PubMed · 7348134
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G Santucci. 1981. [Visual displays].. https://pubmed.ncbi.nlm.nih.gov/7348134/
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The purpose of this study was to calculate the 90Sr + 90Y bremsstrahlung yield generated in bone quantitatively, and to determine the optimum conditions required for in vivo measurements of the yield, assuming that a given amount of contamination, due to the ordinary activities of 137Cs and 40K, is present within the human body. Several approximations in the distribution of activities in various body phantoms, simulating the human leg, waist and head, were made for simplicity. All the calculations were carried out using an in-house Monte Carlo code. The photon spectra incident on a detector window, of diameter 200 mm, positioned 1 mm from the surface of each phantom were obtained. A pseudo-peak of 90Sr + 90Y bremsstrahlung was observed at approximately 50 keV with a full width at half maximum of 60 keV (FWHM). The signal-to-background ratio, eta, where eta represents the ratio of the number of photons in the energy interval between 30 to 160 keV in the bremsstrahlung spectrum produced by 1 Bq kg(-1) of 90Sr and the background spectrum, which is assumed to comprise of 1 Bq kg(-1) of 137Cs and 60 Bq kg(-1) of 40K, was evaluated in order to determine the optimum measuring conditions. An optimum eta value of 0.0353 was obtained for the leg phantom, of bone diameter 30 mm, covered by a 1 mm layer of soft tissue. Combining the present calculations with the conventional measurements, a new and simpler method for evaluating the body burden activity of a beta emitter, such as 90Sr, is proposed.
The calibration of a catheter-based system to be used for therapeutic radiation treatment to prevent restenosis following interventional coronary procedures is described. The primary dosimetry was performed ionometrically using an extrapolation chamber equipped with a 1-mm diameter collecting electrode to measure absorbed dose in tissue equivalent plastic at a depth of 2 mm. These results are compared with measurements with radiochromic dye film, which is also used to characterize sources for axial and trans-axial uniformity, and to determine dose distributions at various depths. A protocol for dose calculation based on that of AAPM TG43 is suggested for these sources, and examples of its use are given for the calculation of the enhancement effect on dose rate from a single seed source due to neighboring seeds. Monte Carlo calculations were also performed to validate the measured results.
Using a 90Sr applicator for brachytherapy for the reduction of recurrence rates after pterygium excisions has been an effective therapeutic procedure. Accurate knowledge of the dose being applied to the affected area on the sclera has been lacking, and for decades inaccurate estimates for lens dose have thus been made. Small errors in the assumptions which are required to make these estimates lead to dose rates changing exponentially because of the attenuation of beta particles. Monte Carlo simulations have been used to evaluate the assumptions that are now being used for the calculation of the surface dose rate and the corresponding determination of lens dose. For an ideal 90Sr applicator, results from this study indicate dose rates to the most radiosensitive areas of the lens ranging from 8.8 to 15.5 cGy/s. This range is based on different eye dimensions that ultimately corresponds to a range in distance between the applicator surface and the germinative epithelium of the lens of 2-3 mm. Furthermore, the conventional 200 cGy threshold for whole lens cataractogenesis is questioned for predicting complications from scleral brachytherapy. The dose to the germinative epithelium should be used for studying radiocataractogenesis.