3D Radiation Research Articles

First indirect drive inertial confinement fusion campaign at Laser Megajoule

The first indirect drive Inertial Confinement Fusion (ICF) experiments on the Laser Megajoule facility were carried out with approximately 150 kJ of laser energy distributed on 48 beams (12 quads) arranged in two cones. The target consisted of a gold vacuum rugby-shaped hohlraum and a plastic capsule located at its center, filled with deuterium gas fuel. The arrangement of the 12 quads is such that the laser irradiation on the wall generated a three-dimensional (3D) x-ray flux around the capsule creating 3D deformations on the imploding plastic shell. This constraint forced the design of a robust target (relatively thin ablator, around 40 μm) driven by a short laser pulse (3 ns) that delivered about 1011 neutrons. Full-integrated 3D radiation hydrodynamics simulations allowed both the target definition and the data interpretation (mainly radiation temperature, x-ray images, and neutron yield). 3D calculations and experiments compare well.

Mass and Angular Momentum Transport in a Gravitationally Unstable Protoplanetary Disk with Improved 3D Radiative Hydrodynamics

During early phases of a protoplanetary disk's life, gravitational instabilities (GIs) can produce significant mass transport, can dramatically alter disk structure, can mix and shock-process gas and solids, and may be instrumental in planet formation. We present a 3D grid-based radiative hydrodynamics study with varied resolutions of a 0.07 M ⊙ disk orbiting a 0.5 M ⊙ star as it settles over most of its radial extent into a quasi-steady asymptotic state that maintains approximate balance between heating produced by GIs and radiative cooling governed by realistic dust opacities. We assess disk stability criteria, thermodynamic properties, strengths of GIs, characteristics of density waves and torques produced by GIs, radial mass transport arising from these torques, and the level to which transport can be represented as local or nonlocal processes. Physical and thermal processes display distinct differences between inner optically thick and outer optically thin regions of the disk. In the inner region, gravitational torques are dominated by low-order Fourier components of the azimuthal mass distribution. These torques are strongly variable on the local dynamical time and are subject to rapid flaring presumably driven by recurrent swing amplification. In the outer region, m = 1 torques dominate. Ring-like structures exhibiting strong noncircular motions, and vortices develop near the inner edge between 8 and 14 au. We find that GI-induced spiral modes erupt in a chaotic manner over the whole low-Q part of the disk, with many spiral modes appearing and disappearing, producing gravitoturbulence, but dominated by fluctuating large-scale modes, very different from a simple α-disk.

Formation of hot spots at end-on pre-compressed isochoric fuels for fast ignition

It is crucial to form a hot spot that can drive a self-heating nuclear burn propagation into the surrounding cold fuel in ignition process of laser fusion. In this paper, we discuss the formation of a hemispherical hot spot located at the edge of an end-on precompressed isochoric fuel instead of a central spherical hot spot surrounded by cold fuel in a corona plasma shell. This configuration leads to a new energy loss mechanism named hot spot collapse, which originates from mass loss of the hot spot through the interface with the vacuum. A semi-analytical model is proposed including α particle induced burning, hot spot collapse and other energy loss processes. Then a modified ignition criterion is derived. The results show that the competition between the hot spot collapse and the burn propagation is crucial in the formation of the hot spot. The formation of such a hot spot at end-on precompressed isochoric fuels would require a somewhat higher initial temperature of Th=9 keV for a hot spot with an initial areal density ρd=0.6gcm−2 . Simulations are performed with a 3D hybrid particle-in-cell/fluid code for the heating process by fast electrons and a 3D radiation hydrodynamics code for the burning process. Simulation results agree with the model. Our optimized result shows a 10 ps heating laser pulse with an energy as low as 39 kJ can lead to a fast ignition in the ideal case. This study provides an effective reference for design and evaluation of experiments planned for fast ignition schemes.

3D2: Three Decades of Three-Dimensional Dosimetry

The development of three-dimensional (3D) dosimetry was motivated by its promise as an effective methodology for the validation of the complex dose distributions achieved by modern techniques such as Intensity Modulated and Volumetric Arc Radiation Therapy. 3D techniques were first proposed in the 1980s when clinics were just starting to move from two-dimensional contour plan based delivery to more conformal techniques. Advances in dosimeter materials, readout systems, and workflow and software systems for the registration and analysis of the volumetric dose data have made 3D dosimetry more attainable, yet to date it has not made major inroads into the clinic. This keynote address will highlight some 3D dosimetry developments over the years, many of which were first revealed through the past twelve International Conferences on 3D and Advanced Radiation Dosimetry (IC3Ddose). These conferences resulted in the publication of more than 130 didactic review articles and over 650 proffered research papers, the majority openly available on the internet (years before the current drive to publishing in open access journals). In this joint keynote address to the IC3Ddose community (at the end of its conference) and to attendees of the Canadian Organization of Medical Physicists annual scientific meeting (at its start), I will briefly review the radiation sensitive materials used for 3D dosimetry, the imaging systems required to read out the volumetric dose information, the workflows and systems required for efficient analysis, and the protocols required for reproducible dosimetry, and how the dosimetry has come into the clinic. The address includes some personal reflections of the motivational and practical changes in 3D dosimetry over time. And as we are all meeting in person for the first time in over two years, the address will end with some observations on the importance of conferences for the exchange of ideas and associated debate necessary for scientific advancement.

281P 10-year treatment outcome of prostate cancer patients with 3D conformal radiation: Experience of a single cancer institution in Iran

281P 10-year treatment outcome of prostate cancer patients with 3D conformal radiation: Experience of a single cancer institution in Iran

Dynamic ultrasound focusing and centimeter-scale ex vivo tissue ablations with a CMUT probe developed for endocavitary HIFU therapies.

Thermal ablation of localized prostate tumors via endocavitary Ultrasound-guided High Intensity Focused Ultrasound (USgHIFU) faces challenges that could be alleviated by better integration of dual modalities (imaging/therapy). Capacitive Micromachined Ultrasound Transducers (CMUTs) may provide an alternative to existing piezoelectric technologies by exhibiting advanced integration capability through miniaturization, broad frequency bandwidth and potential for high electro-acoustic efficiency. An endocavitary dual-mode USgHIFU probe was built to investigate the potential of using CMUT technologies for transrectal prostate cancer ablative therapy. The USgHIFU probe included a planar 64-element annular HIFU CMUT array (fHIFU = 3 MHz) surrounding a 256-element linear imaging CMUT array. Acoustic characterization of the HIFU array included 3D pressure field mapping and radiation force balance measurements. Ex vivo proof-of-concept experiments consisted in generating HIFU thermal ablations with the CMUT probe on porcine liver tissues. The planar CMUT probe enabled HIFU dynamic focusing (distance range: 32 - 72 mm) while providing acoustic surface intensities of 1 W/cm2 that allowed producing elementary ex vivo ablations in depth of liver tissue (L×W ≈ 10 mm × 5 mm). Combinations of dynamic focusing, along with probe rotation and translation produced larger thermal ablations (L×W ≈ 20 mm × 20 mm) by juxtaposing multiple elementary ablations, consistent with expected results obtained through numerical modeling. The technical feasibility of using a USgHIFU probe, fully-developed using CMUTs for tissue ablation purposes, was demonstrated. The HIFU-CMUT array showed tissue ablation capabilities with volumes compatible with localized cancer targeting thus providing assets for further development of focal therapies.

Optimization of MRI pulse sequences and gadobutrol-doped polymer gel for real time 4D radiation dosimetry on the MRI-Linac

Different MRI pulse sequences can be applied to acquire real time dose distributions on an MRI-Linac. The temporal resolution is affected by the MRI pulse sequence type, the MRI pulse sequence parameters and the NMR relaxation-dose response of the polymer gel. To obtain a sufficiently high temporal resolution, it is crucial to optimize the MRI pulse sequence parameters such as TE, TR and flip angle. The optimization goal is to obtain the highest dose resolution within the shortest time frame, i.e. the smallest temporal uncertainty. We here also demonstrate that it is possible to further improve the temporal uncertainty of the polymer gel dosimeter by adding an MRI contrast agent. The optimization of two MRI pulse sequences in combination with a gadobutrol-doped MAGAT polymer gel dosimeter is discussed.

Preliminary commissioning of a prototype solid tank optical CT scanner for 3D radiation dosimetry

Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters. In previous research, it was shown that a design could significantly reduce the volume of the refractive index baths that are commonly found in optical CT systems. The proposed scanner has been manufactured and is in process of being commissioned. The rays refract through the system and their paths are estimated using a ray-tracing simulator. Reconstruction is preformed through algebraic reconstruction technique and iterated using the FISTA-TV algorithm. A Sylgard®184 edge phantom was created to commission the scanner’s spatial resolution. The scanner is capable of a 0.929 mm−1 spatial resolution, although the spatial resolution is highly dependent on the number of iterations, and method of processing the edge spread function.

Three Dimensional Natures of Massive Star Envelopes

In this paper, we review our current understanding of the outer envelope structures of massive stars based on three-dimensional (3D) radiation hydrodynamic simulations. We briefly summarize the fundamental issues in constructing hydrostatic one-dimensional (1D) stellar evolution models when stellar luminosity approaches the Eddington value. Radiation hydrodynamic simulations in 3D covering the mass range from 13M⊙ to 80M⊙ always find a dynamic envelope structure with the time-averaged radial profiles matching 1D models with an adjusted mixing-length parameter when convection is subsonic. Supersonic turbulence and episodic mass loss are generally found in 3D models when stellar luminosity is super-Eddington locally due to the opacity peaks and convection being inefficient. Turbulent pressure plays an important role in supporting the outer envelope, which makes the photosphere more extended than predictions from 1D models. Massive star lightcurves are always found to vary with a characteristic timescale consistent with the thermal time scale at the location of the iron opacity peak. The amplitude of the variability as well as the power spectrum can explain the commonly observed stochastic low-frequency variability of mass stars observed by TESS over a wide range of parameters in an HR diagram. The 3D simulations can also explain the ubiquitous macro-turbulence that is needed for spectroscopic fitting in massive stars. Implications of 3D simulations for improving 1D stellar evolution models are also discussed.

Four-Dimensional Imaging and Radiation Therapy: A Review of Challenges and Advancements in Clinical Practices

4-Dimensional Radiation therapy (4DRT) has been vastly developed in the past two decades. Motion management has become a vital part of high precision radiotherapy, wherein Stereotactic Body Radiation Therapy (SBRT) turns out to be a great boon for treating thoracic and abdominal tumours with confidence. In this review paper, we have analyzed the development of motion management strategies and the advancement of 4DRT.We have discussed the evolution of Internal target volume (ITV), 4D imaging techniques and the problems of breathing motion. In the second part, we have discussed various methods to tackle breathing motion. We also have reviewed the dosimetric aspects of 4D imaging and its clinical implications. In the last section, we have elaborated the 4D radiation therapy and recent advancements and practices.

Utility of the "All of Us" Database for Radiation Oncology Research.

We provide an overview the All of Us Research Program, a National Institutes of Health funded research database, and report on the utility of this database for Radiation Oncology research. The All of Us Research Program aims to create a large and diverse health database with participants from across the US. Patients consent to join the database and agree to share electronic health records, complete surveys, provide physical measurements, and donate at least one biospecimen. In this observational study, we used the public data browser feature of the All of Us Dataset to evaluate utility for future radiation oncology research. Within the database, we report on the number of cases of common cancers in the US, using ICD10 codes, and also the number of patients treated with common radiotherapy procedures, using CPT4 codes. We then qualitatively report on additional data of interest. Of note, public patient counts in All of Us is rounded to the nearest interval of 20. Additional tiers of data access exist, including individual level data, which were not used in this survey of public data. The database includes 372,380 participants, of which 46,380 patients have a diagnosis of cancer. Within the identified top 10 cancers according to ACS, there were a total of 26,540 primary malignant cancers. The most common type of cancers were breast cancer (ICD10 - c50 [n = 6,960]), Prostate (ICD10 - c61 [n = 4,500]), Non-Hodgkin lymphoma (ICD10 - c85 [n = 2860]), Lung & bronchus (ICD10 - c34 [n = 2000]), Colon (ICD10 - c18 [n = 1940]), Melanoma of the skin (ICD10 - c43 [n = 1740]), Thyroid(ICD10 - c73 [n = 1720]), Kidney (ICD10 - c64 [n = 1300]), Urinary bladder (ICD10 - c67 [n = 1140]). The most common radiation therapy procedures were Computerized Tomography simulation (CPT - 77290 [n = 4,040]), Intensity Modulated Radiation Therapy (CPT - 77386 [n = 780]), 3D conformal radiation therapy (CPT - 77412 [n = 1,720]), Stereotactic Body Radiation Therapy (CPT - 77373 [n = 400]), Brachytherapy (CPT - 77770- 77772 [n = 240]), and Proton Therapy (CPT - 77520-77525 [n = 140]). Qualitatively, other data within All of Us include labs values, drug exposures, comorbidities, other procedures, physical measurements, and wearable biometrics (Fitbit) data. Genomic data typically includes germline testing using whole genome sequencing or genotyping array. Patient surveys include data on personal medical history, family health history, lifestyle, social determinants of health, COVID19 experience, and overall health. Potential outcome variables of interest to oncology research in the database include survival, cause of death, additional procedures or diagnoses after cancer treatment, and quality of life metrics derived from the survey instruments. The All Of Us Research Database includes a large number of cancer cases, of which a substantial number received radiotherapy. Future work will focus on focused hypothesis-driven research questions.

Interpretability of a Deep Learning-Based Prediction Model for Mandibular Osteoradionecrosis.

The development of radiation-induced toxicities is a multifactorial process. Existing DVH-based prediction models use traditional multivariate analysis to combine all the potential risk factors. Recently, deep learning (DL) has been proposed for predicting mandibular osteoradionecrosis (ORN) directly from 3D dose distribution maps [1]. However, with this approach, incorporating non-imaging data such as potential risk factors presents challenges. We investigate the use of DL-based multimodality fusion for the purpose of radiation-induced ORN toxicity prediction. This study explores early and late fusion strategies for combining 3D radiation dose distribution maps and clinical and demographic variables in the prediction of mandibular ORN incidence in head and neck cancer patients treated with radiotherapy. The results are compared to single-modality predictions with a random forest (RF) trained only on clinical variables and a 3D DenseNet40 trained on dose maps alone. We investigate two different fusion approaches. In the first, the image features extracted from the radiation dose maps using a 3D DenseNet40 were concatenated with the clinical variables into one single vector using a type II early fusion strategy. The combined feature vector was input into a fully connected layer for classification of ORN vs. controls. A final softmax activation layer was added to obtain the class predicted probabilities. The second approach used a late fusion strategy, in which the outputs from the 3D DenseNet40 and the RF model were combined by averaging the predicted classification probabilities for each of the two classes (ORN and no ORN) to obtain the final class decision on a case-by-case basis. The AUROC values obtained for the late and early fusion models and the single-modality 3D DenseNet40 and RF models were 0.70, 0.68, 0.69 and 0.60, respectively. The highest AUC ROC was observed with the late fusion approach, which was statistically significantly different to that of the RF single-modality model with a significance level of 0.05. However, after Bonferroni correction (Altman 1999) for multiple comparisons was applied, resulting in a corrected significance level of 0.05/6 = 0.008 for each comparison, no statistically significant difference was observed between any of the models' AUROC values. This is most likely due to the lack of discriminative contribution observed from clinical variables, which on their own resulted in a poorly predictive RF model. To our knowledge, no previous work has been published on the use of multimodal fusion DL methods to combine dose distribution maps and clinical variables in the prediction of mandibular ORN. Although non-conclusive results were obtained, this study demonstrates the potential of DL in the prediction of the multifactorial side effects resulting from radiotherapy treatments. [1] Humbert-Vidan L et al. Prediction of Mandibular ORN Incidence from 3D Radiation Dose Distribution Maps Using DL (2022).

The Outcomes of Intensity Modulated Radiotherapy versus Conventional 2D Radiotherapy in Patients with Oropharyngeal or Hypopharyngeal Squamous Cell Carcinoma. A Case-Control Study

"Introduction: Head and neck cancers’ radiotherapy (RT) is challenging due to the irregular target volumes and the proximity of multiple organs at risk. The purpose of this study is to compare the toxicity, loco-regional control and the pattern of tumour recurrence after intensity modulated radiotherapy (IMRT) or conventional 2D radiotherapy (2D CRT) in patients with squamous cell carcinoma (SCC) oropharyngeal or hypopharyngeal cancers. Material and method: We retrospectively compared the outcomes of SCC oropharyngeal or hypopharyngeal cases treated by IMRT or 2D CRT from 1998 to 2010 in a Canadian Academic Hospital. We matched the patients in the two groups according to primary tumour location and clinical stage. The information on treatment, toxicity and outcomes was retrieved from patients’ medical records. For the patients having a recurrence after IMRT, the CT scan at relapse was fused with the planning CT. For the patients recurring after 2D CRT, we matched the CT images with the relative position of the radiotherapy fields. Statistical analysis was made using GraphPad Prism software. Results: We included a total of 50 patients in the IMRT group and 50 in the 2D CRT group. The median age was 62 and 58 years, respectively, and the median follow-up was 18 and 22.6 months, respectively. Some of the side effects were less frequent on the IMRT group compared to the 2D CRT: xerostomia (16% vs 64%, P=0.0036), mucositis (70% vs 74% P=0.5451), weight loss (18% vs 46% P= 0.0027), radionecrosis/mandibular fracture (0 % vs 2%), fibrosis (0% vs 10%), and telangiectasia (0% vs 4%). However, acute dermatitis and late dysphagia were more frequent in the IMRT group (44% vs 28% P=0.0042; and 14% vs 2% P=0.028; respectively). The overall survival at 2 years was for 74.03% for IMRT and 60% for 2D CRT (P< 0.001) and the 5 years actuarial locoregional control was 89.54 % for IMRT group, and 62.48% for the 2DCRT group (P< 0.001). Three patients from the IMRT group had a local recurrence (2 in-field and 1 marginal), while in the 2D-CRT group, there were 10 patients with a local recurrence (6 in-field and 4 marginal). Conclusion: SCC oropharyngeal and hypopharyngeal patients treated with IMRT and concurrent cisplatin had better outcomes and fewer side effects, when compared to similar cases treated with 2D CRT. The local recurrence had a similar pattern for both techniques."

Risk of Sexual Dysfunction in Men Treated with Pelvic Radiation Therapy for Locally Advanced Rectal Cancer: 20 Years of Experience with 451 Patients

Radiation therapy (RT) is commonly used in the treatment of locally advanced rectal cancer (LARC), but data on its impact on men's sexual health is limited. Given the rising incidence of rectal cancer in younger men, sexual function is an important quality of life factor. We hypothesized that men with LARC treated with RT would be at increased risk of sexual dysfunction compared to men who did not receive RT. This is a single institution retrospective analysis of outcomes of men ≤50 years diagnosed with LARC between 1999 and 2019. Primary outcomes of erectile dysfunction (ED), ejaculatory dysfunction (EjD), and testosterone deficiency (TD) were assessed via ICD-9/10 codes, and TD was captured with free testosterone <300 ng/dL. Cumulative incidences were calculated with death as a competing risk and p values were calculated using Gray's test. Subdistribution hazard ratios from competing risk regression models were used. The combined study sample included 451 men: 347 received RT as part of their multimodality treatment, and 104 did not. Median time to last follow up was 5.6 years (IQR 3.3-8.7). Age at diagnosis, stage, and medical comorbidities for sexual dysfunction were similar between the two groups (p>0.05). Cumulative incidence estimates are shown in Table 1, showing a higher cumulative incidence of ED in the RT group, but no difference in EjD or TD between the 2 groups. On univariable analysis, RT, smoking, dyslipidemia, peripheral artery disease, depression, prostate cancer/hyperplasia, closed or current ileostomy, and undergoing rectal cancer surgery were all independent risk factors for ED (p<0.05). On multivariable analysis, RT maintained statistical significance as an independent risk factor for ED (HR 3.87, 95% CI 1.93-7.75, p<0.001). Within the RT group, IMRT compared to 3D (HR 1.54, 95% CI 1.02-2.32, p = 0.040) and groin RT (HR 2.60, 95% CI 1.21-5.59, p = 0.014) were independent risk factors for ED. Within the RT group, groin RT also approached significance as a risk factor for TD (HR 3.61, 95% CI 0.98-13.3, p = 0.054). No RT dose thresholds to external genitals or penile bulb were identified that increased risks of ED, EjD, or TD. RT for LARC independently increases risk of ED but not EjD or TD. IMRT might increase the risk of ED due to increased scatter dose to the genitals and including the inguinal nodes in the target volumes increases the dose to the genitals/testicles, which could translate into a higher risk for ED and TD. Future research on proton RT and prophylactic sildenafil is needed in men ≤50 to decrease the risk of ED.

Shoulder Muscle Dosimetry and Post-Treatment Rehabilitation Utilization for Early-Stage Breast Cancer Patients

Rehabilitation services for recovery of impaired physical function following breast cancer treatments are largely underutilized. We previously found that breast cancer survivors treated with radiation who received higher radiation doses to the pectoralis major are more likely to self-report shoulder pain and disability. This study aims to address whether radiation dose delivered to the pectoralis major (Pmaj) and pectoralis minor (Pmin) are correlated with referrals for rehabilitation services post-treatment. A retrospective 1:1 matched case-control study was conducted for breast cancer patients who were and were not referred for breast or shoulder rehabilitation services between 2014-2019 at a single academic institution. Patients were included if they had a lumpectomy and adjuvant radiation without regional nodal irradiation. Cohorts were matched based on age, axillary surgery (none vs. sentinel lymph node biopsy (SLNB)), and use of radiation boost. We used non-parametric Mann-Whitney U tests to determine whether Pmaj or Pmin doses (mean, V50Gy, V45Gy, V40Gy, V35Gy, V30Gy, V20Gy) were different between the two groups. Muscle doses were converted to EQD2 assuming an α/β ratio of 2.5. In our study of 30 patients of a median age 57 years (IQR 12.75), 20 (66.67%) patients underwent SLNB in addition to lumpectomy. Median tumor size was 1.1cm (range 0.16 - 7.30cm). Stage was 0 for 11 patients (36.67%), I for 14 patients (46.67%), and II for 5 patients (16.67%). 3D conformal radiation was delivered to the whole breast with a moderately hypofractionated (n = 17) or conventionally fractionated regimen (n = 13). The most common rehabilitation diagnoses were lymphedema (n = 8), scar management (n = 7) and shoulder pain (n = 5). Mean dose to both the Pmaj (20.8Gy vs. 18.6Gy; p = 0.02) and Pmin (30.6Gy vs. 24.6Gy; p = 0.01) were significantly higher in patients who received post-treatment rehabilitation compared to those without. The V40Gy, V35Gy, V30Gy and V20Gy (all p<0.02) for the Pmin and V35Gy, V30Gy and V20Gy for the Pmaj (all p<0.04) were also significantly higher in those who underwent rehabilitation. In this cohort of patients with early-stage breast cancer, increased mean doses to the pectoralis muscles were correlated with increased use of rehabilitation services after radiation. Physicians might consider using these dosimetric data to complement clinical symptoms in the decision-making process for referrals for rehabilitation services. This may help facilitate earlier referral to rehabilitation interventions, which is important since early intervention is correlated with improved shoulder morbidity.

Predicting Prostate VMAT 3D Radiation Doses of Continuously Varying Organ Dose Trade-Offs Using a Conditional Variational Autoencoder

Predicting 3D radiation doses from planning structures is a promising method of knowledge-based treatment planning. However, most models are designed to predict only one 3D dose distribution per patient, based on historical organ dose trade-offs. To allow customizable plan generation, in this study, we aim to show the feasibility of dose prediction in which the degrees of organ dose trade-off could be explicitly specified. Specifically, the bladder vs. rectum dose trade-off in prostate cancer was investigated. In an IRB-approved study, we obtained imaging and structure contours for 167 patients with prostate cancer who received definitive radiotherapy. Training data was generated by automatically creating 3 different plans for each patient: while keeping target dose patterns constant, 1 base plan was generated with optimization objectives directly based on the output of a custom RapidPlan model prediction (S = 0), 1 plan with the goal to significantly lower bladder dose relative to the rectum (S = -1), and 1 plan with the goal to significantly lower rectum dose relative to the bladder (S = 1). This process was achieved by adjusting priority values during optimization. S is a scalar indicating the degree of bladder vs. rectum dose trade-off (higher S = higher dose to the bladder relative to the rectum). A conditional variational autoencoder (cVAE) was constructed as the generative model. Training, validation, and testing sets consist of 124, 10, and 33 patients, respectively. During training, the inputs to the model were 3D structure masks with voxel values modified based on S, and the output was the corresponding 3D dose. For model testing, we selected 7 equispaced values of S in the range [-1, +1] for each of the 33 test patients, generated the 3D doses for each S value (normalized to D2% = 110%), and calculated the differences of key dosimetric parameters (for S levels other than 0) compared to the predicted base plan (S = 0). The mean and standard deviations for these differences were reported. The cVAE model converged after training for 800 epochs. As the value of S increased from -1 to +1, the target coverage remained similar, while the doses to the bladder and rectum increased and decreased, respectively, as expected (Table 1). This pattern was also confirmed by qualitative examination of dose-volume histograms for additional S values. We demonstrated the feasibility of predicting 3D radiation dose distributions for prostate cancer where the degrees of organ dose trade-off could be explicitly specified.

Optimization of extreme ultra-violet light emitted from the CO2 laser-irradiated tin plasmas using 2D radiation hydrodynamic simulations.

We studied Extreme Ultra-Violet (EUV) emission characteristics of the 13.5 nm wavelength from CO2 laser-irradiated pre-formed tin plasmas using 2D radiation hydrodynamic simulations. Our results indicate that when a CO2 laser irradiates pre-formed tin plasma, the heated plasma expands towards the surrounding plasma, steepening the density at the ablation front and lowering the density near the laser axis due to the transverse motion of the plasma. Consequently, the laser absorption fraction decreases, and the contribution to EUV output from the ablation front becomes dominant over that from the low-density plasmas. We estimated that an EUV conversion efficiency of 10% from laser to EUV emission could be achieved with a larger laser spot size, shortened laser pulse width, and longer pre-formed plasma density scale length. Our results offer one optimizing solution to achieve an efficient and powerful EUV light source for the next-generation semiconductors.

Identifying the optimal deep learning architecture and parameters for automatic beam aperture definition in 3D radiotherapy.

Two-dimensional radiotherapy is often used to treat cervical cancer in low- and middle-income countries, but treatment planning can be challenging and time-consuming. Neural networks offer the potential to greatly decrease planning time through automation, but the impact of the wide range of hyperparameters to be set during training on model accuracy has not been exhaustively investigated. In the current study, we evaluated the effect of several convolutional neural network architectures and hyperparameters on 2D radiotherapy treatment field delineation. Six commonly used deep learning architectures were trained to delineate four-field box apertures on digitally reconstructed radiographs for cervical cancer radiotherapy. A comprehensive search of optimal hyperparameters for all models was conducted by varying the initial learning rate, image normalization methods, and (when appropriate) convolutional kernel size, the number of learnable parameters via network depth and the number of feature maps per convolution, and nonlinear activation functions. This yielded over 1700 unique models, which were all trained until performance converged and then tested on a separate dataset. Of all hyperparameters, the choice of initial learning rate was most consistently significant for improved performance on the test set, with all top-performing models using learning rates of 0.0001. The optimal image normalization was not consistent across architectures. High overlap (mean Dice similarity coefficient=0.98) and surface distance agreement (mean surface distance<2mm) were achieved between the treatment field apertures for all architectures using the identified best hyperparameters. Overlap Dice similarity coefficient (DSC) and distance metrics (mean surface distance and Hausdorff distance) indicated that DeepLabv3+ and D-LinkNet architectures were least sensitive to initial hyperparameter selection. DeepLabv3+ and D-LinkNet are most robust to initial hyperparameter selection. Learning rate, nonlinear activation function, and kernel size are also important hyperparameters for improving performance.

Evaluation of the Response Rate to Neoadjuvant Chemoradiotherapy in Patients with Rectal Adenocarcinoma: A Retrospective Long-term Study in Two Terciary Reference Centers

Abstract Objectives To evaluate the complete response (CR) rate and surgeries performed in patients with rectal adenocarcinoma who underwent neoadjuvant therapy (NT) at Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo and at Hospital São Paulo, in Ribeirão Preto, from January 2007 to December 2017. Methods We evaluated 166 medical records of patients with locally advanced rectal adenocarcinoma (T3, T4 or N + ) who underwent NT. The regimen consisted of performing conventional (2D) or conformational (three-dimensional-3D/ radiotherapy with modulated intensity – IMRT) at a dose of 45-50.4Gy associated with capecitabine 1650mg/m2 or 5-fluorouracil (5FU) and leucovorin (LV). The following variables were analyzed: gender, age, pretreatment stage, radiotherapy, CR index, local and distant recurrence rates. Surgical treatment and complications were also evaluated. Results The CR index was 28.3%. Patients treated with 3D/IMRT radiotherapy had a higher rate of CR (36.3% x 4.8%; p &lt; 0.001), higher rates of clinical follow-up (21% x 0%; p &lt; 0.001), lower surgery rates (79% x 100%; p &lt; 0.001), higher rates of transanal resection (37.1% x 9.5%; p = 0.001), lower rates of abdominal rectosigmoidectomy (25.8% x 50%; p = 0.007) and lower rates of abdominoperineal resection of the rectum (16.1% x 40.5%; p = 0.002), when compared to patients treated with 2D radiotherapy. Conclusion Modern radiotherapy techniques such as 3D conformal and IMRT, by offering greater adequacy and precision of treatment, could result in better local control and less toxicity in organs at risk, enabling organ preservation strategies and less invasive approaches in selected cases.

A macroscale heat transfer analysis of the build chamber in a commercial electron beam powder bed fusion (EB-PBF) additive manufacturing system during component fabrication

In this research, a 3D numerical thermal cavity radiation model was developed to predict the evolution of the macroscale thermal field within the build chamber of a commercial EB-PBF system. The model was applied to predict the evolution of the thermal field in a component during fabrication. A combination of quantitative and qualitative data extracted from an ARCAM Q20Plus machine was used to validate the model. The results indicate that the portion of heat transferred to the inner Heat Shield via cavity radiation was a strong function of the Start Plate’s temperature, reaching 88% of the total heat input at a peak temperature of ∼725 °C. Once validated, the thermal model was used to analyse heat transport within the build chamber during the fabrication of a component. The outcomes revealed variability in temperature within the hexagonal base, up to 118 °C, and the powder bed below the platform of 107 °C. Moreover, substantial temperature variations exceeding 200 °C were identified within the component, specifically between the hexagonal base and the platform.