Radiotherapy beyond cancer: target localization in real-time MRI and treatment planning for cardiac radiosurgery

PURPOSE

Atrial fibrillation (AFib) is the most common cardiac arrhythmia that affects millions of patients world-wide. AFib is usually treated with minimally invasive, time consuming catheter ablation techniques. While recently noninvasive radiosurgery to the pulmonary vein antrum (PVA) in the left atrium has been proposed for AFib treatment, precise target location during treatment is challenging due to complex respiratory and cardiac motion. A MRI linear accelerator (MRI-Linac) could solve the problems of motion tracking and compensation using real-time image guidance. In this study, the authors quantified target motion ranges on cardiac magnetic resonance imaging (MRI) and analyzed the dosimetric benefits of margin reduction assuming real-time motion compensation was applied.

METHODS

For the imaging study, six human subjects underwent real-time cardiac MRI under free breathing. The target motion was analyzed retrospectively using a template matching algorithm. The planning study was conducted on a CT of an AFib patient with a centrally located esophagus undergoing catheter ablation, representing an ideal case for cardiac radiosurgery. The target definition was similar to the ablation lesions at the PVA created during catheter treatment. Safety margins of 0 mm (perfect tracking) to 8 mm (untracked respiratory motion) were added to the target, defining the planning target volume (PTV). For each margin, a 30 Gy single fraction IMRT plan was generated. Additionally, the influence of 1 and 3 T magnetic fields on the treatment beam delivery was simulated using Monte Carlo calculations to determine the dosimetric impact of MRI guidance for two different Linac positions.

RESULTS

Real-time cardiac MRI showed mean respiratory target motion of 10.2 mm (superior-inferior), 2.4 mm (anterior-posterior), and 2 mm (left-right). The planning study showed that increasing safety margins to encompass untracked respiratory motion leads to overlapping structures even in the ideal scenario, compromising either normal tissue dose constraints or PTV coverage. The magnetic field caused a slight increase in the PTV dose with the in-line MRI-Linac configuration.

CONCLUSIONS

The authors' results indicate that real-time tracking and motion compensation are mandatory for cardiac radiosurgery and MRI-guidance is feasible, opening the possibility of treating cardiac arrhythmia patients completely noninvasively.

Enzymhistochemische Diagnostik gastrointestinaler Motilitätsstörungen

The enzyme histochemical reactions for acetylcholinesterase, lactic dehydrogenase, succinic dehydrogenase and nitroxide synthase are currently the gold standards for the diagnosis of gastrointestinal motility disorders. The acetylcholinesterase staining reaction shows the cholinergic nerve fibre network of the muscularis mucosae and muscularis propria, and correlates with their acetylcholinesterase activity. Lactic dehydrogenase, succinic dehydrogenase and nitroxide synthase selectively demonstrate the nerve cells of the myenteric and submucous plexus. These enzyme histochemical techniques require fresh, native tissue. Consequently, the transport of biopsies from gastroenterology or surgery to pathology must be well organized and feasible without time loss. Alternatively, biopsies may be mailed on dry ice to more distant pathology institutes. The enzyme histochemical laboratory technique has been optimized and refined over four decades. The optimized reactions are highly reliable and reproducible. In particular, a standardized methodology is a prerequisite for the interinstitutional comparability of results. This laboratory manual provides a detailed methodological description of the most important enzyme histochemical reactions for the diagnosis of gastrointestinal motility disorders.

Perisomatic granules (non-plaque dystrophic dendrites) of hippocampal CA1 neurons in Alzheimer's disease and Pick's disease: a lesion distinct from granulovacuolar degeneration

A number of pathological changes have been reported in relation to CA1 pyramidal cells in Alzheimer's disease (AD), among them hyperphosphorylation of tau protein followed by the formation of filamentous tau lesions, granulovacuolar degeneration (GVD), Hirano bodies and spindle-shaped dilatations of distal apical dendrites. Juxtacellular clusters of glutamate receptor (GluR)-positive granules around pyramidal cells of the CA1 sector have been recently reported under the term "non-plaque dystrophic dendrites". We independently found that CA1 pyramidal cells in AD patients are regularly surrounded by ubiquitin-positive granules measuring 1-4 microns in diameter, which we have termed perisomatic granules (PSG). Using confocal microscopy, ubiquitin- and GluR-reactive granules were found to largely coincide and to correspond to the same structure. By immunoelectron microscopy PSG were found to consist of GluR1-2-reactive enlarged synaptic boutons containing tubulo-filamentous or floccular material. PSG were found to be consistently associated with pyramidal (principal) cells but not with interneurons of the CA1 sector. Dual-labeling experiments have shown that PSG are preferentially associated with tau-immunoreactive "pretangle" neurons but not with cells containing filamentous tau inclusions or with tau-negative nerve cell bodies. The number of PSG was found to increase with the severity of AD changes with almost no PSG found in Braak stages I and II and few in stage III. Furthermore, PSG were not AD specific, as shown by their presence around CA1 pyramidal cells in Pick's disease. The reasons for GluR reactivity and ubiquitin complex formation in enlarged perisomatic boutons are unclear. Marked changes in GluR subunits have been observed in association with even moderate AD pathology in hippocampal pyramidal cells in AD and our findings suggest a pathogenic link between PSG and early tau pathology in CA1 neurons. PSG might represent residual and abnormally clustered GluR subunits in degenerating perisomatic neurites. Our work confirms and extend previous study on perisomatic "non-plaque dystrophic dendrites" in AD and establish PSG as a pathological entity distinct from GVD. In addition PSG should be acknowledged among main histological changes associated with hippocampal neurons in AD and Pick's disease.

Astrocytes expressing hyperphosphorylated tau protein without glial fibrillary tangles in argyrophilic grain disease

Argyrophilic grain disease (AgD), a frequent type of late onset dementia, is characterized by the occurrence of Gallyas-stained neuropil grains in the hippocampus, entorhinal cortex, amygdala and hypothalamus. High numbers of neurons containing hyperphosphorylated tau protein, but devoid of tangles, are encountered in areas rich in argyrophilic grains (ArGs). A third type of change consists of slender argyrophilic and tau-immunoreactive cytoplasmic inclusions in white matter oligodendrocytes, the coiled bodies. We now extend earlier studies on glial pathology in AgD (20 cases) and compare the results with glial changes in old age (10 cases) and Alzheimer's disease (AD; 7 cases). Numerous non-argyrophilic, non-neuronal tau-positive stellate cells in the amygdala and anterior entorhinal cortex were consistently found in all of the 20 AgD cases but not in AD cases. Double-labelling experiments performed on paraffin sections with phosphorylation-dependent anti-tau antibody AT8, anti-glial fibrillary acidic protein and anti-CD44, revealed coexpression of these markers in stellate cells. The high expression of CD44 indicate that they probably correspond to reactive astrocytes. Unlike astrocytic plaques in corticobasal degeneration (CBD), where AT8 reactivity is accumulating in distal astrocytic processes, tau reactivity in AgD was found in all astrocytic cell compartments. The absence of glial fibrillary tangles further distinguished tau-labelled astrocytes in AgD from astrocytic plaques in CBD and tufted astrocytes in progressive supranuclear palsy (PSP). In contrast to AD and aged non-demented control cases tau-positive non-argyrophilic astrocytes represent a consistent finding in anterior limbic structures in AgD. Our findings point to a more widespread pathology of the glial cell population in AgD than previously supposed, and will be of further help in differentiating AgD from other neurodegenerative disorders, including AD, PSP, CBD and Pick's disease.

Argyrophilic grains of Braak: occurrence in dendrites of neurons containing hyperphosphorylated tau protein

Braak's argyrophilic grains (ArGs) are spindle-shaped neuropil structures originally found in patients afflicted with adult onset dementia. We recently observed that tau protein is hyperphosphorylated in most nerve cells in areas rich in ArGs, suggesting that these grains may be a morphological expression of tau protein pathology in local neurons. The aim of this study was therefore to determine in three cases with ArGs whether grains are associated with individual neurons containing hyperphosphorylated tau. A combination of Gallyas silver staining and AT8 immunocytochemistry was used. AT8 is a monoclonal antibody that recognizes tau in a phosphorylation-dependent manner. Up to 80% of pyramidal cells of sector CA1 showed diffuse AT8 staining of their cell bodies and dendrites. Most grains were freely scattered throughout the neuropil. However, some were clearly located in side-branches of apical dendrites of AT8 immunoreactive pyramidal neurons. Dendritic branches often formed bush-like ramifications containing clusters of ArGs. Other dendrites consisted of a single stump containing one or two large grains at their tips. Spheroidal enlargements of dendritic branches, with a size corresponding to ArGs, were also found in Golgi Cox preparations of cases with ArGs but not in Alzheimer's disease cases or in controls. Our results show that some ArGs are formed within dendrites of neurons whose most obvious pathology is a diffuse hyperphosphorylation of the tau protein. Furthermore, morphology of dendrites containing grains suggests that a process of progressive shrinkage of dendrites is taking place in neurons bearing ArGs.

Thrombolysis-related early patency reduces ECG late potentials after acute myocardial infarction

To assess the effects of thrombolysis and reperfusion on late potentials after myocardial infarction, 101 patients (79 men, age 63.2 +/- 10.5 years) underwent signal-averaged ECG studies at 10.7 +/- 9.2 days, with the use of a 40 to 250 Hz band-pass filter. Patients were divided into four groups: (1) 54 patients treated with thrombolytic agents at 2.8 +/- 1.1 hours, with 81% "early" patency/reperfusion (TIMI grades 2 and 3); (2) 47 patients treated conventionally with 45% "late" patency/reperfusion; (3) 56 patients with patency (TIMI grades 2 and 3); and (4) 26 patients without patency (TIMI grades 0 and 1). A late potential was present when greater than or equal to 2 of 3 defined criteria were present. There was a significant difference in the incidence of late potentials between groups 1 and 2 (22% vs 43%, respectively; p = 0.048) and between groups 3 and 4 (18% vs 50%, respectively; p = 0.006). Late potentials also tended to occur less often after "early" than after "late" patency/reperfusion (12.5% vs 25%). The odds ratio for developing a late potential was 0.39 for thrombolysis versus no thrombolysis (p less than 0.05) and 0.22 for patency/reperfusion (TIMI grades 2 and 3) versus no patency/reperfusion (TIMI grades 0 and 1) (p less than 0.05). By analysis of covariance the effects of thrombolysis on late potentials were entirely explained by reperfusion. Thus the risk of late potentials after myocardial infarction is high but is reduced by thrombolysis and reperfusion. In addition, the effectiveness of "early" reperfusion appears to be greater than that of "late" but requires further clarification.

Deposition of beta/A4 protein along neuronal plasma membranes in diffuse senile plaques

The origin of the extracellular beta-amyloid protein (beta/A4) found in senile plaques and the cellular mechanisms responsible for its deposition in cerebral tissues are still an unresolved issue in Alzheimer's disease. In this study we analyzed in detail the distribution of various epitopes of beta/A4 in relation to local cellular elements in diffuse plaques of the hippocampal region. We also correlated our findings with the presence and distribution of non-beta/A4 epitopes of the amyloid precursor protein (APP) and with synaptophysin immunoreactivity in the cortical neuropil. Discontinuous beta/A4-immunoreactive deposits were found along dendrites, and around the soma of neurons included in the plaques. Furthermore, increased synaptophysin reactivity with slightly dilated synaptophysin-immunolabeled presynaptic terminals were found in diffuse plaques. APP epitopes could not be found in diffuse plaques. However, some of the APP antibodies, mainly those to the C-terminal portion of APP, and antibodies to beta/A4 recognized clusters of flat vesicular profiles (0.6-1.4 micron in width and 2-3 microns in length) in the neuropil of cortical areas where plaques had developed. Our findings are compatible with a neuronal origin of beta/A4 in diffuse plaques and with a primary release of beta/A4 at synaptic sites along the immunostained neurites. They also suggest that diffuse plaques might be preceded by minute lesions of the neuropil where beta/A4 is not yet released from the precursor molecule.

Effects of early thrombolytic therapy (anistreplase versus streptokinase) on enzymatic and electrocardiographic infarct size in acute myocardial infarction. TEAM-2 Investigators

The effects of thrombolytic therapy on enzymatic and electrocardiographic indexes of myocardial infarction were examined in 370 patients who were enrolled within 4 hours of onset of symptoms and were randomized to blinded therapy with intravenous anistreplase (30 U/5 min, n = 188) or streptokinase (1.5 million IU/1 hour, n = 182). Creatine kinase and its MB isoenzyme were initially measured every 4 to 6 hours, and lactic dehydrogenase (LDH) and its cardiac isoenzyme (LDH-1) every 8 to 12 hours. Electrocardiograms were obtained before, and at 90 minutes and 8 hours after starting thrombolysis, and on discharge. Enzymatic and electrocardiographic measures of infarction were compared between drug treatment and patency groups. Early patency was associated with significant reductions in peak values for each of 4 cardiac enzymes (averaging 21 to 25%, p less than 0.01 to 0.001), even though later rescue procedures were often used in the nonpatient group; times to peaks were also reduced for 3 of the enzymes. Treatment with anistreplase was associated with enzymatic peaks that tended to be lower than with streptokinase (6 to 16%), approaching or reaching significance for LDH (p less than or equal to 0.07) and LDH-1 (p less than or equal to 0.04); times to peaks were similar. Early patency favorably affected electrocardiographic indexes. Summed ST-segment elevations resolved more rapidly (p less than or equal to 0.04), summed Q-wave amplitude was reduced by 32% (p less than or equal to 0.01), and total QRS infarct score on discharge was 22% less (p less than or equal to 0.006) in those achieving early patency. Small differences in electrocardiographic indexes between the 2 drug treatment groups were not significant. These results support use of early reperfusion to reduce infarct size in acute myocardial infarction with administration of streptokinase and anistreplase.

Senile plaques: staining for acetylcholinesterase and A4 protein: a comparative study in the hippocampus and entorhinal cortex

In 20 unselected autopsy cases tissue blocks from the hippocampus with adjacent entorhinal cortex and neocortex were stained for acetylcholinesterase (AChE). From five brains shown to have large numbers of senile plaques tissue, adjacent to that taken for AChE tissue blocks, was embedded in paraffin and sections were immunostained for the A4 protein. The morphological aspects were compared. Equivalent types of plaques and plaque-like structures were observed in the A4- and ACHE-stained sections. On selected tissue blocks from patients with many senile plaques two immediately adjacent cryostat sections were stained, one for AChE and one for A4 protein. The same individual plaques could be identified on the two sections. These findings suggest that high AChE activity is intimately associated with the process of A4 protein formation and accumulation in plaques and that this association already occurs at a very early stage of plaque formation.