The potential use of three photon positron annihilation in positron emission tomography for tumour hypoxia imaging.

Identifying and localising tumor hypoxia in cancer patients is a challenge in oncology imaging. There are many ongoing clinical trials using conventional positron emission tomography (PET) scans and PET agents as cellular markers for detection of tumour hypoxia depending on the concept of the basic physics of 2gamma annihilation. However, Kacperski and Spyrou (2004) proposed, for the first time, to use 3gamma annihilation as a new PET molecular imaging modality, where the positronium and its annihilation, could serve as an oxygen-sensitive marker. The effective yield of 3gamma annihilation depends on the rates of formation and quenching. The formation of positronium is not only sensitive to the physics parameters, but also behaves as an active chemical particle. A hypoxic cell is a microenviromnent which has an inadequate amount of oxygen. Oxygen is known to be a strong positronium quencher where 2gamma annihilation replaces the 3gamma process. It is thus possible for hypoxic cells to be characterised by higher 3gamma rates than those cells which are well oxygenated. The measurement of 3gamma annihilation to differentiate between oxygenated and non-oxygenated biological samples in order to extract useful information in PET for oncology is a challenging project. It opens up very interesting applications in nuclear medicine imaging as the 3gamma yield has not been measured before in biological tissue and in particular hypoxic tumour cells. The project is multidisciplinary involving physics, biology and chemistry. There are many factors which affect the dissolved oxygen in mineral water, defibrinated horse blood and serum samples. These factors and the challenges to prepare in-vitro hypoxic samples have been experimentally measured using polarography with different chemical reactions e.g. carbon dioxide, nitrogen and AnaeroGen(TM). Results have shown that polarography was more suitable than colorimetery in the measurement of dissolved oxygen in blood due to the high absorption characteristic of blood. AnaeroGen(TM) is the method of choice, unlike carbon dioxide or nitrogen treatment, for preparing hypoxic samples due to the good agreement of the behaviour of the oxygen reduction as in the oxyhaemoglobin dissociation curve which is caused by a decrease in pH, an increase in partial pressure of carbon dioxide and an increase in temperature. The 3gamma yield was measured in normoxic and hypoxic environments using the triple coincidence measurement of three high-energy resolution detectors (HPGe). The AnaeroGen(TM) was used to generate a hypoxic environment. The percentage of the coincidence events qualified as 3gamma was 26.5% higher in the hypoxic environment. This reseach work is a step towards the application of the novel modality of 3gamma PET which in conjunction with conventional 2gamma PET could serve as a non-invasive oxygen sensitive marker. The combination of 3gamma and 2gamma coincidences in nuclear medicine imaging systems may contribute important information for the development and validation of appropriate hypoxia markers. The relative 3gamma/2gamma yield was measured for a positron emitter 22Na with the new generation of scintillator LaC13:Ce and LaBr3:Ce detectors, which had been characterised together with NaI(Tl) and HPGe detectors. The experimental focus was on measuring the relative 3gamma/2gamma yield in different samples by applying the peak-to-peak and the peak-to-valley methods. The value of the ratio 3gamma/2gamma depends on the specimen and is of the order of 10-2. The relative 3gamma/2gamma yields obtained for the peak to peak method in the silica sample were, for example, (3.41+/-0.18)x10 -2, (2.98+/-0.13)x10-2, (4.01+/-0.16)x10 -2 and (2.12+/-0.14)x10-2 for LaBr3:Ce, LaCl3:Ce, NaI(Tl) and HPGe detectors, respectively. The results show that the lanthanum based crystals, LaBr3:Ce and LaCl3:Ce, have the potential to replace NaI(Tl) and HPGe due to both good energy resolution and good detection efficiency and can be the scintillator of choice for determining the yield of 3gamma. The peak-to-valley method was applied to measure the relative yield of 3gamma/2gamma positron annihilation using 18F in 11 haematological samples of different oxygenation levels. The relative 3gamma/2gamma yield was found to vary as much as 11% between the components investigated

Measurement of a wide-range of X-ray doses using specialty doped silica fibres

Using six types of tailor-made doped optical fibres, we carry out thermoluminescent (TL) studies of X-rays, investigating the TL yield for doses from 20 mGy through to 50 Gy. Dosimetric parameters were investigated for nominal 8 wt% Ge doped fibres that in two cases were co-doped, using B in one case and Br in the other. A comparative measurement of surface analysis has also been made for non-annealed and annealed capillary fibres, use being made of X-ray Photoelectron Spectroscopy (XPS) analysis. Comparison was made with the conventional TL phosphor LiF in the form of the proprietary product TLD-100, including dose response and glow curves investigated for X-rays generated at 60 kVp over a dose range from 2 cGy to 50 Gy. The energy response of the fibres was also performed for X-rays generated at peak accelerating potentials of 80 kVp, 140 kVp, 250 kVp and 6 MV photons for an absorbed dose of 2 Gy. Present results show the samples to be suitable for use as TL dosimeters, with good linearity of response and a simple glow curve (simple trap) distribution. It has been established that the TL performance of an irradiated fibre is not only influenced by radiation parameters such as energy, dose-rate and total dose but also the type of fibre

Developments in production of silica-based thermoluminescence dosimeters

This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol–gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1 mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10 s of μGy over a period of several months

The Potential Use of Three Photon Positron Annihilation in Positron Emission Tomography for Tumour Hypoxia Imaging

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Patient radiation biological risk in computed tomography angiography procedure

Computed tomography angiography (CTA) has become the most valuable imaging modality for the diagnosis of blood vessel diseases; however, patients are exposed to high radiation doses and the probability of cancer and other biological effects is increased. The objectives of this study were to measure the patient radiation dose during a CTA procedure and to estimate the radiation dose and biological effects. The study was conducted in two radiology departments equipped with 64-slice CT machines (Aquilion) calibrated according to international protocols. A total of 152 patients underwent brain, lower limb, chest, abdomen, and pelvis examinations. The effective radiation dose was estimated using ImPACT scan software. Cancer and biological risks were estimated using the International Commission on Radiological Protection (ICRP) conversion factors. The mean patient dose value per procedure (dose length product [DLP], mGy·cm) for all examinations was 437.8 ± 166, 568.8 ± 194, 516.0 ± 228, 581.8 ± 175, and 1082.9 ± 290 for the lower limbs, pelvis, abdomen, chest, and cerebral, respectively. The lens of the eye, uterus, and ovaries received high radiation doses compared to thyroid and testis. The overall patient risk per CTA procedure ranged between 15 and 36 cancer risks per 1 million procedures. Patient risk from CTA procedures is high during neck and abdomen procedures. Special concern should be provided to the lens of the eye and thyroid during brain CTA procedures. Patient dose reduction is an important consideration; thus, staff should optimize the radiation dose during CTA procedures

X-ray irradiation-induced structural changes on Single Wall Carbon Nanotubes

Dosimetry devices based on Carbon Nanotubes are a promising new technology. In particular using devices based on single wall carbon nanotubes may offer a tissue equivalent response with the possibility for device miniaturisation, high scale manufacturing and low cost. An important precursor to device fabrication requires a quantitative study of the effects of X-ray radiation on the physical and chemical properties of the individual nanotubes. In this study, we concentrate on the effects of relatively low doses, 20 cGy and 45 cGy, respectively. We use a range of characterization techniques including scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy to quantify the effects of the radiation dose on inherent properties of the nanotubes. Specifically we find that the radiation exposure results in a reduction in the sp2 nature of the nanotube bond structure. Moreover, our analysis indicates that the exposure results in nanotubes that have an increased defect density which ultimately effects the electrical properties of the nanotubes

X-ray irradiation-induced structural changes on Single Wall Carbon Nanotubes

Dosimetry devices based on Carbon Nanotubes are a promising new technology. In particular using devices based on single wall carbon nanotubes may offer a tissue equivalent response with the possibility for device miniaturisation, high scale manufacturing and low cost. An important precursor to device fabrication requires a quantitative study of the effects of X-ray radiation on the physical and chemical properties of the individual nanotubes. In this study, we concentrate on the effects of relatively low doses, 20 cGy and 45 cGy, respectively. We use a range of characterization techniques including scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy to quantify the effects of the radiation dose on inherent properties of the nanotubes. Specifically we find that the radiation exposure results in a reduction in the sp2 nature of the nanotube bond structure. Moreover, our analysis indicates that the exposure results in nanotubes that have an increased defect density which ultimately effects the electrical properties of the nanotubes

High-intensity focused ultrasound (HIFU) in uterine fibroid treatment : review study

Background: High-intensity focused ultrasound (HIFU) is a highly precise medical procedure used locally to heat and destroy diseased tissue through ablation. This study intended to review HIFU in uterine fibroid therapy, to evaluate the role of HIFU in the therapy of leiomyomas as well as to review the actual clinical activities in this field including efficacy and safety measures beside the published clinical literature. Material/Methods: An inclusive literature review was carried out in order to review the scientific foundation, and how it resulted in the development of extracorporeal distinct devices. Studies addressing HIFU in leiomyomas were identified from a search of the Internet scientific databases. The analysis of literature was limited to journal articles written in English and published between 2000 and 2013. Results: In current gynecologic oncology, HIFU is used clinically in the treatment of leiomyomas. Clinical research on HIFU therapy for leiomyomas began in the 1990s, and the majority of patients with leiomyomas were treated predominantly with HIFUNIT 9000 and prototype single focus ultrasound devices. HIFU is a non-invasive and highly effective standard treatment with a large indication range for all sizes of leiomyomas, associated with high efficacy, low operative morbidity and no systemic side effects. Conclusions: Uterine fibroid treatment using HIFU was effective and safe in treating symptomatic uterine fibroids. Few studies are available in the literature regarding uterine artery embolization (UAE). HIFU provides an excellent option to treat uterine fibroids

Urethrographic examinations: Patient and staff exposures and associated radiobiological risks

Medical exposure of the general population due to radiological investigations is the foremost source of all artificial ionising radiation. Here, we focus on a particular diagnostic radiological procedure, as only limited data are published with regard to radiation measurements during urethrograpic imaging. Specifically, this work seeks to estimate patient and occupational effective doses during urethrographic procedures at three radiology hospitals. Both staff and patient X-ray exposure levels were calculated in terms of entrance surface air kerma (ESAK), obtained by means of lithium fluoride thermoluminescent dosimeters (TLD-100(LiF:Mg:Cu.P)) for 243 urethrographic examinations. Patient radiation effective doses per procedure were estimated using conversion factors obtained from the use of Public Health England computer software. In units of mGy, the median and range of ESAK per examination were found to be 10.8 (3.6–26.2), 7.0 (0.2–32.3), and 24.3 (9.0–32.0) in Hospitals A, B, and C, respectively. The overall mean and range of staff doses (in µGy) were found to be 310 (4.0–1750) per procedure. With the exception of hospital C, the present evaluations of radiation dose have been found to be similar to those of previously published research. The wide range of patient and staff doses illustrate the need for radiation dose optimisation. © 202