Technical Note: Real-time image-guided adaptive radiotherapy of a rigid target for a prototype fixed beam radiotherapy system.

PURPOSE: Fixed beam radiotherapy systems utilize couch movement and rotation instead of gantry rotation in order to simplify linear accelerator design. We investigate the ability to deliver fixed beam treatments with the same level of clinical accuracy as conventional (rotating beam) treatments using real-time image guidance to maintain this accuracy in the presence of rigid target motion. METHODS: A prototype fixed beam radiotherapy system was built using a standard linac with the beam fixed in the vertical position and a computer controlled rotation stage that rotated a rigid phantom about the superior-inferior axis. Kilovoltage Intrafraction Monitoring (KIM) and real-time beam adaptation with MLC tracking was applied to a five-field IMRT treatment plan with motion introduced to the phantom. The same IMRT treatment was also delivered with real-time adaptation using the conventional rotating beam geometry. Film dosimetry was used to measure the dose delivered with a fixed beam compared to a rotating beam, as well as to compare treatments delivered with and without real-time adaptation. RESULTS: The dose distributions were found to be equivalent between the fixed beam and rotating beam geometry for real-time adaptive radiotherapy using KIM and MLC tracking beam adaptation. Gamma analysis on the films showed agreement >98% using a 2%/2 mm criteria with adaptation for static shifts and periodic motion. CONCLUSIONS: Fixed beam treatments with real-time beam adaptation are dosimetrically equivalent to conventional treatments with a rotating beam, even in the presence of rigid target motion. This suggests that, for a rigid target, the high clinical accuracy of real-time adaptive radiotherapy can be achieved with simpler beam geometry.

There is no correlation between sublineages and drug resistance of Mycobacterium tuberculosis Beijing/W lineage clinical isolates in Xinjiang, China.

The Beijing/W lineage strains are the major prevalent strains in China. The prevalence, mortality and drug-resistant rates of tuberculosis in Xinjiang, Northwestern China are higher than in other parts of the country. Our previous study results showed that the dominant strains of Mycobacterium tuberculosis (MTB) were 'Beijing/W lineage' MTB in Xinjiang; those strains had no significant correlation with drug resistance. We investigated whether the prevalence of 'Beijing/W lineage' sublineage strains was associated with drug resistance. We collected 478 sputum specimens from patients with pulmonary tuberculosis. Beijing/W strains and their sublineages were identified by distinguishing five specific large sequence polymorphisms, using polymerase chain reaction. All strains were subjected to a drug susceptibility test using the proportion method on Löwenstein-Jensen culture medium. In total, 379 clinical isolates of MTB were isolated and identified, 57·26% of these isolates were identified as Beijing/W strains, of which 11·06% isolates were in sublineage 105, 14·74% isolates in sublineage 207, 69·59% isolates in sublineage 181, and 4·61% isolates in sublineage 150. None of the isolates was in sublineage 142. Our data showed there were four sublineages of Beijing/W isolates in Xinjiang province, China. However, there were no correlations between drug resistance and the sublineages of Beijing/W strains.

Small field dosimetric characterization of a new 160-leaf MLC.

The goal of this work was to perform a 6 MV small field characterization of the new Agility 160-leaf multi-leaf collimator (MLC) from Elekta. This included profile measurement analysis and central axis relative output measurements using various diode detectors and an air-core fiber optic scintillation dosimeter (FOD). Data was acquired at a depth of 10.0 cm for field sizes of 1.0, 0.9, 0.8, 0.7, 0.6 and 0.5 cm. Three experimental data sets, comprised of five readings, were made for both the relative output and profile measurements. Average detector-specific output ratios (OR[overline](f(clin))(det))) were calculated with respect to a field size of 3.0 cm and small field replacement correction factors (k(f(clin),f(msr))(Q(clin),Q(msr))) derived for the diodes using the scintillation dosimeter readings as the baseline. The standard experimental uncertainty on OR[overline](f(clin))(det)) was calculated at a 90% confidence interval and the coefficient of variation (CV) used to characterize the detector-specific measurement precision. The positional accuracy of the collimation system was also investigated by analyzing the repeated profile measurements and field width constancy investigated as a function of collimator rotation. For comparison the output and profile measurements were repeated using the Elekta 80-leaf MLCi2 on a beam matched linac at 6 MV. The measured OR[overline](f(clin))(det)) varied as a function of detector and MLC design. At the smallest field size the standard experimental uncertainty on OR[overline](f(clin))(det)) was consistent across all detectors at approximately 0.5% and 1.0% for Agility and MLCi2 collimators respectively. The CV associated with the FOD measurements were greater than that of the diodes but did not translate into increased measurement uncertainty. At the smallest field size, the diode detector correction factors were approximately 2% greater for MLCi2 than that required for the Agility. Profile data revealed the Agility MLC to have a greater positional reproducibility than both the MLCi2 and the linac diaphragms (jaws), as also reflected in the experimental uncertainties on OR[overline](f(clin))(det)). The relative output, profile widths and associated uncertainties were all found to differ between the two MLC systems investigated, as were the field size specific diode detector replacement correction factors. The data also clearly showed that the Agility 160-leaf MLC performs to a tighter positional tolerance than the MLCi2.

Twisted pair of optic fibers for background removal in radiation fields.

In many situations in which an optic fiber carries a signal through a radiation field, an unwanted background signal is produced consisting of fluorescent and/or Cerenkov light. This presents a major problem in the measurement of the light signal, for example, in scintillation dosimetry of medical therapeutic beams. In this paper, we demonstrate a new method of measuring and removing the background signal through the use of a twisted pair of optic fibers. The twisted pair consists of a fiber carrying the scintillation signal that is twisted with a second optic fiber to form a double helix. The two twisted fibers will experience the same radiation environment provided the periodicity of the twist is correlated to the dose rate gradient. An expression for the required twist periodicity is presented. A scintillation dosimeter with a twisted pair optic fiber was tested in a megavoltage beam and found to accurately measure its beam characteristics. The twisted pair approach is not restricted to medical applications and can be used in many situations in which optical signals are carried through radiation fields.

A method to remove residual signals in fibre optic luminescence dosimeters.

Whenever a fibre optic is used to convey a light signal through a radiation field, it is likely that an unwanted background signal will arise from Cerenkov or fluorescent light which will contaminate the signal. In luminescence dosimetry of high energy beams, when a fibre optic is used to convey the signal from the radiation field to the detector, Cerenkov light is the dominant contributor to the background signal and must be corrected for. In this work, a novel method is demonstrated to separate the signal from the unwanted background. A remotely operated shutter is used to block the signal, allowing the residual background in the fibre optic to be quantified. This background is subtracted from the total measurement acquired in a subsequent irradiation, enabling the luminescence signal to be extracted. Two types of shutter mechanism are considered: an electro-mechanical device to intercept the light path and an LCD device to block the light by cross-polarization. Both shutters were characterized and incorporated into a fibre optic dosimetry system used to measure the radiation dose produced by external beam radiation linear accelerators. The dosimeter using each of the shutters in turn was exposed to a 6 MV photon beam to determine their performance, including the measurement of field size dependent output factors. The mechanical shutter determined the output factors to within 0.29% of those measured with an ionization chamber, whereas the LCD shutter gave results that deviated by up to 2.4%. The switching precision of both shutters was good with standard deviations of less than 0.25% and both were able to completely block the light signal when closed. The use of shutters could therefore be applied to any fibre optic based system to quantify and remove a reproducible background arising from any source including ambient, fluorescent and Cerenkov light.

Plastic scintillation dosimetry: comparison of three solutions for the Cerenkov challenge.

In scintillation dosimetry, a Cerenkov background signal is generated when a conventional fibre optic is exposed to radiation produced by a megavoltage linear accelerator. Three methods of measuring dose in the presence of Cerenkov background are compared. In the first method, a second background fibre is used to estimate the Cerenkov signal in the signal fibre. In the second method, a colour camera is used to measure the combined scintillation and Cerenkov light in two wavelength ranges and a mathematical process is used to extract the scintillation signal. In the third method, a hollow air core light guide is used to carry the scintillation signal through the primary radiation field. In this paper, the strengths and weaknesses of each dosimetry system are identified and recommendations for the optimum method for common clinical dosimetry situations are made.

Abd-B expression in Porcellio scaber Latreille, 1804 (Isopoda: Crustacea): conserved pattern versus novel roles in development and evolution.

The Hox genes are intimately involved in patterning the animal body during development and are considered to have had a pivotal role in the evolution of different body plans among the metazoans. From this perspective, crustaceans, a group that has evolved an extreme diversity of body structures, represent a choice group in which to study the evolution of these genes and their expression. The expression of one of these genes, Abdominal-B (Abd-B), has only been studied in two distantly related crustaceans, Artemia and Sacculina, where it shows dissimilar patterns, highly differentiated from the one described in other arthropods. Moreover, we have no information for the Malacostraca. Thus, we cloned the gene Abd-B and followed its expression through development by in situ hybridization in the isopod Porcellio scaber. We found a highly dynamic expression pattern of PsAbd-B during embryonic development. In early stages, it is expressed in the posterior-most part of the germ band, in a domain common to several arthropods studied to date, and later it is expressed in the developing limb buds of the pleon and still later in the endopodites of the third to fifth pleopodites. This raises the interesting possibility of the involvement of this gene in the later respiratory specialization of these appendages. In association with the above expression domain, Abd-B appears to be expressed in later stages also in the ventral ectoderm, raising the further suggestion of its possible involvement in patterning the developing nervous system. Moreover, we show that the first pleopod and the endopodite of the second pleopod, whereas present as limb buds in early embryonic stages, are later reduced and actually absent in the first postembryonic stage, although they reappear again in adults. These appendages thus represent an example of Lazarus appendages. Our data show strong plasticity in the use of a key developmental gene and point out the necessity of further research that may end with a revision of the current understanding of its role in animal evolution.

New insights into the Rh superfamily of genes and proteins in erythroid cells and nonerythroid tissues.

The past decade has seen extensive studies of the erythrocyte Rh30 polypeptides and Rh-associated glycoprotein, which specify the clinically important Rh blood group system. Here we consider recent advances on these and other Rh homologues in the context of gene organization, molecular evolution, tissue-specific expression, protein structure, and potential biological functions. The Rh family is now known to contain a large number of homologues that form a unique branch in the eucarya life domain. The ancient origin and broad distribution imply central roles for the various Rh proteins in maintaining normal cellular and organismal homeostatic conditions. Rh homologues occur in the form of multiple chromosomal loci in mice and humans, but as single-copy genes in unicellular organisms (e.g., green alga and slime mold). While primitive Rh genes vary largely in exon/intron design, the mammalian Rh homologues bear a similar genomic organization. Sequence comparisons have revealed the signatures and a consensus 12-transmembrane fold characteristic of the Rh family. Phylogenetic analysis has placed all Rh homologues as a related cluster that intercepts ammonium transporter (Amt) clusters, indicating an intimate evolutionary and structural relationship between the Rh and Amt families. The biochemical identification and epithelial expression of RhBG and RhCG orthologues in mammalian kidney, liver, skin, testis, and brain suggest that they serve as transporters likely participating in ammonia homeostasis. Further inquires into the structure, function, biosynthesis, and interaction of Rh proteins will shed new light on ammonia homeostasis in a wide range of human physiological and pathological states.

Molecular biology and genetics of the Rh blood group system.

The Rh (Rhesus) blood group system is the most complex of the known human blood group polymorphisms. The expression of its antigens is controlled by a two-component genetic system consisting of RH and RHAG loci, which encode Rh30 polypeptides and Rh50 glycoprotein, respectively. Over the past decade, there has been a rapid advance in knowledge of the biochemistry, molecular biology, and genetics of the Rh genes and proteins. The primary structures of D and CcEe antigens have become well understood and the molecular genetic basis of a vast array of phenotype polymorphisms has been delineated. The identification of various molecular defects associated with Rh deficiency syndrome clarifies the nature of the amorph, suppressor, and modifier genes. The observed mutation spectrum defines a basic set of components essential for Rh complex assembly in the erythrocyte membrane. The resulting molecular information, combined with new experimental tools, is helping to dissect the fine structure of Rh antigens in terms of epitope mapping. The discovery of novel Rh homologs in primitive organisms and in nonerythroid tissues opens new avenues of research beyond the scope of erythrocytes and Rh antigens. This review provides an update on the Rh family in antigen expression, phenotype diversity, and disease association.

[Timing of follow-up of hyperthyroidism treated with 131I].

The purpose of this study was to explore the optimal reexamination time for the patients who had 131I therapy. The weight of thyroid, serum levels of T3 and T4 were observed in 128 patients with hyperthyroidism in various time before and after 131I therapy. The result indicated that the optimal reexamination time for the patients was 60 to 90 days after 131I treatment if the patient has no special complaints.

Evaluation of penile dorsal arteries and deep arteries in arteriogenic impotence.

The dorsal and deep arteries are the 2 main blood supplies to the penis. High resolution ultrasonography was used to evaluate the role of these 2 sets of arteries in erection. A total of 44 impotent patients entered this study. We used duplex ultrasonography (Diasonic DRF/400) to assess the role of the dorsal and deep arteries in arteriogenic and nonarteriogenic impotent patients. Vascular velocity, as well as the change in diameter, was recorded before and after an intracavernous injection of 60 mg. papaverine. In the arteriogenic impotence group (28 patients, 63.6%), the velocity increments were 37.1 +/- 23.6 (right side) and 35.4 +/- 17.5 (left side) cm. per second in the dorsal arteries, and 8.3 +/- 5.9 (right side) and 12.6 +/- 5.6 (left side) cm. per second in the deep arteries. In the nonarteriogenic group (16 patients, 36.4%) the velocity increments were 46.5 +/- 25.2 and 41.1 +/- 22.4, respectively, in the dorsal arteries, and 37.3 +/- 16.5 and 37.5 +/- 15.8, respectively, in the deep arteries. Comparison of the velocity increments between the arteriogenic and nonarteriogenic groups revealed no difference in the dorsal arteries (p greater than 0.1) but a significant difference was noted in the deep arteries (p less than 0.01). Similar findings were also encountered when the velocities and diameter increments were compared. This study indicates that the deep arteries have an important role in erectile response, while the dorsal arteries are less important.

Clinical application of DSA and evaluation of its methods: analysis of 160 cases and review of literature.

A total of 160 patients of two hospitals received 192 DSA examinations with different contrast administrations, and techniques of performing DSA were analyzed, compared, and evaluated with reference to the literature. It was concluded that (1) the peripheral injection of contrast material for IVDSA via cannula is simpler than that via a short catheter, but the incidences of contrast extravasation in both cases are higher than with central injection. (2) Both the lower part of the superior vena cava and the right atrial cavity are safe sites for central injection. With central injection for IVDSA, the arterial iodine concentration is approximately double that of peripheral injection, and consistent high quality examinations of the intracranial vessels may be obtained. However, neither peripheral nor central injections can visualize the small vessels clearly. (3) IVDSA may be substituted for conventional angiography only in examinations of the aorta and its main branches. (4) IADSA is becoming a superior angiographic technique and its clinical application is increasing. In addition, means of avoiding contrast extravasation during IVDSA and the main points of selecting the optimal technique for DSA are described in this paper.