Effect of synthetic CT on dose-derived toxicity predictors for MR-only prostate radiotherapy.

Objectives: Toxicity-driven adaptive radiotherapy (RT) is enhanced by the superior soft tissue contrast of magnetic resonance (MR) imaging compared with conventional computed tomography (CT). However, in an MR-only RT pathway synthetic CTs (sCT) are required for dose calculation. This study evaluates 3 sCT approaches for accurate rectal toxicity prediction in prostate RT. Methods: Thirty-six patients had MR (T2-weighted acquisition optimized for anatomical delineation, and T1-Dixon) with same day standard-of-care planning CT for prostate RT. Multiple sCT were created per patient using bulk density (BD), tissue stratification (TS, from T1-Dixon) and deep-learning (DL) artificial intelligence (AI) (from T2-weighted) approaches for dose distribution calculation and creation of rectal dose volume histograms (DVH) and dose surface maps (DSM) to assess grade-2 (G2) rectal bleeding risk. Results: Maximum absolute errors using sCT for DVH-based G2 rectal bleeding risk (risk range 1.6% to 6.1%) were 0.6% (BD), 0.3% (TS) and 0.1% (DL). DSM-derived risk prediction errors followed a similar pattern. DL sCT has voxel-wise density generated from T2-weighted MR and improved accuracy for both risk-prediction methods. Conclusions: DL improves dosimetric and predicted risk calculation accuracy. Both TS and DL methods are clinically suitable for sCT generation in toxicity-guided RT, however, DL offers increased accuracy and offers efficiencies by removing the need for T1-Dixon MR. Advances in knowledge: This study demonstrates novel insights regarding the effect of sCT on predictive toxicity metrics, demonstrating clear accuracy improvement with increased sCT resolution. Accuracy of toxicity calculation in MR-only RT should be assessed for all treatment sites where dose to critical structures will guide adaptive-RT strategies. Clinical trial registration number: Patient data were taken from an ethically approved (UK Health Research Authority) clinical trial run at Guy's and St Thomas' NHS Foundation Trust. Study Name: MR-simulation in Radiotherapy for Prostate Cancer. ClinicalTrials.gov Identifier: NCT03238170.

Serial and parallel organ-at-risk-specific noncoplanar arc optimization for small versus large target volumes in liver SBRT.

Noncoplanar arc optimization has been shown to reduce OAR doses in SRS/SRT and has the potential to reduce doses to OARs in SBRT. Extracranial targets have additional considerations, including large OARs and, in the case of the liver, volume constraints on the healthy liver. Considering pathlengths through OARs that encompass target volumes may lead to specific dose reductions as in the encompassing healthy liver tissue. These optimizations must also leverage delivery efficiency and trajectory sampling to ensure ease of clinical translation. The purpose of this research is to generate optimized static-couch arcs that separately consider serial and parallel OARs and arc delivery efficiency, with a trajectory sampling metric, towards the aim of reducing dose to OARs and the surrounding healthy liver tissue. Separate BEV cost maps were created for parallel, and serial OARs by means of a fast ray-triangle intersection algorithm. An additional BEV cost map was created for the liver which, by definition, encompasses the liver tumors. The individual costs of these maps were summed and combined with the sampling metric for 100 000 random combinations of arc trajectories. A search algorithm was applied to find an arc trajectory solution that satisfied BEV cost and sampling optimization, while also ensuring an efficient delivery was possible with a low number of arcs. This method of arc selection was evaluated for 16 liver SBRT patients characterized by small and large target volumes. Comparisons were made with a clinical arc template of coplanar arcs. Dosimetric plan quality was evaluated using published guidelines and metrics from RTOG1112. Four of five plan quality metrics for the liver were significantly reduced when planned with optimized noncoplanar arcs. Median (range) reductions of the volumes receiving 10, 18, and 21 Gy were found of 140.4 (295.8) cc (p = 0.001), 28.2 (230.6) cc (p = 0.002) and 18.5 (155.5) cc (p = 0.04). A significant increase in median (range) dose to the right kidney of 0.2 ± 0.9 Gy (p = 0.03) was also found using optimized noncoplanar arcs, which was below the tolerance of 10 Gy for all cases. The average number of arcs chosen was 4 ± 1. Optimizing serial and parallel OARs separately during static couch noncoplanar arc selection significantly reduced the dose to the liver during SBRT using a moderate number of arcs.

Using ACGME General Surgery Milestones to Define the Competent Foundational Surgical Resident.

OBJECTIVE: In transitioning to competency-based surgical training, the need to clearly define competency is paramount. The purpose of this study is to define the well-prepared foundational resident using the ACGME General Surgery Milestones as our conceptual framework. DESIGN: Participants reflected on their expectations of a well-prepared resident at the end of PGY1, then assigned milestone levels reflecting this level of competence for General Surgery Milestones 1.0 and 2.0. Subcompetency scores were averaged among residents and faculty. The level of the well-prepared foundational resident was determined based on the highest level within one standard deviation of faculty, resident, and total group averages. SETTING: This took place during a dedicated education retreat at a single, large academic general surgery residency program. PARTICIPANTS: Key faculty stakeholders and a representative sample of residents (PGY 1-5) within our institution participated. RESULTS: Eight faculty and five residents completed Milestones 1.0 and 2.0 scoring. Mean scores between faculty and residents were compared. For 1.0, mean scores for Practice-Based Learning and Improvement 3 (PBLI 3) and Interpersonal Communication Skills 3 (ICS 3) were discernably lower for residents than for faculty (PBLI 3 1.3 (0.3) v 0.9 (0.2), p = 0.01; ICS3 1.6 (0.6) v 1.1 (1), p = 0.01). Scores of 2.0 were comparable across all subcompetency domains. With this broad agreement, Milestone-based competency standards were determined. Descriptive narratives of the KSAs were created for each subcompetency, combining the determined Milestones 1.0 and 2.0 levels. CONCLUSIONS: We were able to clearly define the competent foundational resident using the ACGME Milestones as a conceptual framework. These Milestone levels reflect the culture and expectations in our department, providing a foundation upon which to build a program of assessment. This methodology can be readily replicated in other programs to reflect specific expectations of the program within the larger ACGME frameworks of competency.

Future Surgical Leaders: Resident Perception Of Longitudinal Leadership And Non-Technical Skills Curriculum.

OBJECTIVE: A paucity of formal leadership training programs exists for residents, and outcomes of those are limited in reporting. Based on a robust needs assessment, our program created a longitudinal cohort curriculum, Future Surgical Leaders, for residents and fellows of all levels to provide training in nontechnical skills. Our objective was to evaluate surgical resident short-term outcomes and satisfaction with the Future Surgical Leaders (FSL) curriculum. DESIGN: Participants were sent a brief survey after each session of the curriculum from October 2020 to February 2022. The data was compiled after seventeen months of delivery. Likert Scale responses and text comments were analyzed with a 2-sample t-test and 2-way analysis of variance. SETTING: Academic tertiary institution. PARTICIPANTS: General surgery residents. RESULTS: Survey response rate from 54 sessions among all postgraduate year levels was 73%. Overall, 96% of residents/fellows either "agreed" or "strongly agreed" that the topics of the FSL curriculum were important to learn during surgical training. Only 24% of learners knew "a lot" or "a great deal" about the topics prior to the session which rose to 73% afterwards (p < 0.01). Each postgraduate year class showed statistically significant increase in knowledge. About 80% of learners wanted to investigate these topics further. Open comment questions identified themes requesting delivery of specific sessions earlier in residency training and positive overall attitudes toward the FSL curriculum. CONCLUSIONS: FSL is a satisfactory means of teaching leadership skills to surgical residents. Residents recognize the need to develop leadership skills prior to entering practice and want to learn more. The FSL curriculum may be considered for application at other surgical training programs.

Low-dose Paclitaxel with Pembrolizumab Enhances Clinical and Immunologic Responses in Platinum-refractory Urothelial Carcinoma.

PURPOSE: Single-agent checkpoint inhibition is effective in a minority of patients with platinum-refractory urothelial carcinoma; therefore, the efficacy of combining low-dose paclitaxel with pembrolizumab was tested. MATERIALS AND METHODS: This was a prospective, single-arm phase II trial with key inclusion criteria of imaging progression within 12 months of platinum therapy and Eastern Cooperative Oncology Group ≤1. Treatment was pembrolizumab 200 mg day 1 and paclitaxel 80 mg/m2 days 1 and 8 of a 21-day cycle for up to eight cycles unless progression or unacceptable adverse events (AE). The primary endpoint was overall response rate (ORR) with overall survival (OS), 6-month progression-free survival (PFS), and safety as key secondary endpoints. Change in circulating immune cell populations, plasma, and urinary miRs were evaluated. RESULTS: Twenty-seven patients were treated between April 2016 and June 2020, with median follow-up of 12.4 months. Baseline median age was 68 years, with 81% men and 78% non-Hispanic White. ORR was 33% by intention to treat and 36% in imaging-evaluable patients with three complete responses. Six-month PFS rate was 48.1% [95% confidence interval (CI): 28.7-65.2] and median OS 12.4 months (95% CI: 8.7 months to not reached). Common ≥ grade 2 possibly-related AEs were anemia, lymphopenia, hyperglycemia, and fatigue; grade 3/4 AEs occurred in 56%, including two immune-mediated AEs (pneumonitis and nephritis). Responding patients had a higher percentage of circulating CD4+IFNγ+ T cells. Levels of some miRs, including plasma miR 181 and miR 223, varied in responders compared with nonresponders. CONCLUSIONS: The addition of low-dose paclitaxel to pembrolizumab is active and safe in platinum-refractory urothelial carcinoma. SIGNIFICANCE: We found that combining pembrolizumab with low-dose paclitaxel may be effective in patients with urothelial carcinoma progressing on platinum chemotherapy, with favorable safety profiles.

Static couch non-coplanar arc selection optimization for lung SBRT treatment planning.

Objective. Non-coplanar arc geometry optimizations that take advantage of beam's eye view (BEV) geometric overlap information have been proven to reduce dose to healthy organs-at-risk (OARs). Recently, a metric called mean arc distance (MAD) has been developed that quantifies the arc geometry sampling of 4πspace. The purpose of this research is to combine improved BEV overlap information with MAD to generate static couch lung stereotactic body radiotherapy (SBRT) treatment plans deliverable on a C-arm linear accelerator.Approach. An algorithm utilizing the Moller-Trumbore ray-triangle intersection method was employed to compute a cost surrogate for dose to overlapping OARs using distances interpolated onto a PDD. Cost was combined with MAD for 100 000 random combinations of arc trajectories. A pathfinding algorithm for arc selection was created, balancing the contributions of MAD and 4πcost for the final trajectory. This methodology was evaluated for 18 lung SBRT patients. Cases were also planned with arcs from a clinical treatment template protocol for dosimetric and plan quality comparison. Results were evaluated using dose constraints in the context of RTOG0915.Main results. Five of six OARs had maximum dose reductions when planned with the arc trajectory optimization algorithm. Significant maximum dose reductions were found for esophagus (7.41 ± 0.91 Gy,p= 0.00019), trachea (5.56 ± 1.55 Gy,p= 0.0025), spinal cord (2.87 ± 1.13 Gy,p= 0.039), large bronchus (3.47 ± 1.49 Gy,p= 0.0075), and aorta (3.13 ± 0.99 Gy,p= 0.012). Mean dose to contralateral lung was also significantly reduced (0.50 ± 0.06 Gy,p= 0.00019). There were two significant increases in OAR doses: mean dose to ipsilateral lung (0.40 ± 0.09,p= 0.00086) and V5Gyto ipsilateral lung (1.95 ± 0.70%,p= 0.011). Paddick conformity index increased by 0.03 ± 0.02 (p= 0.14), remaining below a limit of 1.2 for both techniques.Significance. Static couch non-coplanar optimization yielded maximum dose reductions to OARs while maintaining target conformity for lung SBRT.

Cystic Fibrosis Reprograms Airway Epithelial IL-33 Release and Licenses IL-33-Dependent Inflammation.

Rationale: Type 2 inflammation has been described in people with cystic fibrosis (CF). Whether loss of CFTR (cystic fibrosis transmembrane conductance regulator) function contributes directly to a type 2 inflammatory response has not been fully defined. Objectives: The potent alarmin IL-33 has emerged as a critical regulator of type 2 inflammation. We tested the hypothesis that CFTR deficiency increases IL-33 expression and/or release and deletion of IL-33 reduces allergen-induced inflammation in the CF lung. Methods: Human airway epithelial cells (AECs) grown from non-CF and CF cell lines and Cftr+/+ and Cftr-/- mice were used in this study. Pulmonary inflammation in Cftr+/+ and Cftr-/- mice with and without IL-33 or ST2 (IL-1 receptor-like 1) germline deletion was determined by histological analysis, BAL, and cytokine analysis. Measurements and Main Results: After allergen challenge, both CF human AECs and Cftr-/- mice had increased IL-33 expression compared with control AECs and Cftr+/+ mice, respectively. DUOX1 (dual oxidase 1) expression was increased in CF human AECs and Cftr-/- mouse lungs compared with control AECs and lungs from Cftr+/+ mice and was necessary for the increased IL-33 release in Cftr-/- mice compared with Cftr+/+ mice. IL-33 stimulation of Cftr-/- CD4+ T cells resulted in increased type 2 cytokine production compared with Cftr+/+ CD4+ T cells. Deletion of IL-33 or ST2 decreased both type 2 inflammation and neutrophil recruitment in Cftr-/- mice compared with Cftr+/+ mice. Conclusions: Absence of CFTR reprograms airway epithelial IL-33 release and licenses IL-33-dependent inflammation. Modulation of the IL-33/ST2 axis represents a novel therapeutic target in CF type 2-high and neutrophilic inflammation.

A First Look at Equity, Diversity, and Inclusion of Canadian Medical Physicists: Results From the 2021 COMP EDI Climate Survey.

PURPOSE: In 2021, the Canadian Organization of Medical Physicists (COMP) conducted its first equity, diversity, and inclusion Climate Survey. The membership's experiences of inclusion, belonging, professional opportunities, discrimination, microaggressions, racism, and harassment in their professional lives are presented. METHODS AND MATERIALS: The ethics-reviewed survey was distributed in English and French to full members of COMP. Participants responded to questions covering demographics and professional climate. Simple descriptive statistics were used to measure frequency of responses. Data pertaining to impressions on the climate within the profession were compared using nonparametric statistical tests. RESULTS: The survey was distributed to 649 eligible members; 243 (37%) responded, and 214 (33%) provided full response sets. From the full response sets, findings showed that in general, age, highest academic degree, and racial and ethnic distribution trends of medical physicists were comparable with previously collected data and/or the Canadian population. The experiences of respondents relating to harassment in the workplace and perception of climate are reported and provide a useful benchmark for future assessments of interventions or training programs. In the workplace, fewer women (58%) reported having professional opportunities compared with men (70%). The survey also found that 17% of respondents (most of whom were women) directly or indirectly experienced sexual harassment in the workplace within the past 5 years. Finding that 23% of survey respondents identified as having a disability is a valuable reminder that accommodations in the workplace are necessary for more than 1 in every 5 medical physicists working in clinics. CONCLUSIONS: This study provided insight into the diversity and experiences of medical physicists in Canada. The majority of respondents had positive perceptions about their professional environment. However, equity-lacking groups were identified, such as women, underrepresented minorities, Indigenous peoples, and people with visible and invisible disabilities.

Risk of Inappropriately Timed Live Vaccination After Pediatric Cardiovascular Surgery.

OBJECTIVE: The American Academy of Pediatrics (AAP), Advisory Committee on Immunization Practices (ACIP), and Centers for Disease Control and Prevention (CDC) recommend delaying live vaccinations up to 11 months after transfusions of certain blood products due to the risk of immunoglobulins decreasing immunization efficacy. Because vaccination schedules recommend live immunizations at 12 months, infants aged 5 to 12 months who undergo cardiac surgery requiring blood products are potentially at risk for improper vaccination. The objective of this study was to identify the risk of inappropriately timed live vaccination in pediatric patients after cardiovascular surgery. METHODS: This single-center, retrospective chart review included 345 patients 5 to 12 months of age who underwent cardiovascular surgery between January 1, 2010, and December 31, 2016. Included patients received packed red blood cells (PRBCs) and/or platelets during the surgical admission and a live vaccine within the first 18 months of life. The primary endpoint was the incidence of live vaccine administration within 7 months of receiving PRBCs and/or platelets. RESULTS: Of the 345 included patients, 67% (n = 230) were inappropriately vaccinated after receiving platelets and/or PRBCs during cardiac surgery. CONCLUSIONS: Infants who undergo cardiac surgery between the ages of 5 and 12 months are at risk for inappropriate live vaccination timing. A clinically significant percentage of pediatric patients who received blood products during a cardiac surgical admission later received live vaccines at times that were inconsistent with AAP, ACIP, and CDC recommendations. Future interventions aimed at educating providers and patients may be warranted.

Comparison of anatomically informed class solution template trajectories with patient-specific trajectories for stereotactic radiosurgery and radiotherapy.

Class solution template trajectories are used clinically for efficiency, safety, and reproducibility. The aim was to develop class solutions for single cranial metastases radiotherapy/radiosurgery based on intracranial target positioning and compare to patient-specific trajectories in the context of 4π optimization. Template trajectories were constructed based on the open-source Montreal Neurological Institute (MNI) average brain. The MNI brain was populated with evenly spaced spherical target volumes (2 cm diameter, N = 243) and organs-at-risk (OARs) were identified. Template trajectories were generated for six anatomical regions (frontal, medial, and posterior, each with laterality dependence) based on previously published 4π optimization methods. Volumetric modulated arc therapy (VMAT) treatment plans generated using anatomically informed template 4π trajectories and patientspecific 4π trajectories were compared against VMAT plans from a standard four-arc template. Four-arc optimization techniques were compared to the standard VMAT template by placing three spherical targets in each of six anatomical regions of a test patient. This yielded 54 plans to compare various plan quality metrics. Increasing plan technique complexity, the total number of OAR maximum dose reductions compared to the standard arc template for the 6 anatomical classes was 4+/-2 (OFIXEDc) and 7+/-2 (OFIXEDi). In 65.6% of all cases, optimized fixed-couch positions outperformed the standard-arc template. Of the three comparisons, the most complex (OFIXEDi) showed the greatest statistical significance compared to the least complex (VMATi) across 12 plan quality metrics of maximum dose to each OAR, V12Gy, total plan Monitor Units, conformity index, and gradient index (p < 0.00417). In approximately 70% of all cases, 4π optimization methods outperformed the standard-arc template in terms of maximum dose reduction to OAR, by exclusively changing the arc geometry. We conclude that a tradeoff exists between complexity of a class solution methodology compared to patient-specific methods for arc selection, in the context of plan quality improvement.

External nasal dilator decreases N95 respirator-related respiratory effort and symptoms in gastrointestinal endoscopy unit staff.

Background and study aims N95-filtering facepiece respirators (FFR) use is associated with physiological changes and symptoms due to impaired nasal airflow and increased breathing resistance. We prospectively studied the effect of using an external nasal dilator (END) in gastroenterology laboratory (gastrointestinal lab) staff using N95FFR. Patients and methods N95FFR qualitative saccharine fit testing was performed on study participants with and without an END. Prospective data collection and comparisons included: 1) survey of perceived symptoms and difficulty of performing one day of gastrointestinal procedures with N95FFR and 1 day of gastrointestinal procedures with END plus N95FFR in random sequence; and 2) vitals and respiratory belt plethysmography in ten gastroenterologists performing simulated colonoscopy while wearing a surgical mask (SM), N95FFR plus SM, END plus N95FFR plus SM for 20 minutes each in random sequence and rapid succession. Results Twenty-nine of 31 participants passed the N95FFR and the END plus N95FFR fit test. Twenty-two participants (12 physicians; 11 males; mean age 44.1 years, range 31-61) performed 1 day of gastrointestinal procedures with an N95FFR and 1 day of gastrointestinal procedures with an END plus N95FFR. Significantly less difficulty with nasal breathing and severity of symptoms including breathing difficulty, headache, fatigue and frustration, occurred while using an END plus N95FFR. Respiratory plethysmography peak-to-trough measurement showed an increase during the N95FFR stage compared to the END plus N95FFR stage and the SM stage. Conclusions N95FFR related respiratory changes and symptom development may be mitigated by END use.

AMPATH surgical app: Low-cost simulator for the open appendectomy.

BACKGROUND: Due to a shortage and maldistribution of surgeons within Kenya, doctors with limited formal surgical training often perform emergency surgical procedures such as appendectomy. This lack of training can compromise patient outcomes and complicate care delivery. Our aim was to develop a low-cost simulator and skills curriculum to effectively teach open appendectomy. METHODS: Surgeons from 4 countries participated in semi-structured interviews to define the steps and technique of open appendectomy using cognitive task analysis. Using this input, our Academic Model Providing Access to Healthcare surgical team developed a curriculum, including a simulator and feedback mechanism. Surgeons and surgical trainees from Kenya and the United States tested the simulator prototype and provided feedback for its refinement based on clarity, utility, and realism. RESULTS: Instructions for a self-constructed simulator were developed at the cost of 70 Kenyan shillings (0.64 US dollars). Fifteen surgeons and surgical residents gave feedback on the simulator and curriculum, and each was presented with an updated version based on feedback. Overall, the curriculum was clear, with each sub-step receiving a median score of ≥83.5 out of 100 for clarity; however, through iterative design, the utility of sub-steps on the simulator improved. CONCLUSION: A comprehensive open appendectomy curriculum, including a low-cost appendectomy simulator model, was developed and refined using surgeon feedback. Such curricula may benefit trainees in low-resource settings who may otherwise have limited access to quality training material.

Mean Arc Distance (MAD): a quantity to compare trajectory 4πsampling in single target cranial stereotactic radiotherapy.

Purpose.C-arm linac-based radiotherapy has seen a recent interest in 4πmethods of delivery using simultaneous rotations of couch and gantry to reduce doses to organs-at-risk (OARs) and increase dose compactness. While many methods use heuristics to generate trajectories that avoid OARs, combined with arbitrary trajectory restrictions to prevent oversampling, a quantity has not yet been developed to succinctly compare sampling of the 4πspace for candidate trajectories as a surrogate for dosimetric compactness.Methods.Evenly spaced sampling points were distributed across a 4πsphere centred on isocentre. A metric, mean arc distance (MAD), was defined that quantifies the average arc distance between all sampling points and their nearest field in a radiotherapy trajectory. The relationship between isodose volume and MAD was examined in 2,047 plans: 900 unique trajectories of fixed port DCA plans, 900 unique trajectories of contiguous field DCA plans, 192 VMAT plans (eight volumes in four locations, each with six trajectories) in matRad with 5 VMAT plans repeated for validation in a clinical planning system, and 10 clinical VMAT cases replanned with five trajectories in a clinical treatment planning system.Results.All isodose volumes greater than 10% of the prescription dose decreased with decreasing MAD in all comparisons. In the range of 10% to 100% of the prescription dose, the rate of isodose volume decrease was exponential as a function of MAD in all comparisons. Reduction of absolute isodose volume is seen with increased 4πsampling, with larger target volumes exhibiting larger absolute reductions. Very low isodoses (0% to 10% of prescription) increased with decreasing MAD.Conclusions.MAD is a 4πsampling quantity useful in quantifying the decrease of isodose volume, relevant for sparing normal tissues. By quantifying this feature, candidate dynamic trajectories can be efficiently compared for 4πsampling. This quantity is explored here for single target cranial radiotherapy but may have applications to other radiotherapy treatment sites.

Intra-arc binary collimation with dynamic axes trajectory optimization for the SRS treatment of multiple metastases with multiple prescriptions.

PURPOSE: This work generates multi-metastases cranial stereotactic radiosurgery/radiotherapy (SRS/SRT) plans using a novel treatment planning technique in which dynamic couch, collimator, and gantry trajectories are used with periodic binary target collimation. The performance of this planning technique is evaluated against conventional volumetric arc therapy (VMAT) planning in terms of various dose and plan quality metrics. METHODS: A 3D cost space (referred to herein as the combined optimization of dynamic axes or CODA cube) was calculated based on an overlap between targets and organs-at-risk (OARs) and uncollimated areas between targets (island blocking) for all combinations of couch, gantry, and collimator angles. Gradient descent through the cube was applied to determine dynamic trajectories. At each control point (CP), each target can either be conformally treated or blocked by the multi-leaf collimator (referred to as intra-arc binary collimation, iABC). Simulated annealing was used to optimize the collimation patterns throughout the arcs as well as the monitor units (MUs) delivered at each CP. Seven previously treated VMAT plans were selected for comparison against the CODA-iABC planning technique. Two CODA-iABC plans were developed: a single gantry arc plan and a plan with one gantry arc and two couch arcs. Plan quality comparison metrics included maximum and mean dose to OARs (brainstem, chiasm, optic nerves, eyes, and lenses), the volume of normal brain receiving 12 Gy (V12Gy), total MUs, target conformity, and dose-gradient index. RESULTS: Treatment plans generated with 1-arc CODA-iABC plans delivered an average of 21% and 30% higher maximum and mean doses to brainstem, respectively, when compared to VMAT plans. Treatment plans generated with 3-arc CODA-iABC used an average of 24% fewer MUs and resulted in an average reduction of 48% maximum dose and 50% mean dose to the OARs, when compared to VMAT. Target conformity values were worse in both CODA-iABC plans than VMAT by an average of 35% and 15%, respectively. There are no significant differences in V12Gy for all three planning techniques; however, 3-arc CODA-iABC is more effective at reducing dose to normal brain in the low-dose region (<12 Gy). CONCLUSION: CODA-iABC is a novel planning technique that has been developed to automatically generate patient-specific multi-axis trajectories for multiple metastases cranial SRS/SRT. This work has demonstrated the feasibility of planning with this novel method. The 1-arc CODA-iABC planning technique is slightly dosimetric inferior to VMAT. With an increased sampling of a three-dimensional CODA cube by using a 3-arc CODA-iABC technique, there was improved total dose sparing to all the OARs and increased MU efficiency, but with a cost in target conformity, when compared to VMAT.

Using multi-centre data to train and validate a knowledge-based model for planning radiotherapy of the head and neck.

Background and purpose: Knowledge-based radiotherapy planning models have been shown to reduce healthy tissue dose and optimisation times, with larger training databases delivering greater robustness. We propose a method of combining knowledge-based models from multiple centres to create a 'super-model' using their collective patient libraries, thereby increasing the breadth of training knowledge. Materials and methods: A head and neck super-model containing 207 patient datasets was created by merging the data libraries of three centres. Validation was performed on 30 independent datasets during which optimiser parameters were tuned to deliver the optimal set of model template objectives. The super-model was tested on a further 40 unseen patients from four radiotherapy centres, including one centre external to the training process. The generated plans were assessed using established plan evaluation criteria. Results: The super-model generated plans that surpassed the dose objectives for all patients with single optimisations in an average time of 10 min. Healthy tissue sparing was significantly improved over manual planning, with dose reductions to parotid of 4.7 ± 2.1 Gy, spinal cord of 3.3 ± 0.9 Gy and brainstem of 2.9 ± 1.7 Gy. Target coverage met the established constraints but was marginally reduced compared with clinical plans. Conclusions: Three centres successfully merged patient libraries to create a super-model capable of generating plans that met plan evaluation criteria for head and neck patients with improvements in healthy tissue sparing. The findings indicate that the super-model could improve head and neck planning quality, efficiency and consistency across radiotherapy centres.

Neural network dose prediction for rectal spacer stratification in dose-escalated prostate radiotherapy.

PURPOSE: To develop a knowledge-based decision-support system capable of stratifying patients for rectal spacer (RS) insertion based on neural network predicted rectal dose, reducing the need for time- and resource-intensive radiotherapy (RT) planning. METHODS: Forty-four patients treated for prostate cancer were enrolled into a clinical trial (NCT03238170). Dose-escalated prostate RT plans were manually created for 30 patients with simulated boost volumes using a conventional treatment planning system (TPS) and used to train a hierarchically dense 3D convolutional neural network to rapidly predict RT dose distributions. The network was used to predict rectal doses for 14 unseen test patients, with associated toxicity risks calculated according to published data. All metrics obtained using the network were compared to conventionally planned values. RESULTS: The neural network stratified patients with an accuracy of 100% based on optimal rectal dose-volume histogram constraints and 78.6% based on mandatory constraints. The network predicted dose-derived grade 2 rectal bleeding risk within 95% confidence limits of -1.9% to +1.7% of conventional risk estimates (risk range 3.5%-9.9%) and late grade 2 fecal incontinence risk within -0.8% to +1.5% (risk range 2.3%-5.7%). Prediction of high-resolution 3D dose distributions took 0.7 s. CONCLUSIONS: The feasibility of using a neural network to provide rapid decision support for RS insertion prior to RT has been demonstrated, and the potential for time and resource savings highlighted. Directly after target and healthy tissue delineation, the network is able to (i) risk stratify most patients with a high degree of accuracy to prioritize which patients would likely derive greatest benefit from RS insertion and (ii) identify patients close to the stratification threshold who would require conventional planning.

Patient-specific collision zones for 4π trajectory optimized radiation therapy.

PURPOSE: The 4π methodology determines optimized noncoplanar subarcs for stereotactic radiation therapy that minimize dose to organs-at-risk. Every combination of treatment angle is examined, but some angles are not appropriate as a collision would occur between the gantry and the couch or the gantry and the patient. Those combinations of couch and gantry angles are referred to as collision zones. A major barrier to applying 4π to stereotactic body radiation therapy (SBRT) is the unknown shape of the collision zones, which are significant as patients take up a large volume within the 4π sphere. This study presents a system that determines patient-specific collision zones, without additional clinical steps, to enable safe and deliverable noncoplanar treatment trajectories for SBRT patients. METHODS: To augment patient's computed tomography (CT) scan, full body scans of patients in treatment position were acquired using an optical scanner. A library of a priori scans (N = 25) was created. Based on the patients' treatment position and their body dimensions, a library scan is selected and registered to the CT scan of the patient. Next, a model of the couch and immobilization equipment is added to the patient model. This results in a patient model that is then aligned with a model of the treatment LINAC in a "virtual treatment room," where both components can be rotated to test for collisions. To test the collision detection algorithm, an end-to-end test was performed using a cranial phantom. The registration algorithm was tested by comparing the registered patient collision zones to those generated by using the patient's matching scan. RESULTS: The collision detection algorithm was found to have a 97.80% accuracy, a 99.99% sensitivity, and a 99.99% negative predictive value (NPV). Analysis of the registration algorithm determined that a 6 cm buffer was required to achieve a 99.65% mean sensitivity, where a sensitivity of unity is considered to be a requirement for safe treatment delivery. With a 6 cm buffer, the mean accuracy was 86.70% and the mean NPV was 99.33%. CONCLUSIONS: Our method of determining patient-specific collision zones can be accomplished with minimal user intervention based on an a priori library of body surface scans, thus enabling the safe application of 4π SBRT.