ABSTRACT
FLASH radiotherapy (FLASH RT) is a technique to deliver ultra-high dose rate in a fraction of a second. Evidence from experimental animal models suggest that FLASH RT spares various normal tissues including the lung, gastrointestinal track, and brain from radiation-induced toxicity (a phenomenon known as FLASH effect), which is otherwise commonly observed with conventional dose rate RT. However, it is not simply the ultra-high dose rate alone that brings the FLASH effect. Multiple parameters such as instantaneous dose rate, pulse size, pulse repetition frequency, and the total duration of exposure all need to be carefully optimized simultaneously. Furthermore it is critical to validate FLASH effects in an in vivo experimental model system. The exact molecular mechanism responsible for this FLASH effect is not yet understood although a number of hypotheses have been proposed including oxygen depletion and less reactive oxygen species (ROS) production by FLASH RT, and enhanced ability of normal tissues to handle ROS and labile iron pool compared to tumors. In this review, we briefly overview the process of ionization event and history of radiotherapy and fractionation of ionizing radiation. We also highlight some of the latest FLASH RT reviews and results with a special interest to neurocognitive protection in rodent model with whole brain irradiation. Lastly we discuss some of the issues remain to be answered with FLASH RT including undefined molecular mechanism, lack of standardized parameters, low penetration depth for electron beam, and tumor hypoxia still being a major hurdle for local control. Nevertheless, researchers are close to having all answers to the issues that we have raised, hence we believe that advancement of FLASH RT will be made more quickly than one can anticipate.
ABSTRACT
BACKGROUND: Osteoporosis is an important health concern among the postmenopausal women. Therefore, it is necessary to find out acceptable screening tools for osteoporotic patients. The purpose of this study was to evaluate the Risk Index by OSTA as a screening test for osteoporosis. METHODS: The study population was 322 naturally caused menopausal women in Korea. Their was of femoral neck and lumbar spine BMD measured by DEXA. Risk Index by OSTA, based on weight and age, was calculated and the sensitivity and specificity for osteoporosis and osteopenia were evaluated. To find out the proper cut-off point for osteoporosis and osteopenia among the postmenopausal women in Korea, we also compared the sensitivity and specificity of each Risk Index value. RESULTS: The mean age and ages at menopause were 59.1(+/-6.2) and 50.7 (+/-2.7) years, respectively. The prevalence of osteoporosis was 9.6% with femoral neck BMD. For oeteoporosis, using a cut-off point of -1 yielded a sensitivity of 74.3% and a specificity of 52.2% with femoral neck BMD. Using a cut-off of -2 yielded a sensitivity of 87.3% and a specificity of 70.9%. The ROC curve showed an AUROC 0.88 for Risk Index in identifying osteoporosis. CONCLUSION: The Risk Index is an acceptable, simple and useful method in the diagnosis of osteoporosis with a Risk Index of -2 in Korean postmenopausal women.