Equivalent dose

Abstract: With the rapid development of clinical hyperthermia for the treatment of cancer either alone or in conjunction with other modalities, a means of measuring a thermal dose in terms which are clinically relevant to the biological effect is needed. A comparison of published data empirically suggests a basic relationship that may be used to calculate a "thermal dose." From a knowledge of the temperature during treatment as a function of time combined with a mathematical description of the time-temperature relationship, an estimate of the actual treatment calculated as an exposure time at some reference temperature can be determined. This could be of great benefit in providing a real-time accumulated dose during actual patient treatment. For the purpose of this study, a reference temperature of 43 degrees C has been arbitrarily chosen to convert all thermal exposures to "equivalent-minutes" at this temperature. This dose calculation can be compared to an integrated calculation of the "degree-minutes" to determine its prognostic ability. The time-temperature relationship upon which this equivalent dose calculation is based does not predict, nor does it require, that different tissues have the same sensitivity to heat. A computer program written in FORTRAN is included for performing calculations of both equivalent-minutes (t43) and degree-minutes (tdm43). Means are provided to alter the reference temperature, the Arrhenius "break" temperature and the time-temperature relationship both above and below the "break" temperature. In addition, the effect of factors such as step-down heating, thermotolerance, and physiological conditions on thermal dose calculations are discussed. The equations and methods described in this report are not intended to represent the only approach for thermal dose estimation; instead, they are intended to provide a simple but effective means for such calculations for clinical use and to stimulate efforts to evaluate data in terms of therapeutically useful thermal units.

Abstract: Objectives This study compares 2 measures of effective dose, E1990 and E2007, for 8 dentoalveolar and maxillofacial cone-beam computerized tomography (CBCT) units and a 64-slice multidetector CT (MDCT) unit. Study design Average tissue-absorbed dose, equivalent dose, and effective dose were calculated using thermoluminescent dosimeter chips in a radiation analog dosimetry phantom. Effective doses were derived using 1990 and the superseding 2007 International Commission on Radiological Protection (ICRP) recommendations. Results Large-field of view (FOV) CBCT E2007 ranged from 68 to 1,073 μSv. Medium-FOV CBCT E2007 ranged from 69 to 560 μSv, whereas a similar-FOV MDCT produced 860 μSv. The E2007 calculations were 23% to 224% greater than E1990. Conclusions The 2007 recommendations of the ICRP, which include salivary glands, extrathoracic region, and oral mucosa in the calculation of effective dose, result in an upward reassessment of fatal cancer risk from oral and maxillofacial radiographic examinations. Dental CBCT can be recommended as a dose-sparing technique in comparison with alternative medical CT scans for common oral and maxillofacial radiographic imaging tasks.

Abstract: The internal dosimetry schema of the Medical Internal Radiation Dose (MIRD) Committee of the Society of Nuclear Medicine has provided a broad framework for assessment of the absorbed dose to whole organs, tissue subregions, voxelized tissue structures, and individual cellular compartments for use in both diagnostic and therapeutic nuclear medicine. The schema was originally published in 1968, revised in 1976, and republished in didactic form with comprehensive examples as the MIRD primer in 1988 and 1991. The International Commission on Radiological Protection (ICRP) is an organization that also supplies dosimetric models and technical data, for use in providing recommendations for limits on ionizing radiation exposure to workers and members of the general public. The ICRP has developed a dosimetry schema similar to that of the MIRD Committee but has used different terminology and symbols for fundamental quantities such as the absorbed fraction, specific absorbed fraction, and various dose coefficients. The MIRD Committee objectives for this pamphlet are 3-fold: to restate its schema for assessment of absorbed dose in a manner consistent with the needs of both the nuclear medicine and the radiation protection communities, with the goal of standardizing nomenclature; to formally adopt the dosimetry quantities equivalent dose and effective dose for use in comparative evaluations of potential risks of radiation-induced stochastic effects to patients after nuclear medicine procedures; and to discuss the need to identify dosimetry quantities based on absorbed dose that address deterministic effects relevant to targeted radionuclide therapy.

Abstract: The Mars Science Laboratory spacecraft, containing the Curiosity rover, was launched to Mars on 26 November 2011, and for most of the 253-day, 560-million-kilometer cruise to Mars, the Radiation Assessment Detector made detailed measurements of the energetic particle radiation environment inside the spacecraft. These data provide insights into the radiation hazards that would be associated with a human mission to Mars. We report measurements of the radiation dose, dose equivalent, and linear energy transfer spectra. The dose equivalent for even the shortest round-trip with current propulsion systems and comparable shielding is found to be 0.66 ± 0.12 sievert.