Machine learning for automated quality assurance in radiotherapy: A proof of principle using EPID data description

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149320/1/mp13433_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149320/2/mp13433.pd

Automating linear accelerator quality assurance

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135049/1/mp1415.pd

Flattening filter-free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group.

This report describes the current state of flattening filter-free (FFF) radiotherapy beams implemented on conventional linear accelerators, and is aimed primarily at practicing medical physicists. The Therapy Emerging Technology Assessment Work Group of the American Association of Physicists in Medicine (AAPM) formed a writing group to assess FFF technology. The published literature on FFF technology was reviewed, along with technical specifications provided by vendors. Based on this information, supplemented by the clinical experience of the group members, consensus guidelines and recommendations for implementation of FFF technology were developed. Areas in need of further investigation were identified. Removing the flattening filter increases beam intensity, especially near the central axis. Increased intensity reduces treatment time, especially for high-dose stereotactic radiotherapy/radiosurgery (SRT/SRS). Furthermore, removing the flattening filter reduces out-of-field dose and improves beam modeling accuracy. FFF beams are advantageous for small field (e.g., SRS) treatments and are appropriate for intensity-modulated radiotherapy (IMRT). For conventional 3D radiotherapy of large targets, FFF beams may be disadvantageous compared to flattened beams because of the heterogeneity of FFF beam across the target (unless modulation is employed). For any application, the nonflat beam characteristics and substantially higher dose rates require consideration during the commissioning and quality assurance processes relative to flattened beams, and the appropriate clinical use of the technology needs to be identified. Consideration also needs to be given to these unique characteristics when undertaking facility planning. Several areas still warrant further research and development. Recommendations pertinent to FFF technology, including acceptance testing, commissioning, quality assurance, radiation safety, and facility planning, are presented. Examples of clinical applications are provided. Several of the areas in which future research and development are needed are also indicated

Determination of transient negative ion lifetimes using Rydberg atoms

Potassium Rydberg atoms are used to investigate the lifetimes, on a picosecond timescale, of transient negative ions formed during dissociative electron attachment to CCl\sb4 and CF\sb3I. The transient negative ions are formed during Rydberg electron transfer reactions of the type{\rm K}(n{\rm p})+AB\to{\rm K}\sp{+}+AB\sp{-*}\to{\rm K}\sp{+}+A\sp{-}+BFor low values of principal quantum number n\ (n\ \sbsp{\sim}{<}\ 20) the electrostatic interaction between the {\rm K}\sp{+}-AB\sp{-*} and {\rm K}\sp{+}+A\sp{-} ion pairs perturbs the ion trajectories. As a consequence, the final angular and velocity distributions of the {\rm K}\sp{+}+A\sp{-} ions are dependent on the lifetime of the AB\sp{-*} intermediate ion. The AB\sp{-*} lifetime is determined by comparing product ion distributions, determined using position sensitive detection techniques, with the results of a Monte Carlo simulation that models the kinematics of the reaction. The data show that the lifetime of the excited \rm CF\sb3\Gamma\sp{*} intermediate formed by Rydberg electron capture is short, \sbsp{\sim}{<}2 ps, and that the lifetime of the CCl\sbsp{4}{-*} intermediate is $7.5\pm2.5$ ps

Investigation of the velocity dependence of free ion production in Rydberg atom collision processes

Experiments to verify a semiclassical model of Rydberg atom collision processes revealed discrepancies between the model predictions and experimental results for the reaction\rm K\sp{**}(np)+SF\sb6\to K\sp{+}+SF\sbsp{6}{-*}at low to intermediate values of the principal quantum number n (n ${<}{\approx}$ 20). Initial measurements using non-velocity selected Rydberg atoms yielded ion angular distributions that did not agree with model calculations. To explore this further, experiments were initiated using velocity selected Rydberg atoms. These data show that the discrepancy between the model and experiment is due to transfer of energy from the SF\sbsp{6}{-*} ion into translational energy of the product ion pair through a close collision. This process is not included in the semiclassical model. This conclusion is substantiated by study of the dissociative electron transfer reaction\rm K\sp{**}(np)+CH\sb3I\to K\sp{+}+CH\sb3I\sp{-*}\to K\sp{+}+I\sp-+CH\sb3for which similar energy transfer cannot occur. The data agree well with model calculations

A comparative analysis of inspector responses to complaints about psychosocial and physical hazards

Work Health and Safety Inspectors are at the front line of efforts to protect workers against harm from psychosocial hazards, yet the application of regulatory theory in this area of practice has not been adequately explored. Drawing on models of responsive regulation (Ayres and Braithwaite, 1992) and strategic enforcement (Weil, 2008, 2010), we analyze extensive (N=46,348) complaint and incident notification data from an Australian Work Health and Safety Inspectorate in order to compare Inspectors’ responses to psychosocial versus non-psychosocial hazards. We found that psychosocial hazards were less likely to be actioned than non-psychosocial hazards. When actioned, psychosocial hazards saw more Inspector activity (phone calls, correspondence, site visits), yet fewer enforcement notices than non-psychosocial hazards. Since these findings are not consistent with the version of responsive regulation adopted by the regulator, our theoretical conclusion is that Weil’s strategic enforcement approach offers greater possibilities for guiding future resource allocation

Are pollen fossils useful for calibrating relaxed molecular clock dating of phylogenies? A comparative study using Myrtaceae

The identification and application of reliable fossil calibrations represents a key component of many molecular studies of evolutionary timescales. In studies of plants, most paleontological calibrations are associated with macrofossils. However, the pollen record can also inform age calibrations if fossils matching extant pollen groups are found. Recent work has shown that pollen of the myrtle family, Myrtaceae, can be classified into a number of morphological groups that are synapomorphic with molecular groups. By assembling a data matrix of pollen morphological characters from extant and fossil Myrtaceae, we were able to measure the fit of 26 pollen fossils to a molecular phylogenetic tree using parsimony optimisation of characters. We identified eight Myrtaceidites fossils as appropriate for calibration based on the most parsimonious placements of these fossils on the tree. These fossils were used to inform age constraints in a Bayesian phylogenetic analysis of a sequence alignment comprising two sequences from the chloroplast genome (matK and ndhF) and one nuclear locus (ITS), sampled from 106 taxa representing 80 genera. Three additional analyses were calibrated by placing pollen fossils using geographic and morphological information (eight calibrations), macrofossils (five calibrations), and macrofossils and pollen fossils in combination (12 calibrations). The addition of new fossil pollen calibrations led to older crown ages than have previously been found for tribes such as Eucalypteae and Myrteae. Estimates of rate variation among lineages were affected by the choice of calibrations, suggesting that the use of multiple calibrations can improve estimates of rate heterogeneity among lineages. This study illustrates the potential of including pollen-based calibrations in molecular studies of divergence times

A novel dynamic field-matching technique for treatment of patients with para-aortic node-positive cervical cancer: Clinical experience

AimTo report outcomes for patients with para-aortic lymph node positive cervical cancer treated with a dynamic field-matching technique.BackgroundPET staging of cervical cancer has increased identification of patients with para-aortic lymph node metastasis. IMRT enables dose escalation in this area, but matching IMRT fields with traditional whole pelvis fields presents a challenge.Materials and methodsFrom 2003 to 2012, 20 patients with cervical cancer and para-aortic lymph node metastasis were treated utilizing the dynamic field-matching technique. As opposed to single-isocenter half-beam junction techniques, this technique employs wedge-shaped dose junctions for the abutment of fields. We reviewed the records of all patients who completed treatment with the technique and abstracted treatment, toxicity, and disease-related outcome data for analysis.ResultsMedian prescribed dose to the whole pelvis field was 45[[ce:hsp sp="0.25"/]]Gy and para-aortic IMRT field 50.4[[ce:hsp sp="0.25"/]]Gy. All but 3 patients underwent HDR (13 pts) or LDR (4 pts) brachytherapy. All patients developed lower GI toxicity; 10 grade 1, 9 grade 2, and 1 grade 4 (enterovaginal fistula). Median DFS was 12.4 months with 1 and 2-year DFS 60.0% and 38.1%. One-year OS was 83.7% and 2-year OS, 64.4%. A total of 10 patients developed recurrence; none occurred at the matched junction.ConclusionsThe dynamic field-matching technique provides a means for joining conventional whole pelvis fields and para-aortic IMRT fields that substantially reduces dose deviations at the junction due to field mismatch. Treatment with the dynamic matching technique is simple, effective, and tolerated with no apparent increase in toxicity