Purpose
Radiochromic film has been established as a detector that can be used without the need for perturbation correction factors for small field dosimetry in water. However, perturbation factors in ...low density media such as lung have yet to be published. This study calculated the factors required to account for the perturbation of radiochromic film when used for small field dosimetry in lung equivalent material.
Method
Monte Carlo simulations were used to calculate dose to Gafchromic EBT3 film when placed inside a lung phantom. The beam simulated had a nominal energy of 6 MV and the field sizes simulated ranged from 10 × 10 mm2 to 30 × 30 mm2. The lung density simulated was varied between 0.2 and 0.3 g/cm3. Each simulation was repeated with the film replaced by lung material (the same as the surrounding medium), and the required correction factors for film dosimetry in lung (DMed,QDDet,Q) were calculated by dividing the dose in lung by the dose in film.
Results
For field sizes 30 × 30 mm2 and larger, no correction factors were required. At a 20 × 20 mm2 field size, small corrections were required, but were within the approximate accuracy of film dosimetry (~2%). For a 10 × 10 mm2 field size, significant correction factors need to be applied (0.935 for lung density of 0.20 g/cm3 to 0.963 for lung density of 0.30 g/cm3). The values lower than one mean that the film is over‐responding. At the “upstream” lung‐water interface the correction factors were close to unity; while at the downstream interface the corrections required were marginally smaller to those at the center of lung. One centimeter or more away from the interfaces, the correction factor did not vary as a function distance from the interface (in the beam direction). Away from the central axis (perpendicular to the beam direction), the correction factors increased slightly (away from unity) as a function of off‐axis distance, before abruptly changing direction at the penumbra, with the film actually under‐responding by ~10% outside the field edges.
Conclusion
Accurate dosimetry of very small fields (15 × 15 mm2 or smaller) using radiochromic film requires correction factors for the perturbation of the film on the surrounding lung material. This correction factor was as high as 6.5% for a 10 × 10 mm2 field size and a density of 0.2 g/cm3. This will increase if either the density or the field size decrease further. This correction factor does not vary as a function of depth in lung once charged particle equilibrium is established.
A microalgae growth model was developed for predicting biomass productivity in outdoor ponds under nutrient-replete conditions and diurnally fluctuating light intensities and water temperatures. The ...model was validated for three different species (Chlorella sorokiniana, Nannochloropsis salina, Picochlorum sp.), successfully predicting biomass growth and productivity in all three cases in raceway pond cultures.
The model can be run in batch and continuous culture mode at different culture depths and, in addition to incident sunlight and water temperature data, requires the following experimentally determined strain-specific input parameters: growth rate as a function of light intensity and temperature, biomass loss rate in the dark as a function of temperature and light intensity during the preceding light period, and the scatter-corrected biomass light absorption coefficient. Light attenuation due to biomass was estimated on the basis of a scatter-corrected Beer–Lambert law in a culture theoretically divided into discrete volume layers which receive decreasing amounts of light with depth.
Sensitivity of model predictions to deviations in input parameters was moderate. To increase the predictive power of this and other microalgae biomass growth models, a better understanding is needed of the effects of mixing-induced rapid light–dark cycles on photo-inhibition and short-term biomass losses due to dark respiration in the aphotic zone of the pond. The model is also applicable to photobioreactor cultures.
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Individuals with developmental disabilities have specific physical and psychosocial needs that can require extra support to participate fully in and enjoy many benefits of recreation activities. ...Unfortunately, little is known about individuals with developmental disabilities' experiences in outdoor recreation. The purpose of this study was to explore adults with developmental disabilities' perceived benefits of outdoor recreation, and the constraints or facilitators that affected their participation.
Qualitative, semi-structured interviews were conducted with seven adults with developmental disabilities. Interviews were analysed using open, axial, and selective coding techniques.
Results revealed three themes: (a) benefits of; (b) constraints to; and (c) facilitators of outdoor recreation. Benefits of outdoor recreation reported by study participants included their experiencing satisfaction, mental reprieve, empowerment, enlightenment, social connectedness, and thrill. Participants also shared intrapersonal, interpersonal, and structural constraints and facilitators related to their outdoor recreation participation.
Practical implications and future research recommendations are discussed.
This study aimed to provide a detailed evaluation and comparison of a range of modulated beam evaluation metrics, in terms of their correlation with QA testing results and their variation between ...treatment sites, for a large number of treatments. Ten metrics including the modulation index (MI), fluence map complexity, modulation complexity score (MCS), mean aperture displacement (MAD) and small aperture score (SAS) were evaluated for 546 beams from 122 intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment plans targeting the anus, rectum, endometrium, brain, head and neck and prostate. The calculated sets of metrics were evaluated in terms of their relationships to each other and their correlation with the results of electronic portal imaging based quality assurance (QA) evaluations of the treatment beams. Evaluation of the MI, MAD and SAS suggested that beams used in treatments of the anus, rectum, head and neck were more complex than the prostate and brain treatment beams. Seven of the ten beam complexity metrics were found to be strongly correlated with the results from QA testing of the IMRT beams (p < 0.00008). For example, values of SAS (with multileaf collimator apertures narrower than 10 mm defined as 'small') less than 0.2 also identified QA passing IMRT beams with 100% specificity. However, few of the metrics are correlated with the results from QA testing of the VMAT beams, whether they were evaluated as whole 360° arcs or as 60° sub-arcs. Select evaluation of beam complexity metrics (at least MI, MCS and SAS) is therefore recommended, as an intermediate step in the IMRT QA chain. Such evaluation may also be useful as a means of periodically reviewing VMAT planning or optimiser performance.
Purpose:
The aim of this work was to use a multicenter audit of modulated radiotherapy quality assurance (QA) data to provide a practical examination of gamma evaluation criteria and action level ...selection. The use of the gamma evaluation method for patient-specific pretreatment QA is widespread, with most commercial solutions implementing the method.
Methods:
Gamma agreement indices were calculated using the criteria 1%/1 mm, 2%/2 mm, 2%/3 mm, 3%/2 mm, 3%/3 mm, and 5%/3 mm for 1265 pretreatment QA measurements, planned at seven treatment centers, using four different treatment planning systems, delivered using three different delivery systems (intensity-modulated radiation therapy, volumetric-modulated arc therapy, and helical tomotherapy) and measured using three different dose measurement systems. The sensitivity of each pair of gamma criteria was evaluated relative to the gamma agreement indices calculated using 3%/3 mm.
Results:
A linear relationship was observed for 2%/2 mm, 2%/3 mm, and 3%/2 mm. This result implies that most beams failing at 3%/3 mm would also fail for those criteria, if the action level was adjusted appropriately. Some borderline plans might be passed or failed depending on the relative priority (tighter tolerance) used for dose difference or distance to agreement evaluation. Dosimeter resolution and treatment modality were found to have a smaller effect on the results of QA measurements than the number of dimensions (2D or 3D) over which the gamma evaluation was calculated.
Conclusions:
This work provides a method (and a large sample of results) for calculating equivalent action levels for different gamma evaluation criteria. This work constitutes a valuable guide for clinical decision making and a means to compare published gamma evaluation results from studies using different evaluation criteria. More generally, the data provided by this work support the recommendation that gamma criteria that specifically prioritize the property of greatest clinical importance for each treatment modality of anatomical site should be selected when using gamma evaluations for modulated radiotherapy QA. It is therefore suggested that departments using the gamma evaluation as a QA analysis tool should consider the relative importance of dose difference and distance to agreement, when selecting gamma evaluation criteria.
Abstract Contemporary models of obsessive-compulsive disorder emphasize the importance of harm avoidance (HA) and related dysfunctional beliefs as motivators of obsessive-compulsive (OC) symptoms. ...Recently, there has been a resurgence of interest in Janet’s (1908) concept of incompleteness (INC) as another potentially important motivator. Contemporary investigators define INC as the sense that one’s actions, intentions, or experiences have not been properly achieved. Janet defined INC more broadly to include alexithymia, depersonalization, derealization, and impaired psychological mindedness. We conducted two studies to address four issues: (a) the clinical correlates of INC; (b) whether INC and HA are distinguishable constructs; (c) whether INC predicts OC symptoms after controlling for HA; and (d) the relative merits of broad versus narrow conceptualizations of INC. Study 1 was a meta-analysis of the clinical correlates of narrowly defined INC (16 studies, N = 5,940). INC was correlated with all types of OC symptoms, and was more strongly correlated with OC symptoms than with general distress. Study 2 ( N = 534 nonclinical participants) showed that (a) INC and HA were strongly correlated but factor analytically distinguishable; (b) INC statistically predicted all types of OC symptoms even after controlling for HA; and (c) narrow INC was most strongly correlated with OC symptoms whereas broad INC was most strongly correlated with general distress. Although the findings are limited by being correlational in nature, they support the hypothesis that INC, especially in its narrow form, is a motivator of OC symptoms.
In the context of a lack of national consensus on the benefits of skull base imaging in children with osteogenesis imperfecta (OI), this study aims to analyse and correlate the clinical symptoms and ...radiological images of children with severe OI.
A retrospective case notes and image analysis was carried out on children with complex OI between 2012 and 2018 at a specialist tertiary centre. Data were collected on patient demographic factors, clinical data, imaging findings (presence of Wormian bones, platybasia, basilar impression (McGregor’s technique) and basilar invagination (McRae’s technique)), and clinical features at the time of imaging.
Of the 127 patients in the OI database, 94 were included. A total of 321 radiographs, 21 CT scans and 39 MRI scans were analysed. Average frequency of radiographs was 8 per 10 years. Of the 94 patients, 58 (62%), 10 (11%), 1 (1%) demonstrated platybasia, basilar impression, and basilar invagination, respectively. Of the radiographs analysed, platybasia, basilar impression, basilar invagination, and the presence of Wormian bones, could not be evaluated in 71 (22.3%), 48 (15.2%), 61 (19.5%) and 28 (9.4%) radiographs respectively (due to poor positioning, anatomical abnormalities, and poor image quality). Of the 140 radiographs with platybasia, 17 (12%) also demonstrated basilar impression compared to only 3 (2.9%) out of the 99 without platybasia (p = 0.03). No significant associations were seen between the presence of Wormian bones and basilar impression.
Of the 39 MRIs, additional information on CSF flow rate, spinal cord signal and cerebellar morphology was reported in 14 (36%). There was a lack of concordance between MRI and matched radiographs in 7.1% (1/14) and 36% (5/14) for platybasia and basilar impression respectively, with full concordance for basilar invagination.
Fewer than 5% had positive clinical symptoms/signs at the time of imaging; 2% (7/321) had macrocephaly, 0.6% (2/321) headache, all other neurological features were absent). Clinical features were not documented in >85% of patients.
The apparent low prevalence of clinical symptoms and signs and of radiologically identified cranio-cervical abnormalities, suggests that current levels of serial imaging may be excessive. Until larger prospective studies clarify these issues, we suggest a clinical pathway for base of skull imaging which proposes a risk stratification approach to radiographic frequency and suggests parameters for proceeding to MRI.
•There appears to be a low prevalence of radiologically identified cranio-cervical abnormalities.•Routine serial imaging may be leading to more skull base imaging than is needed.•MR imaging provides more detailed and accurate evaluation of the skull base.•We propose a risk stratification approach to radiographic frequency and parameters for MRI.
Fourier transform infrared (FT-IR) microspectroscopic imaging, Raman microspectroscopy, optical microscopy and high performance liquid chromatography with mass spectrometric (LC/MS) detection were ...employed to examine a dietary supplement adulterated with an undeclared active pharmaceutical ingredient (API). While a trace level of the API was detected in the capsule contents, a higher concentration of API was found in the capsule shell, which indicated the use of an unconventional manufacturing process to hide the API and thus avoid detection. This study demonstrates the need for a multidisciplinary approach to provide a complete assessment of a suspect adulterated dietary supplement.
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