Single-Isocenter, Multiple-Target Abdominal Cone-Beam Computed Tomography (CBCT)-Guided Online Adaptive Stereotactic Body Radiotherapy (SBRT).

Stereotactic body radiotherapy (SBRT) is increasingly being prescribed for treating patients with multiple metastases, especially in the setting of oligometastatic disease. Treating multiple targets presents unique challenges in radiotherapy planning and delivery, including practical considerations relating to treatment time, resource allocation, and treatment planning complexity. Treating targets in a common isocenter reduces the time required for treatment and simplifies planning, but historically, it has often not been feasible due to inter- and intra-fractional variation in relative target positions.

Dosimetric evaluation of a novel modular cell irradiation platform for multi-modality in vitro studies including high dose rate brachytherapy.

Purpose: High dose-rate (HDR) brachytherapy is integral for the treatment of numerous cancers. Preclinical studies involving HDR brachytherapy are limited. We aimed to describe a novel platform allowing multi-modality studies with clinical HDR brachytherapy and external beam irradiators, establish baseline dosimetry standard of a preclinical orthovoltage irradiator, to determine accurate dosimetric methods.

Script-based implementation of automatic grid placement for lattice stereotactic body radiation therapy.

Background And Purpose: Spatially fractionated radiation therapy (SFRT) has demonstrated promising clinical response in treating large tumors with heterogeneous dose distributions. Lattice stereotactic body radiation therapy (SBRT) is an SFRT technique that leverages inverse optimization to precisely localize regions of high and lose dose within disease. The aim of this study was to evaluate an automated heuristic approach to sphere placement in lattice SBRT treatment planning.

Inter-fractional portability of deep learning models for lung target tracking on cine imaging acquired in MRI-guided radiotherapy.

MRI-guided radiotherapy systems enable beam gating by tracking the target on planar, two-dimensional cine images acquired during treatment. This study aims to evaluate how deep-learning (DL) models for target tracking that are trained on data from one fraction can be translated to subsequent fractions. Cine images were acquired for six patients treated on an MRI-guided radiotherapy platform (MRIdian, Viewray Inc.

Simulation study of a novel small animal FLASH irradiator (SAFI) with integrated inverse-geometry CT based on circularly distributed kV X-ray sources.

Ultra-high dose rate (UHDR) radiotherapy (RT) or FLASH-RT can potentially reduce normal tissue toxicity. A small animal irradiator that can deliver FLASH-RT treatments similar to clinical RT treatments is needed for pre-clinical studies of FLASH-RT. We designed and simulated a novel small animal FLASH irradiator (SAFI) based on distributed x-ray source technology.

Development of a storage phosphor imaging system for proton pencil beam spot profile determination.

Purpose: Accurate two-dimensional (2D) profile measurements at submillimeter precision are necessary for proton beam commissioning and periodic quality assurance (QA) purposes and are currently performed at our institution with a commercial scintillation detector (Lynx PT) with limited means for independent checks. The purpose of this work was to create an independent dosimetry system consisting of an in-house optical scanner and a BaFBrI:Eu storage phosphor dosimeter by: (a) determining the optimal settings for the optical scanner, (b) measuring 2D proton spot profiles with the storage phosphors, and (c) comparing them to similar measurements using a commercial scintillation detector.

Methods: An in-house 2D laboratory optical scanner was constructed and spatially calibrated for accurate 2D photostimulated luminescence (PSL) dosimetry.

An atlas-guided automatic planning approach for rectal cancer intensity-modulated radiotherapy.

We try to develop an atlas-guided automatic planning (AGAP) approach and evaluate its feasibility and performance in rectal cancer intensity-modulated radiotherapy. The developed AGAP approach consisted of four independent modules: patient atlas, similar patient retrieval, beam morphing (BM), and plan fine-tuning (PFT) modules. The atlas was setup using anatomy and plan data from Pinnacle auto-planning (P-auto) plans.

Characterization of Dosimetric Differences in Strut-Adjusted Volume Implant Treatment Plans Calculated With TG-43 Formalism and a Model-Based Dose Calculation Algorithm.

Purpose: To comprehensively characterize dosimetric differences between calculations with a commercial model-based dose calculation algorithm (MBDCA) and the TG-43 formalism in application to accelerated partial breast irradiation (APBI) with the strut-adjusted volume implant (SAVI) applicator.

Methods: Dose for 100 patients treated with the SAVI applicator was recalculated with an MBDCA for comparison to dose calculated via TG-43. For every pair of dose calculations, dose-volume histogram (DVH) metrics including V90%, V95%, V100%, V150%, and V200% for the PTV_EVAL were compared.

Dual-storage phosphor proton therapy dosimetry: Simultaneous quantification of dose and linear energy transfer.

Purpose: To investigate the feasibility of using the high Z storage phosphor material BaFBrI:Eu in conjunction with the low Z storage phosphor material KCl:Eu for simultaneous proton dose and linear energy transfer (LET) measurements by (a) measuring the fundamental optical and dosimetric properties of BaFBrI:Eu , (b) evaluating its compatibility in being readout simultaneously with KCl:Eu dosimeters, and (c) modeling and validating its LET dependence under elevated proton LET irradiation.

Methods: A commercial BaFBrI:Eu storage phosphor detector (Model ST-VI, Fujifilm) was characterized with energy dispersive x-ray spectroscopy (EDS) analysis to obtain its elemental composition. The dosimeters were irradiated using both a Mevion S250 proton therapy unit (at the center of a spread-out Bragg peak, SOBP) and a Varian Clinac iX linear accelerator with the latter being a low LET irradiation.

Technical Note: Cumulative dose modeling for organ motion management in MRI-guided radiation therapy.

Purpose: To develop a method for continuous online dose accumulation during irradiation in MRI-guided radiation therapy (MRgRT) and to demonstrate its application in evaluating the impact of internal organ motion on cumulative dose.

Methods: An intensity-modulated radiation therapy (IMRT) treatment plan is partitioned into its unique apertures. Dose for each planned aperture is calculated using Monte Carlo dose simulation on each phase of a four-dimensional computed tomography (4D-CT) dataset.

Quantitative proton radiation therapy dosimetry using the storage phosphor europium-doped potassium chloride.

Purpose: To (a) characterize the fundamental optical and dosimetric properties of the storage phosphor europium-doped potassium chloride for quantitative proton dosimetry, and (b) investigate if its dose radiation response can be described by an analytic radiation transport model.

Methods: Cylindrical KCl:Eu dosimeters with dimensions of 6 mm diameter and 1 mm thickness were fabricated in-house. The dosimeters were irradiated using both a Mevion S250 passive scattering proton therapy system and a Varian Clinac iX linear accelerator.

Automated and robust beam data validation of a preconfigured ring gantry linear accelerator using a 1D tank with synchronized beam delivery and couch motions.

Purpose: To develop an efficient and automated methodology for beam data validation for a preconfigured ring gantry linear accelerator using scripting and a one-dimensional (1D) tank with automated couch motions.

Materials And Methods: Using an application programming interface, a program was developed to allow the user to choose a set of beam data to validate with measurement. Once selected the program generates a set of instructions for radiation delivery with synchronized couch motions for the linear accelerator in the form of an extensible markup language (XML) file to be delivered on the ring gantry linear accelerator.

Treatment Outcome Prediction for Cancer Patients based on Radiomics and Belief Function Theory.

In this study, we proposed a new radiomics-based treatment outcome prediction model for cancer patients. The prediction model is developed based on belief function theory (BFT) and sparsity learning to address the challenges of redundancy, heterogeneity, and uncertainty of radiomic features, and relatively small-sized and unbalanced training samples. The model first selects the most predictive feature subsets from relatively large amounts of radiomic features extracted from pre- and/or in-treatment positron emission tomography (PET) images and available clinical and demographic features.

Characterization of a prototype rapid kilovoltage x-ray image guidance system designed for a ring shape radiation therapy unit.

Purpose: This study aims to characterize the performance of a prototype rapid kilovoltage (kV) x-ray image guidance system onboard the newly released Halcyon 2.0 linear accelerator (Varian Medical Systems, Palo Alto, CA) by use of conventional and innovatively designed testing procedures.

Methods: Basic imaging system performance tests and radiation dose measurements were performed for all eleven kV-cone beam computed tomography (CBCT) imaging protocols available on a preclinical Halcyon 2.

A novel MRI segmentation method using CNN-based correction network for MRI-guided adaptive radiotherapy.

Purpose: The purpose of this study was to expedite the contouring process for MRI-guided adaptive radiotherapy (MR-IGART), a convolutional neural network (CNN) deep-learning (DL) model is proposed to accurately segment the liver, kidneys, stomach, bowel and duodenum in 3D MR images.

Methods: Images and structure contours for 120 patients were collected retrospectively. Treatment sites included pancreas, liver, stomach, adrenal gland, and prostate.

A rapid, computational approach for assessing interfraction esophageal motion for use in stereotactic body radiation therapy planning.

Purpose: We present a rapid computational method for quantifying interfraction motion of the esophagus in patients undergoing stereotactic body radiation therapy on a magnetic resonance (MR) guided radiation therapy system.

Methods And Materials: Patients who underwent stereotactic body radiation therapy had simulation computed tomography (CT) and on-treatment MR scans performed. The esophagus was contoured on each scan.

A deep Boltzmann machine-driven level set method for heart motion tracking using cine MRI images.

Heart motion tracking for radiation therapy treatment planning can result in effective motion management strategies to minimize radiation-induced cardiotoxicity. However, automatic heart motion tracking is challenging due to factors that include the complex spatial relationship between the heart and its neighboring structures, dynamic changes in heart shape, and limited image contrast, resolution, and volume coverage. In this study, we developed and evaluated a deep generative shape model-driven level set method to address these challenges.

Quantitative FDG-PET/CT predicts local recurrence and survival for squamous cell carcinoma of the anus.

Purpose: F-fluorodeoxyglucose (FDG) positron emission tomography-(PET)/computed tomography (CT) imaging is used for staging and treatment planning of patients with anal cancer. Quantitative pre- and posttreatment metrics that are predictive of recurrence are unknown. We evaluated the association between pre- and posttreatment FDG-PET/CT parameters and outcomes for patients with squamous cell carcinoma of the anus (SCCA).

Development of a fast Monte Carlo dose calculation system for online adaptive radiation therapy quality assurance.

Online adaptive radiation therapy (ART) based on real-time magnetic resonance imaging represents a paradigm-changing treatment scheme. However, conventional quality assurance (QA) methods based on phantom measurements are not feasible with the patient on the treatment couch. The purpose of this work is to develop a fast Monte Carlo system for validating online re-optimized tri-60Co IMRT adaptive plans with both high accuracy and speed.

A method to reconstruct and apply 3D primary fluence for treatment delivery verification.

Motivation: In this study, a method is reported to perform IMRT and VMAT treatment delivery verification using 3D volumetric primary beam fluences reconstructed directly from planned beam parameters and treatment delivery records. The goals of this paper are to demonstrate that 1) 3D beam fluences can be reconstructed efficiently, 2) quality assurance (QA) based on the reconstructed 3D fluences is capable of detecting additional treatment delivery errors, particularly for VMAT plans, beyond those identifiable by other existing treatment delivery verification methods, and 3) QA results based on 3D fluence calculation (3DFC) are correlated with QA results based on physical phantom measurements and radiation dose recalculations.

Methods: Using beam parameters extracted from DICOM plan files and treatment delivery log files, 3D volumetric primary fluences are reconstructed by forward-projecting the beam apertures, defined by the MLC leaf positions and modulated by beam MU values, at all gantry angles using first-order ray tracing.

Technical Note: A method to evaluate dosimetric effects on organs-at-risk for treatment delivery systematic uncertainties.

Purpose: The aim of this study is to provide a practical method to quantify the dosimetric effects on organs-at-risk (OARs) due to systematic uncertainties in linear accelerator treatment delivery in order to aid external beam treatment planning and raise warnings about additional risks to critical OARs.

Methods: A dose approximation method, based on geometrical transformations, was developed to automatically estimate perturbations to dose volumes arising from five important potential uncertainties at the time of treatment delivery, including (a) systematic isocenter misalignment between image guidance and beam delivery systems, and systematic errors in, (b) collimator, (c) gantry, (d) couch table, and (e) multi-leaf collimator (MLC) leaf bank positions. The agreement between the estimated dose volume using the dose approximation method and the re-calculated dose volume obtained from the treatment planning system (TPS) was verified using a dose difference test (2% threshold and 0 mm distance-to-agreement).

Magnetic Resonance Image Guided Radiation Therapy for External Beam Accelerated Partial-Breast Irradiation: Evaluation of Delivered Dose and Intrafractional Cavity Motion.

Purpose: To use magnetic resonance image guided radiation therapy (MR-IGRT) for accelerated partial-breast irradiation (APBI) to (1) determine intrafractional motion of the breast surgical cavity; and (2) assess delivered dose versus planned dose.

Methods And Materials: Thirty women with breast cancer (stages 0-I) who underwent breast-conserving surgery were enrolled in a prospective registry evaluating APBI using a 0.35-T MR-IGRT system.

A GPU-accelerated Monte Carlo dose calculation platform and its application toward validating an MRI-guided radiation therapy beam model.

Purpose: The clinical commissioning of IMRT subject to a magnetic field is challenging. The purpose of this work is to develop a GPU-accelerated Monte Carlo dose calculation platform based on penelope and then use the platform to validate a vendor-provided MRIdian head model toward quality assurance of clinical IMRT treatment plans subject to a 0.35 T magnetic field.

SIFT-based dense pixel tracking on 0.35 T cine-MR images acquired during image-guided radiation therapy with application to gating optimization.

Purpose: To first demonstrate the viability of applying an image processing technique for tracking regions on low-contrast cine-MR images acquired during image-guided radiation therapy, and then outline a scheme that uses tracking data for optimizing gating results in a patient-specific manner.

Methods: A first-generation MR-IGRT system-treating patients since January 2014-integrates a 0.35 T MR scanner into an annular gantry consisting of three independent Co-60 sources.