Dosimetric characterization of a new surface-conforming electron MLC prototype

The purpose is to reduce normal tissue radiation toxicity for electron therapy through the creation of a surface-conforming electron multileaf collimator (SCEM). The SCEM combines the benefits of skin collimation, electron conformal radiotherapy, and modulated electron radiotherapy. An early concept for the SCEM was constructed. It consists of leaves that protrude towards the patient, allowing the leaves to conform closely to irregular patient surfaces. The leaves are made of acrylic to decrease bremsstrahlung, thereby decreasing the out-of-field dose. Water tank scans were performed with the SCEM in place for various field sizes for all available electron energies (6, 9, 12, and 15 MeV) with a 0.5 cm air gap to the water surface at 100 cm source-to-surface distance (SSD). These measurements were compared with Cerrobend cutouts with the field size-matched at 100 and 110 cm SSD. Output factor measurements were taken in solid water for each energy at dmax for both the cerrobend cutouts and SCEM at 100 cm SSD. Percent depth dose (PDD) curves for the SCEM shifted shallower for all energies and field sizes. The SCEM also produced a higher surface dose relative to Cerrobend cutouts, with the maximum being a 9.8% increase for the 3 cm × 9 cm field at 9 MeV. When compared to the Cerrobend cutouts at 110 cm SSD, the SCEM showed a significant decrease in the penumbra, particularly for lower energies (i.e., 6 and 9 MeV). The SCEM also showed reduced out-of-field dose and lower bremsstrahlung production than the Cerrobend cutouts. The SCEM provides significant improvement in the penumbra and out-of-field dose by allowing collimation close to the skin surface compared to Cerrobend cutouts. However, the added scatter from the SCEM increases shallow PDD values. Future work will focus on reducing this scatter while maintaining the penumbra and out-of-field benefits the SCEM has over conventional collimation.

End to end comparison of surface-guided imaging versus stereoscopic X-rays for the SRS treatment of multiple metastases with a single isocenter using 3D anthropomorphic gel phantoms

INTRODUCTION

Two end-to-end tests evaluate the accuracy of a surface-guided radiation therapy (SGRT) system (CRAD Catalyst HD) for position verification in comparison to a stereoscopic x-ray imaging system (Brainlab Exactrac ) for single-isocenter, multiple metastases stereotactic radiosurgery (SRS) using 3D polymer gel inserts.

MATERIALS AND METHODS

A 3D-printed phantom (Prime phantom, RTsafe PC, Athens, Greece) with two separate cylindrical polymer gel inserts were immobilized in open-face masks and treated with a single isocentric, multitarget SRS plan. Planning was done in Brainlab (Elements) to treat five metastatic lesions in one fraction, and initial setup was done using cone beam computed tomography. Positional verification was done using orthogonal X-ray imaging (Brainlab Exactrac) and/or a surface imaging system (CRAD Catalyst HD, Uppsala, Sweden), and shift discrepancies were recorded for each couch angle. Forty-two hours after irradiation, the gel phantom was scanned in a 1.5 Tesla MRI, and images were fused with the patient computed tomography data/structure set for further analysis of spatial dose distribution.

RESULTS

Discrepancies between the CRAD Catalyst HD system and Brainlab Exactrac were <1 mm in the translational direction and <0.5° in the angular direction at noncoplanar couch angles. Dose parameters (DMean% , D95% ) and 3D gamma index passing rates were evaluated for both setup modalities for each planned target volume (PTV) at a variety of thresholds: 3%/2 mm (Exactrac≥93.1% and CRAD ≥87.2%), 5%/2 mm (Exactrac≥95.6% and CRAD ≥94.6%), and 5%/1 mm (Exactrac≥81.8% and CRAD ≥83.7%).

CONCLUSION

Dose metrics for a setup with surface imaging was found to be consistent with setup using x-ray imaging, demonstrating high accuracy and reproducibility for treatment delivery. Results indicate the feasibility of using surface imaging for position verification at noncoplanar couch angles for single-isocenter, multiple-target SRS using end-to-end quality assurance (QA) testing with 3D polymer gel dosimetry.

Interprofessional communication in medical simulation: findings from a scoping review and implications for academic medicine

BACKGROUND

Interprofessional communication is fundamental to the delivery of healthcare and can be taught in medical school and other health professional schools through interprofessional education (IPE) activities. Simulation centers have become a predominant location for simulation IPE activities with infrastructure able to support high fidelity activities in a controlled environment. In this secondary analysis of a scoping review conducted on simulation-based IPE, we describe the characteristics of previously reported simulation IPE activities involving undergraduate medical students in a simulation center focused on interprofessional communication.

METHODS

Electronic searches of PubMed, CINAHL, and ERIC databases in accordance with PRISMA-ScR guidelines were conducted to isolate relevant articles from 2016-2020. In total, 165 peer-reviewed articles met inclusion criteria and data extraction linked to four research questions was applied by one individual and the accuracy was confirmed by a second individual. A secondary analysis was performed to describe what existing approaches for simulation IPE in simulation center settings have been used to explicitly achieve interprofessional communication competencies in undergraduate medical education. A sub-dataset was developed from the original scoping review and identified 21 studies describing simulation IPE activities that took place in dedicated simulation centers, targeted the IPEC interprofessional communication domain, and involved undergraduate medical students.

RESULTS

Though diverse, the majority of simulation IPE activities described high-fidelity approaches involving standardized patients and utilized assessment tools with established validity evidence in IPE activities to measure learning outcomes. A minority of simulation IPE activities were described as hybrid and utilized more than one resource or equipment for the activity and only two were longitudinal in nature. Learning outcomes were focused predominantly on modification of attitudes/perceptions and few targeted higher levels of assessment.

CONCLUSIONS

Educators charged with developing simulation IPE activities for medical students focused on interprofessional communication should incorporate assessment tools that have validity evidence from similar activities, target higher level learning outcomes, and leverage hybrid models to develop longitudinal simulation IPE activities. Though an ideal environment to achieve higher level learning outcomes, simulation centers are not required for meaningful simulation IPE activities.

New antiparasitic derivatives of the furoquinoline alkaloids kokusaginine and flindersiamine

In this work is reported the synthesis of 16 new compounds obtained from kokusaginine and flindersiamine, the main alkaloids isolated from the bark of Balfourodendron riedelianum . The activity of the compounds against axenic cultures of Trypanosoma cruzi epimastigtotes and trypomastigotes, as well as intracellular amastigotes, is described, together with their cytotoxic activity against three different human cell lines. The synthetic strategy for the preparation of the new compounds was based on the reactivity at the position C-4 of the furoquinoline core towards nucleophiles. The new derivatives were synthesized by a Buchwald-Hartwig reaction, in most cases under green, solvent free conditions. Compounds 1c and 1e displayed better in-vitro activity against trypomastigotes than benznidazole and nifurtimox (positive controls) with IC 50 < 4 µM. In addition, both compounds were not cytotoxic activity against the three human cell lines K562 (erytroleukimia), LM2 (breast cancer) and HaCat (keratinocyte). Interestingly, when evaluated against intracellular amastigotes, compound 1c was able to significantly reduce the number of this parasite form, compared to the negative control.

Simulation interprofessional education in health professions education: a scoping review protocol

OBJECTIVE

The objective of this scoping review is to identify, collate, and map the evidence on simulation interprofessional education activities in any setting for the education of health professional students.

INTRODUCTION

Simulation interprofessional education activities comprise in-person and collaborative online learning embedded in formal curricula. Though the number of simulation interprofessional education activities has increased with the knowledge of the importance of effective interprofessional collaboration, the literature still lacks a description of the characteristics of existing activities.

INCLUSION CRITERIA

This scoping review will consider interprofessional education activities taking place within a simulation environment. Included papers will report on activities with two or more types of learners in health professional programs.

METHODS

The proposed scoping review will be conducted in accordance with the JBI methodology for scoping reviews. Databases searched will include PubMed, CINAHL, and ERIC. Results will be limited to English-language publications from 2016 to the present year. Data extraction will be performed using a purposefully developed data extraction tool. Teams of reviewers will screen abstracts and full texts of articles for potential inclusion, and decisions will be determined via consensus of two out of three reviewers. Extracted data will be presented in diagrammatic or tabular form in a manner that aligns with the objective of this scoping review. A narrative summary will accompany the tabulated and/or charted results and will describe how the results relate to the review's objective and questions, and how the results might inform future simulation interprofessional education activities in health professions education.

A customizable aluminum compensator system for total body irradiation

Purpose

To develop a simplified aluminum compensator system for total body irradiation (TBI) that is easy to assemble and modify in a short period of time for customized patient treatments.

Methods

The compensator is composed of a combination of 0.3 cm thick aluminum bars, two aluminum T‐tracks, spacers, and metal bolts. The system is mounted onto a plexiglass block tray. The design consists of 11 fixed sectors spanning from the patient's head to feet. The outermost sectors utilize 7.6 cm wide aluminum bars, while the remaining sectors use 2.5 cm wide aluminum bars. There is a magnification factor of 5 from the compensator to the patient treatment plane. Each bar of aluminum is interconnected at each adjacent sector with a tongue and groove arrangement and fastened to the T‐track using a metal washer, bolt, and nut. Inter‐bar leakage of the compensator was tested using a water tank and diode. End‐to‐end measurements were performed with an ion chamber in a solid water phantom and also with a RANDO phantom using internal and external optically stimulated luminescent detectors (OSLDs). In‐vivo patient measurements from the first 20 patients treated with this aluminum compensator were compared to those from 20 patients treated with our previously used lead compensator system.

Results

The compensator assembly time was reduced to 20–30 min compared to the 2–4 h it would take with the previous lead design. All end‐to‐end measurements were within 10% of that expected. The median absolute in‐vivo error for the aluminum compensator was 3.7%, with 93.8% of measurements being within 10% of that expected. The median error for the lead compensator system was 5.3%, with 85.1% being within 10% of that expected.

Conclusion

This design has become the standard compensator at our clinic. It allows for quick assembly and customization along with meeting the Task Group 29 recommendations for dose uniformity.

Effects of varying statistical uncertainty using a Monte Carlo based treatment planning system for VMAT

PURPOSE

To determine the severity of the effects on VMAT dose calculations caused by varying statistical uncertainties (SU) per control point in a Monte Carlo based treatment planning system (TPS) and to assess the impact of the uncertainty during dose volume histogram (DVH) evaluation.

METHODS

For this study, 13 archived patient plans were selected for recalculation. Treatment sites included prostate, lung, and head and neck. These plans were each recalculated five times with varying uncertainty levels using Elekta's Monaco Version 5.11.00 Monte Carlo Gold Standard XVMC dose calculation algorithm. The statistical uncertainty per control point ranged from 2 to 10% at intervals of 2%, while the grid spacing was set at 3 mm for all calculations. Indices defined by the RTOG describing conformity, coverage, and homogeneity were recorded for each recalculation.

RESULTS

For all indices tested, one-way ANOVA tests failed to reject the null hypothesis that there is no significant difference between SU levels (p>0.05). Using the Bland-Altman analysis method, it was determined that we can expect the indices (with the exception of CIRTOG) to be within 1% of the lowest uncertainty calculation when calculating at 4% SU per control point. Beyond that, we can expect the indices to be within 3% of the lowest uncertainty calculation.

CONCLUSION

Increasing the SU per control point exponentially decreased the amount of time required for dose calculations, while creating minimal observable differences in DVHs and isodose lines.

On the evaluation of mobile target trajectory between four-dimensional computer tomography and four-dimensional cone-beam computer tomography

Purpose

For mobile lung tumors, four‐dimensional computer tomography (4D CT) is often used for simulation and treatment planning. Localization accuracy remains a challenge in lung stereotactic body radiation therapy (SBRT) treatments. An attractive image guidance method to increase localization accuracy is 4D cone‐beam CT (CBCT) as it allows for visualization of tumor motion with reduced motion artifacts. However, acquisition and reconstruction of 4D CBCT differ from that of 4D CT. This study evaluates the discrepancies between the reconstructed motion of 4D CBCT and 4D CT imaging over a wide range of sine target motion parameters and patient waveforms.

Methods

A thorax motion phantom was used to examine 24 sine motions with varying amplitudes and cycle times and seven patient waveforms. Each programmed motion was imaged using 4D CT and 4D CBCT. The images were processed to auto segment the target. For sine motion, the target centroid at each phase was fitted to a sinusoidal curve to evaluate equivalence in amplitude between the two imaging modalities. The patient waveform motion was evaluated based on the average 4D data sets.

Results

The mean difference and root‐mean‐square‐error between the two modalities for sine motion were −0.35 ± 0.22 and 0.60 mm, respectively, with 4D CBCT slightly overestimating amplitude compared with 4D CT. The two imaging methods were determined to be significantly equivalent within ±1 mm based on two one‐sided t tests (p < 0.001). For patient‐specific motion, the mean difference was 1.5 ± 2.1 (0.8 ± 0.6 without outlier), 0.4 ± 0.3, and 0.8 ± 0.6 mm for superior/inferior (SI), anterior/posterior (AP), and left/right (LR), respectively.

Conclusion

In cases where 4D CT is used to image mobile tumors, 4D CBCT is an attractive localization method due to its assessment of motion with respect to 4D CT, particularly for lung SBRT treatments where accuracy is paramount.

Quantifying false positional corrections due to facial motion using SGRT with open-face Masks

Purpose

Studies have evaluated the viability of using open‐face masks as an immobilization technique to treat intracranial and head and neck cancers. This method offers less stress to the patient with comparable accuracy to closed‐face masks. Open‐face masks permit implementation of surface guided radiation therapy (SGRT) to assist in positioning and motion management. Research suggests that changes in patient facial expressions may influence the SGRT system to generate false positional corrections. This study aims to quantify these errors produced by the SGRT system due to face motion.

Methods

Ten human subjects were immobilized using open‐face masks. Four discrete SGRT regions of interest (ROIs) were analyzed based on anatomical features to simulate different mask openings. The largest ROI was lateral to the cheeks, superior to the eyebrows, and inferior to the mouth. The smallest ROI included only the eyes and bridge of the nose. Subjects were asked to open and close their eyes and simulate fear and annoyance and peak isocenter shifts were recorded. This was performed in both standard and SRS specific resolutions with the C‐RAD Catalyst HD system.

Results

All four ROIs analyzed in SRS and Standard resolutions demonstrated an average deviation of 0.3 ± 0.3 mm for eyes closed and 0.4 ± 0.4 mm shift for eyes open, and 0.3 ± 0.3 mm for eyes closed and 0.8 ± 0.9 mm shift for eyes open. The average deviation observed due to changing facial expressions was 1.4 ± 0.9 mm for SRS specific and 1.6 ± 1.6 mm for standard resolution.

Conclusion

The SGRT system can generate false positional corrections for face motion and this is amplified at lower resolutions and smaller ROIs. These errors should be considered in the overall tolerances and treatment plan when using open‐face masks with SGRT and may warrant additional radiographic imaging.

Robustness of single-isocenter multiple-metastasis stereotactic radiosurgery end-to-end testing across institutions

The accuracy of stereotactic radiosurgery (SRS) to multiple metastases with a single-isocenter using high definition dynamic radiosurgery (HDRS) was evaluated across institutions. An SRS plan was delivered at six HDRS-capable institutions to an anthropomorphic phantom consisting of point, film, and 3D-gel dosimeters. Direct dose comparison and gamma analysis were used to evaluate the accuracy. Point measurements averaged across institutions were within 1.2±0.5%. The average gamma passing rate in the film was 96.6±2.2% (3%/2 mm). For targets within 4 cm of the isocenter, the 3D dosimetric gel gamma passing rate averaged across institutions was >90% (3%/2 mm). The targeting accuracy of high definition dynamic radiosurgery assessed by geometrical offset of the center of dose distributions across multiple institutions in this study was within 1 mm for targets within 4 cm of isocenter. Across variations in clinical practice, comparable dosimetry and localization is possible with this treatment planning and delivery technique.

An evaluation of Pencil Beam vs Monte Carlo calculations for intracranial stereotactic radiosurgery

PURPOSE

To compare the accuracy of two separate models when calculating dose distributions in patients undergoing stereotactic radiosurgery (SRS) treatment for brain cancer.

METHODS

For this comparison, two dose calculation algorithms were evaluated on two different treatment planning systems (TPS): Elekta's Monaco Version 5.11.00 Monte Carlo Gold Standard XVMC algorithm and Brainlab's iPlan Pencil Beam algorithm. The DICOM files of 11 patients with a total of 19 targets were exported from iPlan and then imported into Monaco to be recalculated. Using the dose distributions of the original (pencil beam/PB) and recalculated (Monte Carlo/MC) plans, four indices for plan quality were evaluated: coverage (Q), conformity index (CIRTOG), homogeneity index (HI), and gradient index (GI).

RESULTS

There was a significant difference in the CIRTOG and HI between the two TPS calculations. However, the magnitude of these differences is often not substantial enough to cause the plan to fall outside of RTOG protocol deviation limits. Only 3 of the 19 targets had CIRTOG values which moved to a new level of deviation, and these targets were unique in terms of size (<0.1 cm3).

CONCLUSION

It was found that the difference between systems is often not enough to cause the plan to fall outside of RTOG protocol deviation limits. This is an indication that a PB-based treatment planning system is sufficient for the mostly homogeneous conditions of intracranial SRS planning when the target is larger than 0.1 cm3. If below 0.1 cm3, the prescribing physician may need to evaluate TPS differences.

Dose Calculation Comparisons between Three Modern Treatment Planning Systems

Purpose:

Monaco treatment planning system (TPS) version 5.1 uses a Monte-Carlo (MC)-based dose calculation engine. The aim of this study is to verify and compare the Monaco-based dose calculations with both Pinnacle³ collapsed cone convolution superposition (CCCS) and Eclipse anisotropic analytical algorithm (AAA) calculations.

Materials and Methods:

For this study, 18 previously treated lung and head-and-neck (HN) cancer patients were chosen to compare the dose calculations between Pinnacle, Monaco, and Eclipse. Plans were chosen from those that had been treated using the Elekta VersaHD or a Novalis Tx linac. All of the treated volumetric-modulated arc therapy plans used 6 MV or 10 MV photon beams. The original plans calculated with CCCS or AAA along with the recalculated ones using MC from the three TPS were exported into Velocity software for intercomparison.

Results:

To compare the dose calculations, Planning target volume (PTV) heterogeneity indexes and conformity indexes were calculated from the dose volume histograms (DVH) of all plans. While mean lung dose (MLD), lung V5 and V20 values were recorded for lung plans, the computed dose to parotids, brainstem, and mandible were documented for HN plans. In plan evaluation, percent differences of the above dosimetric values in Monaco computation were compared against each of the other TPS computations.

Conclusion:

It could be concluded through this research that there can be differences in the calculation of dose across different TPSs. Although relatively small, these differences could become apparent when compared using DVH. These differences most likely arise from the different dose calculation algorithms used in each TPS. Monaco employs the MC allowing it to have much more detailed calculations that result in it being seen as the most accurate and the gold standard.

Deep learning-based survival analysis for brain metastasis patients with the national cancer database

PURPOSE

Prognostic indices such as the Brain Metastasis Graded Prognostic Assessment have been used in clinical settings to aid physicians and patients in determining an appropriate treatment regimen. These indices are derivative of traditional survival analysis techniques such as Cox proportional hazards (CPH) and recursive partitioning analysis (RPA). Previous studies have shown that by evaluating CPH risk with a nonlinear deep neural network, DeepSurv, patient survival can be modeled more accurately. In this work, we apply DeepSurv to a test case: breast cancer patients with brain metastases who have received stereotactic radiosurgery.

METHODS

Survival times, censorship status, and 27 covariates including age, staging information, and hormone receptor status were provided for 1673 patients by the NCDB. Monte Carlo cross-validation with 50 samples of 1400 patients was used to train and validate the DeepSurv, CPH, and RPA models independently. DeepSurv was implemented with L2 regularization, batch normalization, dropout, Nesterov momentum, and learning rate decay. RPA was implemented as a random survival forest (RSF). Concordance indices of test sets of 140 patients were used for each sample to assess the generalizable predictive capacity of each model.

RESULTS

Following hyperparameter tuning, DeepSurv was trained at 32 min per sample on a 1.33 GHz quad-core CPU. Test set concordance indices of 0.7488 ± 0.0049, 0.6251 ± 0.0047, and 0.7368 ± 0.0047, were found for DeepSurv, CPH, and RSF, respectively. A Tukey HSD test demonstrates a statistically significant difference between the mean concordance indices of the three models.

CONCLUSION

Our results suggest that deep learning-based survival prediction can outperform traditional models, specifically in a case where an accurate prognosis is highly clinically relevant. We recommend that where appropriate data are available, deep learning-based prognostic indicators should be used to supplement classical statistics.

An open-source tool to visualize potential cone collisions while planning SRS cases

Purpose

To create an open‐source visualization program that allows one to find potential cone collisions while planning intracranial stereotactic radiosurgery cases.

Methods

Measurements of physical components in the treatment room (gantry, cone, table, localization stereotactic radiation surgery frame, etc.) were incorporated into a script in MATLAB (MathWorks, Natick, MA) that produces three‐dimensional visualizations of the components. A localization frame, used during simulation, fully contains the patient. This frame was used to represent a safety zone for collisions. Simple geometric objects are used to approximate the simulated components. The couch is represented as boxes, the gantry head and cone are represented by cylinders, and the patient safety zone can be represented by either a box or ellipsoid. These objects are translated and rotated based upon the beam geometry and the treatment isocenter to mimic treatment. A simple graphical user interface (GUI) was made in MATLAB (compatible with GNU Octave) to allow users to pass the treatment isocenter location, the initial and terminal gantry angles, the couch angle, and the number of angular points to visualize between the initial and terminal gantry angle.

Results

The GUI provides a fast and simple way to discover collisions in the treatment room before the treatment plan is completed. Twenty patient arcs were used as an end‐to‐end validation of the system. Seventeen of these appeared the same in the software as in the room. Three of the arcs appeared closer in the software than in the room. This is due to the treatment couch having rounded corners, whereas the software visualizes sharp corners.

Conclusions

This simple GUI can be used to find the best orientation of beams for each patient. By finding collisions before a plan is being simulated in the treatment room, a user can save time due to replanning of cases.

DNA dosimeter measurements of beam profile using a novel simultaneous processing technique

A DNA dosimeter (DNAd) was previously developed that uses double-strand breaks (DSB) to measure dose. This dosimeter has been tested to measure dose in scenarios where transient-charged particle equilibrium (TCPE) has been established. The probability of double strand break (PDSB_o), which is the ratio of broken double-stranded DNA (dsDNA) to the initial unbroken dsDNA in the dosimeter, was used to quantify DSBs and related to dose. The goal of this work is to produce a new technique to process and analyze the DNAd and quantify DNA-DSBs. This technique included simultaneously processing multiple DNAds and also establishing a new form to the probability of double strand break (PDSB_n), which was then used to test the DNAd in a non-TCPE condition by taking beam penumbra measurements. The technique utilized a 384-well plate, and the measurements were made at the edge of a 10 × 10 cm field and compared to film measurements. During these penumbra measurements, while observing the positional differences in the higher gradient region at 4.1 and 4.55 cm from the center of the radiation field, the distance to agreement of PDSB_o to film were 0.38 cm and 0.26 cm while the distance to agreement of PDSB_n to film were 0.11 cm and 0.06 cm, respectively. Finally, the developed new separation technique reduced the time needed for the analysis of 25 samples from 200 min to 30 min.

Clinical Evaluation of a Two-dimensional Liquid-Filled Ion chamber Detector Array for Verification of High Modulation Small Fields in Radiotherapy

INTRODUCTION

Clinical evaluation of a two-dimensional (2D) liquid-filled ion chamber detector array used in the verification of highly modulated small beams of stereotactic body radiation therapy (SBRT) has been conducted.

MATERIALS AND METHODS

Measurements with the Octavius 1000 SRS (PTW, Freiburg, Germany) detector with 977 liquid-filled ion chambers were compared against EDR2 film and PTW Octavius Seven29. The performance of detector array has been evaluated on ten SBRT patient plans. Dose profiles of individual and composite fields' calculated using Pinnacle³ treatment planning system were compared against measurements with Octavius 1000 SRS detector array, EDR2 film, and Octavius Seven29 detector. Gamma index and profile comparison were used in the evaluation and assessment of the detector's performance.

RESULTS

The Gamma index measurements show agreement between Pinnacle³ computations and Octavius 1000 SRS array, PTW Octavius Seven29, and EDR2 film for >90% of the points using 2%, 2 mm tolerance criteria. Profiles obtained with the Octavius 1000 SRS were in agreement with the EDR2 film profiles, demonstrating the detector's superior sampling rate.

CONCLUSIONS

The Octavius 1000 SRS is a dosimetrically accurate device to perform quality assurance checks in SBRT treatments. The broad range of measurements performed in this study quantified the dosimetric accuracy of Octavius 1000 SRS detector in the clinical setup of the small fields in radiotherapy.

Quantifying climate sensitivity and climate-driven change in North American amphibian communities

Changing climate will impact species' ranges only when environmental variability directly impacts the demography of local populations. However, measurement of demographic responses to climate change has largely been limited to single species and locations. Here we show that amphibian communities are responsive to climatic variability, using >500,000 time-series observations for 81 species across 86 North American study areas. The effect of climate on local colonization and persistence probabilities varies among eco-regions and depends on local climate, species life-histories, and taxonomic classification. We found that local species richness is most sensitive to changes in water availability during breeding and changes in winter conditions. Based on the relationships we measure, recent changes in climate cannot explain why local species richness of North American amphibians has rapidly declined. However, changing climate does explain why some populations are declining faster than others. Our results provide important insights into how amphibians respond to climate and a general framework for measuring climate impacts on species richness.

Shifts in phenological distributions reshape interaction potential in natural communities

Climate change has changed the phenologies of species worldwide, but it remains unclear how these phenological changes will affect species interactions and the structure of natural communities. Using a novel approach to analyse long-term data of 66 amphibian species pairs across eight communities, we demonstrate that phenological shifts can significantly alter the interaction potential of coexisting competitors. Importantly, these changes in interaction potential were mediated by non-uniform, species-specific shifts in entire phenological distributions and consequently could not be captured by metrics traditionally used to quantify phenological shifts. Ultimately, these non-uniform shifts in phenological distributions increased the interaction potential for 25% of species pairs (and did not reduce interaction potential for any species pair), altering temporal community structure and potentially increasing interspecific competition. These results demonstrate the potential of phenological shifts to reshape temporal structure of natural communities, emphasising the importance of considering entire phenological distributions of natural populations.

Dosimetric differences in flattened and flattening filter-free beam treatment plans

This study investigated the dosimetric differences in treatment plans from flattened and flattening filter-free (FFF) beams from the TrueBeam System. A total of 104 treatment plans with static (sliding window) intensity-modulated radiotherapy beams and volumetric-modulated arc therapy (VMAT) beams were generated for 15 patients involving three cancer sites. In general, the FFF beam provides similar target coverage as the flattened beam with improved dose sparing to organ-at-risk (OAR). Among all three cancer sites, the head and neck showed more important differences between the flattened beam and FFF beam. The maximum reduction of the FFF beam in the mean dose reached up to 2.82 Gy for larynx in head and neck case. Compared to the 6 MV flattened beam, the 10 MV FFF beam provided improved dose sparing to certain OARs, especially for VMAT cases. Thus, 10 MV FFF beam could be used to improve the treatment plan.

Commissioning an Elekta Versa HD linear accelerator

The purpose of this study is to report the dosimetric aspects of commissioning performed on an Elekta Versa HD linear accelerator (linac) with high-dose-rate flattening filter-free (FFF) photon modes and electron modes. Acceptance and commissioning was performed on the Elekta Versa HD linac with five photon energies (6 MV, 10 MV, 18 MV, 6 MV FFF, 10 MV FFF), four electron energies (6 MeV, 9MeV, 12 MeV, 15 MeV) and 160-leaf (5 mm wide) multileaf collimators (MLCs). Mechanical and dosimetric data were measured and evaluated. The measurements include percent depth doses (PDDs), in-plane and cross-plane profiles, head scatter factor (Sc), relative photon output factors (Scp), universal wedge transmission factor, MLC transmission factors, and electron cone factors. Gantry, collimator, and couch isocentricity measurements were within 1 mm, 0.7 mm, and 0.7 mm diameter, respectively. The PDDs of 6 MV FFF and 10 MV FFF beams show deeper dmax and steeper falloff with depth than the corresponding flattened beams. While flatness values of 6 MV FFF and 10 MV FFF normalized profiles were expectedly higher than the corresponding flattened beams, the symmetry values were almost identical. The cross-plane penumbra values were higher than the in-plane penumbra values for all the energies. The MLC transmission values were 0.5%, 0.6%, and 0.6% for 6 MV, 10 MV, and 18 MV photon beams, respectively. The electron PDDs, profiles, and cone factors agree well with the literature. The outcome of radiation treatment is directly related to the accuracy in the dose modeled in the treatment planning system, which is based on the commissioned data. Commissioning data provided us a valuable insight into the dosimetric characteristics of the beam. This set of commissioning data can provide comparison data to others performing Versa HD commissioning, thereby improving patient safety.

Naturally occurring variation in tadpole morphology and performance linked to predator regime

Divergent natural selection drives a considerable amount of the phenotypic and genetic variation observed in natural populations. For example, variation in the predator community can generate conflicting selection on behavioral, life-history, morphological, and performance traits. Differences in predator regime can subsequently increase phenotypic and genetic variations in the population and result in the evolution of reproductive barriers (ecological speciation) or phenotypic plasticity. We evaluated morphology and swimming performance in field collected Bronze Frog larvae (Lithobates clamitans) in ponds dominated by predatory fish and those dominated by invertebrate predators. Based on previous experimental findings, we hypothesized that tadpoles from fish-dominated ponds would have small bodies, long tails, and large tail muscles and that these features would facilitate fast-start speed. We also expected to see increased tail fin depth (i.e., the tail-lure morphology) in tadpoles from invertebrate-dominated ponds. Our results support our expectations with respect to morphology in affecting swimming performance of tadpoles in fish-dominated ponds. Furthermore, it is likely that divergent natural selection is playing a role in the diversification on morphology and locomotor performance in this system.

Synergistic effects of the invasive Chinese tallow (Triadica sebifera) and climate change on aquatic amphibian survival

Changes in climate and the introduction of invasive species are two major stressors to amphibians, although little is known about the interaction between these two factors with regard to impacts on amphibians. We focused our study on an invasive tree species, the Chinese tallow (Triadica sebifera), that annually sheds its leaves and produces leaf litter that is known to negatively impact aquatic amphibian survival. The purpose of our research was to determine whether the timing of leaf fall from Chinese tallow and the timing of amphibian breeding (determined by weather) influence survival of amphibian larvae. We simulated a range of winter weather scenarios, ranging from cold to warm, by altering the relative timing of when leaf litter and amphibian larvae were introduced into aquatic mesocosms. Our results indicate that amphibian larvae survival was greatly affected by the length of time Chinese tallow leaf litter decomposes in water prior to the introduction of the larvae. Larvae in treatments simulating warm winters (early amphibian breeding) were introduced to the mesocosms early in the aquatic decomposition process of the leaf litter and had significantly lower survival compared with cold winters (late amphibian breeding), likely due to significantly lower dissolved oxygen levels. Shifts to earlier breeding phenology, linked to warming climate, have already been observed in many amphibian taxa, and with most climate models predicting a significant warming trend over the next century, the trend toward earlier breeding should continue if not increase. Our results strongly suggest that a warming climate can interact with the effects of invasive plant species, in ways we have not previously considered, to reduce the survival of an already declining group of organisms.