Inverse Planning Research Articles

Fixed-Field IMRT for Cervix Carcinoma Patients on an MR-LINAC Platform: Dosimetric Feasibility and Challenges

To investigate the impact of MR-LINAC performance characteristics and inverse planning implementation on the feasibility of fixed-field IMRT for cervix carcinoma patients by benchmarking MR-LINAC plans against clinically used VMAT plans in a single institution study and multi-institutional treatment planning challenge. For 10 cervix cancer patients who had previously received Linac-based VMAT, new treatment plans were optimized for MR-LINAC IMRT using 6X FFF fixed fields with maximum available field size of 27.4 x 24.1 cm2. Dose optimization was performed on the clinically used planning CT and structure set. Prescribed dose was 48.6 Gy in 27 fractions for all patients with 6 patients receiving an additional integrated boost for a total of 58.05 Gy to involved nodes. Constraints were based on our institutional protocol as per Table 1. IMRT delivery time was limited to 20 min. Original clinically used VMAT plans were generated on Eclipse (Varian Medical System) using 3 to 4 arcs. For the multi-institutional planning challenge, the data set from a single patient was anonymized and shared to participants. Participants used a single MR-based Linac planning platform to generate a plan based on our institutional constraints, with maximum treatment time limited to 20 min. For all analyses, a paired samples t-test was used to compare the significance defined at p < 0.05. For MR-LINAC plans, the mean number of fields used was 23, mean number of segments 229, and the average estimated treatment delivery time was 17.3 minutes. MR-LINAC plans showed a significantly higher heterogeneity and dose to organs at risk compared to VMAT plans (Table 1). For the planning challenge, a total of 30 participants registered interest. Of this, seven plans were submitted to the challenge. On average, participants generated a plan that would be acceptable based on our institutional constraints (Table 1). However, the volumetric dose to bowel and pelvic bones were higher on MR-LINAC plans compared to the reference VMAT plan. MR-LINAC fixed-field IMRT for cervix cancer patients is feasible but system constraints and optimization implementation result in greater dose heterogeneity and worse organ-at-risk sparing compared to Linac based VMAT. Further research is needed to determine if potential reduction of treatment margins, allowed by better MRI soft-tissue visualization, will result in MR-LINAC IMRT superior to Linac VMAT.

Image-Guided High-Dose-Rate Brachytherapy for Definitive Management of Primary Vaginal Cancer: A Single Institutional Experience

To assess the safety and efficacy of image-guided high-dose-rate brachytherapy (IGBT) alone or in combination with external beam radiation therapy (EBRT) for the treatment of vaginal cancers. The study analyzed patients diagnosed with primary vaginal cancers from 2004 to 2021 who received definitive radiotherapy at a single institution. Interstitial implants were performed using a freehand technique and transvaginal or transrectal-ultrasound for imaging guidance. IGBT was planned using inverse planning simulated annealing (IPSA) software. Data collected and analyzed included patient and tumor characteristics, dose and fractionation, and treatment outcomes. Complications were assessed using CTCAEv4 scores, and descriptive and survival analyses were performed using R-studio. Sixty-six patients met inclusion criteria. Patients were staged as I (14), II (23), III (19), and IV (10) based on revised FIGO 2018 staging. 47 (72%) had squamous cell carcinoma histology, and median age was 65 years. The most common regimen was 45 Gy in 25 fractions of EBRT followed by IGBT boost of 18 Gy in 3 fractions with 1 implant (n = 40). For melanoma, an IGBT boost of 19 Gy in 2 fractions with a single implant was used (n = 7). For IGBT monotherapy, the most common regimen was 36 Gy in 6 fractions delivered over 2 implants (n = 3). 41 (66%) of the patients received systemic therapy. Local failures occurred in 8 (12%) patients, while 8 (12%) developed distant metastases. Median overall survival was 64.7 months. Overall survival was 64.3% (95% CI 51.9-79.7%) at 3 years, and 50.9% (95% CI 35.7-72.5%) at 5 years. Grade 3 or 4 toxicities were reported in 4 (6%) patients including vaginal fistula (n = 3) and urethral stricture (n = 1). The results suggest that utilizing IGBT for freehand interstitial implants in combination with EBRT is a safe and effective primary treatment for vaginal cancer, with durable local control and low toxicity. Further research is needed to establish multi-institutional practice patterns and recommendations.

Influence of optimisation parameters on directly deliverable Pareto fronts explored for prostate cancer

PurposeIn inverse radiotherapy treatment planning, the Pareto front is the set of optimal solutions to the multi-criteria problem of adequately irradiating the planning target volume (PTV) while reducing dose to organs at risk (OAR). The Pareto front depends on the chosen optimisation parameters whose influence (clinically relevant versus not clinically relevant) is investigated in this paper. MethodsThirty-one prostate cancer patients treated at our clinic were randomly selected. We developed an in-house Python script that controlled the commercial treatment planning system RayStation to calculate directly deliverable Pareto fronts. We calculated reference Pareto fronts for a given set of objective functions, varying the PTV coverage and the mean dose of the primary OAR (rectum) and fixing the mean doses of the secondary OARs (bladder and femoral heads). We calculated the fronts for different sets of objective functions and different mean doses to secondary OARs. We compared all fronts using a specific metric (clinical distance measure). ResultsThe in-house script was validated for directly deliverable Pareto front calculations in two and three dimensions. The Pareto fronts depended on the choice of objective functions and fixed mean doses to secondary OARs, whereas the parameters most influencing the front and leading to clinically relevant differences were the dose gradient around the PTV, the weight of the PTV objective function, and the bladder mean dose. ConclusionsOur study suggests that for multi-criteria optimisation of prostate treatments using external therapy, dose gradient around the PTV and bladder mean dose are the most influencial parameters.

Receding horizon dispatch of multi-period look-ahead market for energy storage integration

Although noteworthy efforts towards energy storage participation in electricity markets have been witnessed worldwide during the last decades, market mechanisms for optimal storage integration are yet to be comprehensively studied. This paper presents a novel approach wherein a multi-period look-ahead market is proposed to progressively solve the optimisation problem over a receding horizon, incorporating intertemporal constraints to enable forward planning. The focus is specifically on modelling the bidding behaviour of energy storage, and to address this, we develop two distinct models for the participation of energy storage in the market. The integrated model aims to schedule the future dispatch of the storage to minimise total operational cost, taking into account the fixed costs of the storage, while the strategic model pursues the dual ambition to maximise storage profit by formulating a bilevel optimisation problem. We validate the viability of our proposed market mechanisms through case studies on the Australian National Electricity Market. We conduct case studies which provide evidence that both the strategic and integrated bidding models effectively address the requirement for forward planning, resulting in reduced market costs and volatility. Notably, the strategic model outperforms in terms of generating higher storage revenue, while the integrated model exhibits a slight advantage in terms of lower market costs compared to the strategic model.

A discrete ordinates Boltzmann solver for application to inverse planning of photons and protons

The aim of this work is to develop a discrete ordinates Boltzmann solver that can be used for calculation of absorbed dose from both photons and protons within an inverse planning optimiser, so as to perform accurate dose calculation throughout the whole of the inverse planning process. With photons, five transport sweeps were performed to obtain scattered photon fluence, and unscattered electron fluence was then obtained and used as a fixed source for solution of the electron transport equations. With protons, continuous slowing down was treated as a fixed source, and five transport sweeps were used to calculate scattered fluence. The total electron or proton fluence was multiplied by the stopping power ratio for the transport medium to obtain absorbed dose. The method was evaluated in homogeneous media and in a lung case where the planning target volume was surrounded by low-density lung material. Photon arc, proton passive scattering and proton arc treatments were considered. The results were compared to a clinically validated convolution dose calculation for photons, and with an analytical method for protons. In water-equivalent media, the discrete ordinates method agrees with the alternative algorithms to within 2%. Convergence is found to be sufficiently complete for water-, lung- and bone-equivalent materials after five iterations. The dose calculated by the relatively simple angular quadrature is seen to be very close to that calculated by a more comprehensive quadrature. For inhomogeneous lung plans, the method shows more heterogeneity of dose to the planning target volume than the comparative methods. The discrete ordinates Boltzmann solver provides a general framework for dose calculation with both photons and protons. The method is suitable for incorporation into an inverse planning optimiser, so that accurate dose calculation in a heterogeneous medium can be obtained throughout inverse planning, with the result that the final dose distribution is as predicted by the optimiser.

A cognitive task analysis of expert surgeons performing the robotic roux-en-y gastric bypass.

The safe and effective performance of a robotic roux-en-y gastric bypass (RRNY) requires the application of a complex body of knowledge and skills. This qualitative study aims to: (1)define the tasks, subtasks, decision points, and pitfalls in a RRNY; (2)create a framework upon which training and objective evaluation of a RRNY can be based. Hierarchical and cognitive task analyses for a RRNY were performed using semi-structured interviews of expert bariatric surgeons to describe the thoughts and behaviors that exemplify optimal performance. Verbal data was recorded, transcribed verbatim, supplemented with literary and video resources, coded, and thematically analyzed. A conceptual framework was synthesized based on three book chapters, three articles, eight online videos, nine field observations, and interviews of four subject matter experts (SME). At the time of the interview, SME had practiced a median of 12.5years and had completed a median of 424 RRNY cases. They estimated the number of RRNY to achieve competence and expertise were 25 cases and 237.5 cases, respectively. After four rounds of inductive analysis, 83 subtasks, 75 potential errors, 60 technical tips, and 15 decision points were identified and categorized into eight major procedural steps (pre-procedure preparation, abdominal entry & port placement, gastric pouch creation, omega loop creation, gastrojejunal anastomosis, jejunojejunal anastomosis, closure of mesenteric defects, leak test & port closure). Nine cognitive behaviors were elucidated (respect for patient-specific factors, tactical modification, adherence to core surgical principles, task completion,judicious technique & instrument selection, visuospatial awareness, team-based communication, anticipation & forward planning, finessed tissue handling). This study defines the key elements that formed the basis of a conceptual framework used by expert bariatric surgeons to perform the RRNY safely and effectively. This framework has the potential to serve as foundational tool for training novices.

Finding Zion: Spectral intimacy and state indeterminacy at an erased American cemetery

ABSTRACT In 2018, a previously erased African American cemetery was dramatically rediscovered in Tampa, Florida. The rediscovery was accompanied by multiple acts of remembrance: archaeologists set about confirming the presence of coffins and bodies; people living on top or nearby this and other burial grounds began reporting a series of ghostly visions and visitations; and the city government and its contractors put forward plans to memorialize the erased cemetery. Based on participant-observation with city employees, developers, and activists undertaken as part of a broader project on the politics of race, empire, and urban life in South Florida, this article investigates the erasure and rediscovery of this and other historic cemeteries in order to inquire into the social and political life of indeterminacy at sites of necropolitical violence. While some residents attempted to enter into meaningful interpersonal relations with the spirits of actual deceased persons, taking their existence as a potentially transparent fact, agents of the state instead developed a position on the question of haunting more in line with social theories of the spectral as an impossible possibility. Attending to this fact ethnographically reveals the relationship between statecraft, the nonsecular, and the politics of indeterminacy in a new light.

Why skills anticipation in African VET systems needs to be decolonized: The wide-spread use and limited value of occupational standards and competency-based qualifications

The shift from manpower-planning to labour market analysis and skills anticipation has been analyzed since the 80 s in this journal and elsewhere, with the aim of improving.insights into how education can contribute to economic growth and development. This paper considers recent trends in policies for skills anticipation and curriculum reform in Africa, with a focus on technical and vocational education and training (TVET) systems.The data consists of 2 continent-wide surveys of a range of TVET stakeholders, document analysis of skills and TVET policy as well as industrial policy where available.online, and 21 in-depth interviews with key roleplayers and experts in 13 countries. Our research found considerable activity developing pre-determined rules and tools that don’t work in their own right, and are inappropriate for African labour markets because they are not used in formal work, and have little engagement with informal work. A set of ‘rules and tools’, such as occupational standards, qualifications frameworks, and part qualifications/ modularization, is promoted by international organizations. These pre-developed and uniform solutions continues to dominate policy agendas. We found considerable focus on developing and (to some extent) using these rules and tools for forward planning, system improvement, and curriculum design. Most noticeable was a strong emphasis on competency-based qualifications, which are described as a tool for skills anticipation as well as curriculum reform, drawing on employer input into skills requirements. There is considerable focus on employer-identified skills needs as the tool for both understanding current and emerging economic demand for skills as well as medium to longer term skills needs. The dependence on employer-specified competencies means there is little engagement with the reality of informal work in the African context—other than strong rhetorical emphasis on entrepreneurship as an add on in curriculum design. Amongst other problems, the ‘rules and tools’ which are being implemented in many countries start from an idealized vision, and are more preoccupied with their own internal logic than the systems with which they are dealing. The rules and tools present a level playing field for individuals and for countries, constrained only by a lack of skills, and a world view in which everyone could come out on top.

Matching between Clinical and Dosimetric Results in Comparing Intensity Modulated Radiotherapy with Three-Dimensional Conformal Radiotherapy in Locally Advanced Lung Cancer

Background Radiation therapy plays an essential role in the treatment of locally advanced lung cancer, but it inevitably leads to incidental and unnecessary dose to critical organs, including the lung, heart, and esophagus. Objective A dosimetric study to compare 3D CRT to IMRT in locally advanced lung cancer as regards normal tissue irradiation and target coverage using COSI &amp; modified COSI indices, DVH, homogeneity index, conformity index, target coverage index. Also to evaluate acute and late toxicity of esophagus, heart and lung in three-dimensional conformal radiotherapy and intensity modulated radiotherapy, in patients with locally advanced lung cancer who received definitive concurrent chemo-radiation or sequential chemo-radiation according to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Patients and Methods 20 patients were selected to participate in our retrospective study from 2014 till 2019. They were recruited from bronchogenic cancer clinic, clinical oncology department in Ain Shams University Hospitals using a convenient sampling method. Diagnosis of NSCLC or SCLC was confirmed histologically and further radiological assessment for TNM staging was performed. All patients where 18 years old or older and were prescribed for either combined or sequential chemoradiotherapy for treatment of locally invasive lung cancer with ECOG PS equal or less than 2. They received 3D CRT of total 60 Gy. On the same CT contour defined for 3D CRT another plan was done for IMRT by computer based inverse planning with specific dose constrains to surrounding organs. Results In our study IMRT technique helped in sparing doses delivered to heart, lung &amp; esophagus in comparison with 3D CRT, but it was statistically significant for the lung only with p-value = 0.003. As regard the dosimetric indices IMRT showed better target coverage, dose homogenity &amp; dose conformity in comaparison with 3D CRT, but it was statistically significant for CI with p-value= 0.028. Using the COSI &amp; mCOSI also was in favor of IMRT but it was stastistically significant in mCOSI with pvalue=0.023 Conclusion IMRT showed superior outcomes as regards delivered doses (both to target and at-risk organs) compared to the conventional 3D CRT achieving the main purpose for patients with locally advanced lung cancer receiving chemoradiothrapy which is better target volume coverage and less unnecessary dose to at-risk nearby vital organs. As IMRT spares OAR it’s expected that clinical toxicity noticed with 3DCRT will be less thus, more tolerability to CCRT.

Continuous photon energy modulation in IMRT of pancreatic cancer

Purpose: To develop a novel IMRT optimization method based on the principle of photon energy synthesis that simultaneously optimizes fluence map and beamlet energy. The method was validated on pancreatic cancers to demonstrate the benefits of the additional degree of freedom of photon energy in IMRT.Methods: Previous work has demonstrated that the effect of a photon beam of known energy can be achieved by the combination of two existing energy photons in the proper ratio. It further implied that any energy photon can be synthesized. Based on this, we propose the concept of continuous beamlet energy modulation in IMRT, or IMRT-BEM. The IMRT-BEM was modeled as the simultaneous optimization of two fluence maps, one for the low energy beam and one for the high energy beam, and it was implemented in an in-house inverse planning system. The IMRT-BEM was applied on 10 pancreatic cancer cases, where the IMRT-BEM plan was compared with single-energy IMRT plans of 6 MV (IMRT-6MV) and 15 MV photons (IMRT-15MV).Results: The IMRT-BEM plan provides a noticeable reduction to the volume irradiated at the high dose level (PTV105%) for PTV, at least 24.7% (6.4 ± 6.8 vs. 31.1 ± 18.7 (p = 0.005) and 43.8 ± 19.8 (p = 0.005) for IMRT-BEM, IMRT-6MV, and IMRT-15MV respectively). For target dose coverage, there were statistically significant improvements between the IMRT-BEM plans and the other two plans in terms of CI and HI. Compared to the IMRT-6MV plan, there were significant reductions in the Dmean of the spinal cord, liver, bowel, duodenum, and stomach. The irradiation volumes of the medium dose (V20Gy, and V40Gy) for the duodenum and bowel were reduced significantly. There were no significant differences between the IMRT-BEM and IMRT-15MV plans except for the Dmean of the spinal cord and the duodenum, the V20Gy, and V40Gy for the duodenum, and the V20Gy of the stomach.Conclusion: IMRT-BEM has certain dosimetric advantages for PTV and improves OAR sparing in pancreatic cancer, and can be effectively used in radiation treatment planning, providing another degree of freedom for planners to improve treatment plan quality.

What makes an excellent labour ward co-ordinator? Insights from the multidisciplinary team

Background/Aims Poor multidisciplinary teamwork on labour wards may lead to adverse consequences for women and babies. The labour ward co-ordinator is a central role in the multidisciplinary team; however, there has been little research into explore the skills and attributes necessary for this role. This study aimed to explore the labour ward co-ordinator's skills and attributes and their impact on multidisciplinary team working. Methods Constructive grounded theory was used to explore the perceptions of 21 labour ward multidisciplinary team members recruited using theoretical sampling from a maternity unit in northern England. Results Labour ward co-ordinators play significant roles in ward organisation, team situational awareness and a well-functioning multidisciplinary team. Co-ordinators had situational awareness through a ‘helicopter view’ of the ward, supported decision making and were approachable. Excellent labour ward co-ordinators used situational awareness to pre-empt emergencies and forward plan. Conclusions The labour ward co-ordinator role requires a different skillset to that of midwives delivering one-to-one care in labour. To develop midwives into the co-ordinator role, attention to continuing professional development is essential. Recruitment of consultant midwives dedicated to supporting midwives delivering care to women in labour should be considered.

Evaluation of inverse treatment planning for gamma knife radiosurgery using fMRI brain activation maps as organs at risk.

Stereotactic radiosurgery (SRS) can be an effective primary or adjuvant treatment option for intracranial tumors. However, it carries risks of various radiation toxicities, which can lead to functional deficits for the patients. Current inverse planning algorithms for SRS provide an efficient way for sparing organs at risk (OARs) by setting maximum radiation dose constraints in the treatment planningprocess. We propose using activation maps from functional MRI (fMRI) to map the eloquent regions of the brain and define functional OARs (fOARs) for Gamma Knife SRS treatment planning. We implemented a pipeline for analyzing patient fMRI data, generating fOARs from the resulting activation maps, and loading them onto the GammaPlan treatment planning software. We used the Lightning inverse planner to generate multiple treatment plans from open MRI data of five subjects, and evaluated the effects of incorporating the proposed fOARs. The Lightning optimizer designs treatment plans with high conformity to the specified parameters. Setting maximum dose constraints on fOARs successfully limits the radiation dose incident on them, but can have a negative impact on treatment plan quality metrics. By masking out fOAR voxels surrounding the tumor target it is possible to achieve high quality treatment plans while controlling the radiation dose on fOARs. The proposed method can effectively reduce the radiation dose incident on the eloquent brain areas during Gamma Knife SRS of braintumors.

A linear optimization model for high dose rate brachytherapy using a novel distance metric.

Purpose.We propose a linear network-based optimization model (LNBM) for high dose rate brachytherapy (HDR-BT) that uses a novel distance metric to measure the discrepancy between the dose delivered and the prescription. Unlike models in the literature, LNBM takes advantage of the adjacency structure of the patients' voxels by formalizing them into a network.Methods.We apply LNBM to a set of 7 cervical cancer cases treated with HDR-BT. State-of-the-art commercial optimization software solves LNBM to global optimality. The results of LNBM are compared with those of inverse planning by simulated annealing (IPSA) based on tumor coverage, dosimetric indices for the critical organs at risk (OARs), isodose contour plots, and two metrics of homogeneity new to this work (hot-spots volumes and diameters).Results.LNBM produces plans with improved tumor coverage and with improved isodose contour plots and dosimetric indices for OARs that receive highest dose (bladder and rectum in this study) when compared with IPSA. Using new metrics of homogeneity, we also demonstrate that LNBM produces more homogeneous plans on these cases. An analysis of the solutions of LNBM shows that they use a significant part of the voxel network structure, providing evidence that the plans produced are different from those created using traditional penalty approaches and are more directly guided by the geometry of the patients' anatomy.Conclusions.The proposed linear network-based optimization model efficiently generates more homogeneous high quality treatment plans for HDR-BT.

Embedding expertise knowledge into inverse treatment planning for low-dose-rate brachytherapy of hepatic malignancies.

Leveraging the precision of its radiation dose distribution and the minimization of postoperative complications, low-dose-rate (LDR) permanent seed brachytherapy is progressively adopted in addressing hepatic malignancies. The present study endeavors to devise a sophisticated treatment planning system (TPS) to optimize LDR brachytherapy for hepatic lesions. Our TPS encompasses four integral modules: multi-organ segmentation, seed distribution initialization, puncture pathway selection, and inverse dose planning. By amalgamating an array of deep learning models, the segmentation module proficiently labels 17 discrete abdominal targets within the images. We introduce a knowledge-based seed distribution initialization methodology that discerns the most analogous tumor shape in the reference treatment plan from the knowledge base. Subsequently, the seed distribution from the reference plan is transmuted to the current case, thus establishing seed distribution initialization. Furthermore, we parameterize the puncture needles and seeds, while concurrently constraining the puncture needle angle through the employment of a virtual puncture panel to augment planning algorithm efficiency. We also presented a user interface that includes a range of interactive features, seamlessly integrated with the treatment planning generation function. The multi-organ segmentation module, which is trained by 50 cases of in-house CT scans and 694 cases of publicly available CT scans, achieved average Dice of 0.80 and Hausdorff distance of 5.2mm in testing datasets. The results demonstrate that knowledge-based initialization exhibits a marked enhancement in expediting the convergence rate. Our TPS also demonstrates a dominant advantage in dose-volume-histogram criteria and execution time in comparison to commercial TPS. The study proposes an innovative treatment planning system for low-dose-rate permanent seed brachytherapy for hepatic malignancies. We show that the generated treatment plans meet clinical requirement.

Why the Car Is Not Always King in Global South Cities: Evidence From Ulaanbaatar

Access to a private car has established itself as a critical control on mobility and access to opportunities for residents living in a diverse range of settings, globally. Across cities of the Global South, the benefits of private car access are often intensified by the absence of viable alternative modes of travel. This article explores the influence of private car access and mobility in relation to residents living in “ger district” areas of Ulaanbaatar, Mongolia’s capital city. These peri-urban areas are informally created when rural migrants set up home on the edge of the city, initially using mobile felt dwellings called “ger” that become augmented or replaced by permanent structures over time. An absence of forward planning as well as unmade roads and hilly topography mean that the ger districts are often poorly served by public transport, while the low density of the built environment also means that informal transport services can be limited in coverage and relatively expensive. This article utilises a database of household questionnaires collected in 2020 to compare mobility patterns and accessibility between car-owning and non-car-owning households in three case study ger districts, capturing seasonal differences between the extreme cold of the wintertime and warmer summer conditions. The findings not only reveal stark mobility and access differences in relation to car ownership but also discrepancies between car ownership and actual car use for important and routine journeys. This indicates that despite a lack of public transport available, many households opt to use what public transport they can. This pattern provides a potentially important basis for future policies that aim to limit car use in order to reduce traffic congestion and broaden access to the city for non-car-owning households by providing more accessible public transport.

3D-conformal very-high energy electron therapy as candidate modality for FLASH-RT: A treatment planning study for glioblastoma and lung cancer.

Pre-clinical ultra-high dose rate (UHDR) electron irradiations on time scales of 100ms have demonstrated a remarkable sparing of brain and lung tissues while retaining tumor efficacy when compared to conventional dose rate irradiations. While clinically-used gantries and intensity modulation techniques are too slow to match such time scales, novel very-high energy electron (VHEE, 50-250MeV) radiotherapy (RT) devices using 3D-conformed broad VHEE beams are designed to deliver UHDR treatments that fulfill these timing requirements. To assess the dosimetric plan quality obtained using VHEE-based 3D-conformal RT (3D-CRT) for treatments of glioblastoma and lung cancer patients and compare the resulting treatment plans to those delivered by standard-of-care intensity modulated photon RT (IMRT) techniques. Seven glioblastoma patients and seven lung cancer patients were planned with VHEE-based 3D-CRT using 3 to 16 coplanar beams with equidistant angular spacing and energies of 100 and 200MeV using a forward planning approach. Dose distributions, dose-volume histograms, coverage (V95% ) and homogeneity (HI98% ) for the planning target volume (PTV), as well as near-maximum doses (D2% ) and mean doses (Dmean ) for organs-at-risk (OAR) were evaluated and compared to clinical IMRT plans. Mean differences of V95% and HI98% of all VHEE plans were within 2% or better of the IMRT reference plans. Glioblastoma plan dose metrics obtained with VHEE configurations of 200MeV and 3-16 beams were either not significantly different or were significantly improved compared to the clinical IMRT reference plans. All OAR plan dose metrics evaluated for VHEE plans created using 5 beams of 100MeV were either not significantly different or within 3% on average, except for Dmean for the body, Dmean for the brain, D2% for the brain stem, and D2% for the chiasm, which were significantly increased by 1, 2, 6, and 8Gy, respectively (however below clinical constraints). Similarly, the dose metrics for lung cancer patients were also either not significantly different or were significantly improved compared to the reference plans for VHEE configurations with 200MeV and 5 to 16 beams with the exception of D2% and Dmean to the spinal canal (however below clinical constraints). For the lung cancer cases, the VHEE configurations using 100MeV or only 3 beams resulted in significantly worse dose metrics for some OAR. Differences in dose metrics were, however, strongly patient-specific and similar for some patient cases. VHEE-based 3D-CRT may deliver conformal treatments to simple, mostly convex target shapes in the brain and the thorax with a limited number of critical adjacent OAR using a limited number of beams (as low as 3 to 7). Using such treatment techniques, a dosimetric plan quality comparable to that of standard-of-care IMRT can be achieved. Hence, from a treatment planning perspective, 3D-conformal UHDR VHEE treatments delivered on time scales of 100ms represent a promising candidate technique for the clinical transfer of the FLASH effect.

A study on inter-planner plan quality variability using a manual planning- or Lightning dose optimizer-approach for single brain lesions treated with the Gamma Knife® Icon™.

The purpose of this study is to investigate inter-planner plan quality variability using a manual forward planning (MFP)- or fast inverse planning (FIP, Lightning)-approach for single brain lesions treated with the Gamma Knife® (GK) Icon™. Thirty patients who were previously treated with GK stereotactic radiosurgery or radiotherapy were selected and divided into three groups (post-operative resection cavity, intact brain metastasis, and vestibular schwannoma [10 patients per group]). Clinical plans for the 30 patients were generated by multiple planners using FIP only (1), a combination of FIP and MFP (12), and MFP only (17). Three planners (Senior, Junior, and Novice) with varying experience levels re-planned the 30 patients using MFP and FIP (two plans per patient) with planning time limit of 60min. Statistical analysis was performed to compare plan quality metrics (Paddick conformity index, gradient index, number of shots, prescription isodose line, target coverage, beam-on-time (BOT), and organs-at-risk doses) of MFP or FIP plans among three planners and to compare plan quality metrics between each planner's MFP/FIP plans and clinical plans. Variability in FIP parameter settings (BOT, low dose, and target max dose) and in planning time among the planners was also evaluated. Variations in plan quality metrics of FIP plans among three planners were smaller than those of MFP plans for all three groups. Junior's MFP plans were the most comparable to the clinical plans, whereas Senior's and Novice's MFP plans were superior and inferior, respectively. All three planners' FIP plans were comparable or superior to the clinical plans. Differences in FIP parameter settings among the planners were observed. Planning time was shorter and variations in planning time among the planners were smaller for FIP plans in all three groups. The FIP approach is less planner dependent and more time-honored than the MFP approach.

Improving plan quality in cervical brachytherapy using a simple knowledge-based prediction tool for OAR dose (D2cm3)

PurposeToxicity from cervical brachytherapy has been demonstrated to correlate with the D2cm3 of the bladder, rectum, and bowel. This suggests a simplified version of knowledge-based planning investigating the relationship of the overlap distance for 2cm3 and the D2cm3 from planning may be possible. This work demonstrates the feasibility of simple knowledge-based planning to predict the D2cm3, detect suboptimal plans, and improve plan quality. Methods and materialsThe overlap volume histogram (OVH) method was used to determine the distance for 2cm3 of overlap between the OAR and CTV_HR. Linear plots modeled the OAR D2cm3 and 2cm3 overlap distance. Two datasets of 20 patients (plans from 43 insertions in each dataset) were used to create two independent models, and the performance of each model was compared using cross-validation. Doses were scaled to ensure consistent CTV_HR D90 values. The predicted D2cm3 is entered as the maximum constraint in the inverse planning algorithm. ResultsMean bladder D2cm3 decreased by 2.9% for the models from each dataset, mean rectal D2cm3 decreased 14.9% for the model from dataset 1 and 6.0% for the model from dataset 2, mean sigmoid D2cm3 decreased 10.7% for the model from dataset 1 and 6.1% for the model from dataset 2, mean bowel D2cm3 decreased 4.1% for the model from dataset 1 but no statistically significant difference was observed for the model from dataset 2. ConclusionsA simplified knowledge-based planning method was used to predict D2cm3 and was able to automate optimization of brachytherapy plans for locally advanced cervical cancer.

Emotion prediction as computation over a generative theory of mind.

From sparse descriptions of events, observers can make systematic andnuanced predictions of what emotions the people involvedwill experience. We propose a formal model of emotion prediction in the context of a public high-stakes social dilemma. This model uses inverse planning to infer a person's beliefs and preferences, including social preferences for equity and for maintaining a good reputation. The model then combines these inferred mental contents with the event to compute 'appraisals': whether the situation conformed to the expectations and fulfilled the preferences. We learn functions mapping computed appraisals to emotion labels, allowing the model to match human observers' quantitative predictions of 20 emotions, including joy, relief, guilt and envy. Model comparison indicates that inferred monetary preferences are not sufficient to explain observers' emotion predictions; inferred social preferences are factored into predictions for nearly every emotion. Human observers and the model both use minimal individualizing information to adjust predictions of how different people will respond to the same event. Thus, our framework integrates inverse planning, event appraisals and emotion concepts in a single computational model to reverse-engineer people's intuitive theory of emotions. This article is part of a discussion meeting issue 'Cognitive artificial intelligence'.

Inverse planning optimization with lead block effectively suppresses dose to the mandible in high-dose-rate brachytherapy for tongue cancer

PurposeIn this study, we developed in-house software to evaluate the effect of the lead block (LB)-inserted spacer on the mandibular dose in interstitial brachytherapy (ISBT) for tongue cancer. In addition, an inverse planning algorithm for LB attenuation was developed, and its performance in mandibular dose reduction was evaluated.MethodsTreatment plans of 30 patients with tongue cancer treated with ISBT were evaluated. The prescribed dose was 54 Gy/9 fractions. An in-house software was developed to calculate the dose distribution based on the American Association of Physicists in Medicine (AAPM) Task Group No.43 (TG-43) formalism. The mandibular dose was calculated with consideration of the LB attenuation. The attenuation coefficient of the lead was computed using the PHITS Monte Carlo simulation. The software further optimized the treatment plans using an attraction–repulsion model (ARM) to account for the LB attenuation.ResultsCompared to the calculation in water, the D2 cc of the mandible changed by − 2.4 ± 2.3 Gy (range, − 8.6 to − 0.1 Gy) when the LB attenuation was considered. The ARM optimization with consideration of the LB resulted in a − 2.4 ± 2.4 Gy (range, − 8.2 to 0.0 Gy) change in mandibular D2 cc.ConclusionsThis study enabled the evaluation of the dose distribution with consideration of the LB attenuation. The ARM optimization with lead attenuation further reduced the mandibular dose.