the IOV. While dosimetric differences could be as large as 23% of the clinical goal, treatment plans fulfilled all imposed clinical goals for the gold standard OARs. Correlations between geometric and dosimetric measures were low with R2  <  0.5. The geometric accuracy and the ability to achieve clinically acceptable treatment plans indicate the suitability of using atlas-based contours for RT treatment planning purposes. The low correlations between geometric and dosimetric measures suggest that geometric measures alone are not sufficient to predict the dosimetric impact of segmentation inaccuracies on treatment planning for the data utilised in this study.

Geometric and dosimetric evaluations of atlas-based segmentation methods of MR images in the head and neck region

Owing to its excellent soft-tissue contrast, magnetic resonance (MR) imaging has found an increased application in radiation therapy (RT). By harnessing these properties for treatment planning, automated segmentation methods can alleviate the manual workload burden to the clinical workflow. We investigated atlas-based segmentation methods of organs at risk (OARs) in the head and neck (H&N) region using one approach that selected the most similar atlas from a library of segmented images and two multi-atlas approaches. The latter were based on weighted majority voting and an iterative atlas-fusion approach called STEPS. We built the atlas library from pre-treatment T1-weighted MR images of 12 patients with manual contours of the parotids, spinal cord and mandible, delineated by a clinician. Following a leave-one-out cross-validation strategy, we measured the geometric accuracy by calculating Dice similarity coefficients (DSC), standard and 95% Hausdorff distances (HD and HD95), and the mean surface distance (MSD), whereby the manual contours served as the gold standard. To benchmark the algorithm, we determined the inter-observer variability (IOV) between three observers. To investigate the dosimetric effect of segmentation inaccuracies, we implemented an auto-planning strategy within the treatment planning system Monaco (Elekta AB, Stockholm, Sweden). For each set of auto-segmented OARs, we generated a plan for a 9-beam step and shoot intensity modulated RT treatment, designed according to our institution's clinical H&N protocol. Superimposing the dose distributions on the gold standard OARs, we calculated dose differences to OARs caused by delineation differences between auto-segmented and gold standard OARs. We investigated the correlations between geometric and dosimetric differences. The mean DSC was larger than 0.8 and the mean MSD smaller than 2 mm for the multi-atlas approaches, resulting in a geometric accuracy comparable to previously published results and within the range of the IOV. While dosimetric differences could be as large as 23% of the clinical goal, treatment plans fulfilled all imposed clinical goals for the gold standard OARs. Correlations between geometric and dosimetric measures were low with R²  <  0.5. The geometric accuracy and the ability to achieve clinically acceptable treatment plans indicate the suitability of using atlas-based contours for RT treatment planning purposes. The low correlations between geometric and dosimetric measures suggest that geometric measures alone are not sufficient to predict the dosimetric impact of segmentation inaccuracies on treatment planning for the data utilised in this study.

Evaluation of a multi-atlas CT synthesis approach for MRI-only radiotherapy treatment planning

BACKGROUND AND PURPOSE

Computed tomography (CT) imaging is the current gold standard for radiotherapy treatment planning (RTP). The establishment of a magnetic resonance imaging (MRI) only RTP workflow requires the generation of a synthetic CT (sCT) for dose calculation. This study evaluates the feasibility of using a multi-atlas sCT synthesis approach (sCTa) for head and neck and prostate patients.

MATERIAL AND METHODS

The multi-atlas method was based on pairs of non-rigidly aligned MR and CT images. The sCTa was obtained by registering the MRI atlases to the patient's MRI and by fusing the mapped atlases according to morphological similarity to the patient. For comparison, a bulk density assignment approach (sCTbda) was also evaluated. The sCTbda was obtained by assigning density values to MRI tissue classes (air, bone and soft-tissue). After evaluating the synthesis accuracy of the sCTs (mean absolute error), sCT-based delineations were geometrically compared to the CT-based delineations. Clinical plans were re-calculated on both sCTs and a dose-volume histogram and a gamma analysis was performed using the CT dose as ground truth.

RESULTS

Results showed that both sCTs were suitable to perform clinical dose calculations with mean dose differences less than 1% for both the planning target volume and the organs at risk. However, only the sCTa provided an accurate and automatic delineation of bone.

CONCLUSIONS

Combining MR delineations with our multi-atlas CT synthesis method could enable MRI-only treatment planning and thus improve the dosimetric and geometric accuracy of the treatment, and reduce the number of imaging procedures.

Use of herbs, spices and their bioactive compounds in active food packaging

Natural additives obtained from herbs and spices are being increasingly used in the food packaging industry.

Behavioural symptoms of children with HIV infection living in the Dominican Republic

OBJECTIVE

The purpose of this report is to describe behavioural problems encountered in a group of Dominican children living with Human Immunodeficency Virus/Acquired Immunodeficiency Syndrome (HIV/AIDS) in the Dominican Republic. They were not receiving antiretroviral treatment.

METHOD

The participants were 43 children with HIV infection (2 to 8 years of age) who were attending an immunology clinic in the largest paediatric hospital in the Dominican Republic. All of the participants were vertically infected with the HIV virus (mother-to-child transmission) and had a very low socio-economic status. The children's caregivers were administered the Child Behavioural Checklist (CBCL) by trained psychologists to determine the caregivers 'perception of the children's behavioural problems. Behavioural findings were examined according to the CBCL age format: younger children (under 5 years of age) and older children (over 6 years of age).

RESULTS

Descriptive statistics revealed a high proportion of the children, both younger (approximately 40%) and older (46%) scored in the borderline/clinical ranges for internalizing problems, including anxiety, withdrawn-depressed and somatic complaints. In addition, 46% of the older children were perceived as having externalizing problems (rule breaking and aggressive behaviour).

CONCLUSION

These findings suggest that a high incidence of behavioural and mood problems may be prevalent among Dominican children with HIV Thefindings are discussed in terms of future research to examine other risk factors that might contribute to the high rate of maladaptive behaviours observed in the present report, including the contribution of socio-economic status, caregiver illness, caregiver education and parental loss.

Caregivers' perception of HIV-infected Dominican children's behaviour

Caregivers (mothers and non-mothers) of HIV children face many challenges related to both physical demands and emotional well-being. The perception of caregivers in the Dominican Republic, a country greatly impacted by HIV/AIDS, in regard to their children's behaviour, has not been investigated to date. To extend understanding of the potential behavioural issues involved in providing care to children without access to antiretroviral therapy, the Child Behaviour Checklist was administered to 52 caregivers of HIV Dominican children (2-8 years old). Both mothers and non-mothers perceived significant pathological internalizing behavioural symptoms in immunosuppressed children, compared to children with less disease progression. Analyses of gender comparisons revealed that older female children were perceived as withdrawn/depressed by their caregivers. These findings suggest that children's disease status may be an important contributor to caregiver perception in mothers, as well as non-mothers and indicate that gender-specific relationships warrant further study.

[Acute poisoning with methotrexate used as an abortifacient: description of 2 cases]

Acute intoxication with methotrexate, used as an abortive, has not been described in Chile. We report two female patients, aged 15 and 24 years old, who presented with mucositis, erythrodermia, pancytopenia, and elevation of hepatic enzymes. Plasma methotrexate levels confirmed the clinical diagnosis and both patients were treated with high leucovorin doses and management of associated complications. In one patient, pregnancy continued, giving birth to a newborn with cranial, face and limb malformations. The second patient had a late rescue with leucovorin and was discharged with a persistent sensory motor neuropathy. Considering the severity of complications and that patients may deny its use, when there is reasonable clinical suspicion of methotrexate intoxication, leucovorin treatment should be started.

Influence of Whitacre spinal needle orifice direction on the level of sensory blockade

The purposes of the present study were to determine if the direction of the needle orifice during injection of anesthetic into the subarachnoid space, using a 25-gauge Whitacre spinal needle (Becton Dickinson, Franklin Lakes, NJ) to deliver 15 mg of 0.75% hyperbaric bupivacaine, affected the level of sensory blockade achieved, and if there was a difference in time from injection to surgical anesthesia based on needle orifice direction. A convenience sample was selected from patients presenting for elective surgical procedures. All patients received a standard anesthetic solution using a standard technique and duration of injection. Mean maximum height of sensory blockade was compared between treatment groups using a Student t test. Progression of the sensory blockade was compared at each data collection point using a chi-square test. There was no statistically significant difference in the mean maximum height of block between the treatment groups. The mean maximum height of block for the cephalad group was T4 with an SD of 2.5 dermatomes, and T5 with an SD of 4.57 dermatomes for the caudad group. An incidental finding was that all failed blocks were from the caudad group. There was no statistically significant difference in time from injection to surgical anesthesia between the treatment groups. Although the data support no statistically significant difference between the treatment groups for either research question, the cephalad group provides for a more precise height of block.