Ionizing Radiation Ebooks Catalog
Epidemiologic observations suggest that exposure of breast tissue to ionizing radiation is associated with an increased risk of breast cancer. In particular, an increased risk of breast carcinoma has been clearly documented in young women that have survived atomic bombs, in patients who have undergone repeated fluoroscopies (eg, in patients with tuberculosis), and in patients treated with radiation for postpartum mastitis, thymic enlargement, and Hodgkin's disease.26-37 Subsequent reports directed attention to the carcinogenic risk associated with radiation exposure and the latency time between exposure and clinical manifestations of breast can The hypothetical risk of breast cancer derived from prolonged screening needs to be mentioned. Using a risk estimate provided by the Biological Effects of Ionizing Radiation (BEIR) V Report of the National Academy of Sciences and a mean breast glandular dose of 4 mGy from bilateral mammography, with two views per breast, one can estimate that...
In general, all imaging technologies require the use of electromagnetic energy. Each imaging modality exploits a different part of the electromagnetic energy spectrum. The spectrum includes gamma rays, X-rays, visible light, ultrasonic waves, and radiowaves. All of these waves are photons of energy, but they differ in their wavelength and, therefore, energy. Each imaging instrument is designed to detect a particular range of electromagnetic energy. Most often, the instrument also generates the requisite energy for the imaging application, and the detection occurs after interaction with the imaging subject. The exception is with gamma-ray imaging, where the requisite energy is provided by decay of an administered radioactive probe that is not part of the instrument.
Simulations due to Abel, Bryan & Norman (2000, 2002) place the epoch of population III formation at z 18. These massive stars eventually evolve into type II supernovae and may produce not only sufficient ionizing radiation to reionize the Universe (which was primarily neutral following the formation of atomic hydrogen at z 1000) but may also produce and explosively eject heavy elements. The location in time of this epoch of reionization, expected to be coincident with the formation of the first heavy elements, is poorly constrained observationally. Recent observations with the WMAP instrument indicate, albeit with a large uncertainty, that reionization may already have been occuring at z 20 (c.f. Kogut 2003 Bennett et al. 2003). Combined with the Gunn-Peterson trough observations2 (Fan et al. 2001 Gunn & Peterson 1965) this hints at an epoch of reionization that may be quite extended and patchy, rather than a sharp and smooth transition (c.f. Razoumov et al. 2002 Ciardi et al. 2000).
Questions have been raised relevant to potential carcinogenic risk of radiation exposure for women who harbor the BRCA1 or BRCA2 mutations. Scully and colleagues44 raised the possibility that there may be an interaction between BRCA1 and BRCA2 gene products with respect to proteins involved in the repair of radiation-induced DNA errors. However, this issue remains controversial due to lack of confirmation of this risk in the past by other inves-tigators.45 Nevertheless, recent evidence has indicated that both BRCA1 and BRCA2 are associated with defective repair of radiation-induced DNA damage.44,46
Stoll et al. 23 suggested that in their relatively small sample, fathers of ARM babies were more exposed to hazardous substances than fathers of controls. Other environmental factors such as exposure to electromagnetic radiation have proved to be difficult to determine from an epidemiological point of view.
Over the years, a great deal of information has been acquired concerning the many variants of ARM. The current mortality for these anomalies has for the most part been very low and is related to associated anomalies and unfavorable chromosomal and genetic syndromes rather than the result of treatment of the ARM per se. In general, agreement has been reached regarding some embryologic and anatomic considerations, diagnostic evaluation, and preoperative assessment 123, 146, 150 . Most investigators would agree that results are better following repair of low defects when compared to intermediate and high anomalies and those with cloaca. There remain several areas of controversy regarding the choice and timing of the procedure and methodology used to assess results. Certain poor prognostic factors have been identified, including abnormal sacrum, deficient pelvic innervation, poor perineal musculature, and disorders of colonic motility. It may be difficult to establish a prospective...
They then examined double-strand break repair with attention given to sensitivity to drugs and radiation effect that induce double-strand breaks. Their findings disclose that BRCA2-defective cells are unable to repair the double-strand DNA breaks induced by ionizing radiation. These cells were also markedly sensitive to mitoxantrone, amsacrine, and etoposide (two-sided p .002) and to ionizing radiation (two-sided p .001). Introduction of antisense BRCA2 deoxyribonu-cleotides into cells possessing normal BRCA2 function led to increased sensitivity to mitox-antrone (two-sided p .008). Tumors formed by injection of BRCA2-defective cells into nude mice were highly sensitive ( 90 tumor size reduction, two-sided p .002) to both ionizing radiation and mitoxantrone when compared with tumors exhibiting normal BRCA2 function. Abbott and colleagues concluded that these BRCA2-defective cancer cells were highly sensitive to agents that contribute to doublestrand...
As follows from a consideration of quantum mechanics, an atom or molecule has discrete energy states. Spectroscopy is the measurement of the energy differences between these states. The energy differences AE can be measured by the absorption spectra of electromagnetic radiation. In conventional spectroscopy, the frequency is varied and the frequency at which maximal absorption occurs reflects the difference between the states. The frequencies vary from the MHz range for NMR to the GHz (microwave) range for EPR spectroscopy. The frequencies for absorption spectroscopy range from 1012 Hz for IR to 1016 Hz for UV light. The frequencies of X-rays and 7-irradiation are 1019 Hz and 1021 Hz, respectively.
Spectroscopic methods are used at some point in the structural characterization of biomolecules (Bell, 1981 Campbell and Dwek, 1984 Gendreau, 1986). These methods are usually rapid and noninvasive, generally require small amount of samples, and can be adapted for analytical purposes. Spectroscopy is defined as the study of the interaction of electromagnetic radiation with matter, excluding chemical effects. The electromagnetic spectrum covers a very wide range of wavelengths (Figure 5.2). Figure 5.2. Electromagnetic radiation and its corresponding spectra.
Analogous to EPR spectroscopy, NMR spec-troscopy is based on the resonance absorption of electromagnetic radiation by the system during the transition between two discrete energy states. The energy differences studied in NMR spectroscopy are due to the interaction of nuclear magnetic moments with the magnetic field (Zeeman splitting for nuclei). The energy differences are smaller than those in EPR because of the smaller magnetic moment of nuclei. This explains why electromagnetic radiation in the radiofrequency range is required to excite the transitions that produce the NMR signal, whereas that in the microwave range is used in EPR spectroscopy.
Twenty years ago, few scientists were involved in the field of risk perception and communication. Today, the literature contains hundreds of articles on this topic (Fishhoff et al. 1993). This increased interest has resulted from a number of factors (Covello 1995). First, the public has become increasingly concerned about environmental health issues, such as those related to nuclear power and electromagnetic fields. Second, laws have been enacted mandating that environmental risk information be communicated to the public, media, and special interest groups. Finally, the public increasingly does not believe in government and other institutions as sources of information.
In this Section, a comparison is presented between the risks of breast cancer induced by radiation exposure of the breast during mammography and the possible reduction in breast cancer mortality arising from mammographic screening. Risks are estimated in terms of the BEIR V models (NAS NRC, 1990), presented above, and benefits are considered in terms of various assumed reductions in breast cancer mortality rates as a consequence of mammo-graphic screening. The benefit risk model uses standard life table
A second Guy's Hospital study enrolled 50 patients between 1990 and 1992 (Fentiman et al. 2004). Patient selection criteria, and surgical and implant techniques were similar to those in the first Guy's Hospital series except for three aspects. First, only patients aged 40 years or older were eligible. Second, to reduce radiation exposure to medical and nursing staff, a MDR remote-controlled afterloading system employing caesium-137 was used to give a total dose of 45 Gy in four fractions over 4 days. Third, 92 of patients received adjuvant systemic therapy. At a median follow-up of 6.3 years, 8 of 49 eligible patients (18 ) developed a breast relapse, which was located in the index quadrant in seven (78 ). Only one LR (4 ) occurred among patients with lesions smaller than 2 cm, while the rate was 35 among patients with tumors of 2 cm or larger. Cosmetic outcome was considered excellent or good in 81 of patients.
MRI employs radio frequency pulses as opposed to ionizing radiation for mapping internal structures. Although MRI and CT scanning are comparable in their ability for determining lymph node status, MRI is far superior to CT scanning in soft tissue contrast resolution. MRI provides a detailed survey of pelvic anatomy and has proven useful for determining tumour size, the depth of invasion and parametrial involvement and identifying bladder and rectal extension. Several authors have demonstrated the accuracy of MRI for pre-treatment staging to be greater than 90 .5,9-13 The primary use of MRI appears to be in assisting in the determination of a patient's operability.
Until now, the clinical demise of cancer has relied on surgical resection and the inhibition of tumor cell proliferation using ionizing radiation or chemo-therapeutic drugs designed to perturb DNA synthesis or the mitotic event. The development of cytotoxic agents has resulted in improvements in the treatment of leukemia, lymphoma, testicular cancer, and many other solid tumor types (1). Hormone-based drugs have also been useful for breast and prostate cancers (2). Although much success has been achieved, cytotoxic modalities walk the therapeutic tightrope of toxicities to normal tissues vs cancer cells, and drug resistance is generally present de novo or develops with treatment. Over the last decade or so, more attention has been focused on different therapeutic approaches. These include the development of monoclonal antibodies (MAbs) to specifically target cancer cells, and small molecule-inhibitors of cell-signaling pathways that have been linked to oncogenesis or maintenance of...
MR imaging is increasingly becoming a first-line investigation for the evaluation of diseases of the aorta1. Advantages of MRI include avoidance of ionizing radiation and the use of contrast agents, which are not nephrotoxic. Over the last years, major technological advances resulted in significant increases in acquisition speed.
Intravascular ultrasound (IVUS) is an imaging modality that has evolved from transcutaneous and intralumenal gastrointestinal ultrasound technology. It has been adapted for uses along side other endovascular interventional technology. IVUS has the capacity to provide unique information regarding extent and morphology of aortic pathology. When compared to conventional imaging, IVUS adds a heightened level of accuracy when it comes to defining particular complex vascular anatomy. IVUS is easily applied during other types of interventional procedures and it can reduce or completely avoid the need for ionizing radiation. Currently IVUS is limited by the added expense for the instrumentation. It also requires an invasive procedure for catheter introduction.
The technique of contrast-enhanced MRA bears a strong resemblance to CTA, which probably inspired its development. There are, however, several differences between the two techniques. Unlike CT, MR does not employ ionizing radiation. CT images are always acquired in the transverse plane but they may be reconstructed into other planes with postprocessing. Magnetic resonance angiograms may be acquired in arbitrary planes, and also reconstructed. The total volume of contrast agent injected is lower with MRI, and as mentioned above, Gd-DTPA is not nephrotoxic. MRA and CTA are prone to different artifacts. Certain artifacts on MRA are dependent on the pattern of blood flow, and these can be complex. CTA is relatively independent of the blood flow pattern.
The success of MRI in characterizing plaque composition derives from its excellent contrast between soft tissues, which provides excellent anatomical and compositional detail. Contrast can also be changed by adjusting any of several imaging parameters. Multiple images with different contrast weightings can thus be combined for increased sensitivity to tissue differences. Additionally, MRI is noninvasive and does not use ionizing radiation, making it ideal for serial studies.
Recombination repair is any DNA repair or damage tolerance strategy involving homologous recombination (q.v.). The existence of such repair mechanisms is indicated by differences in sensitivity to ionizing radiation demonstrated by haploid yeast ceils arrested in Gi and C2 (and similarly for stationary phase and log phase bacterial cells) in each case, the cell with more copies of its genome is more resistant. More direct evidence for recombination repair comes from studies of recombination deficient mutants of E. coli and S. cerevisiae, which are also radiation-sensitive.
Apoptosis is frequently induced in experimental systems by a defined signal, such as ionizing radiation, dexamethasone, or camptothecin. In these cases, it is important to differentiate between first-round transcriptional targets of the inducing agents and subsequent knock-on effects. This can be accomplished by inclusion of a protein synthesis inhibitor (cycloheximide), but it is important to generate representations from both cycloheximide-treated and untreated controls to ensure that identified transcripts are not artefacts of treatment with the inhibitor. In some systems, apoptosis can result from the expression of an exogenous transgene, which can either be inducible or show constitutive expression. Appropriate controls include the preparation of representations from vector-only transfectants, with or without inducing agents. Control representations can then be mixed in the Driver to prevent the cloning of unwanted transcripts such as antibiotic resistance marker (e.g., Neo).
For the majority of anticancer drugs, previous studies not only ruled out an essential role for the Fas FasL pathway in drug-induced apoptosis (see first paragraph of this Section) but also directly implicated the mitochondrial pathway in this process. Observations that are important in this regard include the demonstration that cytochrome c release accompanies induction of apoptosis by a variety of agents (113,120,223,224), the determination that Bax translocates to mitochondria in response to various drugs independent of (i.e., upstream of) caspase activity (83,225), and the demonstration that combined deletion of BAX and BAK inhibits drug-induced apoptosis (87,226). As might be expected, if the mitochondrial pathway plays a predominant role, dominant-negative caspase-9 constructs (227,228) and antiapoptotic Bcl-2 family members (210,229) inhibit drug-induced apoptosis. The demonstration that Caspase9 or Apaf-1 gene deletion delays the induction of apoptosis by staurosporine,...
The proton is the element responsible for the signal generation in proton MRI, and can be viewed as a minimagnet due to the spinning single electron. MRI utilizes two energies, a strong magnetic field and pulses of radio frequency (RF) electromagnetic energy. RF energy is not ionizing, and a trillion times less in magnitude than X-rays. The sensitivity of the technology is related to the large number of protons that are present in water and fat, the primary constituents of a human or animal. When protons are placed in a magnetic field, they become aligned with, or opposed to, the external field. Excitation with a precise resonance frequency (MHz) results in excited-state protons, all of which are in phase, but tilted away from the direction of the external magnetic field. The in-phase aspect is unique to the excited state, since ground-state protons are not in phase. Therefore, to summarize, absorption of a resonance RF energy by the proton results in an excited state, where all the...
Magnets have been used to provide the force needed for orthodontic tooth movement. Classically an unerupted tooth has a magnet attached to it and a second magnet is placed on an orthodontic appliance with the poles orientated to provide an attractive force. It is unlikely that the magnetic forces alone have any actions on tissues. If magnetic fields are broken (as in pulsed electromagnetic fields) then there is some evidence that tissues will respond. It is worth making the following points about the effects of magnetic and electric fields on tooth movement
It highly reactive and destructive to cells produced by intrinsic processes such as aerobic respiration and by extrinsic agents such as chemicals and ionizing radiation. frontal plane An anatomical plane that passes through the body or an organ from right to left and superior to inferior also called a coronal plane. fig. A.3 functional group A group of atoms, such as a car-boxyl or amino group, that determines the functional characteristics of an organic molecule. fundus The base, the broadest part, or the part farthest from the opening of certain viscera such as the stomach and uterus. fusiform (FEW-zih-form) Spindle-shaped elongated, thick in the middle, and tapered at both ends, such as the shape of a smooth muscle cell or a muscle spindle.
There are two widely used noncontrast-based MRA techniques time-of-flight (TOF) MRA and phase contrast (PC) MRA. The physical principles underlying both techniques are far more complicated than those underlying catheter angiogra-phy and CTA and are beyond the scope of this chapter. Both are unlike other vascular imaging techniques used in acute stroke, in that they are completely noninvasive, requiring no exogenous contrast material whatsoever, thereby obviating concerns regarding contrast allergies and contrast-induced nephropathy (Fig. 2.4). Unlike catheter angiography and CTA, MRI uses no ionizing radiation. Like catheter angiography (but not CTA), both TOF and PC MRA can be used to demonstrate the direction of blood flow, which can be helpful in assessing the direction of flow in a vessel providing collateral perfusion or in situations such as suspected subclavian steal. Additionally, PC MRA can quantitatively measure the velocity of flow, an ability shared only by ultrasound, a...
There is little, if any, opposition to the practice of diagnostic mammography, probably because of the compelling clinical need for the information obtained. Many mammography examinations are performed for diagnostic purposes, and mammographic screening programs have also been widely implemented. There has been some opposition to screening in the past for a variety of reasons (1) concern over a few published indications of a relatively unfavorable benefit risk ratio, (2) concern about exposure to ionizing radiation, (3) concern about benefit in comparison to the number of false-positive mammograms, (4) the relatively high cost of mammography examinations and the cost of the biopsy procedures
Trauma, chronic infection and chronic radiation exposure are possible aetiological factors human papillomavirus (HPV) has been incriminated in some cases. Two reported cases had associated congenital ectodermal dysplasia. Most lesions occur on the fingers, particularly the thumbs and index fingers (Figure 5.31). The presenting symptoms include pain, swelling, inflammation, elevation of the nail, ulceration, a tumour 'mass', ingrowing of the nail, 'pyogenic granuloma' and bleeding. Bone involvement is a rare, very late sign. The duration of symptoms before diagnosis is greater than 12 months in over half the cases. Only in one published case (with ectodermal dysplasia) has the condition led to death, from rapid generalized metastases.
The goal in screen-film mammography for mass screening and diagnosis is to produce consistently high-contrast, high-resolution, low-noise images at the lowest radiation dose consistent with these image-quality requirements. In recent years, there have been many significant technologic improvements in mammographic screen-film combinations (AAPM, 1990 Haus, 1991 1999b KimmeSmith, 1991 Rothenberg and Haus, 1995 Yaffe, 1990). Until the early 1970s, direct-exposure (industrial type) x-ray films were used which often required long exposure times (causing blur due to motion) and resulted in high radiation exposure (Bassett et al., 1992 Egan, 1976 Gold et al., 1990 Haus and Cullinan, 1989). Films were processed manually in tanks or in film processors with long processing times. In the early 1970s, screen-film combinations for mammography became commercially available (Bassett et al., 1992 Haus and Cullinan, 1989 Ostrum et al, 1973 Wayrynen, 1979).
Radiologists should be aware that the relative risk of cancer could be increased in these patients by cumulative radiation exposure. Therefore, every effort should be made to keep the radiation exposure to the lowest feasible levels. Useful techniques in this regard include gonadal, thyroid, and breast shielding, highspeed screen-film combinations, and the use of digital radiography.
The obliterative endarteritis associated with ionizing radiation in therapeutic dosage proceeds over many years and may result in fistula formation long after the primary malignancy has been treated. Of the 14 radiation fistulas in the author's series, the interval between fistula development and radiotherapy ranged from 1 year to 30 years. The associated devascularization in the adjacent tissues means that ordinary surgical repair has a high likelihood of failure, and modified surgical techniques are required.
The first demonstration of lifetime detection for DNA sequencing occurred in 1998.12 Three new dyes were synthesized and combined with a commercially available cyanine dye (Figure 2.6) to create a set of dyes with distinct fluorescence lifetimes. The dyes had varied absorbance maxima (from 624 to 6669 nm). A semiconductor laser emitting at 630 nm was used for excitation. The average laser power was only 0.6 mW. High laser powers are not needed in the red region of the electromagnetic spectrum because there is low background signal in this region. The dyes were conjugated to a sequencing primer (5'-TGT17ACGACGGCCAGT-3'). The conjugated Cy5 exhibited a lifetime of 1.6 ns, conjugated JA242 exhibited a lifetime of 2.4 ns, conjugated JA169 exhibited a fluorescence lifetime of 2.9 ns, and conjugated MR200-1 exhibited a fluorescence lifetime of 3.7 ns. Utilizing this dye set, 660 bp were sequenced with 90 accuracy. The accuracy was adversely affected by two dyes, JA242 and JA169, exhibiting...
Other breast imaging methods currently have less widespread application these include ultrasonography, magnetic resonance imaging (MRI), thermography, transillumination, CT, and nuclear imaging. Except for ultrasonography, all involve electromagnetic wave radiation. CT exposes breast tissue to higher levels of ionizing radiation than screen-film or digital mammography, making it unsuitable for annual screening and it does not have the spatial resolution of conventional mammography. Thermography, and nuclear imaging have not been shown to contribute significantly to either lesion detection or characterization. Ultrasound has specific applications for evaluating breast masses and guiding interven-tional procedures. MRI is currently being studied for its potential roles in screening for and staging breast cancer, as well as other indications.
NMR spectroscopy studies the interaction of electromagnetic radiation with matter. It is a powerful tool for the studies of kinetic motion of water in tissues and of macro-molecule water or membrane water interactions. Solid-state NMR can be used to determine the molecular structure of solid tissue samples. Solid-state H-NMR is often used to investigate the relaxation characteristics of the protons of water molecules in low-moisture biological systems (Mathur-de Vre, 1979 Seewaldt et al., 1981 Rorschach and Hazlewood, 1986 Ratkovic, 1987 Chapter 4). The basic principle of H-NMR is that each of two hydrogen nuclei in a water molecule possesses a single spin proton, which will cause the nucleus to produce an NMR signal. When an atom is placed in a magnetic field, the spin of its electrons will orient toward the direction of the applied magnetic field. This orientation produces a small local magnetic field at the nucleus that opposes the externally applied field, resulting in a smaller...
There he was assigned back to Wright Field just as the Korean War broke out and he would spend the next 30 months on duty in the Far East. Eventually he would return to Holloman as chief of the Space Biology Laboratory, but his involvement this time would be in the area of cosmic radiation exposure during high-altitude balloon flights.
P53 alterations appear to affect sensitivity to both ionizing radiation and drugs. Studies in tissue culture have led to the conclusion that p53 deficiency can render both ElA ras-transformed fibroblasts (265) and HCT116 colon cancer cells (266) resistant to the induction of apoptosis by various anticancer drugs in vitro. When the same cell lines are grown as xenografts, responses are diminished in the absence of p53. Consistent with these results, studies have also established that ionizing radiation or high-dose 5-fluorouracil induces less apoptosis in epithelial cells of the small and large intestines of p53+ + mice compared with that of p53+ + littermates (267,268). Collectively, these results suggest that changes in p53 status can affect drug sensitivity in at least some cell types. Information regarding the role of BH3-only protein alterations in drug resistance is likewise incomplete. In perhaps the best-studied example, Bim gene deletion not only renders murine thymocytes...
Conventional multimodality therapy for lung cancer incorporates surgery, radiation, and chemotherapy using a variety of clinical protocols dictated by the subtype and extent of disease. Theoretically, gene therapies may play important synergistic roles in augmenting the effectiveness of conventional approaches. For many such strategies, there already exists a scientific rationale to test them in combination with conventional multimodality therapy. For example, one may enhance the radiation-sensitivity or chemosensitivity of tumor cells (e.g., p53 or kBa gene therapy) 127, 128 or modify normal tissue susceptibility to cytoablative therapy (e.g., mucosal tissue protection by virtue of MDR-1 or bFGF gene transfer). Examples of synergism with the suicide gene therapy approaches have also been studied. The HSV thymidine kinase gene ganciclovir system induces radiation sensitivity into transduced tumor cells 129 , suggesting that these two forms of therapy can be combined to potentiate...
A number of epidemiologic studies of adult women have contributed knowledge of the long-term risks of ionizing radiation to the female breast (Boice, 2001 Preston et al., 2002a UNSCEAR, 2000). Among these studies are those of Japanese atomic-bomb survivors (Shimizu et al., 1990 Thompson et al., 1994) female tuberculosis patients in Massachusetts who received multiple chest fluoroscopies in conjunction with artificial pneumothorax (Boice et al., 1991) a similar series of female tuberculosis patients in Canada (Howe and McLaughlin, 1996) women in New York State receiving radiotherapy for postpartum mastitis (Shore et al., 1986) and Swedish women receiving x-ray treatment for fibroadenomatosis and other benign breast conditions (Baral et al., 1977 Mattsson et al., 1993).
In the electromagnetic energy spectrum, the highest energy photons (shortest wavelength, highest frequency) are gamma rays. Gamma rays arise out of nuclear events during radioactive decay. For in vivo imaging purposes, the best gamma rays are of low energy, in the range of 100-511 keV. Gamma rays in this energy range can be efficiently stopped and therefore measured
Radiation is a form of energy and shows both electrical and magnetic characteristics, hence the term electromagnetic radiation (Figure 2.1). It can be considered as being composed of a stream of separate groups of electromagnetic waves and the energy associated with the radiation can be mathematically related to the waveform. Figure 2.1 Electromagnetic radiation. A representation of electromagnetic radiation with the electric field (E) and the magnetic field (M) at right angles to the direction of the wave movement. Both fields oscillate at the same frequency. Figure 2.1 Electromagnetic radiation. A representation of electromagnetic radiation with the electric field (E) and the magnetic field (M) at right angles to the direction of the wave movement. Both fields oscillate at the same frequency.
Radial dose function 346, 348, 354 radial electric field 23 radial symmetry 378 radiation action 214 radiation damage 220, 226 radiation dose 380 radiation dosimetry 108 radiation effect 214-215, 296 radiation exposure 411 radiation hardness 225 radiation hormesis 421 radiation length 28 radiation product 209-210 radiation quality 329, 333 radiation track 209 radiation tree 223 radiation weighting factor 412 radiation worker 381, 417, 424 radiation-less transition 175 radiative capture 123, 126 radiative mass stopping power 82 width 125 2 07
The only established environmental risk factor for PTC is radiation exposure to the thyroid in childhood. In subjects with a childhood history of external irradiation to the head and neck region, PTC typically develops after a latency period of at least 5 years, reaching its peak incidence at about 20 years and then declining gradually in incidence after another 20 years. Besides external irradiation, the Chernobyl nuclear accident proved that radioactive isotopes of iodine also have a direct tumori-genic effect on the thyroid. In Belarus and Ukraine, PTC develops mostly in children who were younger than 10 years old at the time of the accident, with onset noted as early as 4 years after exposure.5
The genetic changes involved are likely to determine both the histologic appearance and the biologic behavior of the thyroid cancer. PTC appears to arise de novo within the thyroid gland as a result of receptor tyrosine kinase activation by RET or NTRK1 gene rearrangement. Intrachromosomal inversion of the RET proto-oncogene (chromosome 10q11.2) has been reported in 10 to 70 of PTCs, being found most commonly in tumors arising after exposure to ionizing radiation. Four types of RET rearrangements have been observed, designated RET PTC1 to RET PTC4, respectively (Figure 2-1). Constitutive RET activation occurs with these rearrangements, which is believed to play a direct role in carcinogene-sis.6 RET PTC variants are found in less than half of PTCs in the adult population, whereas the prevalence is 70 in children with radiation-induced PTC. Children with post-Chernobyl PTC showed a striking preponderance of the RET PTC3 gene and pheno-typic association with a solid variant...
Among patients with palpable thyroid nodules, the history is usually not helpful in detecting underlying thyroid malignancy. Symptoms such as hoarseness of voice, dysphagia, or shortness of breath are uncommon and suggest advanced malignancy. However, an increased risk for malignancy is recognized in individuals with a history of ionizing radiation exposure in childhood, appearance of nodules at an age younger than 20 years or older than 60 years, and the male sex in general. Virtually all patients with DTC are clini-
N R* x fp x ne x fl x fi x fc x L where N the number of civilisations in the galaxy from which electromagnetic emissions are detectable R* the rate of formation of stars that are compatible with the development of life fp the fraction of those stars that have planetary systems ne the number of planets with life-supporting environments orbiting each of these stars fl the fraction of these planets on which life appears fi the fraction of life-bearing planets on which intelligent life evolves fc the fraction of civilisations that develop an advanced technology, emitting detectable radio signals and L the length of time during which these civilisations release detectable signals.
Epidemiologic studies may have limited power to address the effects of exposures in a range that would be of concern for the general population Metaanalysis has been used to summarize data for the steps of hazard identification and dose-response assessment. It has been used increasingly as a tool for summarizing experimental and observational studies (Petitti 1994), and methods for epidemiologic data have been extensively reviewed (see Chapter 2) (Greenland 1987 Dickersin and Berlin 1992). For experimental data, meta-analysis of observational data provides a potentially more informative interpretation of the evidence when sampling variation and small studies have obscured the status of the evidence. Thus, statistical power for detecting an effect is gained and dose-response relationships can be described with greater precision. Meta-analysis has now been applied to a number of environmental agents including environmental tobacco smoke (US EPA 1992a), electromagnetic radiation (NRC...
NMR measures the response of nuclear spins in a large, homogenous magnetic field to perturbations caused by the irradiation of electromagnetic fields in the radio-frequency range (Wider 1998). In practice, a sequence of radiofrequency pulses is applied, with the pulses being separated by interpulse time periods, tte response to such an NMR pulse sequence (Fig. 5.1) is the sum of the radiofrequencies that have been emitted by the nuclei.
Rapid advances in MDCT make evaluation of coronary artery involvement possible. Drawbacks of CT are radiation exposure and the risks inherent to iodinated contrast material MR evaluation is preferred for young patients undergoing serial evaluation of known aortic pathology.
The drawbacks of CT are radiation exposure and use of iodinated contrast material. Radiation risk is certainly negligible in the case of elderly patients who undergo CT for suspected aortic dissection. However, younger patients undergoing unlimited follow-up examinations may experience significant radiation exposure, and MR imaging should be preferred in this patient population.
The International Commission on Radiation Protection (ICRP) aims to provide a general system of radiological protection that can be applied to any situation in which humans are, or are likely to be, exposed to radiation 1 , It publishes recommendations, the latest being ICRP 60 1 , which draw on scientific evidence as well as using value judgements to assess the relative risks of radiation exposure. For the sole purpose of expressing dose limits, Equivalent Dose and Effective Dose have been recommended by ICRP as being the best way to correlate radiation exposure with the risk of developing cancer.
Radionuclide cystogram demonstrating bilateral vesicoureteral reflux (VUR). This method using 99mtechnetium pertechnetate is useful in detecting VUR. Advantages of radionuclide cystography include lower radiation exposure, less interference with overlying bowel contents and bones, and higher sensitivity in detection of VUR. Radionuclide cystography is useful in follow-up examinations of patients known to have VUR, as a screening test in asymptomatic siblings of children with reflux and girls with urinary tract infections, and in serial examinations of children with neuropathic bladders at risk for developing VUR. Disadvantages of this method include less anatomic detail and inadequacy in evaluating the male urethra, making it unsuitable for screening boys for urinary tract infections 7 .
MRI was first used as a structural imaging technique that had better spatial resolution than CAT scans for many organs without any radiation exposure. Originally called nuclear magnetic resonance (NMR), MRI uses a strong magnetic field to align spinning protons in hydrogen atoms throughout the body into a north south orientation. The stronger the magnet, the greater number of protons are aligned. There is no subjective feeling of this alignment taking place while the person lies in the MRI scanner tube, surrounded by the powerful magnetic field. Radio frequencies are pulsed into the magnetic field very rapidly each pulse briefly throws protons out of the magnetic north south alignment but because the body is always in the magnetic field during the procedure, the protons realign immediately. As the protons lose and then regain alignment in the magnetic gradient, different radio frequencies that contain spatial information are produced. These frequencies are detected by antenna-like...
Ionizing radiation has the same effect as light on photographic film and the extent of blackening of the film is related to the amount of radiation. Autoradiography is particularly useful for demonstrating the location of radioactive isotopes in tissues or chromatograms (Figure 5.6).
Radiation nephropathy refers to damage to the kidney parenchyma and vasculature as a result of ionizing radiation 14 . Fortunately, this disease is relatively uncommon. It was more prevalent before meticulous detail to abdominal organ shielding was widely practiced or understood. Historically, patients receiving whole abdominal radiation therapy for lymphoma, seminoma, or other retroperitoneal tumors were the most likely to suffer the consequences of this disorder. Doses greater than 30 to 35 gray and single large fractions were likely to cause damage.
The analyses of data from cohort studies of radon-exposed underground miners are illustrative. The dose-response relationship observed in the underground miners has been extended to the general population for the purpose of estimating the lung cancer risk associated with indoor radon. Dose-response relationships can be obtained from individual studies but variation exists among the studies in the magnitude of the estimated excess risk. To characterize the dose-response relationship between indoor radon and lung cancer, the Biological Effects of Ionizing Radiation (BEIR) IV Committee obtained data from four epidemiologic studies, including about 22,000 subjects who had experienced 350 lung cancer deaths during follow-up. The data were analyzed with regression methods to characterize the dose-response relationship. A linear model was used and the risks were found to decline with increasing time since exposure and increasing age at observation. With the completion of additional studies,...
It has been well established for many years that at least one other mode of cell death, that of mitotic catastrophe, is quite common, particularly in tumors that have been exposed to ionizing radiation. However, the basis for the cell choosing or preferring a particular mode of cell death is not understood, even at the most fundamental level. Relatively recently, at least one additional mode of cell death has been recognized, known as autophagy. Autophagy is a complex response because, unlike apoptosis or mitotic catastrophe, autophagy can function as a cytoprotective mechanism when initiated under certain modes of cell stress, such as nutrient deprivation. Finally, an area that is appropriately receiving renewed attention is a subspecies of apoptosis that is termed anoikis, or cell death subsequent to loss of adhesion to substratum. The ability of tumor cells to resist anoikis may provide the necessary survival advantage that permits a tumor cell to metastasize.
Its ability to detect a cancer before the tumor mass becomes large enough to be palpable, thereby permitting early diagnosis. It has also been proven an invaluable tool to distinguish benign from malignant lesions and can facilitate prompt biopsy of cancers, while encouraging clinical observation (rather than biopsy) of many benign masses. Other breast imaging methods have, thus far, been considered less successful these include thermography, transillumination, ultrasonography, and MRI and MRS all of which do not utilize ionizing radiation. Computed tomography (Section 8.4) and digital mammography (Section 3.3) which use x rays, and therefore involve the potential risk of mammary carcinogenesis are being subjected to clinical investigation to determine their role in breast cancer diagnosis. Explanations of the principles of operation, a chronology of developments, and an extensive discussion of the limitations of each of these methods is contained in Sections 3.3 and 8.4.
In Egypt, irradiation with 0.04, 0.06 or 0.08 kGy completely inhibited sprouting in stored bulbs (El-Gizawy et al., 1993). In Poland, ionizing radiation at 0.05-0.06 kGy prevented onion sprouting and also inhibited reproduction and development of the bulb mite Rhizoglyphus echinopus (Ignatowicz, 1998). When Polish onions were treated with 0.08 kGy gamma rays, a slight darkening of the apex occurred this did not affect the commercial value of the bulbs (Smierzchalska et al., 1988). The best results after irradiation and storage of cv. 'Sochaczewska' (89.5 marketable bulbs vs. 20.5 in non-irradiated bulbs) were found with 0.06 kGy treatment 1 month after harvest, followed by storage at 1 C (Gajewski, 1994).
Allows reformation of images in any plane without loss of resolution (isotropic) 59 . This technologic advance, allowing multiplanar postprocessing, puts CT on par with or ahead of (because of better spatial resolution) MR imaging. Nonetheless, a remaining advantage of MR imaging is the lack of ionizing radiation.
Numerous issues are evolving as the technology and approach undergo changes. Radiation-exposure can be quite low in a screening setting because of the intrinsic contrast between air and soft tissue. Typical doses for CTC are between 3.6 and 12.2 mSvforboth acquisitions 86 with microamperage as low as 10 mA being reported to produce diagnostic images 87 . Patient comfort studies compared with colonoscopy have varied, with generally good results in favor of high acceptance for CTC 88,89 . Reimbursement by the Center for Medicare and Medicaid Services continues to evolve based on evidence in the literature. Coverage varies with local
Imaging studies to assess long-term anorectal function in patients with ARM have been reported infrequently. Dynamic radiographic examination of the anorectal function by defecography has been used to objectively analyze anorectal function 44-46 , but has not gained widespread popularity, mainly because it is cumbersome and requires the full cooperation of the patients to provide valid information. Modern imaging modalities such as intra-anal ultrasound, computed tomography (CT) and MRI provide excellent information about the postoperative anatomy of an ARM. Anal ultrasound has been found to be a reliable tool in the evaluation of sphincter integrity in patients with repaired ARM 47,48 . Good sphincter anatomy at ultrasound is also correlated with good function 47 . CT provides good anatomical data concerning the relationship between a pulled-through bowel and the sphincter system 49 , but gives a high dose of ionizing radiation. Only a few studies have shown any correlation between...
Vision (sight) is the perception of objects in the environment by means of the light that they emit or reflect. Light is visible electromagnetic radiation. Human vision is limited to wavelengths ranging from about 400 to 750 nm. The ultraviolet (UV) radiation just below 400 nm and the infrared (IR) radiation just above 700 nm are invisible to us, although some animals can see a little farther into those ranges than we can. Most solar radiation that reaches the surface of the earth falls within this range radiation of shorter and longer wavelengths is generally filtered out by ozone, carbon dioxide, and water vapor in the atmosphere. Vision is thus adapted to take advantage of the radiation that is most available to us.
Animals would prove to be our bridge to the future. They gave substance to the vision. If humans could not yet travel in space, animals could. Their contribution has been profound and continuous. In a biological sense, from 1948 to I960 they were the space programmes. They were writing the future. In a host of laboratory and field tests, in high-altitude balloons and occupying the cramped nose cones of early rockets, animals became the test subjects for the U.S. and Soviet space programmes. To settle questions about acceleration, vibration, noise, radiation exposure, extremes of pressure and temperature, weightlessness and basic survival in sealed capsules, animals stood in for humans. To test the rockets, capsules, parachutes, recovery systems, environmental systems and satellites, animals gave their lives. We saw ourselves, and
By January 1953, the cosmic-ray programme had become a function of the USAF Missile Development Center at Holloman, which would ensure it received better support than when it was just one of numerous programme activities being carried out at Wright Field. At Holloman, Simons recalled, he would serve as chief of the Space Biology Laboratory, exploring problems associated with cosmic radiation exposure to animals at high altitudes, using balloons.
Diamond is essentially a macromolecular crystal made by sp3 hybridized carbon in which each atom is bonded tetrahedrally to four other carbon atoms and the whole crystal possesses cubic symmetry with ao 0.356679 nm . The C-C bond is given by a 3 4 0.15545 nm which is the normal bond length for alkanes (Holliday et al. 1973 Greenwood and Earnshaw 1984). The strong bonding throughout the crystal makes diamond one of the hardest known substances. Its high boiling point and low coefficient of cubical expansion are due to this bonding. In the absence of impurities, there is a large energy gap (6 eV) between the highest occupied and lowest unoccupied molecular orbitals resulting in a colourless material that is an excellent electrical insulator. The presence of impurities (e.g., nitrogen or boron) or defect-induced by ionizing radiation may produce colour. Defects can be annealed from a diamond to a point, depending on the degree of radiation damage. Diamonds have two main classifications...
Ultrasonography employs mechanical energy (sound) rather than electromagnetic radiation to produce a pictorial representation of the internal structure of the breast. The image is produced by transmission of sound pulses into the breast and measurement of the returning echoes at later times, depending upon the depth of interfaces between different tissue types. The transducer functions as both transmitter and receiver. An attractive feature of sono-graphic imaging is that there are no known carcinogenic effects of ultrasound at the power levels employed for diagnostic purposes.
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