Apertural Margin Research Articles

Dose–Volume Comparison of Proton Therapy and Intensity-Modulated Radiotherapy for Prostate Cancer

The contrast in dose distribution between proton radiotherapy (RT) and intensity-modulated RT (IMRT) is unclear, particularly in regard to critical structures such as the rectum and bladder. Between August and November 2006, the first 10 consecutive patients treated in our Phase II low-risk prostate proton protocol (University of Florida Proton Therapy Institute protocol 0001) were reviewed. The double-scatter proton beam plans used in treatment were analyzed for various dosimetric endpoints. For all plans, each beam dose distribution, angle, smearing, and aperture margin were optimized. IMRT plans were created for all patients and simultaneously analyzed. The IMRT plans were optimized through multiple volume objectives, beam weighting, and individual leaf movement. The patients were treated to 78 Gray-equivalents (GE) in 2-GE fractions with a biologically equivalent dose of 1.1. All rectal and rectal wall volumes treated to 10-80 GE (percentage of volume receiving 10-80 GE [V(10)-V(80)]) were significantly lower with proton therapy (p < 0.05). The rectal V(50) was reduced from 31.3% +/- 4.1% with IMRT to 14.6% +/- 3.0% with proton therapy for a relative improvement of 53.4% and an absolute benefit of 16.7% (p < 0.001). The mean rectal dose decreased 59% with proton therapy (p < 0.001). For the bladder and bladder wall, proton therapy produced significantly smaller volumes treated to doses of 10-35 GE (p < 0.05) with a nonsignificant advantage demonstrated for the volume receiving < or =60 GE. The bladder V(30) was reduced with proton therapy for a relative improvement of 35.3% and an absolute benefit of 15.1% (p = 0.02). The mean bladder dose decreased 35% with proton therapy (p = 0.002). Compared with IMRT, proton therapy reduced the dose to the dose-limiting normal structures while maintaining excellent planning target volume coverage.

Sexual dimorphism in shells of the southwestern Atlantic gastropod Olivella plata (Ihering, 1908) (Gastropoda: Olividae)

Sexual dimorphism in shells of the southwestern Atlantic gastropod Olivella plata (Ihering, 1908) (Gastropoda: Olividae)

Hábitos de vida dos Gastropoda e Bellerophontida da formação Maecuru, Devoniano Médio, Bacia do Amazonas, Brasil

The Maecuru Formation comprises the Devonian-Carboniferous sedimentary sequence of Amazonas Basin and consists of fluvialdeltaics to neritics sandstones and pelites layers. Its fossiliferous sediments (the uppermost part of the Lontra Member) consists of hummocky cross-stratified fine-grained to very coarse sandstones beds.With the purpose of adding more information about the palaeoecology of The Maecuru Formation fossils, the life habits of gastropods and bellerophontids were inferred based on functional analysis and similarities with the living forms. The more significant features used were: (1) total frontal cross-sectional area, (2) height and relative positions of pressure point and center of gravity, (3) apertural margin morphology, (4) kind of symmetry and (5) surface smoothness. The species Platyceras (Orthonychia) steinmanni; Platyceras (Tumbophalus) hartti; Platyceras (Platyostoma) darwini; Platyceras (Platyostoma) (?) agassizi; Platyceras (Orthonychia) meerwarthi; Platyceras (Orthonychia) gracilis; Platyceras (Tumbophalus) coutoanus; "Platyceras" tschernischewi; "Platyceras" subconicum; "Platyceras" (Ortonychia) hussaki; "Platyceras" (Ortonychia) whitii; "Platyceras" (Ortonychia) whitii var. curua and "Platyceras" symmetricum var. maecuruensis represent the epifaunal gastropods with low mobility (coprophagous/suspension feeders) of the Maecuru Formation, living symbiotically directly over the anus of a crinoid or nearby. This coprophagous mode of life was probably a non-obligate relationship, because only the closest organisms will get all the advantages of using the crinoid host as a nutrient source. The others adult platyceratids would have a broader feeding repertoire, like as suspension feeders. The bellerophonts Plectonotus (Plectonotus) derbyi, Plectonotus (?) (Plectonotus) salteri e Bucanella reissi would have an epifaunal medium to high mobility, showing a predator habit preferably. On the other hand Bucania freitasi, Ptomatis forbesi and Bellerophon steltzneri showed morphologies compable to a grazer habit with medium mobility. This relative high diversity of gastropods and bellerophonts corroborates the environment of medium and inner shelf inferred for the Maecuru Formation among the others macrofossils, since the majority of Paleozoic fauna of gastropods were typically from shallow seas.

Submicron optical near-field diffraction patterns obtained by irradiation of octadecyltrimethoxysilane self-assembled monolayers with light at 157 nm

Nanostructures less than 200 nm in size are created by the Fresnel diffraction of 157 nm light at the aperture margins of a photomask through proximity irradiation of an octadecyltrimethoxysilane self-assembled monolayer. Photochemical decomposition of the organic monolayer creates complex nanostructure patterns, according to the light intensity distribution at the substrate location. Dimensions and distribution of the nanostructures correlate well with the spatial distribution of the light intensity calculated using the Fresnel equations.

Pollen morphology of families Quillajaceae and Surianaceae (Fabales)

The Fabales clade comprises four families: Leguminosae, Polygalaceae, Quillajaceae and Surianaceae. This study presents new information on the pollen morphology of Quillaja, the only genus of Quillajaceae, and Recchia, Guilfoylia, Cadellia, Suriana and Stylobasium, the five genera that comprise Surianaceae. The pollen of 9 of the 11 species currently recognised within the two families was examined using light microscopy (LM), scanning electron microscopy (SEM) and, selectively, with transmission electron microscopy (TEM). Pollen of all taxa is isopolar with tri-zonocolporate apertures, lalongate endoapertures with fastigia adjacent to the endoaperture, and long ectoapertures that are nearly equal to the polar length. Apocolpia are correspondingly small. Quillaja pollen is subprolate to prolate, and striate with a granular aperture surface membrane. Ectexine protrudes over the endoapertures. In thin section the foot layer is thicker in mesocolpial areas and thin to discontinuous around the apertures, where the endexine is thicker. Cadellia pollen is prolate spheroidal, and striate with a granular aperture surface membrane. Exine protrudes over the endoapertures. In thin section the endexine is thicker and lamellate around the endoaperture area, and the foot layer is thicker in mesocolpial regions. Guilfoylia pollen is oblate and gemmate-verrucate, with a granular aperture surface membrane. Columellae are short. Recchia pollen is suboblate to oblate spheroidal, and microreticulate-perforate with a granular aperture surface membrane. Exine protrudes over the endoapertures. The foot layer is thin to discontinuous around aperture margins and thick in mesocolpial regions. Stylobasium pollen is suboblate, and finely rugulate-perforate with a granular aperture surface membrane. Columellae are short, the foot layer is thin or absent. Suriana pollen is suboblate, and finely rugulate-perforate with a granular aperture surface membrane. Pollen of Cadellia and Recchia, and Stylobasium and Suriana are morphologically similar. Verrucate surface ornamentation is only present in Guilfoylia. Quillaja, Cadellia and Recchia share the character of protruding exine over the endoaperture area. Striate ornamentation occurs in Quillaja and Cadellia. The pollen morphology of Quillajaceae has more in common with that of Leguminosae and Surianaceae, and with Cadellia in particular, than with Polygalaceae.

Shell repair and shell form in Jurassic pleurotomarioid gastropods from England

Traces of unsuccessful predatory attacks can be found in the hard parts of shell-bearing organisms as repaired shell injuries and are often preserved in the fossil record. These repaired shell injuries can help to deduce the relationship between predator and prey in the past. Gastropods afford an excellent opportunity for study since their shells are easily recognized from the Cambrian onwards, and usually preserve a full record of their life history. Predation is a phenomenon which has led to a great variety of adaptations among prey organisms in their quest to avoid being eaten. Increased predation pressure seems to have been one of the factors that has fueled the evolution of predation-resistant shell morphologies.Individual case studies examine the frequency of shell repair in assemblages of Palaeozoic gastropods from different geological periods. The Silurian species Poleumita discors showed a shell repair frequency of 10 %, while only 4 % of the Devonian species Praenatica gregaria have been repaired. The Palaeozoic bilaterally symmetrical bellorphontiform molluscs also showed low levels of shell repair.Similar shell morphologies in the long-lived group of pleurotomarioid gastropods were examined and shell repair frequenceis calculated to investigate potential variation through geological time. The Palaeozoic species showed repair frequencies of 17.1 % and 4.2 %. The frequency increased in the Mesozoic to between 28.8 % and 46.6 %, while all shells of Recent pleurotomarioids in the study showed repaired injuries. The repaired injuries found do not change in appearance through time, which is probably a reflection of the presence of the slit in the apertural margin. Which type of injury is the most abundant can be seen to change with time, and there is also an increase in size with time. This may be a defensive strategy taken up by the pleurotomarioids as a response to more abundant predators.

Presence or absence of the shell aperture: a criterion to identify shell breakage induced by durophagy in Umbonium (Mollusca: Gastropoda: Trochidae)

The pattern of shell breakage in the Recent trochid gastropods Umbonium (Suchium) moniliferum (Lamarck) and U. (S.) giganteum (Lesson) was observed under durophagous predation by crabs and in tumbling experiments, and the results of these experiments were applied to recent population samples from the natural environment. The experiments were carried out in order to learn if the pattern of shell breakage by durophagy (shell crushing) is different from that induced by water currents and waves. After predation by the predatory crabs Calappa lophos (Herbst) and Portunus trituberculatus (Miers), shell apertures of U. (S.) moniliferum and U. (S.) giganteum were broken in a characteristic fashion. In contrast, shells tumbled with sand and artificial seawater rarely lost the apertural margins, although other parts of the shells were relatively severely abraded. These results suggest that a shell from the natural environment with a similarly broken apertural margin was probably attacked by a durophagous crab, and that water currents and waves are not agents that cause breakage of shell apertures. The results were then applied to samples of Recent U. (S.) moniliferum from Lake Hamana-ko and fossil U. (S.) costatum (Kiener) from the Pleistocene Jizodo Formation in Japan. Shells with broken apertural margins amounted to 60% of all dead empty shells in the sample of Recent U. (S.) moniliferum, and over 90% in the sample of Pleistocene U. (S.) costatum, suggesting that these shells were extensively preyed upon by durophagous crabs. Shell repair frequencies of Recent U. (S.) moniliferum, calculated as a percentage of individuals with one or more repair scars, were 24–55%. The high repair frequencies indicate that considerable numbers of U. (S.) moniliferum can escape from attacks by crabs. All the results suggest that shell breakage along the apertural margins of gastropods is a good indicator of durophagy and that broken apertures, as well as shell repairs, are a useful tool for the investigation of predatory-prey interaction.

A new problematic Early Ordovician univalve mollusc from France

Lamaureriella vizcainoi gen. et sp. nov., from the Montagne Noire region of southern France, is a coiled, laterally compressed, bilaterally symmetrical mollusc in which prominent folds in the apertural margin produce a characteristic spiral plication across each lateral surface. Similar plications are present in technophorid rostroconchs but the prominent coiling and lack of a pegma suggest that Lamaureriella is a helcionelloid. It is the second such genus described from Early Ordovician rocks.

TANNUOLINA AND MICRINA (TANNUOLINIDAE) FROM THE LOWER CAMBRIAN OF EASTERN YUNNAN, SOUTH CHINA, AND THEIR SCLERITOME RECONSTRUCTION

The Tannuolinidae includes only two known genera—Micrina Laurie, 1986 and Tannuolina Fonin and Smirnova, 1967, both from the Lower Cambrian. They are phosphatic bimembrate small shelly fossils, consisting of two types of sclerites—the mitral and sellate sclerites. These sclerites show basal-internal accretional growth, spaced growth lamellae, carinae (in mitral sclerites of Tannuolina) or teeth (in mitral sclerites of Micrina), and unevenly distributed pores and canals. The scleritome of tannuolinids is poorly known because they are often preserved as disarticulated sclerites. Here we describe Micrina xiaotanensis new species and Tannuolina zhangwentangi Qian and Bengtson, 1989 from the Lower Cambrian Shiyantou and Yu'anshan formations (upper Meishucunian to Qiongzhusian stages) at Xiaotan, eastern Yunnan, South China. The new material not only extends the geographic range of Micrina, previously known only in Australia, but also includes two composite specimens of T. zhangwentangi: one with a pair of dextral and sinistral mitrals juxtaposed along the apertural margin of their decrescent sides, and the other with a smaller sellate ontogenetically merged with the sella of a larger sellate. Perhaps as a result of being contacting or imbricating surfaces, the decrescent, sella, and duplicature sides are also characterized by negative allometry (relative to other sides) and a sparse distribution of pores. The new fossils do not support reconstructions that place a sellate and a mitral sclerite, respectively, at the anterior and posterior end of the Tannuolina animal, in a way similar to Halkieria evangelista Conway Morris and Peel, 1995. Instead, they are consistent with the traditional view that the scleritome of Tannuolina consisted of four anterior–posterior files of sclerites: two opposing mitral rows flanked by two imbricated sellate series. The bimembrate Micrina may or may not have had a similar scleritome. If Tannuolina and Micrina form a monophyletic group outside the total group of brachiopods, then Micrina is likely to have had a multisclerite scleritome similar to that of Tannuolina. This implies that microstructural similarities between the tannuolinids and some linguliformean brachiopods are probably symplesiomorphic or convergent. Alternatively, Tannuolina and Micrina may represent stem groups leading to the linguliformeans while Halkieria represents a stem group leading to the calcareous brachiopods—a radical hypothesis that would imply that the two brachiopod groups independently evolved the bivalved body plan.

Shell breakage in two pleurotomarioid gastropods from the Upper Carboniferous of Texas, and its relation to shell morphology

Shells of two widespread Palaeozoic pleurotomarioid gastropods from North America, Worthenia tabulata (Conrad, 1835) and Glabrocingulum grayvillense (Norwood & Pratten, 1855), were scanned for evidence of shell breakage in the form of injuries repaired during the snail's life. Such injuries can result from a variety of agents but failed predation is normally believed to be the most common cause. Characteristic of these gastropods and other pleurotomarioids is the open slit in the aperture margin, which generates a selenizone. The length of the slit is often thought to influence the strength of the shell in the aperture area and through this, the frequency of shell repair. However, the large difference in shell repair frequency observed between Worthenia and Glabrocingulum cannot be attributed to the length of the slit alone. Apparently, Worthenia was much better suited to withstand attack than Glabrocingulum because of its shorter slit and general shell morphology. A higher spire and the relatively prominent angulations in the aperture seem to limit the extent of fractures effectively. The slit and the selenizone strongly influence the shape and location of shell injuires. The observed patterns show a remarkable similarity with repaired injuries in extant pleurotomarioids.

Perspectives of ammonite paleobiology from shell abnormalities in the genus Baculites

Many Baculites specimens from the Upper Cretaceous of the United States Western Interior show exceptional preservation of the original aragonitic shell and its fine-scale surface ornamentation. Growth lines are ubiquitous, with two orders of these structures represented on some shells, and reflect the incremental addition of new shell at the apertural margin. Growth line interruption in the form of repair of minor shell damage at the aperture, commonplace in contemporary Nautilus, is essentially absent in Baculites, suggesting that its members fed on small prey in the water column. As typical of Mesozoic ammonites in general, and in striking contrast to contemporary Nautilus, no in vivo epizoans have been recognized on specimens of Baculites. It is inferred that the shell of Baculites was covered in periostracum to eliminate epizoic colonization. By analogy with Nautilus, a distinctive micro-ornament oriented at right angles to growth lines and visible on parts of some specimens was probably associated with periostracal attachment. A small proportion of Baculites specimens show abnormalities in shell growth categorized as v-shaped indentations of growth lines, shell grooves, fine-scale folds on the surface of growth lines and feather structures. We view this entire set of structures as due to abnormalities in mantle growth induced at the leading edge, impressed into the periostracum during its fabrication, and then in turn into the shell surface. As many of the Baculites with shell abnormalities are smooth, the proposal by Checa linking homologous structures recognized on other ammonites to the formation of comarginal ribs is rejected. A case of sutural inversion, in which the form of minor divisions of the major saddles and lobes are transposed, is recognized in a specimen of Baculites codyensis Reeside. We consider sutural pattern in ammonites, an expression of septal fluting, as replicating the genetically specified standing form of an elastic adapical visceral mass. The inverted sutural pattern, and by implication the style of septal fluting, was transcribed exactly in the three successive septa preserved on the specimen. The abnormality appears to be a case of homeotic mutation in which the plan for one body region becomes translocated to another. The conservatism of major elements of sutural (=septal) patterns for Mesozoic ammonites in their evolutionary spectrum suggests that a homeobox of conserved DNA sequence, with the transcription factors encoded in homeotic genes, is likely to have been involved.

Post‐pathological keel‐loss compensation in ammonoid growth

Among the various pathologies documented in ammonoids, impairs affecting the apertural margin may have long-lasting sequelae on subsequent shell geometry. An interesting healing pattern, known as sculptural compensation, led to the permanent replacement of an ornament by adjacent sculptural elements. Moreover, in several ventrally impaired individuals the symmetry was preserved. Those developed annular ribs in place of any previous ventral ornamentation (keel, sulcus or smooth area). This phenomenon is known from diverse ammonite families. Monestieria resouchei (Monestier 1931), type species of ‘Monestieriinae’ Sapunov 1965, displays exactly that type of annularly-ribbed morphology and has been shown to be otherwise similar to species of Grammoceratinae Buckman 1904 occurring in the same beds, thus corroborating its pathological nature and leading to the rejection of that taxon. Now, keel absence in Praehaploceras Monestier 1931 and Buckmanites Guex 1973 cannot be explained by the same process as they do not have annular ribs. Moreover, the absence of any clue of malformation, their relative frequency and specific characteristics exclude the previously suggested synonymies with Pseudolioceras Buckman 1889 as equivalent pathological forms. In consequence, their rehabilitation is herein proposed. They should be included within Harpoceratinae Neumayr 1875.

Pollen Characters ofAmborella trichopoda(Amborellaceae): A Reinvestigation

Pollen of Amborella trichopoda was reinvestigated. Pollen is oblate to spheroidal and monoaperturate (ulcerate) at the distal pole, with a poorly defined aperture margin. The exine consists in the nonapertural region of ektexinous tectal elements (“cupules”), a smooth foot layer, and a thin, nonlamellate endexine. In the apertural area, the foot layer is lacking, as are most of the tectal elements. However, a thick endexine (including some ektexinous globular elements) and a conspicuous, channeled intine are present. The thick apertural endexine generally ruptures along the circular apertural area and forms an operculum. Orbicules show the same electron density as the tectal elements and recall their shape. Pollen characters of Amborella are compared with those of other basalmost angiosperms. The unique tectal elements (cupules) and the thick homogeneous endexine, which form an odd operculum in the apertural area, are unusual angiosperm pollen characters. Only Austrobaileya (Austrobaileyaceae) shares some...

Evolution and development of gastropod larval shell morphology: experimental evidence for mechanical defense and repair

The structural diversity of gastropod veliger larvae offers an instructive counterpoint to the view of larval forms as conservative archetypes. Larval structure, function, and development are fine-tuned for survival in the plankton. Accordingly, the study of larval adaptation provides an important perspective for evolutionary-developmental biology as an integrated science. Patterns of breakage and repair in the field, as well as patterns of breakage in arranged encounters with zooplankton under laboratory conditions, are two powerful sources of data on the adaptive significance of morphological and microsculptural features of the gastropod larval shell. Shells of the planktonic veliger larvae of the caenogastropod Nassarius paupertus [GOULD] preserve multiple repaired breaks, attributed to unsuccessful zooplankton predators. In culture, larvae isolated from concentrated zooplankton samples rapidly repaired broken apertural margins and restored the "ideal" apertural form, in which an elaborate projection or "beak" covers the head of the swimming veliger. When individuals with repaired apertures were reintroduced to a concentrated mixture of potential zooplankton predators, the repaired margins were rapidly chipped and broken back. The projecting beak of the larval shell is the first line of mechanical defense, covering the larval head and mouth and potentially the most vulnerable part of the shell to breakage. Patterns of mechanical failure show that spiral ridges do reinforce the beak and retard breakage. The capacity for rapid shell repair and regeneration, and the evolution of features that resist or retard mechanical damage, may play a more prominent role than previously thought in enhancing the ability of larvae to survive in the plankton.

Pollen morphology and wood anatomy of the Crudia group (Leguminosae, Caesalpinioideae, Detarieae)

Pollen from all 12 and wood from 11 genera in the Crudia group have been examined using light, scanning electron and transmission electron microscopy. This group is currently of systematic interest because it is part of a tribe undergoing taxonomic revision. The pollen grains fall into four groups: (1) Oxystigma, Kingiodendron, Gossweilerodendron, Bathiaea, Neoapaloxylon, Stemonocoleus, Guibourtia and Prioria have pollen of a widespread and generalized caesalpinioid type that are small to medium sized, spheroidal to prolate, tricolporate and with a perforate exine, with some variation in surface ornamentation, aperture margins and ultrastructure. (2) Crudia pollen is tricolporate, coarsely striate with a coarsely scabrate to vermiculate aperture membrane. (3) Augouardia is tricolporate and coarsely reticulate. (4) Hardwickia and Colophospermum are pantoporate and reticulate or microreticulate-rugulate. The wood of Prioria, Oxystigma, Kingiodendron and Gossweilerodendron has diffusely arranged axial canals, and these are four genera that have recently been merged into Prioria. Bathiaea has tangentially arranged axial canals. The other genera lack normal axial canals. Crudia is distinct, with banded parenchyma and variably storied short rays, Augouardia has much less abundant axial parenchyma that is mainly scanty paratracheal and vasicentric, Guibourtia has mainly aliform parenchyma and rays variable in height and width, and Colophospermum and Hardwickia have similar paratracheal parenchyma patterns, although the rays tend to be wider in the latter. Our conclusion is that the Crudia group is not monophyletic.

Pollen morphology and wood anatomy of the Crudia group (Leguminosae, Caesalpinioideae, Detarieae)

Pollen from all 12 and wood from 11 genera in the Crudia group have been examined using light, scanning electron and transmission electron microscopy. This group is currently of systematic interest because it is part of a tribe undergoing taxonomic revision. The pollen grains fall into four groups: (1) Oxystigma, Kingiodendmn, Gossweilerodendron, Bathiaea,. Neoapaloxylon, Stemonocoleus, Guibourlia and Prioria have pollen of a widespread and generalized cacsalpinioid type that are small to medium sized, spheroidal to prolate, tricolporate and with a perforate exine, with some variation in surface ornamentation, aperture margins and ultrastructure. (2) Crudia pollen is tricolporate, coarsely striate with a coarsely scabrate to vcrmiculate aperture membrane. (3) Augouardia is tricolporate and coarsely reticulate. (4) Hardwickia and Colophosperrnum are pantoporate and reticulate or microreticulate-rugulate. The wood of Prioria, Oxystigma, Kingiodendmn and Gossweilerodendron has diffusely arranged axial canals, and these are four genera that have recently been merged into Prioria. Bathiaea has tangentially arranged axial canals. The other genera lack normal axial canals. Crudia is distinct, with banded parenchyma and variably storied short rays, Augouardia has much less abundant axial parenchyma that is mainly scanty paratracheal and vasiccntric, Guibourtia has mainly aliform parenchyma and rays variable in height and width, and Colophosperrnum and Hardwickia have similar paratracheal parenchyma patterns, although the rays tend to be wider in the latter. Our conclusion is that the Crudia group is not monophyletic.

Compensation of x-ray beam penumbra in conformal radiotherapy.

In radiotherapy, the gross tumor volume is surrounded by a clinically defined margin to allow for the presence of undetected malignant cells. Additional margins are added to accommodate positioning uncertainties and organ motion, creating a planning target volume, or PTV. Finally, a margin is included in the beam apertures surrounding the PTV to account for the dose fall-off at the beam edges (i.e., the "penumbra"). For higher energy beams and for low density tissues adjacent to the PTV, the beam aperture margin should be increased to account for the increased range of scattered photons and electrons. However, increased margins also increase the volume of normal tissue irradiated. In this work, the beam aperture margin is reduced by using filters and multileaf collimator (MLC) techniques to create compensating rinds of increased beam intensity. These compensation techniques were evaluated for 6 and 18 MV x rays by calculating penumbral widths as a function of the increased beam intensity in the rind, the rind width, and tissue density. Dose calculations were performed using a 3D superposition algorithm, which includes an extrafocal source model. Calculations were validated experimentally with film dosimetry. Results show the distance between the 95%-50% isodose lines is reduced from 11 mm to 4 mm for 6 MV x rays in the lung phantom, when the beam intensity is increased by 20% in a 10 mm wide rind. At 18 MV, this distance is reduced from 16 mm to 6 mm with a 20% increase in rind intensity, but a 15 mm wide rind is required. In all cases, penumbra compensation did not result in any appreciable increase in scatter dose outside the field boundaries. These results suggest that penumbra compensation is a practical means of controlling the beam aperture margin.

Proton beam therapy for age-related macular degeneration: development of a standard plan

Age-related macular degeneration is the leading cause of blindness in developing countries. Irradiating the exudative form, in which a choroidal neovascular membrane develops in the subfoveal area, is presently a treatment under investigation. In 1995, Massachusetts General Hospital, collaborating with Massachusetts Eye and Ear Infirmary, initiated a protocol to treat SCNV membranes using the proton beam at the Harvard Cyclotron Laboratory and the EYEPLAN program with a light-field setup. EYEPLAN requires the axial eye length, membrane dimensions, and manipulation of the eye to include a 4.0-mm radial margin around the membrane so that the aperture margin (50% isodose line on the posterior retina) abuts the inferior aspect of the limbus. Review of 100 individually prepared plans showed that 95% of the fabricated apertures were circular (aspect ratio < 1.095) with diameters 9.5 to 15.0 mm. This information was used to develop an automated standard plan. Thirty-nine plans were developed for axial lengths ranging from 21.0 to 25.0 mm and membrane sizes from 1.5 to 6.75 mm in the usual way as the reviewed ones. Circular targets were outlined centered on the fovea. Distal and proximal 90% ranges (modulation) to the target, and doses to macula, optic disc, lens, ciliary body, retina, and globe were calculated. An automated standard plan requiring the same input data, but avoiding the need for individual plans, was developed. The program outputs the aperture diameter, fixation angle for the light-field setup, range and modulation, and calculates dose to the macula and optic nerve and percentage of retina receiving ≥ 50% and ≥ 90% of the prescribed dose. Individual plans require approximately 1.5 hours; the standard plan, 5 minutes. The standard plan could have treated 86% of the reviewed plans. The automated plan provides accurate and efficient treatment parameters for the majority of patients.

Microspore and tapetal development in Echinodorus cordifolìus (Alismaceae)

In the microspore tetrad period the exine begins as rods that originate from the plasma membrane. These rods are exine units that on further development become columellae as well as part of the tectum, foot layer and “transitory endexine”. The primexine matrix is very thin in the future sites of the pores. At these sites the plasma membrane and its surface coating (glycocalyx) are without exine units and adjacent to the callose envelope. The exine around the aperture margin is characterized by units of reduced height. After the exine units and primexine matrix have become ca 0.2 μm in height a fibrillar zone forms under the aperture margin. It is the exine units around the aperture that are templates for exine processes on apertures of mature pollen. Oblique sections of the early exine show that the tectum consists of the distal portions of close‐packed exine units. The exine enlarges in the free microspore period but initially its substructure (tectum, columellae, foot layer and transitory endexine) is not homogeneous and unit structures are visible until after the vacuolate microspore period. There are indications of a commissural line/plane (junction plane) which separates the foot layer from the endexine during early development. Our observations of development in Echinodorus pollen extend a growing number of reports of “transitory endexines” in monocot pollen. The exine unit‐structures become 0.2 μm or more in diameter and many columellae are composed of only one exine unit. Spinules become exceptionally tall, many protruding ca 0.7 μm above the level of the tectum as units only ca 0.1 μm in diameter. The outer portion of the tectum fills in around spinules and by maturity they are microechinate with their bases spread out to ca 1 μm or more. Unit structures can be seen with SEM in mature pollen following oxidation by plasma ashing and in the tapetum these units are arranged both radially, as in spinules, and parallel with the tapetal surfaces. There are clear indications of such an arrangement of units in untreated fresh pollen. Units comprising the basal part of the exine are not completely fused by sporopollenin accumulated during development. This would seem to be a characteristic feature, based on published work, of the alismacean pollen. Our use of a tracer shows, however, that there is considerable space within or between exine structure of mature Echinodorus pollen. Based upon the ca 0.1 μm size of exine‐units formed early in development and exine components seen after oxidative treatment it seems that the early (primary) accumulated sporopollenin has greater resistance to oxidation than sporopollenin added, secondarily, around and between units later in development. Both primarily and secondarily accumulated sporopollenin are resistant to acetolysis but published work indicates that acetolysis alters exine material. At the microspore tetrad time and until the vacuolate stages tapetal cells are arranged as in secretory tapetums. During early microspore stages there are orbicules at the inner surface of tapetal cells. At free microspore period tapetal cells greatly elongate into the loculus and surround the microspores. By the end of the microspore vacuolate period tapetal cells release their cellular contents and microspores are for a time enveloped by tapetal organelles and translocation material.

Multimodality nuclear medicine imaging in three-dimensional radiation treatment planning for lung cancer: challenges and prospects

The purpose of this study was to determine the utility of quantitative single photon emission computed tomography (SPECT) lung perfusion scans and F-18 fluorodeoxyglucose positron emission computed tomography (PET) during X-ray computed tomography (CT)-based treatment planning for patients with lung cancer. Pre-radiotherapy SPECT ( n=104) and PET ( n=35) images were available to the clinician to assist in radiation field design for patients with bronchogenic cancer. The SPECT and PET scans were registered with anatomic information derived from CT. The information from SPECT and PET provides the treatment planner with functional data not seen with CT. SPECT yields three-dimensional (3D) lung perfusion maps. PET provides 3D metabolic images that assist in tumor localization. The impact of the nuclear medicine images on the treatment planning process was assessed by determining the frequency, type, and extent of changes to plans. Pre-radiotherapy SPECT scans were used to modify 11 (11%) treatment plans; primarily altering beam angles to avoid highly functioning tissue. Fifty (48%) SPECT datasets were judged to be ‘potentially useful’ due to the detection of hypoperfused regions of the lungs, but were not used during treatment planning. PET data influenced 34% (12 of 35) of the treatment plans examined, and resulted in enlarging portions of the beam aperture (margins) up to 15 mm. Challenges associated with image quality and registration arise when utilizing nuclear medicine data in the treatment planning process. Initial implementation of advanced SPECT image reconstruction techniques that are not typically used in the clinic suggests that the reconstruction method may influence dose response data derived from the SPECT images and improve image registration with CT. The use of nuclear medicine transmission computed tomography (TCT) for both SPECT and PET is presented as a possible tool to reconstruct more accurate emission images and to aid in the registration of emission data with the planning CT. Nuclear medicine imaging techniques appear to be a potentially valuable tool during radiotherapy treatment planning for patients with lung cancer. The utilization of accurate nuclear medicine image reconstruction techniques and TCT may improve the treatment planning process.