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Diagnostic Imaging Using X-rays
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
Debbie Peet, Richard Farley, Elizabeth Davies
While absorbed dose can provide a good indication of the severity of deterministic effects, this does not give an indication of stochastic risks associated with an exposure in terms of the increased risk of cancer. Absorbed dose is converted to equivalent dose by using a radiation weighting factor (1 for X-rays). The concept of effective dose takes the equivalent dose to each organ, the proportion of that organ irradiated and sums these to give a whole body effective dose. This allows risks to be compared between different types of scans and between organs, for example, comparing a chest X-ray to an X-ray of the pelvis. As we cannot measure the dose absorbed within the organ of an individual, how do we estimate effective dose? We estimate it using computerised models such as those described in the sections below.
Radiation Dose and Exposure Indicators
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
Equivalent dose allows the effect of radiation exposure on human tissue to be determined. It relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. The SI unit of equivalent dose is the Sievert (Sv) and represents the stochastic biological effect. The Sievert is a large unit and for normal radiation protection levels a series of pre-fixes are used:Microsievert (μSv) is one millionth of a Sievert (1 × 10−6)Millisievert (mSv) is one thousandth of a Sievert (1 × 10−3)
Area and Individual Radiation Monitoring
Published in Arash Darafsheh, Radiation Therapy Dosimetry: A Practical Handbook, 2021
The equivalent dose,, in a tissue or organ is given by , where is the mean absorbed dose in the tissue or organ, T, due to radiation, R, and is the corresponding radiation weighting factor. The unit of equivalent dose is the Sievert.
Implementation of simplified stochastic microdosimetric kinetic models into PHITS for application to radiation treatment planning
Published in International Journal of Radiation Biology, 2021
Tatsuhiko Sato, Shintaro Hashimoto, Taku Inaniwa, Kenta Takada, Hiroaki Kumada
Radiation therapy using high linear energy transfer (LET) particles such as carbon-ion radiotherapy (CRT), boron neutron capture therapy (BNCT), and targeted alpha therapy (TAT) have gained increasing public attention, especially for the treatment against radioresistant and malignant tumors. The therapeutic and side effects of these modalities are generally estimated from the absorbed doses multiplied by their relative biological effectiveness (RBE). Various terms have been used to describe this quantity, such as RBE-weighted dose, biological dose, photon isoeffective dose, photon equivalent dose, and equieffective dose. Among them, we use the term photon isoeffective dose, DisoE, following the joint proposal of the International Atomic Energy Agency (IAEA) and the International Commission on Radiation Units and Measurements (ICRU) (IAEA 2008).
Challenges in the quantification approach to a radiation relevant adverse outcome pathway for lung cancer
Published in International Journal of Radiation Biology, 2021
Robert Stainforth, Jan Schuemann, Aimee L. McNamara, Ruth C. Wilkins, Vinita Chauhan
Values of equivalent dose (Sv) were converted to absorbed dose (Gy) using the relevant radiation weighting factors defined by the International Commission of Radiation Protection (ICRP 2007). Radon exposure of the lungs reported in units of working level months (WLM) were converted to estimates of absorbed dose by using the recommended ICRP effective dose coefficient for mine and general indoor environments (=10 mSv/WLM; ICRP 2017), tissue weighting factor (=0.12 for the lungs), and radiation weighting factor (=20 for alpha-particles; ICRP 2007). Studies contributing to the WoE of NAd-KER7 were predominantly from occupational cohorts of miners that only provide a summary on the average career-span of a worker, and any lag-period, if any, following the end of employment for which a RR of lung cancer was assessed. In these cases, missing values of the dose rate were estimated as the ratio of the average dose and career-span. The exposure was therefore assumed chronic and constant. The time after exposure was estimated as the average career-span in addition to any lag-period following employment. Missing dose rate values for studies contributing to the upstream KEs for Ad-KER1, NAd-KER1, and NAd-KER2 could not be estimated using the same assumption as the nature of the radiation exposure in these studies was often acute.
Radiation metabolomics in the quest of cardiotoxicity biomarkers: the review
Published in International Journal of Radiation Biology, 2020
Michalina Gramatyka, Maria Sokół
Biological effects of ionizing radiation are related to the energy deposition in living matter. The units to measure a dose and its biological effects are required to assess the impact of ionizing radiation on human health and to set the guidelines in radioprotection (Hall and Giaccia 2018). The fundamental dosimetric quantities of ionizing radiation are absorbed and equivalent dose. Absorbed dose is indicated in Grays – 1 Gy equals 1 Joule of absorbed energy per kilogram of mass, e.g. tissue. Because equal doses of different types of ionizing radiation are not equally absorbed in biological matters radiation exposure can be expressed as tissue equivalent dose in Sieverts: 1 Sv is the absorbed dose multiplied by a radiation weighting factor accounting for differences in the biological response (Pfalzner 1983).