Atmospheric physics and Earth observations: atmospheric spectral imaging.

An array of imaging spectrometers flown on the Spacelab 1 mission was capable of providing spectra of the atmospheric emissions over a broad wavelength range from 300 to 12,700 angstroms and acquiring each complete spectrum nearly simultaneously. The instrument was used to make observations on the day side and night side of the earth, looking down in the nadir direction, radially away from the earth, and in various limb-scanning modes. Observations were made looking at various angles to the vehicle velocity vector and during thruster firings and water dumps as well as at times when such events were inhibited. As a result of the mission a data base has been acquired that is valuable for studies of both the upper atmosphere and the shuttle-Spacelab vehicle environment.

Correlation of breast dose heterogeneity with breast size using 3D CT planning and dose-volume histograms.

The aim of this study was to evaluate the effect of breast size on dose heterogeneity. Twenty women underwent a planning CT scan of the thorax. A three-dimensional treatment plan was devised for each patient using a standard technique of isocentric medial and lateral wedged tangential fields. Three-dimensional dose distributions were derived using an equivalent path length (EPL) inhomogeneity correction and cumulative dose-volume histogram (DVH) data calculated for the breast. Analysis of the DVHs for each patient reveals that 0.2-23.8% of the breast received an absorbed dose outside the desired 95-105% of that prescribed at the isocentre. The degree of dose heterogeneity was most strongly correlated with breast volume (r = 0.70, 95% confidence interval (C.I.) 0.37-0.87). There was also a positive correlation for breast dose heterogeneity versus brassière (bra) cup size (Spearman rank correlation rho = 0.62), breast area (r = 0.39, 95% C.I. -0.06-0.71) and chest wall separation (r = 0.31, 95% C.I. -0.15-0.66). We conclude that breast size is an important determinant of dose heterogeneity within the breast.

Design of compensators for breast radiotherapy using electronic portal imaging.

A novel method of designing intensity modulated beams (IMBs) to achieve compensation in external beam radiotherapy of the breast, without the need for CT scans, is presented. The design method comprises three parts: (1) an electronic portal image is used to generate a map of radiological thickness; (2) this map is then used to obtain an estimate of the breast and lung outline; (3) a TMR-based dose calculation algorithm is then used to determine the optimum beam profile to achieve the best dose distribution. The dose distributions calculated for IMBs were compared with those calculated for the use of simple wedges. The results for two patients studied indicate that the dose inhomogeneity for IMBs is +/- 5%, compared with a value of +/- 10% for a wedged plan. The uncertainty in radiological thickness measurement corresponds to a dosimetric error of +/- 2%. Other errors associated with outline estimation are typically less than 2%, with a largest value of +5% for one of the patients who had a large and highly asymmetrical breast. The results for the two patients studied suggest that the uncertainties in the method are significantly smaller than the improvement in dose uniformity produced.

Factors affecting acute skin toxicity in patients having breast irradiation after conservative surgery: a prospective study of treatment practice at the Royal Marsden Hospital.

The results are presented of a prospective study of acute skin toxicity in 197 patients with early stage breast cancer, who were treated by conservative surgery and postoperative radiotherapy. We have examined the factors determining the severity of the acute skin reaction with particular reference to the degree of dry or moist desquamation at the completion of treatment. One hundred and ten patients had treatment with radiotherapy alone. The remaining 87 received synchronous chemotherapy with breast irradiation, using either the 3M or the 2M regimen, consisting of mitoxantrone and methotrexate, with (3M) or without Mitomycin-C (2M). Patients were analysed according to both the severity and the site of the skin reaction, age, dose, dose variation across the central outline, treatment technique, beam energy, field separation and breast size. A univariate analysis of these results, which has been presented as an odds ratio of the likelihood of developing a moderate or severe reaction in comparison with those scored as mild, has shown that several factors are associated with an increase in the acute skin reaction. These include the use of the semi-supine technique (odds ratio (OR) = 7.3 (95% CI 3.7-14.6)), beam energy (60Co: 6-10 MV photons OR = 5.9 (95% CI 2.6-13.4)), field separation (> or = 20 cm: < 20 cm OR = 4.1 (95% CI 2.2-7.8)), dose variation across the central outline (> or = 10%: < 10% OR = 9.7 (95% CI 2.6-36.4)), inclusion of the axilla (OR = 4.6 (95% CI 2.4-8.9)), and bust size (bra cup size C and D: A and B OR = 4.6 (95% CI 2.7-11.9)). Using multivariate logistic regression, the technique of radiation delivery and bust size were shown to be independently significant variables affecting acute skin reaction. In view of the high correlation between variables (e.g. radiotherapy technique and beam energy) it is still not possible to specify with definite certainty which is the primary variable causing the skin reaction. However 20/57 (35%) of patients treated by the semisupine technique sustained a severe skin reaction, with > 10% dry or moist desquamation in the treatment field. This compares with only 6/140 (4%) patients treated by the supine method. A possible mechanism by which treatment using the semisupine technique may enhance acute toxicity is discussed. We conclude that there are both treatment and patient related factors that will increase the acute skin reaction after breast irradiation.

Imaging spectrometer for high resolution measurements of stratospheric trace constituents in the ultraviolet.

A high resolution spectrometer has been developed for studies of minor constituents in the middle atmosphere at ultraviolet wavelengths. In particular, the instrument is intended for observations of upper stratospheric U V bands. The spectrometer has a slit width of 0.08 A obtained by means of an echelle grating and a cross-disperser grating. The image plane detector is an intensified charge coupled device consisting of a high gain proximity focused image intensifier that is fiber optically coupled to a 2-D CCD array. An instantaneous bandwidth of 9.2 A is resolved across 488 pixels at 0.018 A/pixel, permitting simultaneous acquisition of multiple lines of selected OH bands and the neighboring background. The spectrometer and the approach have been successfully demonstrated as a technique for measuring the concentration of OH on two high altitude balloon flights. We report the instrument design and its achieved performance.

Compact imaging spectrograph for broadband spectral simultaneity.

We report on the design of a small spectrograph that is capable of imaging several thousand angstrom simultaneously at a moderate spectral resolution. The prototype instrument included a number of developmental items that were used to assess their utility in this and other applications. Some we would recommend using again, some we would not. In the configuration that was built and tested, the instantaneous wavelength range was chosen to be 3700-11,700 Å. However, the wavelength range could be selected for a lower wavelength, as low as ~ 1200 Å. The spectral imaging was achieved with an intensified-CCD focal-plane detector. The broad wavelength coverage was achieved with a matrix of four diffraction gratings and a custom-designed photocathode system. The photocathode was specially built to provide a response over the chosen broad wavelength range by use of a single image intensifier. The theoretical spectral resolution of the instrument varied from 12 to 20 Å depending on waveleng th segment. A higher spectral resolution can be selected at the expense of total wavelength coverage. The optical system was designed to be moderately fast (f/6) when considered at the level of each of the four optical subchannels and suitable for use on relatively weak airglow signals. The instrument was designed to be readily portable, weighing 15 kg, with an envelope of 37 cm × 37 cm × 48 cm. The advantages and weaknesses of such an instrument are discussed, and improvements are suggested for specific applications. This study represents a stepping stone in the evolution of electronic spectrographs and leads to later designs that are currently being evaluated.

Extreme ultraviolet imaging spectrometer for thermospheric emissions.

One of the instruments that has been developed to fly on the Space Shuttle is the Imaging Spectrometric Observatory, an array of five imaging spectrometers to cover the 300-12,000-A wavelength range. In this paper we describe the spectrometer designed to operate in the extreme ultraviolet (300-1200 A). The instrument is intended for studies of the thermosphere and magnetosphere and support of various plasma experiments to be performed from the Shuttle. The design is modular so that various components such as gratings and detectors can be changed and optimized for a range of specific studies following the first survey mission. The detector is an intensified 2-D CCD which permits simultaneous spectral and spatial imaging. The spectral multiplexing gives the spectrometer a considerable speed advantage. The instrument has a small field of view (0.65 degrees ) and is thus capable of obtaining much needed scale height information on the atmospheric EUV emissions. Operating from the Shuttle, global and temporal coverage will be obtained, and the EUV data will be enhanced by the simultaneously acquired UV, visible, and near-IR observations.

Intensified charge coupled devices for use as a spaceborne spectrographic image-plane detector system.

An instrument that has been developed for studies of atmospheric emissions from the Space Shuttle comprises an array of imaging spectrometers to observe features over the 300-12,000-A wavelength range. Each spectrometer has a 2-D image-plane detector system on which spectral information is dispersed in one direction and spatial information is resolved in the other. The detectors consist of CCD arrays to which are coupled to proximity focused image intensifiers. The intensifier in each case is selected for the wavelength range covered by the particular spectrometer. The result is a compact low-power spectrographic detector system whose properties are described in this paper. In the course of building the five flight detector systems, we had occasion to evaluate a larger number of the charge coupled devices and the proximity focused image intensifiers. We report here various characteristics, advantages, and shortcomings of these devices and the overall intensified CCD system.

Spectroscopic imaging of the thermosphere from the Space Shuttle.

An important need for studies of the thermospheric chemistry and dynamics is multispectral information on the emissions over a broad wavelength range. An instrument that has been developed to meet this need is the Imaging Spectrometric Observatory which is currently undergoing integration for flight on the Shuttle Spacelab 1 mission (mid-1983). The instrument represents the coincidence of three major factors: the payload capacity of the Shuttle which permits the placing into orbit of a sufficiently large and comprehensive spectrometric system; the recent advances in solid state imaging detector components which have permitted use of very fast multiplexing detectors; and the maturing of knowledge of the thermosphere permitting clear identification of the desired measurements. The instrument consists of an array of five imaging spectrometers, each covering a portion of the 300-12000-A total wavelength range. The five spectrometers operate simultaneously with the spectrum being dispersed in one dimension on the focal plane detectors and spatial information along the slit length being resolved in the other. The detector system in each spectrometer is an intensified-charge coupled device, optimized for the wavelength region in question. The instrument has been designed in a modular fashion to permit variation in instrument parameters on subsequent flights. For the first flight the typical spectral resolution is 3 A (6 A below 1200 A). The sensitivity has been selected to permit coverage of a large dynamic range extending from weak nocturnal signals (approximately 1 R) to the bright earth (approximately10(7) R/A). The instrument has a minicomputer system which is located in the Spacelab module itself allowing payload crew interaction with the observation sequences. In addition, during the actual 7 days in orbit, the telemetry data stream from the instrument will be recorded directly on an instrument ground support minicomputer, permitting real-time and near-real-time evaluation of the data. The objectives on the initial flight are to obtain a survey atlas of the dayglow, nightglow, and twilightglow over the full wavelength range together with obtaining data necessary for the solution of several specific problems.

Vacuum ultraviolet thin films. 1: Optical constants of BaF(2), CaF(2), LaF(3), MgF(2), Al(2)O(3), HfO(2), and SiO(2) thin films.

The optical constants of MgF(2) (bulk) and BaF(2), CaF(2), LaF(3), MgF(2), Al(2)O(3), HfO(2), and SiO(2) films deposited on MgF(2) substrates are determined from photometric measurements through an iteration process of matching calculated and measured values of the reflectance and transmittance in the 120-230-nm vacuum ultraviolet wavelength region. The potential use of the listed fluorides and oxides as vacuum ultraviolet coating materials is discussed in part 2 of this paper.

Vacuum ultraviolet thin films. 2: Vacuum ultraviolet all-dielectric narrowband filters.

We report the design and performance of narrowband transmission filters employing the rapidly changing extinction coefficient that is characteristic of BaF(2) and SiO(2) films within certain wavelength intervals in the vacuum ultraviolet. We demonstrate the design concept for two filters centered at 135 nm for BaF(2) and at 141 nm for SiO(2). It is found that these filters provide excellent narrowband spectral performance when combined with narrowband reflection filters. The filter centered at 135 nm has a peak transmittance of 24% and a bandwidth of 4 nm at full width at half-maximum for collimated incident light. The transmittance for lambda(0)

Radiation damage effects in far-ultraviolet filters, thin films, and substrates.

Advances in vacuum ultraviolet thin-film filter technology have been made through the use of filter designs with multilayers of materials such as Al(2)O(3), BaF(2), CaF(2), HfO(2), LaF(3), MgF(2), and SiO(2). Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 × 9 R(E) orbit will expose the instrument to approximately 250 krad of radiation. Because to our knowledge no previous studies have been made on the potential radiation damage of these materials in the thin-film format, we report on such an assessment here. Transmittances and reflectances of BaF(2), CaF(2), HfO(2), MgF(2), and SiO(2) thin films on MgF(2) substrates, Al(2)O(3) thin films on fused-silica substrates, uncoated fused silica and MgF(2), and four multilayer filters made from these materials were measured from 120 to 180 nm beforeand after irradiation by 250 krad from a (60)Co gamma radiation source. No radiation-induced losses in transmittance or reflectance occurred in this wavelength range. Additional postradiation measurements from 160 to 300 nm indicates 2-5% radiation-induced absorption near 260 nm in some of the samples with MgF(2) substrates. From these measurements we conclude that far-ultraviolet filters made from the materials tested should experience less than 5% change from exposure to up to 250 krad of high-energy radiation in space applications.