Saint Francis University

About: Saint Francis University is a education organization based out in Loretto, Pennsylvania, United States. It is known for research contribution in the topics: Population & Osteoblast. The organization has 1694 authors who have published 2038 publications receiving 87149 citations.

Parathyroid Hormone-Related Protein Modulates the Effect of Transforming Growth Factor-β on Deoxyribonucleic Acid and Collagen Synthesis in Fetal Rat Bone Cells

Abstract: Proteins with biochemical function and sequence similarity to PTH are produced by many tumors associated with hypercalcemia and may have a role in pathological bone remodeling. Synthetic polypeptides comprising the aminoterminus of human PTH-related protein (PTH-rp) were examined for effects in intact fetal rat calvariae, and in osteoblastenriched (ob) cultures isolated from fetal rat parietal bone. In cultured calvariae, 0.5–5 nM PTH-rp stimulated [3H]thymidine incorporation into DNA by 25–70% after 24 h of treatment and decreased relative [3H]proline incorporation into collagen by 50%; the inhibitory effect on collagen production was not altered by hydroxyurea, which decreased DNA synthesis by 85%. PTHrp also increased [3H]hydroxyproline levels by 100% in culture medium from bones prelabeled with [3H]proline, indicating accelerated matrix turnover. In contrast to results in intact calvariae, PTH-rp had little effect on basal DNA and collagen synthesis in serum-deprived ob cultures. However, whe...

Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for 6 MV photon fields smaller than 4 cm produced by Cyberknife

Abstract: For the small radiation field sizes used in stereotactic radiosurgery, lateral electronic disequilibrium and steep dose gradients exist in a large portion of these fields, requiring the use of high-resolution measurement techniques. These relatively large areas of electronic disequilibrium make accurate dosimetry as well as dose calculation more difficult, and this is exacerbated in regions of tissue heterogeneity. Tissue heterogeneity was considered insignificant in the brain where stereotactic radiosurgery was first used. However, as this technique is expanded to the head and neck and other body sites, dose calculations need to account for dose perturbations in and beyond air cavities, lung, and bone. In a previous study we have evaluated EBT Gafchromic film (International Specialty Products, Wayne, NJ) for dosimetry and characterization of the Cyberknife radiation beams and found that it was comparable to other common detectors used for small photon beams in solid water equivalent phantoms. In the present work EBT film is used to measure dose in heterogeneous slab phantoms containing lung and bone equivalent materials for the 6 MV radiation beams of diameter 7.5 to 40 mm produced by the Cyberknife (Accuray, Sunnyvale, CA). These measurements are compared to calculations done with both the clinically utilized Raytrace algorithm as well as the newly developed Monte Carlo based algorithm available on the Cyberknife treatment planning system. Within the low density material both the measurements and Monte Carlo calculations correctly model the decrease in dose produced by a loss of electronic equilibrium, whereas the Raytrace algorithm incorrectly predicts an enhancement of dose in this region. Beyond the low density material an enhancement of dose is correctly calculated by both algorithms. Within the high density bone heterogeneity the EBT film measurements represent dose to unit density tissue in bone and agree with the Monte Carlo results when corrected to dose to unit density tissue in bone. We conclude that EBT film is an appropriate dosimeter for measuring dose in heterogeneous materials and these measurements agree with Monte Carlo calculations of dose as implemented in the Cyberknife treatment planning system.