Toward a Transportable Cell Culture Platform for Evaluating Radiotherapy Dose Modifying Factors.

The current tools for validating dose delivery and optimizing new radiotherapy technologies in radiation therapy do not account for important dose modifying factors (DMFs), such as variations in cellular repair capability, tumor oxygenation, ultra-high dose rates and the type of ionizing radiation used. These factors play a crucial role in tumor control and normal tissue complications. To address this need, we explored the feasibility of developing a transportable cell culture platform (TCCP) to assess the relative biological effectiveness (RBE) of ionizing radiation.

Assessing the DNA Damaging Effectiveness of Ionizing Radiation Using Plasmid DNA.

Plasmid DNA is useful for investigating the DNA damaging effects of ionizing radiation. In this study, we have explored the feasibility of plasmid DNA-based detectors to assess the DNA damaging effectiveness of two radiotherapy X-ray beam qualities after undergoing return shipment of ~8000 km between two institutions. The detectors consisted of 18 μL of pBR322 DNA enclosed with an aluminum seal in nine cylindrical cavities drilled into polycarbonate blocks.

Quantifying the DNA-damaging Effects of FLASH Irradiation With Plasmid DNA.

Purpose: To investigate a plasmid DNA nicking assay approach for isolating and quantifying the DNA-damaging effects of ultrahigh-dose-rate (ie, FLASH) irradiation relative to conventional dose-rate irradiation.

Methods And Materials: We constructed and irradiated phantoms containing plasmid DNA to nominal doses of 20 Gy and 30 Gy using 16 MeV electrons at conventional (0.167 Gy/s) and FLASH (46.

Impact of a 1.5 T magnetic field on DNA damage in MRI-guided HDR brachytherapy.

Purpose: Some studies have suggested that the presence of a static magnetic field (SMF) during irradiation alters biological damage. Since MRI-guided radiotherapy is becoming increasingly common, we constructed a DNA-based detector to assess the effect of a 1.5 T SMF on DNA damage during high dose rate (HDR) brachytherapy irradiation.

Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic phantom.

We present an experimental validation of a kilovoltage (kV) X-ray source characterization model in an anthropomorphic phantom to estimate patient-specific absorbed dose from kV cone-beam computed tomography (CBCT) imaging procedures and compare these doses to nominal weighted CT-dose index (CTDIw) dose estimates. We simulated the default Varian on-board imager 1.4 (OBI) default CBCT imaging protocols (i.

A measurement-based X-ray source model characterization for CT dosimetry computations.

The purpose of this study was to show that the nominal peak tube voltage potential (kVp) and measured half-value layer (HVL) can be used to generate energy spectra and fluence profiles for characterizing a computed tomography (CT) X-ray source, and to validate the source model and an in-house kV X-ray dose computation algorithm (kVDoseCalc) for computing machine- and patient-specific CT dose. Spatial variation of the X-ray source spectra of a Philips Brilliance and a GE Optima Big Bore CT scanner were found by measuring the HVL along the direction of the internal bow-tie filter axes. Third-party software, Spektr, and the nominal kVp settings were used to generate the energy spectra.

A rapid noninvasive characterization of CT x-ray sources.

Purpose: The aim of this study is to generate spatially varying half value layers (HVLs) that can be used to construct virtual equivalent source models of computed tomography (CT) x-ray sources for use in Monte Carlo CT dose computations.

Methods: To measure the spatially varying HVLs, the authors combined a cylindrical HVL measurement technique with the characterization of bowtie filter relative attenuation (COBRA) geometry. An apparatus given the name "HVL Jig" was fabricated to accurately position a real-time dosimeter off-isocenter while surrounded by concentric cylindrical aluminum filters (CAFs).

Modeling a superficial radiotherapy X-ray source for relative dose calculations.

The purpose of this study was to empirically characterize and validate a kilovoltage (kV) X-ray beam source model of a superficial X-ray unit for relative dose calculations in water and assess the accuracy of the British Journal of Radiology Supplement 25 (BJR 25) percentage depth dose (PDD) data. We measured central axis PDDs and dose profiles using an Xstrahl 150 X-ray system. We also compared the measured and calculated PDDs to those in the BJR 25.

Digital differentiation of non-small cell carcinomas of the lung by the fractal dimension of their epithelial architecture.

Introduction: In recent years, differences have emerged in the treatment of squamous and non-squamous non-small cell lung carcinomas (NSCLCs). This highlights the importance of accurate histopathologic classification. However, there remains inter-observer disagreement when making diagnoses based on histology.

Experimental validation of a kilovoltage x-ray source model for computing imaging dose.

Purpose: To introduce and validate a kilovoltage (kV) x-ray source model and characterization method to compute absorbed dose accrued from kV x-rays.

Methods: The authors propose a simplified virtual point source model and characterization method for a kV x-ray source. The source is modeled by: (1) characterizing the spatial spectral and fluence distributions of the photons at a plane at the isocenter, and (2) creating a virtual point source from which photons are generated to yield the derived spatial spectral and fluence distribution at isocenter of an imaging system.

Scale-specific multifractal medical image analysis.

Fractal geometry has been applied widely in the analysis of medical images to characterize the irregular complex tissue structures that do not lend themselves to straightforward analysis with traditional Euclidean geometry. In this study, we treat the nonfractal behaviour of medical images over large-scale ranges by considering their box-counting fractal dimension as a scale-dependent parameter rather than a single number. We describe this approach in the context of the more generalized Rényi entropy, in which we can also compute the information and correlation dimensions of images.

FracMod: a computational tool for assessing IMRT field modulation.

The authors develop and investigate a user-friendly computational tool (FracMod) to quantify modulation complexity in planned IMRT fields. FracMod comprises a graphical user interface and variogram fractal dimension (FD) analysis tool developed by the authors using MATLAB(®), and made freely available at http://www.medphysfiles.

A simplified approach to characterizing a kilovoltage source spectrum for accurate dose computation.

Purpose: To investigate and validate the clinical feasibility of using half-value layer (HVL) and peak tube potential (kVp) for characterizing a kilovoltage (kV) source spectrum for the purpose of computing kV x-ray dose accrued from imaging procedures. To use this approach to characterize a Varian® On-Board Imager® (OBI) source and perform experimental validation of a novel in-house hybrid dose computation algorithm for kV x-rays.

Methods: We characterized the spectrum of an imaging kV x-ray source using the HVL and the kVp as the sole beam quality identifiers using third-party freeware Spektr to generate the spectra.

Effects of image resolution and noise on estimating the fractal dimension of tissue specimens.

Objective: To investigate the effects of imaging system noise and resolution on the ability to estimate and distinguish relative differences in the fractal dimension of tissue specimens.

Study Design: Mathematically derived test images of known fractal dimension mimicking the complexity of epithelial morphology were created. The box-counting method was used to compute fractal dimension.

Fractal analysis for assessing the level of modulation of IMRT fields.

Purpose: To investigate the potential of three fractal dimension (FD) analysis methods (i.e., the variation, power spectrum, and variogram methods) as metrics for quantifying the degree of modulation in planned intensity modulated radiation therapy (IMRT) treatment fields, and compare the most suitable FD method to the number of monitor units (MUs), the average leaf gap, and the 2D modulation index (2D MI) for assessing modulation.

A hybrid approach for rapid, accurate, and direct kilovoltage radiation dose calculations in CT voxel space.

Purpose: To develop and validate a fast and accurate method that uses computed tomography (CT) voxel data to estimate absorbed radiation dose at a point of interest (POI) or series of POIs from a kilovoltage (kV) imaging procedure.

Methods: The authors developed an approach that computes absorbed radiation dose at a POI by numerically evaluating the linear Boltzmann transport equation (LBTE) using a combination of deterministic and Monte Carlo (MC) techniques. This hybrid approach accounts for material heterogeneity with a level of accuracy comparable to the general MC algorithms.

Morphologic complexity of epithelial architecture for predicting invasive breast cancer survival.

Background: Precise criteria for optimal patient selection for adjuvant chemotherapy remain controversial and include subjective components such as tumour morphometry (pathological grade). There is a need to replace subjective criteria with objective measurements to improve risk assessment and therapeutic decisions. We assessed the prognostic value of fractal dimension (an objective measure of morphologic complexity) for invasive ductal carcinoma of the breast.

Angular dependence of the output of a kilovoltage X-ray therapy unit.

During the recommissioning of a Philips RT-250 kilovoltage X-ray unit, unexpected output variations with tube head rotation (cross-plane) and tube head tilt (in-plane) were observed. The measured output showed an increase of up to 7.3% relative to the neutral position (0? in-plane and 0? cross-plane) over the possible range of angles of in-plane rotation for 75 kVp (half-value layer, HVL = 1.

Quantifying the architectural complexity of microscopic images of histology specimens.

Tumour grade (a measure of the degree of cellular differentiation of malignant neoplasm) is an important prognostic factor in many types of cancer. In general, poorly differentiated tumours are characterized by a higher degree of architectural irregularity and complexity of histological structures. Fractal dimension is a useful parameter for characterizing complex irregular structures.

Relationship between tumor grade and computed architectural complexity in breast cancer specimens.

Breast cancer is the leading form of cancer diagnosed in women, and the second leading cause of cancer mortality in this group. A commonly accepted grading system for breast cancer that has proven useful for guiding treatment strategy is the modified Bloom-Richardson system. However, this system is subject to interobserver variability, which can affect patient management and outcome.

Path-dependent hemodynamics of the stenosed carotid bifurcation.

Previous work using computational simulations and experimental flow visualizations has demonstrated marked differences in local flow patterns between stenosed carotid bifurcation models having the same stenosis severity but different stenosis geometries. Since local blood flow patterns are known to influence thrombosis and atherosclerotic plaque development and rupture, such differences may in turn reflect differences in thromboembolic and atherosclerotic potential, and hence risk of ischemic stroke. Towards testing this hypothesis, we tracked point particles, representing uniformly distributed blood elements, through concentrically and eccentrically stenosed carotid bifurcation models, and computed and compared various path-dependent hemodynamic parameters between the models.

On assessing the quality of particle tracking through computational fluid dynamic models.

Quantification of particle deposition patterns, transit times, and shear exposure is important for computational fluid dynamic (CFD) studies involving respiratory and arterial models. To numerically compute such path-dependent quantities, it is necessary to employ a Lagrangian approach where particles are tracked through a pre-computed velocity field. However, it is difficult to determine in advance whether a particular velocity field is sufficiently resolved for the purposes of tracking particles accurately.