Algorithm and performance of a clinical IMRT beam-angle optimization system

This paper describes the algorithm and examines the performance of an IMRT beam-angle optimization (BAO) system. In this algorithm successive sets of beam angles are selected from a set of predefined directions using a fast simulated annealing (FSA) algorithm. An IMRT beam-profile optimization is performed on each generated set of beams. The IMRT optimization is accelerated by using a fast dose calculation method that utilizes a precomputed dose kernel. A compact kernel is constructed for each of the predefined beams prior to starting the FSA algorithm. The IMRT optimizations during the BAO are then performed using these kernels in a fast dose calculation engine. This technique allows the IMRT optimization to be performed more than two orders of magnitude faster than a similar optimization that uses a convolution dose calculation engine.Comment: Final version that appeared in Phys. Med. Biol. 48 (2003) 3191-3212. Original EPS figures have been converted to PNG files due to size limi

Chemoradiotherapy of locally-advanced non-small cell lung cancer: Analysis of radiation dose–response, chemotherapy and survival-limiting toxicity effects indicates a low α/β ratio

Purpose: To analyse changes in 2-year overall survival (OS2yr) with radiotherapy (RT) dose, dose-per-fraction, treatment duration and chemotherapy use, in data compiled from prospective trials of RT and chemo-RT (CRT) for locally-advanced non-small cell lung cancer (LA-NSCLC). Material and methods: OS2yr data was analysed for 6957 patients treated on 68 trial arms (21 RT-only, 27 sequential CRT, 20 concurrent CRT) delivering doses-per-fraction ≤4.0 Gy. An initial model considering dose, dose-per-fraction and RT duration was fitted using maximum-likelihood techniques. Model extensions describing chemotherapy effects and survival-limiting toxicity at high doses were assessed using likelihood-ratio testing, the Akaike Information Criterion (AIC) and cross-validation. Results: A model including chemotherapy effects and survival-limiting toxicity described the data significantly better than simpler models (p < 10−14), and had better AIC and cross-validation scores. The fitted α/β ratio for LA-NSCLC was 4.0 Gy (95%CI: 2.8–6.0 Gy), repopulation negated 0.38 (95%CI: 0.31–0.47) Gy EQD2/day beyond day 12 of RT, and concurrent CRT increased the effective tumour EQD2 by 23% (95%CI: 16–31%). For schedules delivered in 2 Gy fractions over 40 days, maximum modelled OS2yr for RT was 52% and 38% for stages IIIA and IIIB NSCLC respectively, rising to 59% and 42% for CRT. These survival rates required 80 and 87 Gy (RT or sequential CRT) and 67 and 73 Gy (concurrent CRT). Modelled OS2yr rates fell at higher doses. Conclusions: Fitted dose–response curves indicate that gains of ~10% in OS2yr can be made by escalating RT and sequential CRT beyond 64 Gy, with smaller gains for concurrent CRT. Schedule acceleration achieved via hypofractionation potentially offers an additional 5–10% improvement in OS2yr. Further 10–20% OS2yr gains might be made, according to the model fit, if critical normal structures in which survival-limiting toxicities arise can be identified and selectively spared

Does Scientific Progress Consist in Increasing Knowledge or Understanding?

Bird argues that scientific progress consists in increasing knowledge. Dellsén objects that increasing knowledge is neither necessary nor sufficient for scientific progress, and argues that scientific progress rather consists in increasing understanding. Dellsén also contends that unlike Bird’s view, his view can account for the scientific practices of using idealizations and of choosing simple theories over complex ones. I argue that Dellsén’s criticisms against Bird’s view fail, and that increasing understanding cannot account for scientific progress, if acceptance, as opposed to belief, is required for scientific understanding

Design and development of a novel upper-limb cycling prosthesis

The rise in popularity of the Paralympics in recent years has created a need for effective, low-cost sports-prosthetic devices for upper-limb amputees. There are various opportunities for lower-limb amputees to participate in cycling; however, there are only few options for those with upper-limb amputations. If the individual previously participated in cycling, a cycling-specific prosthesis could allow these activities to be integrated into rehabilitation methods. This article describes the processes involved with designing, developing and manufacturing such a prosthesis. The fundamental needs of people with upper-limb amputation were assessed and realised in the prototype of a transradial terminal device with two release mechanisms, including a sliding mechanism (for falls and minor collisions) and clamping mechanism (for head-on collisions). The sliding mechanism requires the rider to exert approximately 200 N, while the clamping mechanism requires about 700 N. The force ranges can be customised to match rider requirements. Experiments were conducted in a controlled environment to demonstrate stability of the device during normal cycling. Moreover, a volunteer test-rider was able to successfully activate the release mechanism during a simulated emergency scenario. The development of this prosthesis has the potential to enable traumatic upper-limb amputees to participate in cycling for rehabilitation or recreation

The PTW microSilicon diode: Performance in small 6 and 15 MV photon fields and utility of density compensation

PURPOSE: We have experimentally and computationally characterized the PTW microSilicon 60023-type diode's performance in 6 and 15 MV photon fields ≥5 × 5 mm2 projected to isocenter. We tested the detector on- and off-axis at 5 and 15 cm depths in water, and investigated whether its response could be improved by including within it a thin airgap. METHODS: Experimentally, detector readings were taken in fields generated by a Varian TrueBeam linac and compared with doses-to-water measured using Gafchromic film and ionization chambers. An unmodified 60023-type diode was tested along with detectors modified to include 0.6, 0.8, and 1.0 mm thick airgaps. Computationally, doses absorbed by water and detectors’ sensitive volumes were calculated using the EGSnrc/BEAMnrc Monte Carlo radiation transport code. Detector response was characterized using K^{fdin, 4cm}_{Qclin, 4cm}, a factor that corrects for differences in the ratio of dose-to-water to detector reading between small fields and the reference condition, in this study 5 cm deep on-axis in a 4 × 4 cm2 field. RESULTS: The greatest errors in measurements of small field doses made using uncorrected readings from the unmodified 60023-type detector were over-responses of 2.6% ± 0.5% and 5.3% ± 2.0% determined computationally and experimentally, relative to the reading-per-dose in the reference field. Corresponding largest errors for the earlier 60017-type detector were 11.9% ± 0.6% and 11.7% ± 1.4% over-responses. Adding even the thinnest, 0.6 mm, airgap to the 60023-type detector over-corrected it, leading to under-responses of up to 4.8% ± 0.6% and 5.0% ± 1.8% determined computationally and experimentally. Further, Monte Carlo calculations indicate that a detector with a 0.3 mm airgap would read correctly to within 1.3% on-axis. The ratio of doses at 15 and 5 cm depths in water in a 6 MV 4 × 4 cm2 field was measured more accurately using the unmodified 60023-type detector than using the 60017-type detector, and was within 0.3% of the ratio measured using an ion chamber. The 60023-type diode's sensitivity also varied negligibly as dose-rate was reduced from 13 to 4 Gy min–1 by decreasing the linac pulse repetition frequency, whereas the sensitivity of the 60017-type detector fell by 1.5%. CONCLUSIONS: The 60023-type detector performed well in small fields across a wide range of beam energies, field sizes, depths, and off-axis positions. Its response can potentially be further improved by adding a thin, 0.3 mm, airgap

Density compensated diodes for small field dosimetry: Comprehensive testing and implications for design

Purpose. In small megavoltage photon fields, the accuracies of an unmodified PTW 60017-type diode dosimeter and six diodes modified by adding airgaps of thickness 0.6-1.6 mm and diameter 3.6 mm have been comprehensively characterized experimentally and computationally. The optimally thick airgap for density compensation was determined, and detectors were micro-CT imaged to investigate differences between experimentally measured radiation responses and those predicted computationally. Methods. Detectors were tested on- and off-axis, at 5 and 15 cm depths in 6 and 15 MV fields ≥ 0.5 0.5 cm2. Computational studies were carried out using the EGSnrc/BEAMnrc Monte Carlo radiation transport code. Experimentally, radiation was delivered using a Varian TrueBeam linac and doses absorbed by water were measured using Gafchromic EBT3 film and ionization chambers, and compared with diode readings. Detector response was characterized via the formalism, choosing a 4 4 cm2 reference field. Results. For the unmodified 60017 diode, the maximum error in small field doses obtained from diode readings uncorrected by factors was determined as 11.9% computationally at +0.25 mm off-axis and 5 cm depth in a 15 MV 0.5 0.5 cm2 field, and 11.7% experimentally at -0.30 mm off-axis and 5 cm depth in the same field. A detector modified to include a 1.6 mm thick airgap performed best, with maximum computationally and experimentally determined errors of 2.2% and 4.1%. The 1.6 mm airgap deepened the modified dosimeter's effective point of measurement by 0.5 mm. For some detectors significant differences existed between responses in small fields determined computationally and experimentally, micro-CT imaging indicating that these differences were due to within-tolerance variations in the thickness of an epoxy resin layer. Conclusions. The dosimetric performance of a 60017 diode detector was comprehensively improved throughout 6 and 15 MV small photon fields via density compensation. For this approach to work well with good detector-to-detector reproducibility, tolerances on dense component dimensions should be reduced to limit associated variations of response in small fields, or these components should be modified to have more water-like densities

Feasibility randomized controlled trial of a self-guided online intervention to promote psychosocial adjustment to unmet parenthood goals

STUDY QUESTION Is it feasible to implement and evaluate an online self-guided psychosocial intervention for people with an unmet parenthood goal (UPG), aimed to improve well-being, in an online randomized controlled trial (RCT)? SUMMARY ANSWER The evaluation of an online bilingual self-guided psychosocial intervention for people with a UPG is feasible, reflected by high demand, good acceptability, good adaptation and promise of efficacy, but minor adjustments to the intervention and study design of the RCT should be made to enhance practicality. WHAT IS KNOWN ALREADY Self-identifying as having a UPG, defined as being unable to have children or as many as desired, is associated with impaired well-being and mental health. Practice guidelines and regulatory bodies have highlighted the need to address the lack of evidence-based support for this population. It is unknown if MyJourney (www.myjourney.pt), the first online self-guided intervention for people with UPGs, can be implemented and evaluated in an RCT. STUDY DESIGN, SIZE, DURATION To evaluate the feasibility of MyJourney, we conducted a registered, two-arm, parallel group, non-blinded feasibility RCT, with a 1:1 computer-generated randomized allocation and embedded qualitative process evaluation. Participants were included between November 2020 and March 2021. Assessments were made before randomization (T1), 10 weeks (T2) and 6 months after (T3, intervention group only). Participants allocated to the intervention group received an email to access MyJourney immediately after randomization. Participants in the waitlist control group were given access to MyJourney after completing the 10-week assessment (T2). PARTICIPANTS/MATERIALS, SETTING, METHODS Participants were recruited via social media advertising of MyJourney and its feasibility study. People who self-identified as having a UPG could click on a link to participate, and of these 235 were randomized. Outcome measures related to demand, acceptability, implementation, practicality, adaptation and limited efficacy were assessed via online surveys. The primary outcome in limited efficacy testing was hedonic well-being, measured with the World Health Organisation Wellbeing Index (WHO-5). MAIN RESULTS AND THE ROLE OF CHANCE Participation and retention rates were 58.3%, 31.7% (T2) and 45.2% (T3, intervention group only), respectively. Of participants invited to register with MyJourney, 91 (76.5%) set up an account, 51 (47.2%) completed the first Step of MyJourney, 12 (11.1%) completed six Steps (sufficient dose) and 6 (5.6%) completed all Steps within the 10-week recommended period. Acceptability ranged from 2.79 (successful at supporting) to 4.42 (easy to understand) on a 1 (not at all) to 5 (extremely acceptable) scale. Average time to complete sufficient dose was 15.6 h (SD = 18.15) and to complete all Steps was 12.4 h (SD = 18.15), with no differences found for participants using MyJourney in Portuguese and English. Modified intention-to-treat analysis showed a moderate increase in well-being from T1 to T2 in the intervention group (ηp2 = 0.156, mean difference (MD) = 9.300 (2.285, 16.315)) and no changes in the control group (ηp2 = 0.000, MD = 0.047 (−3.265, 3.358)). Participants in the process evaluation reported MyJourney was needed and answered their needs for support (reflecting high demand and acceptability), the recommended period to engage with MyJourney was short, and their engagement was influenced by multiple factors, including personal (e.g. lack of time) and MyJourney related (e.g. reminders). LIMITATIONS, REASONS FOR CAUTION Participants were mostly white, well-educated, employed, childless women. Non-blinded allocation, use of self-reported questionnaire assessments and high attrition in the intervention group could have triggered bias favourable to positive evaluations of MyJourney and resulted in low power to detect T2 to T3 changes in limited efficacy outcomes. WIDER IMPLICATIONS OF THE FINDINGS MyJourney can proceed to efficacy testing, but future work should eliminate barriers for engagement and explore strategies to maximize adherence. Entities wanting to support people with UPGs now have a freely accessible and promising resource that can be further tested and evaluated in different settings

'Word from the street' : when non-electoral representative claims meet electoral representation in the United Kingdom

Taking the specific case of street protests in the UK – the ‘word from the street’– this article examines recent (re)conceptualizations of political representation, most particularly Saward’s notion of ‘representative claim’. The specific example of nonelectoral claims articulated by protestors and demonstrators in the UK is used to illustrate: the processes of making, constituting, evaluating and accepting claims for and by constituencies and audiences; and the continuing distinctiveness of claims based upon electoral representation. Two basic questions structure the analysis: first, why would the political representative claims of elected representatives trump the nonelectoral claims of mass demonstrators and, second, in what ways does the ‘perceived legitimacy’ of the former differ from the latter