 Good morning. I want to give lessons or now courses on dosimetry, fundamentals and then also details for calibration with photons and electrons and later on we will do or perform an exercise. These lectures do not exactly fit to the time schedule which was given to me. So I take the freedom that we will stop at 10 minutes before one then we have lunch but I will not still finish my lecture. I will continue later on and I take the freedom to move freely with my time because I have a lot of time for electron dosimetry which is the smallest one of them. So let's start. So this is a content I want to just to say this once more. I will tell you especially for those who are working in the field of radiotherapy you are familiar with many of the things. Nevertheless I will repeat them and offer to you what I want to discuss is this term radiation dose. We are always saying the dose and we as physicists we should at least to be aware of the precise meaning of what is dose and what is the definition of dose. I want to give general methods for those measurements and there I want to discuss these principles of dosimetry with ionization chambers. In my eyes dosimetry with ionization chambers is still by far the most important one because why. What is what maybe is the reason why it is so important I think from a physical point of view. The reason is that we understand the details the physical details much better than any others. Do we really understand a diet? Who is a physicist who has learned solid state physics? It can be awful. It's cramped mechanics and it's not easy to understand the same with a diamond. I think we don't know exactly understand how a diamond works. I think dosimetry how it really works is that then the developing all this physical process are quite complex and it's easy to use but to really understand and then to describe them in mathematical formulas how the energy deposition goes up into our signal is not always so easy with ionization chamber is much more easy still we do not understand everything it's still I do not understand having having been studied ionization for 30 years. Principles, dose and air stopping power conversion into dose in water burglary condition spends the ethics formulation. So this is what I've used this is this famous book from the agency and this is also a very very good book I think it's it's in my eyes it's the best textbook available now for medical physicists handbook of radiotherapy and it was issued by mace naham and Rosenwald by the way I just maybe you know that but you can get the book directly from the agency website and you can also get slides which are based on that such the slides may be helpful if you are all do your own teaching and if just to say that because I was involved in this preparation of the sliding if someone really needs a source file it's I'm free to give it all the S as power point files in order that if you want to use it as a teacher you can change them in newer ways and you can improve them that's better to use this power the PDF files. So exact physical meaning of dose of radiation so as I already said dose may be a little bit sloppy and as the dose of radiation is currently known by the physical physical well-defined critical point of observed dose D and the definition of this is given in this report number 60 which is here but now we have a new one though this is the new ICU report number 85 and in this report and I can really strongly recommend you to get this ICU report which is summarized the mentals of what are the physical quantities required in radiology it's not so much but this is the most important source for that according to that the absorbed dose is defined by a ratio of the mean energy imparted to a matter of mass divided by a small element of mass the unit is of course you know joule per kilogram and the special name is grain so we can a little bit discuss it now because they are combined with this definition there are some characteristics and I have put here four characteristics number one is the term energy imparted can be considered to be rich and absorbed in a volume in such a way that the energy absorbed is that what the radiation is coming into the volume minus the energy going out of the volume radiology plus some other energies which may occur if there are processes which are releasing mass for instance if you are creating a new particle so then you have to put out the energy of the radiation in order to create the mass and vice versa so there may be some changes of energy of radiation and this has all be taken to count in this definition the term absorbed dose refers to an exactly defined volume that is so important so if you think in dose you always think in terms of a volume or a mass with a certain volume so not a point a point in the metamethic consensus has no volume despite the fact it is defined as a differential ratio you have to think in volumes for those who are working as in Monte Carlo they are they are quite familiar with that you you cannot calculate the dose in a point you have to calculate the dose in a volume you have to define the volume for that first next point is it refers to the material of the volume so absorbed those always refers so it may be the dose in air or it may be dose in water or whatever it may be dose in tissue and I think many of them are you are familiar with this discussion in treatment planning what is important do we calc should we offer to the doctors information on the dose in tissue or in water we have always done in water we have always used the term absorb dose to water but of course it is not water maybe it's it's bones whatever it's of tissue so maybe a better concept to to use it especially and that is again important treatment planning systems modern treatment planning systems which are already commercial available they are introducing Monte Carlo techniques and in Monte Carlo it's much more directly to to calculate the dose in the volume of the tissue of the patient or some approximation they they can calculate the dose in the tissue so to get they get now the dose of diffusion in tissue and bone so now they have to translate it into our old-fashioned water absorb dose so just to to see that that that dose absorb dose refers to a material next one that is very interesting the dose absorb dose is a quantity which is steadily in space and time that means it is a quantity you can differentiate so it is it is defined in a point it refers to a point and if you look to that that may be a contradiction to to I said it refers to a to a volume so what about this thing we have absorb dose referring to a point you can say this is expressed in this r vector and but at the same time it refers to a volume so in order to understand this a little bit more closer I want to discuss now a little bit more background on what's really going on in the especially if we have this definition this question is the same into the question what energy imparted is so you know the dose is defined by the energy imparted so the question is we need a definition now for energy imparted and here's a definition the energy imparted to matter in a given volume is a sum of all energy deposit in the volume quite nice we have one definition and we substitute it for with another definition with another quantity the energy deposit maybe that is again not really helping so we have again but let's see what what is meant with that I have made this picture so we have photons coming from the left side and there is a component effect so we have created secondary electrons here and this is again we have another one which is a photo effect another one photo effect though that happens if tissue or water is you already did it so in regard to our definition now we have to introduce a volume and what is energy imparted oh why it's not coming oh yes let's go back one this is important step the energy imparted is all the energy just to to remind you if an if an electron is traversing to material is it is giving energy continuously all the way the famous question is why electrons have a final range in contrast to photons photons are exponentially decreasing why photons by electrons have a final range very simple why yeah okay they allude the energy and then it's gone then I have to stop that's a very nice question to medical students because we also have to teach the medical physics the medical students and they need some understanding for that and such a simple question they all it's so simple and really it helps to understand why or what is the process with with charge pardon they continuously are losing energy so this is the illustration that the electrons are continuously lost in losing energy and only this part which is within the volume this is the energy imparted so this is not energy imparted here and that's all the energy imparted the volume so this is a clear illustration what is meant by energy imparted what we need for the definition of absorbed dose so and this the energy imparted is a sum of all elemental energy deposits by those basic interaction process which have been occurred in the volume during a time interval considered so this is the formula this are this is our energy imparted and these are the single energy deposits so we need a definition of what what is an energy deposit and again we use this formula but what is important now it refers to a single interaction process between the particle the photons or electrons and the medium so we have single interaction process and with each interaction process we are looking on this equation we have energy going into again we can imagine a very small volume some energy is going out and we have again change of energy now it gives three examples electron on interaction pair production postman annihilation so we have here an electron coming into in this very small uh volume and we have the primary electron and we have a secondary electron and this way it's a quite good question what is a primary electron and what is a secondary electron can we can we see what is a primary can we can we associate one is a primary one is secondary no but this is something which is again basic physics yeah yeah but which one how we can you see we have a knock on process and two electrons are coming out which one is primary which one is secondary it's a very simple it's a higher energy we call the primary very simple okay so there may be some process here fluorescence radiation may come out and even all electrons may come out and this now is the formula the energy the energy to possess is the energy the kinetic energy coming in with these electrons and these are now escaping so all these terms are going out so this is now a definition of an energy deposit of a single event another one is we have photon radiation creating two electrons and this is now another formula the energy deposit is the energy of the photon then these energies of the electrons are escaping but we also have to subtract the amount of energy to create this tool and this is another one absorbed those it is positron and annihilation process and again we have such a formula just to say now I think we have now a better understanding what an energy deposit is can be very different in size and type and so on again this is a formula energy of the incident you only say a particle excluding the rest energy the sum of energies leaving and the change of rest energies now we can this was theory but very simple what if you do a measurement we are simply adding together all this we our measurement signal is proportional to the imparted energy okay now a thing which is not so well aware but I think it is important especially if you are thinking in things now in what really happens in tissue or in a cell or in an enzyme what really happens there I have offered you the illustration of different energy deposits that's very clear that the energy deposit one single can be quite different in size so we never know which will come first because it's a stochastic process this again this is the principle of physics it there's some probability for a process but we don't you cannot say this single photon will have this type of interaction it will have some probability for anyone okay so if if we add up stochastic quantities the result will also be stochastic so our energy imparted is stochastic and what does it mean it means that with respect to repeated measurements of energy imparted that's what you really measure it means that it will never have the same value is that really true it's something strange if you do a dose measurement expect that if you do a careful measurement you want to have an accuracy or uncertainty say of 1% and it should be not change the answer is very simple if you have a huge number of of of a deposit then on average they will be almost not change but in certain cases you can you can see changes and when of course if the number of events is small and when is the number under what conditions the number of deposits is small it's a tectas small or if the dose rate is small dose rate is small in radiation protection so in radiation protection we have such problems the detector is small if we measure dose the data normally is not small so even if you go to one millimeter diameter or say one centimeter diameter but you can you can you can use a detector which has reduced pressure air pressure and there are some detectors are available you can they are called so-called Rossi counters that are filled with they with the equivalent and the pressure is only say 100 1 1 1 over 100 of normed pressure and if you do measure that you will see a huge variation and it's interesting so if you are interested in in study such variations you could use there's a method technique available which has been introduced 30 40 years ago it's called microtosimetry so microtosimetry is a specific special discipline which is dealing with this thing and the other thing of course is what is happening in a cell what is happening in the size of of of a dna of course so you if you you cannot really speak of absorb dose within us in a small cell it will be have some variation and the variation can be huge it can be say it can be if you if you apply one gray in a small size it could be 0.5 graze at the range small so in radiation in the radiation biology it may be important to take such things in account but not for normative symmetry as normal medical physicists we will never never came across with this thing but I think it's quite interesting to know that that this we have this variation and I show you this one picture it's showing the ratio of energy imparted by the mass and now the mass is here really a big mass and it's it's going on smaller and smaller and you see that that the energy imparted is really strongly variation it's a famous graph which is taken from textbook 30 40 years ago and I think it's I like this picture because it underlines the the the knowledge that that this is the case of energy imparted so and this is a reason why this is not the correct definition but it's a mean value by because I am telling you in just to explain it's defined the absorbed dose is defined by the mean value of the energy imparted and thus by this definition it's now a quantity which refers to a point and which is steadily in time and which can differentiate it so this mean value is quite important here so the energy imparted is a stochastic quantity and the absorbed dose is a non-stochastic quantity this is the the conclusion from that so in in in textbooks especially for for for a really assistant you always see this this definition it's so it's just to say this it's not quite correct and I as if you are in the role of a teacher I think you should really use the the exact definition according to the ice report now we have a precise idea what is meant is those really there there are all the other dosimetal quantities and one important oh okay one important example is karma and this is the definition which is again taken directly out of this ice report and I think we have to read it the karma is quotient by d e and this d e whose tr is the sum of the initial kinetic energy of all charged particles liberated by uncharged particles in a mass of material so again it has the same the same unit it is jowl per curicum and it's again gray so this is again our illustration of of absorbed dose so the absorbed dose is is here coming photons and we all here have the energy deposits by the electrons on everything which is within these volume is taken as for the definition of absorbed dose and again this part of energy is not taken and this is not taken so this is the energy absorbed in this example another one also no let's show that here we have we have an ah let's go to that one here is another one interaction which is outside of the volume and the secondary electron is going through within this part is also counting so this is now the karma and we have almost the same structure of secondary electrons created by the photons and now we are taking the kinetic energy the initial kinetic energy of each of these electrons and put this together and the karma is a sum of all these kinetic energies so and remember these is outside the volume and therefore it's not counting so all this energy is not counting for the karma what is important is the difference between absorbed dose the definition and karma absorb those we want to measure and i think we can measure it not always directly but we have our ionization chamber and finally we will get the information absorb dose or we can diet or whatever can we measure the karma we should differentiate between the energies in the detector which are created outside we cannot it's very difficult so the typical difference is that karma can be calculated and the absorb dose can be measured on the contrast absorb dose is not easy to really to calculate there are some exceptions with Monte Carlo where you can do but still it's some approximation there some tiny approximation but the definition of absorb dose is made to have a quantity to be measured the definition of karma is made to be calculated and here are the way how it can be calculated if we have our interaction coefficients there are a number of interaction coefficients available which describe what happens in total if a photon is interacting with material so we have the attenuation coefficient we have the energy transfer coefficient or we have the energy absorbed coefficient that this is the most important coefficient and the calculation follows always a very simple rule if we know the fluence differential in energy if we multiply the fluence with the energy itself then it's called the energy fluence and if we calculate with this interaction coefficient and this this has to be divided by the density factor row then it's called the mass energy transfer coefficient then this product and you have to integrate this over all energies then this is the karma this is the definition of karma and if we want to be more realistic to be what may be stay in the volume and not escape from the volume you should take you should take into account only which is given by the energy absorbed coefficient though the difference between the energy transfer coefficient on one side and energy absorption coefficient is just that the energy which is going into radiation and is escaping is not counted it's taking away so we have just to remind you we have other dosimeter quantities compared to observe those typically here karma and collision karma which are these are for photons and as I already told you absorb those is a quantity which is successful mainly by measurement and karma is a dosimeter quantity which cannot be measured but calculated only based on knowledge of photon fluence differential in energy so let's look now on on the absorb those which are coming from charged particles charged particles that means normally electrons for calculations of those which are created by charged particles we need to introduce a concept of stopping power and again this is our iso report which is saying what is the mass stopping power the mass stopping power of a material for charged particles so stopping power only refers to charged particles of a given type of energy it's a quotient by the by e and role dl del is where e is a mean energy lost by charged particles and traversing a distance in the material of density rule see again we have a definition of energy which is a mean energy lost again the this is refers to to the overall process it's again a non-stochastic character or a description of the energy process which goes from radiation into material the stopping mass can be expressed as a sum of independent components and we have three which are given here and this is the explanation this is called the mass electronic or collision stopping power due to interactions with atomic electrons resulting in interactions the second one is the mass radiation stopping power due to emission of bremsstrahlung in the electric field of atomic nuclear or atomic electrons and we have also a mass nuclear stopping power though we have also some interaction from the electrons with the nucleus which is a if the energy of the electrons is small it's not so important but we have three components and again this is the most important or the most interesting in why this component is small and this component if we think on our volume absorb those it's escaping from the volume we are interested in absorb those so this one is most interesting part so why stopping power is such important concept to see there are two under energy loss at the same time is energy absorbed wonderful and there's a fundamental relationship between absorb those from charge parting and the mass electron stopping power for this there there is another introduction of an often dosimeter quantity which is called chamber who knows that i'm afraid no one it's it it does not play an important role but the people who has written the isoo report there is someone they are insist we have to include the chamber the chamber is given here this explanation the chamber for ionization charge particle is a quotient again it's very similar to the karma definition but what is interesting in is that the that the chamber is can be calculated by again our the fluence of the electrons differential energy times the electronics stopping power so if we know the fluence of electrons by some way by calculation by Monte Carlo calculation for instance we multiply this with this stopping power we can calculate the chamber and the chamber to see is very similar to absorb those so what we can say is absorb those from electrons can be calculated with this way therefore this is important to have all this introduction so this is summary now a very summary which i that's good it fits with that time on on on the first part energy absorption and absorb those this is the definition of absorb those this is the definition of energy imparted being the sum of energy deposit and the energy deposits are referring to single interactions with this balance of energy energy coming in energy coming out and some changes of fresh energy and also which i think is interesting it's not necessary to know it's nice to know but to knows the energy absorber is a stochastic process so i think i will make a break now because now it's time for lunch and i will simply continue after the lunch with this course yeah well the time is because 12 50 lunch break 14 10 14 10 10 minutes after two i will continue