J.L. Gräfe

J.L. Gräfe
Ryerson University · Department of Physics

PhD

About

49
Publications
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240
Citations

Publications

Publications (49)
Article
Full-text available
Development of portable X-ray fluorescence devices has made it easier to quickly assess trace elements such as zinc in human tissue. A TOPAS Monte Carlo code was used to investigate the use of a portable X-ray fluorescence system for detecting zinc in nail clippings. The obtained energy spectra from different nail thicknesses were analyzed and thre...
Conference Paper
Development of portable X-ray fluorescence devices has made it easier to quickly assess trace elements such as zinc in human tissue. Zinc deficiency can have serious implications on growth and development of the human body. From recent studies zinc content in nail clippings has been suggested to be an effective biomarker for zinc status. In this st...
Article
Full-text available
Purpose: A multi-scale investigation of the biological properties of gadolinium neutron capture (GdNC) therapy is conducted using Monte Carlo (MC) simulation code. The simulation results are used to quantify the amount of gadolinium dose enhancement produced from different neutron sources. The amount of dose enhancement is quantified as a result o...
Article
Purpose The purpose of this work was to present a new single-arc mixed photon (6&18MV) VMAT (SAMP) optimization framework that concurrently optimizes for two photon energies with corresponding partial arc lengths. Methods and materials Owing to simultaneous optimization of energy dependent intensity maps and corresponding arc locations, the propos...
Article
The air kerma rate constant is important for estimating radiation dose and shielding calculations to ensure radiation exposure is as low as reasonably achievable (ALARA). Currently, there are significant deviations in this constant reported for ²⁴¹Am by various institutions. Therefore, through first principle calculations and simulation, we investi...
Conference Paper
Full-text available
Purpose: A multi-scale investigation of the biological properties of gadolinium neutron capture (GdNC) therapy was conducted using the radiobiology extension TOol for PArticle Simulation TOPAS-nBIO Monte Carlo simulation code [1]. The simulation results are used to quantify the amount of gadolinium dose enhancement produced from different neutron s...
Article
Full-text available
This study investigates the photon production from thermal neutron capture in a gadolinium (Gd) infused tumor as a result of secondary neutrons from particle therapy. Gadolinium contrast agents used in MRI are distributed within the tumor volume and can act as neutron capture agents. As a result of particle therapy, secondary neutrons are produced...
Conference Paper
Full-text available
Purpose: To investigate the secondary thermal neutron production from ten different charged particles for the application of gadolinium (Gd) based tumor dose enhancement [1] and particle neutron gamma-x detection technique (PNGXD) [2]. Methods: We simulated using MCNP6 (Vr.6.1.1), a 5-10 cm spread-out Bragg peak (SOBP) for ten different particles o...
Conference Paper
Full-text available
Particle neutron gamma-x detection (PNGXD) is a novel imaging concept proposed for tumor localization during proton therapy. The premise is to use secondary neutron interactions with a gadolinium contrast agent (GDCA) to produce photons within the 40–200 keV energy region that can be used for spectroscopic detection [1]. Previous work has investiga...
Article
Objectives: Lanthanum (La) retention in bone has been shown to occur in individuals who are orally administered lanthanum carbonate (LaC), a drug to treat hyperphosphatemia. The breakdown of LaC in the gastrointestinal tract into La3+ and carbonate ions results in residual quantities of La being deposited in bone. We previously reported on a non-i...
Article
The purpose of this work was to investigate the use of a commercial cadmium-telluride detector as an absolute thermal neutron measurement device on a proton therapy unit. Experimental measurements were performed on water phantoms using a 25 mm², 1 mm thick uncollimated CdTe spectrometer. The detector was shielded using sheets of borated polyethylen...
Article
Proton neutron gamma-x detection (PNGXD) is a novel imaging concept being investigated for tumor localization during proton therapy that uses secondary neutron interactions with a gadolinium contrast agent (GDCA) to produce characteristic photons within the 40-200 keV energy region. The purpose of this study is to experimentally investigate the fea...
Article
Objectives : Lanthanum (La) and gadolinium (Gd) are known to deposit in bone of exposed populations; namely those who are orally administered lanthanum carbonate (LaC, La<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>) or are injected with Gd-based contrast agents, respectively. In this work, bone La and Gd concentrations from the environment and diet wer...
Article
Purpose: In vivo x-ray fluorescence is a non-invasive analytical technique for determining trace and toxic element exposures. In this work we measure the dose for a portable handheld X-ray system (pXRF). Materials and methods: We used EBT3 radiochromic film calibrated with a clinical orthovoltage unit for absolute dose measurement. Films were pl...
Article
Purpose: Despite the availability of multiple energy photon beams on clinical linear accelerators, volumetric modulated arc therapy (VMAT) optimization is currently limited to a single photon beam. The purpose of this work was to present a proof of principle study on an algorithm for simultaneous optimization of mixed photon beams for VMAT (MP - V...
Article
Full-text available
Purpose The purpose of this work was to investigate the dosimetric impact of mixed energy (6‐MV, 15‐MV) partial arcs (MEPAs) technique on prostate cancer VMAT plans. Methods This work involved prostate only patients, planned with 79.2 Gy in 44 fractions to the planning target volume (PTV). Femoral heads, bladder, and rectum were considered organs...
Conference Paper
Full-text available
Purpose: To investigate the use of a cadmium-telluride detector (CdTe) as an absolute slowneutron detector with superior photon-to-neutron discrimination for applications in clinicalproton therapy. Methods: Four different experimental setups were measured with varied parameters from aMevion S250 passive scatter proton therapy unit. Spectra were rec...
Conference Paper
Full-text available
Purpose: To statistically quantify the spectrum produced from a gadolinium contrast agent (GDCA) used for a novel tumor localization method in proton therapy, and to determine the origin of the dominant characteristic X-rays produced. Methods: We irradiated a GDCA with varying concentrations (0-10,000 ppm) with a clinical proton beam. Spectra were...
Article
Objective: To report additional gadolinium bone and urine data that can contribute to gaps in knowledge with respect to gadolinium uptake and retention in the body. Approach: In vivo measurements of gadolinium retention in the tibia bone were performed on individuals self-identified as exhibiting symptoms of gadolinium toxicity as a result of re...
Conference Paper
Full-text available
Purpose: To experimentally investigate a new concept for tumor localization during proton therapy via proton and secondary neutron interactions in gadolinium (Gd) producing a series of characteristic photons in the energy region of 40–200 keV. Methods: Gadolinium solutions of 1 mg/g and 10 mg/g were irradiated using a 5 cm (0–5 cm) SOBP from a pas...
Conference Paper
Purpose: Simultaneous optimization for dual‐energy (6 MV, 18 MV) IMRT may produce complex fluence maps, which could impact deliverability resulting in a poor dosimetric outcome. This study focuses on reducing the complexity of simultaneously optimized dual‐energy fluence maps (DEFMs) by controlling sum of positive gradients (SPG) weighting factors...
Poster
Full-text available
Gafchromic films are a powerful 2D dosimeter that have an effective atomic number, Zeff = 6.98, close to that of water, Zeff = 7.3. The sensitive dose range for the films is between 1 mGy and 10 Gy, which is useful for clinical dosimetry and radiation protection purposes. Compared to traditional thermoluminescence dosimeters, Gafchromic films are p...
Article
Objective: This article briefly reviews the main measurement techniques for the non-invasive detection of residual gadolinium (Gd) in those exposed to gadolinium based contrast agents (GBCAs). Approach and Main Results: The current status of in vivo Gd measurement is discussed and is put into the context of concerns within the radiology community....
Article
Purpose To perform a preliminary evaluation of a noninvasive measurement system to assess gadolinium deposition in bone and to investigate the relationship between the administration of gadolinium-based contrast agents (GBCAs) and gadolinium retention in bone. Materials and Methods In vivo measurement of gadolinium retention in tibia bones was perf...
Article
Full-text available
Purpose: To compare dosimetric and treatment delivery parameter differences between volumetric-modulated arc radiotherapy (VMAT) and intensity-modulated radiotherapy (IMRT) for large volume retroperitoneal sarcomas (RPS). Materials and methods: Both VMAT and IMRT planning were performed on CT datasets of 10 patients with RPS who had been previou...
Article
Proton therapy is an alternative external beam cancer treatment modality to the conventional linear accelerator-based X-ray radiotherapy. An inherent by-product of proton-nuclear interactions is the production of secondary neutrons. These neutrons have long been thought of as a secondary contaminant, nuisance, and source of secondary cancer risk. I...
Article
Objective: Recent evidence of gadolinium (Gd) deposition in bones of healthy individuals who have previously received Gd-based contrast agents (GBCAs) for MRI has led to a demand for in vivo measurement techniques. The technique of x-ray fluorescence provides a low risk and painless method to assess Gd deposition in bone, and has the potential to...
Article
Objective: Lanthanum (La) is commonly used in phosphate binders in the form of lanthanum carbonate in patients with end-stage kidney disease undergoing hemodialysis treatments. With this administration, there is the potential for La storage in the body with bone being the main site of concern. However, the long-term effects of residual La in the b...
Article
The safety of using Gd in MRI contrast agents has recently been questioned, due to recent evidence of the retention of Gd in individuals with healthy renal function. Bone has proven to be a storage site for Gd, as unusually high concentrations have been measured in femoral heads of patients undergoing hip replacement surgery, as well as in autopsy...
Poster
Gadolinium-based agents have been in clinical use as contrast agents for magnetic resonance imaging (MRI) scans and are recently being examined as radio-sensitizers to enhance therapeutic indices of radiation therapy treatment plans. Quantification of residual and potentially long-term storage of gadolinium is essential to our understanding of the...
Article
A new megavoltage (MV) energy was recently introduced on Varian TrueBeam linear accelerators for imaging applications. This work describes the experimental characterization of a 2.5 MV inline portal imaging beam for commissioning, routine clinical use, and quality assurance purposes. The beam quality of the 2.5 MV beam was determined by measuring a...
Article
Full-text available
Building on previous simulation and experimental work on in vivo detection of gadolinium via PGNAA, we extend this work to incorporate the detection of samarium. Samarium, like gadolinium is a rare earth metal with an enormous cross section for neutron capture. The ab initio Monte-Carlo model agrees with experiment to within 2%. There is a wide dis...
Article
Full-text available
Purpose To evaluate the role of in vivo dosimetry with radiochromic films for dose verification in cutaneous radiation therapy (RT). Methods Five patients with 8 cutaneous or sub-cutaneous malignancies of the face, neck, trunk and extremity receiving RT were included. Orthovoltage, megavoltage photon therapies were applied based on anatomic locati...
Article
Full-text available
In this report, we quantify the divergence from the inverse square law (ISL) of the beam output as a function of distance (standoff) from closed‐ended applicators for a modern clinical orthovoltage unit. The divergence is clinically significant exceeding 3% at a 1.2 cm distance for 4 × 4 and 10×10cm2 closed‐ended applicators. For all investigated c...
Article
Full-text available
Gadolinium (Gd) based contrast agents are routinely used as part of many magnetic resonance imaging (MRI) procedures. The widespread use of these agents and concerns about Gd toxicity, motivated us to develop a monitoring procedure that could non-invasively measure quantitatively potential retention of toxic free Gd in tissues after use of the agen...
Article
Purpose: To present an empirically-based beam model for computing dose deposited by kilovoltage (kV) x-rays and validate it for radiographic, CT, CBCT, superficial, and orthovoltage kV sources.
Article
In this study we investigate the deliverability of dosimetric plans generated by the irregular surface compensator (ISCOMP) algorithm for 6 MV photon beams in Eclipse (Varian Medical System, CA). In contrast to physical tissue compensation, the electronic ISCOMP uses MLCs to dynamically modulate the fluence of a photon beam in order to deliver a un...
Article
We have extended our previous experimental and Monte–Carlo work on the detection of Gd by in vivo prompt gamma neutron activation analysis to include X ray emission. In this paper we incorporate the characteristic K X ray emission that occurs due to internal conversion from the de-excitation of the 155Gd(n,γ)156Gd∗ and 157Gd(n,γ)158Gd∗ reactions. T...
Article
Full-text available
Humans can be exposed to fluorine (F) through their diet, occupation, environment and oral dental care products. Fluorine, at proper dosages, is believed to have positive effects by reducing the incidence of dental caries, but fluorine toxicity can occur when people are exposed to excessive quantities of fluorine. In this paper we present the resul...
Article
Full-text available
Fluorine (F) plays an important role in dental health and bone formation. Many studies have shown that excess fluoride (F(-)) can result in dental or skeletal fluorosis, while other studies have indicated that a proper dosage of fluoride may have a protective effect on bone fracture incidence. Fluorine is stored almost completely in the skeleton ma...
Article
The feasibility of using the McMaster University in vivo prompt gamma neutron activation analysis system for the detection of gadolinium has been investigated. Phantoms have been developed for the kidney, liver, and the leg muscle. The initial detection limits are determined to be 7.2 ± 0.3 ppm for the kidney, 3.0 ± 0.1 ppm for the liver, and 2.33...
Article
Gadolinium (Gd)-based contrast agents are a valuable diagnostic aid for magnetic resonance imaging (MRI). The amount of free Gd deposited in tissues following contrast enhanced MRI is of toxicological concern. The McMaster University in vivo prompt gamma neutron activation analysis facility has been adapted for the detection of Gd in the kidney, li...

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