Medical Physics Blog
by Thirumurugan
8M ago
Medical Physics Blog
by Thiru
1y ago
Briefly on Specific gamma ray constant and Exposure rate constant The specific gamma ray constant is the quotient of Where, is the distance from point source is the exposure rate A is the activity of the nuclide unit : R cm2 h-1 Ci-1 The exposure rate constant has been introduced later on to replace the specific gamma ray constant . Specific gamma ray constant is calculated for each gamma rays emitted by radionuclide and summed. Exposure rate constant has been similarly defined but it includes all photon energies greater than , thus including the characteristic X-rays and bremsstrahlung r ..read more
Medical Physics Blog
by Thiru
1y ago
Introduction Dose volume histogram was first introduced in 1979 by Goitien and Verhey. Dose Volume Histogram (DVH) are presented as structure based DVH and non- structure based DVH. Non structure based DVH are less occasionally used and predominantly structure based DVH is used, though it has gross uncertainties in the precise location of structure. DVH are the result of statistical analysis of the discrete dose sampling points with respect to volume ( dose sampling points either be a 3D grid or randomly distributed dose sampling points). The volume of interest is either Target, Organ At Risk ..read more
Medical Physics Blog
by Thiru
1y ago
D1 : reading of dosimeter under Cu-Al filter D2 : reading of dosimeter under plastic window D3 : reading of Dosimeter under open window RV : Reporting Value D1′ , D2′ , D3′ = D1,D2,D3 minus control card reading Reporting value = 0.2 mSv for gamma, 0.5 mSv for beta, 0.05 mSv for low energy X-rays. If the value obtained are less the reporting value then the values are not reported Depending on the nature of radiation, following algorithm is used Nature of radiation Condition Formulae Gamma only D3′ / D1′ < 1.3 Gamma dose = D1′ Beta dose only D3’/D1′ > 1.3, D3’/D2′ > 1.3, D1′ is v ..read more
Medical Physics Blog
by Thiru
1y ago
The density of ionization in particle track is described by the term Linear Energy Transfer (LET). In other words, it is the measure of number of ions produced per unit path length of the track. What is difference between path length and range? The thickness of medium required for entire energy of the particle to be absorbed is called range The entire zig-zag distance travelled is called path length Is = Sc/W Where, Is is linear density of Ionization. Sc is unrestricted collision stopping power W is avg. energy expended per ionization event. Not all energy accounted for for stopping power Sc ..read more
Medical Physics Blog
by Thiru
1y ago
Transport index is the maximum radiation level in mSv/hr, at a distance of 1 meter from the external surface of the package, multiplied by 100 TI = Radiation level at 1m (mSv/hr) x 100 TI 0.05 can be considered as 0 The packages can be categorized based on the Transport Index What is package? The packaging with its radioactive content as presented for transport what is packaging? The assembly of components necessary to enclose the radioactive contents completely Packaging + radioactive content = package Packages are categorized based on TI into three categories I – white II – yellow III – yel ..read more
Medical Physics Blog
by Thiru
1y ago
Radioactive decay is a stochastic process i.e. probabilistic in nature. In simple words, if we have just one unstable atom we will not know when that atom will disintegrate. But when we have a very large number of unstable atoms of same species, The decay can be estimated using probability distribution i.e. we can say with certain probability that a certain amount of radioactive nuclei will decay in a certain amount of time. There are various modes of radioactive decay i.e. Alpha decay, beta decay and gamma decay. Though all these modes of decay are different in various aspects including the r ..read more
Medical Physics Blog
by Thiru
1y ago
The process are divided into three phases Physical Phase Chemical Phase Biological Phase Physical Phase In physical phase the interaction between the charged particle with the atoms of the tissues occurs. It mainly interacts with orbital electrons, ejecting some of them from atoms while exciting some electrons to higher energy levels. The secondary electrons with sufficient energy can induce further ionization and excitation along the tract(cascade of ionization events). In case of indirect action the fast electrons occurs in approximately 10-15 seconds. A high speed electrons takes about 10 ..read more
Medical Physics Blog
by Thiru
1y ago
Types of Neutron Interaction The neutron interaction is one among the major types Scattering and absorption. In case of scattering, when the neutron interact with the nucleus the speed and direction of the neutron changes but the nucleus will be left with same number of neutron and proton as before. The energy imparted to the nucleus depends upon the angle of scattered neutron and mass of the nucleus. Eventually the nucleus will have some recoil velocity and will be in excited state that will result in the release of radiation. The Scattering is subdivided into two types Elastic scattering I ..read more
Medical Physics Blog
by Thiru
1y ago
Let us consider a system, The system in itself is not a stochastic or non stochastic one. We define a system to be Stochastic or to be deterministic, thus it can be used to measure the physical quantities in it. In Deterministic model we assume we know everything that’s happening in the system and it can be measured using mathematical formulae and equations. In case of Stochastic model the events happens in a random nature, Hence we find the probability distribution of the event in a particular time interval because the values vary discontinuously in space and time. The value obtained will be ..read more

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