Modifications to a commercially available linear mass spectrometer for mass-resolved microscopy with the pixel imaging mass spectrometry (PImMS) camera

RATIONALE

Imaging mass spectrometry is a powerful analytical technique capable of accessing a large volume of spatially resolved, chemical data from two-dimensional samples. Probing the entire surface of a sample simultaneously requires a detector with high spatial and temporal resolutions, and the ability to observe events relating to different mass-to-charge ratios.

METHODS

A commercially available time-of-flight mass spectrometer, designed for matrix-assisted laser desorption/ionization (MALDI) analysis, was combined with the novel pixel imaging mass spectrometry (PImMS) camera in order to perform multi-mass, microscope-mode imaging experiments. A number of minor modifications were made to the spectrometer hardware and ion optics so that spatial imaging was achieved for a number of small molecules.

RESULTS

It was shown that a peak width of Δm50 %  <  1  m/z unit across the range 200 ≤ m/z  ≤  800 can be obtained while also achieving an optimum spatial resolution of 25 µm. It was further shown that these data were obtained simultaneously for all analytes present without the need to scan the experimental parameters.

CONCLUSIONS

This work demonstrates the capability of multi-mass, microscope-mode imaging to reduce the acquisition time of spatially distributed analytes such as multi-arrays or biological tissue sections. It also shows that such an instrument can be commissioned by effecting relatively minor modifications to a conventional commercial machine.

Posttransplantation lymphoproliferative disorder initially seen as iris mass and uveitis

Primary ocular posttransplantation lymphoproliferative disorder is rare. Epstein-Barr virus is implicated as the cause as a result of systemic immunosuppression after transplant surgery. We studied a patient who developed ocular posttransplantation lymphoproliferative disorder after orthotopic liver transplantation. Slitlamp and light microscopic photographs confirmed the diagnosis.

Geometry function of a linear brachytherapy source

An equation is derived for the TG43 geometry function, G(r,theta), of a linear brachytherapy source in terms of its active length. This equation is validated by comparison to published values. It is then used to calculate values of the geometry function for the Model 200 (103)Pd seed, which is a segmented linear source.

An assessment of intraocular pressure rise in patients with gas-filled eyes during simulated air flight

PURPOSE

To investigate the safety of aircraft flight for patients with small volumes of residual postoperative intraocular gas.

DESIGN

Nonrandomized comparative trial.

PARTICIPANTS

Seventeen eyes (nine gas filled and eight control eyes) of nine patients and one eye of one control subject were tested.

METHODS

Patients with postoperative intraocular gas and the control subject were tested in the controlled environment of a hypobaric chamber to simulate the cabin depressurization associated with a typical commercial aircraft flight. Before, during, and after a simulated flight, the intraocular pressure (IOP) in the gas-containing and contralateral eyes was tested using the Perkins (Edinburgh, UK) and Tono-Pen XL (Jacksonville, FL) tonometers.

MAIN OUTCOME MEASURES

The absolute and percentage change in IOP with varied cabin pressurization.

RESULTS

Of the nine patients with intraocular gas, seven had 10% to 15% gas volume and two had 20% gas volume. In the 10% to 15% gas volume group, the IOP rose by an average of 109% from baseline during ascent to an average cabin altitude of 7429 feet above sea level. The IOP dropped to an average of 30% above baseline IOP during the cruise phase and further decreased to an average of 38% below baseline IOP on return to baseline altitude. In the 20% gas volume group, the IOP rose by an average of 84% from baseline during ascent to an average cabin altitude of 3400 feet above sea level. The IOP dropped to an average of 42% below baseline IOP on return to baseline altitude. The IOP in the contralateral control eyes did not vary with altitude changes. No patient experienced pain or visual loss during the experiments.

CONCLUSIONS

Our results demonstrate that IOP may rise significantly in gas-filled eyes during simulated air flight, supporting the current conservative recommendation against air travel for most patients with intraocular gas bubbles. Further testing is warranted to develop a more objective measure of intraocular gas volume estimation and to define better the tolerability of aircraft flight for patients with intraocular gas.

The role of drug treatment in children with strabismus and amblyopia

Strabismus, or misalignment of the eyes, is a common ophthalmic problem in childhood, affecting 2 to 5% of the preschool population. Amblyopia is an important cause of visual morbidity frequently associated with strabismus, and both conditions should be treated simultaneously. Pharmacological means for treating strabismus and amblyopia can be divided into 3 categories: paralytic agents (botulinum toxin) used directly on the extraocular muscles to affect eye movements; autonomic agents (atropine, miotics) used topically to manipulate the refractive status of the eye and thereby affect alignment, focus and amblyopia; and centrally acting agents, including levodopa and citicoline, which affect the central visual system abnormalities in amblyopia. Botulinum toxin, the paralytic agent that causes the clinical symptoms of botulism poisoning, can be injected in minute quantities to achieve controlled paralysis of the extraocular muscles. Although the role of botulinum toxin is established in adults with paralytic strabismus, its usefulness in the treatment of comitant childhood strabismus (primary esotropia and exotropia) is not universally accepted. Botulinum injections tend to be more effective with smaller degrees of strabismus, in patients with good binocular fusion, and in managing overcorrections or undercorrections after traditional muscle surgery. Inadvertent ptosis and paralysis of adjacent muscles, unpredictable responses and technical constraints of the injections limit its use in children. Miotic therapy, by altering the refractive state of the treated eye, offers an alternative to optical correction with bifocals in treating esotropia due to excessive accommodative convergence. It is also effective in treating residual esotropia following surgery. The ease of use of glasses restricts the wide application of miotics in these common strabismus syndromes. Atropine, an anticholinergic agent, paralyses the ability of the eye to focus or accommodate. In amblyopia therapy, atropine is used to blur vision in the non-amblyopic eye and offers a useful alternative to traditional occlusion therapy with patching, especially in older children who are not compliant with patching. The neurotransmitter precursor levodopa and the related compound citicoline have been demonstrated to improve vision in amblyopic eyes. The therapeutic role of these centrally acting agents in the clinical management of amblyopia remains unproven.

Anterior segment ischemia after strabismus surgery with microvascular dissection

Anterior segment ischemia is a rare but well-known complication of extraocular muscle surgery.(1) Several surgical techniques have been used to prevent this complication in high-risk patients. A number of studies have suggested that microvascular dissection and preservation of the anterior ciliary vessels during strabismus surgery may reduce the risk of ischemic complications. (2-4) We present a case in which anterior segment ischemia occurred despite the use of this vessel-sparing technique.

The eye in childhood

Normal visual development is rapid during the first six months of life and continues through the first decade. Young children are uniquely sensitive to conditions that interfere with vision and visual development. Amblyopia, or functionally defective development of the central visual system, may be caused by common vision problems such as strabismus, uncorrected refractive errors and deprivation secondary to occlusion. Prematurity is especially associated with eye pathology, including retinopathy of prematurity, amblyopia, strabismus and refractive errors. When detected early, amblyopia and many other childhood vision abnormalities are treatable, but the potential for correction and normal visual development is inversely related to age. Since many affected children are asymptomatic, early detection of abnormal visual function requires effective screening throughout early childhood. Special considerations apply to screening examinations of children born prematurely.

Retinoblastoma in transgenic mice: models of hereditary retinoblastoma

Retinoblastoma, the most common intraocular malignancy ill childhood, has served as a paradigm for the study of genetic mechanisms of oncogenesis. The retinoblastoma susceptibility gene RB1 was the first tumor suppressor gene to be cloned, and genetic and molecular biologic studies of this tumor have greatly expanded the understanding of the mechanics of tumorigenesis. Human retinoblastoma has essentially no naturally occuring animal counterpart. The development of transgenic murine models of retinoblastoma have created an experimental tool for manipulation of a tumor gene system in vivo. These models have also enabled studies of new therapeutic modalities. This review outlines the development of the transgenic murine models of retinoblastoma, together with the genetic mechanisms of retinoblastoma origin. Current therapeutic innovations developed by means of the transgenic models are described.

Retinoblastoma in an eye with congenital uveal coloboma

Retinoblastoma and congenital ocular abnormalities rarely coexist. The appearance of an intraocular tumor in a child with preexisting leukokoria may make the diagnosis of retinoblastoma more challenging. This report describes a unique case of unilateral congenital uveal coloboma and ipsilateral retinoblastoma in a patient with no family history of either abnormality and normal cytogenetic analysis.

Perianesthesia care of adult and pediatric strabismus surgery patients

Strabismus procedures on children and adults are frequently performed in an outpatient setting. Perianesthesia care of patients having strabismus procedures may be optimized by recognizing the characteristics of strabismus patients, the frequently associated diagnoses that may affect perioperative care, and the specific surgical techniques used to treat strabismus. Complications including postoperative nausea, pain, prolonged PACU stay, and unplanned postoperative admissions can be minimized and treatment facilitated by preparing patients with preoperative instructions, careful choice of anesthetic agents and postoperative medications, and appropriate perioperative care. This report will provide a brief review of surgical strabismus, including current techniques, and present guidelines for perioperative care of pediatric and adult strabismus patients.

Pharmacotherapy of photorefractive keratectomy

PURPOSE

To compare the pharmacotherapeutic practices of high-volume photorefractive keratectomy (PRK) surgeons with suggested practices gleaned from the current literature.

SETTING

York Finch Eye Associates, Toronto, Canada.

METHODS

Seventy-five ophthalmic surgeons believed by the authors to do a high-volume of PRKs were surveyed over the summer of 1994 about their pharmacotherapeutic practices. The results were compared with suggested practices extracted from a review of the current literature.

RESULTS

Relatively consistent approaches to the management of post-PRK pain and prevention of acute post-PRK subepithelial infiltrative keratitis were reported. The administration of topical steroids after PRK was almost universally employed. Post-PRK analgesia was most commonly achieved with nonsteroidal anti-inflammatory drugs (NSAIDs) and a soft contact lens, but surgeons were not convinced of the benefits of long-term NSAID administration to control myopic regression and haze. There seemed to be no agreed-on solution to the infrequent problems of severe haze and regression and steroid-induced elevated intraocular pressure after PRK; however, many useful suggestions for the management of these problems were proposed.

CONCLUSION

In general, high-volume PRK surgeons use topical steroids, NSAIDs, and a soft contact lens in the immediate postoperative period, although they are uncertain about the long-term effectiveness of NSAIDs in controlling regression and haze.

Glaucoma following childhood cataract surgery

Glaucoma has been recognized as an infrequent but serious complication following surgery for congenital and acquired cataracts in childhood. Little is known concerning the influence of factors on the risk of glaucoma such as age at surgery, type of cataract, associated ocular abnormalities, and type of surgery. We reviewed records of 240 eyes of 155 patients on whom cataract surgery had been performed between January 1965 and July 1990 at Children's Hospital, Boston. After excluding those patients who had been followed up less than 5 years after surgery, and those who had had surgery after the age of 10 years, 125 eyes of 82 patients were included in the study group. We identified 14 eyes of 9 patients that had developed open-angle glaucoma 5.3 to 13.1 years following surgery (average 7.4 years). An additional 4 eyes of 3 patients developed angle closure glaucoma, which was diagnosed at 146, 177, 2911, and 2939 days following surgery. A fifth patient developed acute angle closure 1.7 years following primary cataract surgery and 53 days following secondary discission. All but one of the patients who developed glaucoma had cataract surgery at less than 1 year of age. Age at surgery for the entire study group averaged 1.9 years, and ranged from 25 days to 9.6 years. We conclude that patients having cataract surgery before 1 year of age are at the greatest risk of developing postoperative open-angle glaucoma. Additional increased relative risk was found in eyes with microcornea, congenital rubella syndrome, and poor pupillary dilation with 1% cyclopentolate (Cyclogyl). No significant difference was seen among the various surgical methods of cataract removal.

Periocular xanthogranulomas associated with severe adult-onset asthma

This article describes six patients who presented, usually bilaterally, with yellow-orange, elevated, indurated, and nonulcerated xanthomatous eyelid lesions, typically extending into the anterior orbital fat, and sometimes involving the extraocular muscles and the lacrimal gland. Because the eyelids remained intact and because the process did not reach the deep orbital and perioptic connective tissues, visual acuity was well preserved. There is cosmetic morbidity and occasionally motility restriction with advancing involvement of the extraocular muscles. All patients had variably severe adult-onset asthma that required treatment with systemic prednisone and inhalants. No evidence of Erdheim-Chester disease was found in any patient, but the appearance in one patient, after 25 years of follow-up, of a separate subcutaneous necrobiotic xanthogranulomatous lesion in the mandibular region with an associated paraproteinemia, suggests that at least some of our cases might be a mild form of necrobiotic xanthogranuloma. For this reason, we would suggest repeated periodic serum protein immunoelectrophoretic studies as well as evaluation for lymphoma. Therapy probably should consist of low doses of periorbital radiotherapy coupled with high doses of corticosteroids. Should this not be successful, then systemic administration of corticosteroids with chemotherapeutic agents might be efficacious, as in necrobiotic xanthogranuloma.

Growth and development of Haemonchus contortus in jirds, Meriones unguiculatus

Growth and development of Haemonchus contortus were examined in jirds and were compared to these processes in lambs. Number, sex, size, and stage of development were determined for worms recovered at necropsy at various times postinoculation (PI) from immunosuppressed jirds inoculated with approximately 1,000 exsheathed infective larvae (L3) of H. contortus. In addition, gastric tissue samples from jirds were examined histologically. Parallel studies were done in lambs inoculated with approximately 7,500 L3. Typically, 5-30% of the inoculum established and survived in jirds at reasonably stable numbers to day 14 PI. By day 21 PI, worm numbers in jirds decreased dramatically. Although the parasite was similar in size and development on day 4 PI in jirds and lambs, from day 7 PI on, worms were significantly smaller and less developed in jirds. On histological examination, the parasite was found only in the glandular portion of the stomach of jirds (anatomically similar to its predilection site in the abomasum of lambs), and histological changes were consistent for both host species. Although growth and development of H. contortus are slower and incomplete in jirds, the parasite establishes, grows, and develops (at anatomically comparable sites in both hosts) in this model. Thus, the model appears to provide a useful laboratory host to study H. contortus.

Evaluation of a total scalp electron irradiation technique

A dosimetric evaluation of a total scalp electron-beam irradiation technique that uses six stationary fields was performed. The initial treatment plan specified a) that there be a 3-mm gap between abutted fields and b) that the field junctions be shifted 1 cm after 50% of the prescribed dose had been delivered. Dosimetric measurements were made at the scalp surface, scalp-skull interface, and the skull-brain interface in an anthropomorphic head phantom using both film and thermoluminescent dosimeters (TLD-100). The measurements showed that the initial technique yields areas of increased and decreased dose ranging from -50% to +70% in the region of the field junctions. To reduce regions of nonuniform dose, the treatment protocol was changed by eliminating the gap between the coronal borders of abutted fields and by increasing the field shift from 1 cm to 2 cm for all borders. Subsequent measurements showed that these changes in treatment protocol resulted in a significantly more uniform dose to the scalp and decreased variation of doses near field junctions (-10% to +50%).

Reliability of ultrasonographic formulary in the prediction of fetal weight and survival of very-low-birth-weight infants

Antenatal management of very-low-birth-weight infants often requires difficult obstetric decisions. This study was designed to evaluate the predictive value for neonatal outcome of antenatally acquired estimation of gestational age and ultrasonographically estimated fetal weight or a combination of both in very-low-birth-weight infants. Sixty-seven fetuses with estimated gestational ages between 22 0/7 and 28 6/7 weeks were studied ultrasonographically to estimate fetal weight. A comparison of accuracy of estimated fetal weight with actual birth weight showed good correlation (r = 0.93). Neonatal outcome of these infants was analyzed by estimated gestational age and estimated fetal weight. Estimated gestational age and estimated fetal weight greater than 25 weeks and greater than 750 gm were associated with 50% survival, respectively. However, when both of these conditions were met survival reached 85%. This information may be useful to guide antepartum management decisions in this very-low-birth-weight group.

Shielding considerations for an operating room based intraoperative electron radiotherapy unit

The leakage radiation characteristics of a dedicated intraoperative radiotherapy linear accelerator have been measured on a machine designed to minimize the shielding required to allow it to be placed in an operating room suite. The scattering foil design was optimized to produce a flat beam for the field sizes employed while generating minimal bremsstrahlung contamination over the available energy range. More lead shielding was used in the treatment head than is used in conventional accelerators. A small amount of borated polyethylene shielding was also employed since neutron production was present at measurable levels. The room shielding installed in the operating room was demonstrated to be adequate to treat at least 20 patients each month to an average dose of 20 Gy. The worst case exposure was found to be 73% maximum permissible exposure. Administrative control was required for adjoining areas when calibrations and maintenance were performed.

The exposure rate constant for a silver wire 125I seed

The physical characteristics of the newer silver wire 125I seed were measured with a scintillation spectrometer to compare them with those of the original gold sphere 125I seed. The exposure rate constant was determined by converting the count rate from a scintillation spectrometer into the photon-fluence rate incident upon the detector, then calculating the exposure rate from the photon-fluence rate. The exposure rate constant measured perpendicular to the long axis of the seed is 1.361 R cm2/mCi h (1.192 cGy cm2/mCi h) +/- 3.7%, a value that compares favorably with the theoretical exposure rate constant of 1.354 R cm2/mCi h (1.186 cGy cm2/mCi h) calculated from the 125I emissions data. A value of 1.309 R cm2/mCi h was previously reported for the gold sphere 125I seed using the same technique. The angular intensity distribution and anisotropy factor of the silver wire 125I seed are shown to be very similar to those of the gold sphere 125I seed, leading to the conclusion that the clinical application of the two types of 125I seeds need not change.

Spinal cord dose reduction using an anterior 13 MeV electron field situated between a split anterior 60Co supraclavicular field

As part of the treatment for lymphoma, disease involving the supraclavicular region has been treated with megavoltage 60Co photons to a midline dose of 30 to 45 Gy through an anterior involved field and a supplementary posterior field when necessary. The spinal cord was shielded with a 5 cm lead block during treatment to the posterior field. A typical 40 Gy treatment results in a dose to the lower cervical and upper thoracic spinal cord in the range of 22 to 26 Gy, a level that could compromise subsequent mediastinal treatment in the event of a relapse. To reduce this cord dose, the midportion of the anterior supraclavicular 60Co To reduce this cord dose, the midportion of the anterior supraclavicular 60Co field was replaced with a high-energy (13 MeV) electron port, which reduces the dose to the cord to below 6 Gy in the average adult patient. This modification of the routine supraclavicular treatment allows greater flexibility in future treatment in the event of a mediastinal relapse.

Electron beam therapy for eyelid carcinomas

Forty-six (85%) basal cell and eight (15%) squamous cell carcinomas of the eyelids were treated with electron beams between 1963 and 1983. Lesion sizes ranged from microscopic to 4 cm, with 28 lesions larger than 1 cm. Thirty-eight lesions were treated with radiotherapy after incisional biopsy, and 16 were treated after excisional biopsy (specimens showed positive margins). Doses varied from 45 to 72 Gy, with daily fractions ranging from 2.12 to 4.0 Gy. There were six disease recurrences (10.9%): three in the treatment field and three at the treatment margin. Four of six recurrences were subsequently controlled by limited surgical excision and repair with preservation of the eye, whereas the other two required enucleation. Treatment sequelae such as skin atrophy, telangiectasis, and cosmetic results were evaluated in terms of radiotherapy parameters, pretreatment surgery, and size of the lesion. In 44 patients, the overall cosmetic result was judged as good to excellent, five patients had a mild to modest degree of deformity, and five had significant deformity. Such deformity was usually associated with tumor destruction or previous surgery. No major complications were noted.

Determination of electron beam output factors for a 20-MeV linear accelerator

The demands of a busy clinic require that basic machine calculations be performed as accurately, rapidly, and simply as possible. For the electron beam of the Therac 20 Saturne linear accelerator, a method suitable for a programmable calculator is described to predict the dose output from the measurement of selected fields. One-dimensional output factors were measured; these are defined as output factors of rectangular fields where one side is always equal to the side of the square reference field. The output of an arbitrary rectangular field X, Y is given by the product of the output factors OF(X,Y) = OF(X,10) X OF(10,Y), where 10 is the side of the square reference field. The measured data indicate that the output of very large rectangular and square fields is underestimated using this method for the lower energies. A correction factor of the form CF = C X [(X - 10)(Y - 10)/(X - 10)(Y - 10) 1/2] results in agreement with measured data to within 1.5% for all energies.

Dosimetric evaluation of a pencil-beam algorithm for electrons employing a two-dimensional heterogeneity correction

The accuracy of a pencil-beam algorithm for electrons employing a two-dimensional heterogeneity correction is demonstrated by comparing calculation with measurement. Ionization measurements have been made in a water phantom for a variety of non-standard geometries. Geometries to demonstrate the effect of an extended treatment distance, a sloping skin surface, and an irregular skin surface have been selected. Additionally, thermoluminescent dosimeters have been used to measure distributions in tissue-substitute phantoms, which were designed from individual patient computerized tomographic scans. Three patient scans have been selected: (1) diffuse hystiocytic lymphoma of the left buccal mucosa and retromolar trigone; (2) squamous cell carcinoma of the nose at the columnella ; and (3) carcinoma of the maxillary antrum. Results demonstrate the algorithm's ability to simultaneously account for the isodose shifting as a result of internal heterogeneities and for sidescatter non-equilibrium caused by lateral discontinuities of the skin surface and internal anatomy. The algorithm is shown to generally be accurate to within +/- 4% in the treatment volume or +/- 4 mm in regions of sharp dose gradients as found in the penumbra and distal edge of the beam. Examples of greater disagreement are shown and their physical interpretation discussed.

Hyperthermic potentiation of unrejoined DNA strand breaks following irradiation

Previous reports have suggested that the potentiation of cellular radiation sensitivity by hyperthermia may be due to its inhibition of the repair of single-strand breaks in DNA. Such inhibition could result in increased numbers of unrejoined breaks at long times following irradiation, lesions that are presumed to be lethal to the cell. As a test of this hypothesis, the amounts of residual strand-break damage in cells following combined hyperthermia and ionizing radiation were measured. The results show that hyperthermia does significantly enhance the relative number of unrejoined strand breaks as measured by the technique of alkaline elution and that the degree of enhancement is dependent on both the temperature and duration of the hyperthermia treatment. For example, compared to unheated cells, the proportion of unrejoined breaks measured 8 hr after irradiation was increased by a factor of 1.5 in cells that were treated for 30 min at 43 degrees C, by a factor of 6 for cells treated for 30 min at 45 degrees C, and by a factor of 4 for cells treated at 43 degrees C for 2 hr. In experiments in which the sequence of heat and irradiation were varied, a high degree of correlation was observed between the resulting level of cell killing and the relative numbers of unrejoined strand breaks. The greatest effects on both of these parameters were observed in those protocols in which the irradiation was delivered either during, just before, or just after the heat treatment.

Noncontact profiling techniques for intraocular lens edge measurements

Two techniques, focal spot projection and fringe projection, have been developed for profiling the edges of anterior-chamber style intraocular lenses (IOL). The techniques are based on measurement of the trajectory of reflected light when an incident beam is focused and stepped across the edge surface (spot projection) or when two focused beams combine to form an optical interference pattern on the edge (fringe projection). The optical configurations for performing the projection techniques are described along with the mathematical relationship between the reflected-beam trajectories and the edge profile. An automated system for the implementation of focal spot projection was developed. The system has the capability of positioning the IOL edge at the focal point of the incident beam, acquiring trajectory data via stepper motors and a TV camera, processing the data to generate a profile, and displaying the profile on the computer video monitor or in hard-copy form via a printer. On one lens tested, three profiles corresponding to different locations along the IOL edge could be generated without user intervention. However, the user has the option of manually positioning the IOL to permit greater versatility. The typical 300-microm wide IOL edges are profiled to a resolution of approximately 20 microm. To constrain optical and microprocessor hardware costs, compromises were made in operating speeds so that approximately 20 min is required per profile. With current trends in integrated circuit technology future generations of the system could be made faster and prove useful as a QC tool for the IOL industry. Furthermore, the present device can be used in determining appropriate IOL profile standards.

Prediction of electron beam output factors

A method to predict square and rectangular field output factors from the measurement of selected fields of electron beams on the Therac 20 Saturne has been developed. A two parameter fit of the square field output factor data, based on the functional dependence as predicted by a pencil beam calculational model, has proven clinically acceptable. The pencil beam distributions are given by the Fermi-Eyges theory of multiple Coulomb scattering. For a rectangular field, the output factor can be calculated from the square root of the product of the two square field output factors wtih sides equal to those of the rectangular field. If however, there is a significant asymmetry between the X and Y collimator systems, then rectangular field output factors should be predicted from the product of the X and Y one-dimensional output factors. One-dimensional output factors are defined as output factors of rectangular fields where one side remains constant and equal to the side of the square reference field. Measured data indicate either of the two methods of determining rectangular field output factors to be clinically acceptable for the Therac 20, the use of one-dimensional output factors demonstrating greater accuracy. Data show agreement to within approximately 1.5% at electron energies of 6, 9, 13, and 17 MeV.

Electron beam dose calculations

Electron beam dose distributions in the presence of inhomogeneous tissue are calculated by an algorithm that sums the dose distribution of individual pencil beams. The off-axis dependence of the pencil beam dose distribution is described by the Fermi-Eyges theory of thick-target multiple Coulomb scattering. Measured square-field depth-dose data serve as input for the calculations. Air gap corrections are incorporated and use data from'in-air' measurements in the penumbra of the beam. The effective depth, used to evaluate depth-dose, and the sigma of the off-axis Gaussian spread against depth are calculated by recursion relations from a CT data matrix for the material underlying individual pencil beams. The correlation of CT number with relative linear stopping power and relative linear scattering power for various tissues is shown. The results of calculations are verified by comparison with measurements in a 17 MeV electron beam from the Therac 20 linear accelerator. Calculated isodose lines agree nominally to within 2 mm of measurements in a water phantom. Similar agreement is observed in cork slabs simulating lung. Calculations beneath a bone substitute illustrate a weakness in the calculation. Finally a case of carcinoma in the maxillary antrum is studied. The theory suggests an alternative method for the calculation of depth-dose of rectangular fields.

Electron beam dose calculations

Electron beam dose distributions in the presence of inhomogeneous tissue are calculated by an algorithm that sums the dose distribution of individual pencil beams. The off-axis dependence of the pencil beam dose distribution is described by the Fermi-Eyges theory of thick-target multiple Coulomb scattering. Measured square-field depth-dose data serve as input for the calculations. Air gap corrections are incorporated and use data from'in-air' measurements in the penumbra of the beam. The effective depth, used to evaluate depth-dose, and the sigma of the off-axis Gaussian spread against depth are calculated by recursion relations from a CT data matrix for the material underlying individual pencil beams. The correlation of CT number with relative linear stopping power and relative linear scattering power for various tissues is shown. The results of calculations are verified by comparison with measurements in a 17 MeV electron beam from the Therac 20 linear accelerator. Calculated isodose lines agree nominally to within 2 mm of measurements in a water phantom. Similar agreement is observed in cork slabs simulating lung. Calculations beneath a bone substitute illustrate a weakness in the calculation. Finally a case of carcinoma in the maxillary antrum is studied. The theory suggests an alternative method for the calculation of depth-dose of rectangular fields.

Localization of fibronectin within the renal glomerulus and its production by cultured glomerular cells

Fibronectin was shown in the kidney glomerulus by the use of the peroxidase-labeled antibody technique. At the ultrastructural level, fibronectin was present in greatest quantities along those cell surfaces that abut the capillary basement membrane, especially along the capillary epithelial cell foot process. Intracellular staining was also seen in the glomerulus, most notably in the mesangial cell. Fibronectin was present extracellularly in large amounts in glomerular cell culture and was also demonstrated on the cell membrane and intracellularly.

Culture of human glomerular cells

Human glomeruli were routinely cultured in Waymouth's medium supplemented with insulin and conditioned medium. Three cell types were seen in the culture of both adult and infant kidneys, but the morphology of the glomerular cellular outgrowths depended on the age of the patient from which the kidney was obtained. Cultures of glomeruli from older individuals resulted in more "differentiated" cells, but both adult and infant glomerular cells rapidly became "dedifferentiated" as the length of time in culture increased. Outgrowths of cultured glomeruli did not contain fibroblasts or tubular cells. Finally, synthesis of basement membrane material by these cultured glomerular cells was demonstrated.