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In this work we estimate the yield of the radioisotope [Formula: see text] in a thorium metal target geometry similar to that described by Roberston et al.. We do so in three different yet complimentary studies. In the first study, we pose a three-way coupled time-dependent model describing beam position, temperature field, and local growth of the activity of the radioisotope and solve this numerically. In the second study, we present an analytical solution of the model equations for a generalized solid target in the "beam-thin" limit, i.e. where only a small fraction of the incoming energy of the proton beam is deposited into the thorium material. In the third study, we use the insight gained from the analytical solution and describe an operating strategy to maximize yield by modulating the beam flux temporally., (© 2023. Springer Nature Limited.)

Increased interest in radiometals for nuclear medicine and imaging can be hampered by radionuclide supply. 89 Zr for example, is a PET imaging nuclide for which no radionuclide generator exists. One method to produce 89 Zr involves irradiating aqueous solutions of yttrium nitrate salt on small medical cyclotrons. However, in irradiating these solutions the radiolysis of water can cause significant H 2 and O 2 gas buildup, which can eventually rupture a sealed target vessel. We examine the role of nitrate and nitrite in radiolysis. Here, we find that using copper-coated cadmium pellets to chemically reduce nitrate to nitrite in solution prior to irradiation can reduce in-target radiolysis by approximately 60% as compared to other published methods of radiolysis reduction, but only in acidic solutions. We hypothesize that during irradiation, nitrate is converted to nitrite, consuming free radicals which would otherwise be available to eliminate molecular gas species. Performing this conversion before irradiation may limit the consumption of these beneficial free radicals., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

While the dose deposition of charged hadrons has received much attention over the last decades starting in 1930 with the publication of the Bethe equation, there are still practical obstacles in implementing it in fields like radiotherapy and isotope production on cyclotrons. This is especially true if the target material consists of non-homogeneous materials, either consisting of a mixture of different elements or experiencing phase changes during irradiation. While Monte-Carlo methods have had great success in describing these more difficult target materials, they come at a computational cost, especially if the problem is time-dependent. This can greatly hinder optimal advancement in therapy and isotope targetry. Here, a regular perturbation method is used to solve the Bethe equation in the limit of small relativistic effects. Particular focus is given to incident energy level relevant to radionuclide production and radiotherapy applications, i.e. 10-200 MeV. We present a series solution for the range and dose distribution in terms of elementary functions, as opposed to special functions which will aid in uptake by practitioners.

A forced-convection gas target for the production of [ 11 C]CH 4 on a 13 MeV cyclotron was constructed and tested. A small fan was incorporated into the back of the target, which mixes the target gas during irradiation. The effect of the forced convection alone on the target operation and the [ 11 C]CH 4 yield was measured. Forced convection improved the target yield by up to 16 ± 4%. In addition, improvement in heat transfer of up to 70% was observed to be a function of fan speed. Operating with forced convection allowed delivery of 21% higher beam currents while still staying in the acceptable pressure rise during irradiation, providing a 25 ± 7% greater yield., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Gas target systems have been used for decades on cyclotrons to produce radionuclides for medical imaging. However, the activity recovered from such targets is often lower than its theoretically predicted value. Past research has suggested that nuclide interactions with the walls of the target body may play a key role in the loss of recoverable radionuclide activity. Here, we consider gas targets and modify the standard radionuclide production equation by adding a loss term representing radionuclides depositing on the walls of the target. We derive the form of the deposition term based on a simple adsorption model which is then linearized by solving for leading order terms. The resulting production equation uses one fitting parameter to give an estimate of the recoverable activity produced in a target system, taking adsorption into account. The model is then fit to six data series, taken in-house and reported in the literature and a parity plot compares model predictions to experimental data. The model is able to better track the data than any previous models, and points towards a phenomenological understanding of adsorption in target systems.

A new method for the design of stepless beam modulators for proton therapy is described and verified. Simulations of the classic designs are compared against the stepless method for various modulation widths which are clinically applicable in proton eye therapy. Three modulator wheels were printed using a Stratasys Objet30 3D printer. The resulting depth dose distributions showed improved uniformity over the classic stepped designs. Simulated results imply a possible improvement in distal penumbra width; however, more accurate measurements are needed to fully verify this effect. Lastly, simulations were done to model bio-equivalence to Co-60 cell kill. A wheel was successfully designed to flatten this metric.

A novel algorithm has been developed and validated to isolate individual papermaking fibres in micro-computed tomographic images of paper handsheets as a first step to characterize the structure of the paper. The three-step fibre segmentation algorithm segments the papermaking fibres by (i) tracking the hollow inside the fibres via a modified connected component methodology, (ii) extracting the fibre walls using a distance transform and (iii) labelling the fibres through collapsed sections by a final refinement step. Furthermore, postprocessing algorithms have been developed to calculate the length and coarseness of the segmented fibres. The fibre segmentation algorithm is the first ever reported method for the automated segmentation of the tortuous three-dimensional morphology of papermaking fibres within microstructural images of paper handsheets. The method is not limited to papermaking fibres, but can be applied to any material consisting of tortuous and hollow fibres., (© 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.)

Two 3D printing methods, fused filament fabrication (FFF) and PolyJet™ (PJ) were investigated for suitability in clinical proton therapy (PT) energy modulation. Measurements of printing precision, printed density and mean stopping power are presented. FFF is found to be accurate to 0.1 mm, to contain a void fraction of 13% due to air pockets and to have a mean stopping power dependent on geometry. PJ was found to print accurate to 0.05 mm, with a material density and mean stopping power consistent with solid poly(methyl methacrylate) (PMMA). Both FFF and PJ were found to print significant, sporadic defects associated with sharp edges on the order of 0.2 mm. Site standard PT modulator wheels were printed using both methods. Measured depth-dose profiles with a 74 MeV beam show poor agreement between PMMA and printed FFF wheels. PJ printed wheel depth-dose agreed with PMMA within 1% of treatment dose except for a distal falloff discrepancy of 0.5 mm.

Complaints of vertigo and dizziness are common problems referred to otolaryngologists for evaluation. Awareness of uncommon causes of dizziness increases the physician's ability to diagnose and treat these patients. We present the case of a middle-aged woman who presented with episodes of vertigo and symptoms suggestive of vertebrobasilar insufficiency. These symptoms were the result of a persistent trigeminal artery (PTA) and occlusive carotid artery disease. A PTA is a carotid-basilar anastomosis that has been reported to be demonstrated on 0.1% to 0.6% of all cerebral angiograms. Persistence of this vessel usually leads to hypoplasia or agenesis of the ipsilateral posterior communicating artery, and leaves the internal carotid artery as the main source of blood supply to the region of the upper brainstem. The appearance and clinical significance of this unusual condition will be discussed.

Between July 1975 and May 1985, 219 procedures were performed on the vertebral system; two were intracranial, 118 were at the skull base and 99 were at the neck base. Of the 108 patients operated on at the skull base, procedures were multiple in five and bilateral in two. Bypass to the vertebral artery between the transverse process of C1 and C2 was performed 91 times. The blood supply for the bypass was the common carotid (70), the external carotid (9), the internal carotid (9), the subclavian (3), and the occipital artery (3). Decompression was performed in three patients, segmental resection in seven, and ligation in two. The primary objective was to increase the flow capacity of the vertebral artery. This flow to the Circle of Willis supplies the forebrain and the hindbrain if the internal carotid artery is obstructed and the posterior communicating artery is patent, or it may supply only the hindbrain when no communication exists. The pathologic processes include atherosclerosis, thrombosis, dissection, compression, and vasospasm. The male:female ratio is 2:3. Long-term mortality is 19% for the male and 4.6% for the female. Hindbrain symptoms in the male predates cardiac symptoms by 2 to 4 years. Operative mortality and stroke rate is less than 3% combined. Long-term graft patency is 87%. Vertebral artery surgery at the skull base produces results superior to those following proximal segment reconstruction when measured by dynamic computerized tomographic scanning, neurofunctional testing, and symptom relief. Success following reconstruction depends on careful patient selection and surgical expertise. The techniques of reconstruction are well established and results have been durable for over a decade.

The recent world literature on mediastinal emphysema has been reviewed and two cases added. This condition is relatively benign, and the supportive treatment is discussed. Subsequent pregnancies have been uncomplicated.