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Objective:To investigate the impacts of the composition and physical density of tissue on the dose distribution of implanted 125I seeds, in order to provide references for the clinical dose calculation and assessment of implanted radioactive particles. Methods:The OncoSeed 6711 physical model of 125I seeds was established using thes of twareegs_brachy and was validated through the calculation of dose rate constant and the radial dose function [ g( r)] in water. Then, based on the element composition and physical density of different types of tissue, the g( r) and absorbed dose ratein water, prostate, breast, muscle, and bone were calculated. Results:The calculated dose rate constant (0.950 cGy·h -1·U -1) and g( r)in water approached the values in related literature. The absorbed dose in bone was 6.042 times than that in water at a distance of 0.05 cm from the implanted source. The difference between the absorbed doses in breast and water was more than 10% at a distance of less than 1.7 cm from the implanted source. The difference between the absorbed doses in prostate/muscle and water was less than 5% at the same radial location. Conclusions:The dose distribution of 125I seeds in some types of human tissue is significantly different from that in water, which should be carefully considered in clinical dose calculation.
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Aim: The aim of this study is to evaluate soft-tissue composition effect on dose distribution for various soft tissues in radiotherapy with a 6 MV photon beam of a medical linac. Background: The compositions of various soft tissues are different which could affect dose calculations. Materials and Methods: A phantom and Siemens Primus linear accelerator were simulated using MCNPX Monte Carlo code. In a homogeneous cubic phantom, six types of soft tissue and three types of tissue-equivalent materials were defined separately. The soft tissues were muscle (skeletal), adipose tissue, blood (whole), breast tissue, soft tissue (9-component), and soft tissue (4-component). The tissue-equivalent materials included water, A-150 tissue equivalent plastic and perspex. Photon dose relative to dose in 9-component soft tissue at various depths on the beam's central axis was determined for the 6 MV photon beam. The relative dose was also calculated and compared for various MCNPX tallies including *F8, F6, and *F4. Results: The results of the relative photon dose in various materials relative to dose in 9-component soft tissue using different tallies are reported in the form of tabulated data. Minor differences between dose distributions in various soft tissues and tissue-equivalent materials were observed. The results from F6 and F4 were practically the same but differ with the *F8 tally. Conclusions: Based on the calculations performed, the differences in dose distributions in various soft tissues and tissue-equivalent materials are minor but they could be corrected in radiotherapy calculations to upgrade the accuracy of the dosimetric calculations
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The relationship between the serum values of prostate-specific antigen (PSA) and the histologic composition of benign prostatic hyperplasia (BPH) was investigated in 32 symptomatic BPH patients undergoing transurethral resection of the prostate. We evaluated the free and total PSA concentrations by ACS-PSA2 (Ciba-Corning) assay. The stereological analysis was made by computer aided-area densitometry using H & E stained slides to quantify stromal and glandular areas in the resected prostate tissue. The total PSA concentration versus percentage of glandular area (%G) and stromal-glandular ratio (SGR) correlated significantly (p0.05 for both). These data suggest that total PSA is directly correlated with the histologic composition of the prostate in men with BPH, however, the proportion of free to total PSA was not informative to predict the histology. Thus, pretreatment evaluation of total PSA would be useful as part of an evaluation method of BPH for medical therapy.