strontium-radioisotopes and Eye-Diseases

(90)Sr+(90)Y clinical applicators are used for brachytherapy in Brazilian clinics even though they are not manufactured anymore. Such sources must be calibrated periodically, and one of the calibration methods in use is ionometry with extrapolation ionization chambers. (90)Sr+(90)Y clinical applicators were calibrated using an extrapolation minichamber developed at the Calibration Laboratory at IPEN. The obtained results agree satisfactorily with the data provided in calibration certificates of the sources.

Topics: Beta Particles; Brachytherapy; Brazil; Calibration; Eye Diseases; Humans; Radiometry; Radiotherapy Dosage; Skin Diseases; Strontium Radioisotopes; Yttrium Radioisotopes

Postoperative adjuvant treatment using β-radiotherapy (RT) is a proven technique for reducing the recurrence of pterygium. A randomized trial was conducted to determine whether a low fractionation dose of 2 Gy within 10 fractions would provide local control similar to that after a high fractionation dose of 5 Gy within 7 fractions for surgically resected pterygium.. A randomized trial was conducted in 200 patients (216 pterygia) between February 2006 and July 2007. Only patients with fresh pterygium resected using a bare sclera method and given RT within 3 days were included. Postoperative RT was delivered using a strontium-90 eye applicator. The pterygia were randomly treated using either 5 Gy within 7 fractions (Group 1) or 2 Gy within 10 fractions (Group 2). The local control rate was calculated from the date of surgery.. Of the 216 pterygia included, 112 were allocated to Group 1 and 104 to Group 2. The 3-year local control rate for Groups 1 and 2 was 93.8% and 92.3%, respectively (p = .616). A statistically significant difference for cosmetic effect (p = .034), photophobia (p = .02), irritation (p = .001), and scleromalacia (p = .017) was noted in favor of Group 2.. No better local control rate for postoperative pterygium was obtained using high-dose fractionation vs. low-dose fractionation. However, a low-dose fractionation schedule produced better cosmetic effects and resulted in fewer symptoms than high-dose fractionation. Moreover, pterygia can be safely treated in terms of local recurrence using RT schedules with a biologic effective dose of 24-52.5 Gy(10.).

Topics: Adult; Aged, 80 and over; Algorithms; Beta Particles; Dose Fractionation, Radiation; Eye Diseases; Female; Granuloma; Humans; Male; Middle Aged; Photophobia; Prospective Studies; Pterygium; Radiotherapy; Recurrence; Sclera; Strontium Radioisotopes; Treatment Outcome; Young Adult

Latent canine herpesvirus-1 (CHV-1) infections are common in domestic dogs, but stimuli causing viral reactivation and recrudescent disease are poorly understood. Immunosuppressive pharmaceuticals are currently the only experimentally established triggers for recurrent ocular CHV-1 infection in dogs; however, ocular CHV-1 shedding has been reported clinically following strontium-90 beta radiotherapy of the ocular surface and it has been speculated that radiotherapy can directly induce viral reactivation. Strontium-90 is used as a beta radiation source for the treatment of a variety of neoplastic and immune-mediated canine ocular surface diseases. In the present study, the effects of ocular surface strontium-90 beta radiotherapy in dogs latently infected with CHV-1 were evaluated. Ten mature dogs with experimentally induced latent CHV-1 infections were randomly divided into two groups: one group received a single fraction 50 Gy radiation dose in one application from a strontium-90 ophthalmic applicator and the second group received sham radiotherapy. Dogs were then monitored for 45 days for recurrent ocular CHV-1 infection using clinical and virological outcome measures. Clinical ophthalmic examinations, ocular sample CHV-1 PCR assays, and serum CHV-1 virus neutralizing antibody assays were performed at specified intervals. No abnormalities suggestive of recurrent CHV-1 ocular disease were observed on clinical examination in any dog during the study. Ocular viral shedding was not detected and CHV-1 virus neutralizing titers remained stable in all dogs. A single fraction 50 Gy radiation dose administered to the ocular surface by strontium-90 beta radiotherapy did not result in detectable recurrent ocular CHV-1 infection in mature dogs with experimentally induced latent infection.

Topics: Animals; Beta Particles; Dog Diseases; Dogs; Eye; Eye Diseases; Female; Herpesviridae Infections; Herpesvirus 1, Canid; Male; Recurrence; Strontium Radioisotopes; Viral Load; Virus Shedding

An international intercomparison of the dosimetry of three beta particle emitting ophthalmic applicators was performed, which involved measurements with radiochromic film, thermoluminescence dosimeters (TLDs), alanine pellets, plastic scintillators, extrapolation ionization chambers, a small fixed-volume ionization chambers, a diode detector and a diamond detector. The sources studied were planar applicators of 90Sr-90Y and 106Ru-106Rh, and a concave applicator of 106Ru-106Rh. Comparisons were made of absolute dosimetry determined at 1 mm from the source surface in water or water-equivalent plastic, and relative dosimetry along and perpendicular to the source axes. The results of the intercomparison indicate that the various methods yield consistent absolute dosimetry results at the level of 10%-14% (one standard deviation) depending on the source. For relative dosimetry along the source axis at depths of 5 mm or less, the agreement was 3%-9% (one standard deviation) depending on the source and the depth. Crucial to the proper interpretation of the measurement results is an accurate knowledge of the detector geometry, i.e., sensitive volume and amount of insensitive covering material. From the results of these measurements, functions which describe the relative dose rate along and perpendicular to the source axes are suggested.

Topics: Alanine; Beta Particles; Biophysical Phenomena; Biophysics; Brachytherapy; Eye Diseases; Models, Statistical; Phantoms, Imaging; Radioisotopes; Radiometry; Rhodium; Ruthenium; Strontium Radioisotopes; X-Ray Film; Yttrium Radioisotopes

Dose distributions throughout the eye, from three types of beta-ray ophthalmic applicators, were calculated using the EGS4, ACCEPT 3.0, and other Monte Carlo codes. The applicators were those for which doses were measured in a recent international intercomparison [Med. Phys. 28, 1373 (2001)], planar applicators of 106Ru-106Rh and 90Sr-90Y and a concave 106Ru-106Rh applicator. The main purpose was to compare the results of the various codes with average experimental values. For the planar applicators, calculated and measured doses on the source axis agreed within the experimental errors (<10%) to a depth of 7 mm for 106Ru-106Rh and 5 mm for 90Sr-90Y. At greater distances the measured values are larger than those calculated. For the concave 106Ru-106Rh applicator, there was poor agreement among available calculations and only those calculated by ACCEPT 3.0 agreed with measured values. In the past, attempts have been made to derive such dose distributions simply, by integrating the appropriate point-source dose function over the source. Here, we investigated the accuracy of this procedure for encapsulated sources, by comparing such results with values calculated by Monte Carlo. An attempt was made to allow for the effects of the silver source window but no corrections were made for scattering from the source backing. In these circumstances, at 6 mm depth, the difference in the results of the two calculations was 14%-18% for a planar 106Ru-l06Rh applicator and up to 30% for the concave applicator. It becomes worse at greater depths. These errors are probably caused mainly by differences between the spectrum of beta particles transmitted by the silver window and those transmitted by a thickness of water having the same attenuation properties.

Topics: Beta Particles; Biophysical Phenomena; Biophysics; Brachytherapy; Eye; Eye Diseases; Models, Statistical; Monte Carlo Method; Phantoms, Imaging; Radioisotopes; Radiometry; Rhodium; Ruthenium; Strontium Radioisotopes; Water; X-Ray Film; Yttrium Radioisotopes

The treatment of various superficial lesions of the eye has, for many years, been conducted using strontium 90 (90Sr) ophthalmic applicators that have a steep dose gradient near their surface. A new applicator acquired by a treatment facility must have its output compared with that of any older applicators already in use to ensure consistent treatments. These measurements may be done using available dosimeters such as film and thermoluminescent detectors. Our work made use of radiochromic film and a document scanner to perform relative output measurements for 4 different 90Sr ophthalmic applicators acquired from the same manufacturer (Amersham Healthcare, Arlington Heights, IL) over a span of 28 years. Relative outputs were found to vary by < 10% with respect to the manufacturer's values, which is well within the uncertainty limit for absolute output of 20% specified by the manufacturer. The film measurements were verified using thermoluminescent dosimeters. Radiochromic film was also used to obtain a percentage depth dose curve and a 2 dimensional isodose distribution in a plane perpendicular to the active surface for the newest applicator (SIA 20).

Topics: Eye Diseases; Humans; Radiotherapy Dosage; Strontium Radioisotopes

The average surface absorbed dose rate, given by flat ophthalmic applicators (90Sr/90Y, 925 MBq) is determined in equivalent soft tissue using an extrapolation chamber with two flat parallel electrodes of variable separation; the input electrode is fixed in relation to the collector electrode of constant area. When estimating the extrapolation curve slope using a linear regression model, it has been observed that average surface dose rate values were underestimated by up to 19%, as compared to estimations of these values by means of a second degree polynomial regression model, while an improvement of up to 37% is observed in the standard error of the slope in the quadratic model, as compared to that of the linear model. With the aim of validating the results of these models, goodness of fit tests to a Normal (the Shapiro-Wilk test) as well as homogeneity tests on treatment variance (the Bartlett test) were applied. The analysis of variance (ANOVA) tables of fit and residual error breakdown are given: table 3a and 3b for linear fit; 7a and 7b for quadratic fit, and table 10 to error breakdown. Also presented is the global uncertainty of the average dose rate, taking into account the reproducibility of the experimental set-up. It may be inferred that by using this type of measurement for the extrapolation curve slope, quadratic regression models allow for a greater degree of accuracy and precision in determining surface dose rate values. The effective area of the collector electrode and the effective electrode separation in the chamber are also determined by measuring the chamber's electric capacity. Finally, there is an attempt to relate the use of the regression models to the experimental conditions during the measurement of ionization currents (diameter of collector electrode, electrical field gradient, radiation field uniformity, radiation field intensity, etc.). In this particular case, deviations in the distance inverse square law and the "screening" effects during the collection of negative charges (both for primary radiation and the ionization generated by it), are presented as necessary, but insufficient, conditions to explain thoroughly the quadratic behavior of ionizing currents.

Topics: Electrodes; Eye Diseases; Models, Structural; Radiation, Ionizing; Radiometry; Radiotherapy Dosage; Regression Analysis; Strontium Radioisotopes; Yttrium Radioisotopes

Analysis of eye tumors and other eye lesions among beagles given either 90Sr or 226Ra, and among control animals, indicated that intraocular tumors in excess of the rate for our control animals were not associated with radiation from incorporated 90Sr + 90Y. It is unequivocal that eye melanomas were produced by injected 226Ra. Intraocular neoplasia, hyperplasia, hyperpigmentation, and melanosis in the eye all occurred in our control beagles given no radioactivity; however, tumor experience as currently reported for different beagle colonies may not be directly comparable because of differing rates of discovery, nonuniform nomenclature, and varying criteria for classification of lesions with their discordant interpretation by different pathologists.

Topics: Animals; Dogs; Eye Diseases; Eye Neoplasms; Melanoma, Experimental; Radium; Strontium Radioisotopes

Aspects of extrapolation chamber dose-rate measurements of 90Sr + 90Y beta-particle ophthalmic applicators are examined in this report, including the proper choice of collector electrode size, the gap width over which the measurement should be done, the effect of the entrance window materials, and the stopping-power ratio. Experiments, a simple analytic model for the effect of chamber geometry and nonzero gap width, and more detailed Monte Carlo simulations were used. The variation of the planar flux density as a function of angle for a thick 90Sr + 90Y source was measured and used as input for the model. From Monte Carlo simulation, the dose rate for tissue irradiation falls off by 8% between the surface and a depth of 7 mg/cm2. The derivative of chamber ionization as a function of gap width, needed for the dose-rate calibration, increases rapidly as the gap width decreases, typically by a factor of about 2 between gap widths of 1.5 and 0.15 mm. About half of this change is due to ionizing electrons leaving the collection volume at the larger gap widths as shown by the analytic model; the rest of the change is due to ionizing electrons which backscatter from the collector electrode and its backing as shown by Monte Carlo simulations. The backscattering effect increases the derived surface dose by a factor of 1.46. A satisfactory dose-rate extrapolation is obtained from gap widths of 0.1-0.25 mm, where the total ionization current is observed to be nearly linear in gap width.

Topics: Beta Particles; Biophysical Phenomena; Biophysics; Brachytherapy; Computer Simulation; Electrodes; Eye Diseases; Humans; Models, Structural; Models, Theoretical; Monte Carlo Method; Radiometry; Radiotherapy Dosage; Scattering, Radiation; Strontium Radioisotopes; Yttrium Radioisotopes

Topics: Calibration; Eye Diseases; Humans; Ophthalmology; Strontium Radioisotopes

Topics: Electrons; Eye Diseases; Humans; Promethium; Radioisotopes; Radiotherapy; Radiotherapy Dosage; Strontium Radioisotopes; Thallium; USSR; Yttrium Radioisotopes

A modification of the conventional extrapolation chamber to perform absolute dose measurements from surfaces of spherical beta applicators (type SIA.I, SIA.3, SIA.6) is described. A stack of Ilford N 550 films has been used in a spherical geometry to obtain the variation of surface dose, the depth dose data and the isodose curves. The results obtained are compared with data available in the literature.

Topics: Eye Diseases; Humans; Methods; Radiation Dosage; Radioisotopes; Radiometry; Radiotherapy; Radiotherapy Dosage; Strontium Radioisotopes; Yttrium Isotopes

Topics: Eye Diseases; Humans; Ophthalmology; Radioactivity; Radiotherapy; Strontium; Strontium Radioisotopes

Topics: Eye Diseases; Humans; Radioactivity; Radiotherapy; Strontium; Strontium Radioisotopes

Topics: Beta Particles; Eye Diseases; Humans; Ophthalmology; Radioactivity; Strontium; Strontium Radioisotopes

Topics: Beta Particles; Eye Diseases; Humans; Radioactivity; Radiotherapy; Strontium; Strontium Radioisotopes

Topics: Cornea; Eye Diseases; Humans; Ophthalmology; Radioactivity; Strontium; Strontium Radioisotopes

Topics: Eye; Eye Diseases; Humans; Radiotherapy; Strontium; Strontium Radioisotopes

Topics: Beta Particles; Eye Diseases; Humans; Radiation; Radioactivity; Strontium; Strontium Radioisotopes

Topics: Beta Particles; Eye Diseases; Humans; Radioactivity; Strontium; Strontium Radioisotopes