01.Fizica Radiatiilor

Fizica RadiatiilorIAEA Training Material: Radiation Protection in RadiotherapyIAEA Training Material: Radiation Protection in Radiotherapy

IAEA Training Course: Radiation Protection in Radiotherapy

GeneralitatiGenerarea radiatiei, transportul si interactia cu materia sunt procese fizice:Desi radiatia nu poate fi vazuta sau simtita, ea poate fi foarte bine descrisa si cuantificata din punct de vedere fizic;Ea poate fi determinata cu precizie folosind mijloace experimentale adecvate.


Obiectivele ModululuiDe a familiariza cursantul cu diversele tipuri de radiatii ionizanteDe a-l face sa inteleaga cele mai importante procese de interactie care au loc intre radiatie si materieSa-l faca capabil de a folosi si inteleaga toate marimile si unitatile de radiatie de bazaSa aiba cunostinte de baza privind mijloacele de detectie a radiatiilor


ATOMUL si Radiatia Ionizanta

ATOMUL: Nucleu (Z-protoni+N-neutroni= A-nucleoni) + E (-electroni)

Sarcina e- = Sarcina p+ = 1,6 x 10-19 C Z = E ATOM NEUTRU (din punct de vedere electric)

RADIATIA IONIZANTA : Energie suficienta pentru a ioniza atomul (scoate un electron sau adauga unul atomului neutru, din p.d.v. electric)Ia nastere un ion ( incarcat,+ sau - ).


Procesul de Ionizare


Radiatia ionizantaIonul va afecta legaturile chimice.Daca ionul afecteaza ( fie direct, fie indirect ) molecule critice, cum ar fi AND-ul, rezultatul ar putea fi lezarea, mutatia sau moartea celulei.


Spectrul electromagnetic


Continut1. Radioactivitatea2. Tipuri de radiatie ionizanta3. Interactia radiatiei cu materia4. Marimi si unitati de masura a radiatiilor


Identificarea unui IzotopNucleoniAtomulElectroni


Henri Becquerel (1852-1908)Descoperitorul radioactivitatii , 1896


1. RadioactivitateaO proprietate a nucleelorDatorita proprietatilor fizice inerente, un nucleu s-ar putea sa nu fie stabil si sa fie dispus sa sufere o transformare nucleara. Acest proces poate fi rapid (durata de injumatatire scurta) sau lent (durata de injumatatire lunga). In oricare caz, timpul de transformare nu poate fi prevazut pentru un nucleu individual - este un eveniment intamplator care poate fi descris corespunzator, numai folosind statistica


Durata de injumatatire t1/2Descrie cat de rapid un nucleu particular se transformaEste timpul necesar pentru jumatate din cantitatea de material radioactiv sa se transforme (deseori,timp de dezintegrare)


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A(t) = A(0) exp(-t ln2 / t1/2)A(t) activitatea la timpul tA(0) activitatea initiala la timpul 0t timpult1/2 durata de injumatatire ( fizica )


Durata de injumatatire - trasarea logaritmica


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Tipuri de radioactivitateParticule alfa (Nucleu de heliu) - grea, sarcina pozitiva dubla, interactioneaza puternic cu materia.Particule beta/radiatie (electron) - particula usoara, interactioneaza lent,parcurs relativ netRadiatia gama (fotoni)


Dezintegrarea alfa


Dezintegrarea beta


Tranzitia gama


2. Radioactivitatea si Radiatia ionizantaRadioactivitatea este UNA din sursele pentru producerea radiatiei ionizante Depune in materie o cantitate de energie care este suficienta pentru a determina (dupa ionizare) ruperea unor legaturi chimiceDescrierile ca particula sau unda sunt ambele folosite si sunt corecteO particula de radiatie deseori depune energie in mai multe locuri- fie in mod direct, fie pe calea formarii unor alte particule


Tipuri de radiatie (1)radiatiile X si radiatia gama = fotonielectronii si particulele beta - sarcina negativaneutroniiprotonii - sarcina pozitivapaticule alfa si particule incarcate grele


Tipuri de radiatie (2)Radiatii-X si radiatii gama = fotonielectroni si particule beta - sarcina negativaneutroniprotoni- sarcina pozitivaparticule alfa si particule incarcate grele Fotonii si electronii sunt tipurile de radiatii cele mai importante in radioterapie


FotoniiRadiatia gama:radiatie monoenergetica (una sau mai multe linii)Radiatia X: spectru continuuDiferenta apare privind calea de producere :Gama in nucleuRadiatia X-nivel atomic CW Roentgen, discoverer of X-rays


Producerea radiatiei XElectroni de mare energie lovesc o tinta (metalica) unde o parte a energiei lor este convertita in radiatietintaelectroniRadiatii XEnergie joasa sau medie(10-400keV)Energieinalta > 1Me


Aspecte legate de producerea radiatiei XDistributia unghiulara: radiatia X de mare energie este directionata preponderent inainte, in timp ce radiatia X de energie joasa este emisa in principal perpendicularpe fasciculul incident de electroni - tintaEnergie joasa si medie(10-400keV)Energie inalta > 1MeV


Tubul de radiatie X pentru producerea de radiatie X joasa si medie


Acceleratorul linear pentru producerea de radiatie X de energie inalta


Aspecte legate de producerea radiatiei X

Eficienta de producere: In general,cu cat energia este mai mare,cu atat este mai mare eficienta de producere a radiatiei X - aceasta inseamna ca la energii joase cea mai mare parte a energiei electronilor (>98%) este transformata in caldura si, ca urmare - racirea tintei este importanta


Modul de producere a radiatiei X Radiatia X caracteristica: 1 electronul incident scoate un electron de pe un nivel al unui atom din materialul anodului 2 un electron de pe un nivel energetic superior ocupa locul liber iar diferenta de energie este emisa ca radiatie X avand o energie caraceristica acelei tranzitii12


Producerea radiatiei XBremsstrahlung: Electronul incident este deflectat in nivelele atomului si desaccelerat.Diferenta de energie este emisa ca radiatie X


Spectrul rezultat de radiatie X


Efectul filtrarii adaugate


Tipuri de radiatie (3)Radiatia direct ionizanta - energia este depusa de particula in mod direct materiei (electroni, protoni)Radiatia indirect ionizanta - particula primara transfera energia particulei secundare, care la randul sau va determina ionizarea (fotoni, neutroni)


3. Interactia radiatiei cu materiaDetermina penetrarea (masura in care radiatia ajunge la tinta)Determina doza depusa in tinta ?


Tipuri of RadiatieIonizari


Care dintre ele ionizeaza indirect?Ionizare


Compararea caracteristicilor dozelor in profunzime


pentru fotonii cei mai utilizati


Fotonii sunt parte a spectrului electromagneticLumina vizibilaRad X & Rad GamaUVInfrarosiiUnde radioEnergie suficientapentru a produce ionizarea


Interactia fotonilor


Albert EinsteinExplicarea efectului fotoelectric


Consecinte:Ecranarea cu plumb este foarte eficienta la energii joase ale fotonului (diagnostic)In general, fotonii sunt dificil de atenuat,mai ales la energiile de MV folosite pentru terapie Fotonii de energie MV sunt inutilizabili pentru imagistica


Interactia eletronului in materieProcese de ionizare si de excitare a atomilor au loc dealungul parcursului electronului in materie. Depunerile individuale de energie sunt mici iar un electron de energie MV poate depune energie in >10000 locatiiBremsstrahlung (= radiatia de frinare). Electronul pierde continuu energie sub forma de radiatie X pe masura ce este deflectat de campul nucleului


De la radiatie la Doza intr-un fascicul de fotoni


4. Marimi si unitati radiologice Sunt necesare cuantificarii efectelor radiatiei pentru a determina si cuantifica riscurilea determina probabilitatea beneficiilor (tratamentul cancerului sau paleativ)de a analiza beneficiile si riscurilede a optimiza abordarile terapeuticede a lua decizii documentate


Caracterizarea radiatieiSursaDepunereade energiePrimainteractieTransport


Marimi fizice ce pot fi masurateLa sursa: activitatea, mA, kVIn timpul transportului: Flux, fluentaLa punctul primei interactii:Energie Cinetica Eliberata in Materie (KERMA)In materie: Doza absorbita


ActivitateaCantitatea unui radionuclidin SI unitatea este Becquerel (Bq) - o transformare nucleara pe secunda Vechea unitate este Curie (Ci)1 Ci = 37 x 109 Bq = 37 GBq


1 Bq este o cantitate micaPotasiul-40 din fiecare persoana > 1000Bqcele mai multe din sursele radioactive au > 100,000BqSursele radioactive din radioterapie au in mod obisnuit > 100,000,000Bq


Multiplii & prefixe (Activitate)Multiplii Prefix Prescurtare1 - Bq1,000.000 Mega (M) MBq1,000,000,000 Giga (G) GBq1,000,000,000,000 Tera (T) TBq


ExpunereaNumarul de sarcini electrice produse de radiatie in aerEste relativ usor de determinat In SI , se masoara in C/kg ;vechea unitate: Roentgen 1 R = 2.58 x 10-4 C/kg


Doza absorbitaEnergia depusa in materieD = E/m (1 Gy = 1 J/kg)Unitatea este in relatie directa cu efectele in materieNu este obligatoriu in relatie directa cu intensitatea fasciculului de radiatie


Doza absorbitaAceasta marime este definita pentru toate tipurile de radiatii ionizante (nu numai pentru radiatia electromagnetica, cum a fost in cazul expunerii), si pentru orice material .D = dE/dm. In SI unitatea pentru D este Gray [Gy]. 1 Gy = J/kg.Vechea unitate a fost rad. 1 Gy = 100 rad


De la Expunere la DozaEXPUNEREAeste definita numai in aercantitate aprimului impact DOZAfolosind rapoartele puterilor de oprire, poate fi definita in orice mediupoate fi rezultata din expunere folosind W/e


Expunere/Doza absorbitaD [Gy]. = f . X [Ckg-1] f = factor de conversie, depinzand de mediul absorbant

Energia absorbita intr-un gram de aer expus la 1 [Ckg-1] de radiatie X este 0.869 [Gy]f(air) = 0.869


1 Gy este o cantitate relativ mareDozele in radioterapie > 1GyDozele in diagnosticul radiologic, de obicei < 0.001GyRadiatia de fond anuala datorita radiatiei naturale (terestra, cosmica,datorita radioactivitatii interne, Radonului,) : in jur de 0.002Gy


Fractiuni & Prefixe (Doza)Fractiuni Prefix Prescurtare

1 - Sv1/1000 mili (m) mSv1/1,000,000 micro () Sv


Doza echivalenta: HDoza echivalenta H este doza absorbita multiplicata printr-un factor de ponderare pentru radiatie, wR , nedimensional, care exprima eficacitatea biologica a tipului dat de radiatiePentru a evita confuzia cu doza absorbita, in SI unitatea de doza echivalenta este numita Sievert (Sv). Unitatea veche a fost rem 1 Sv = 100 rem


Factorul de ponderare pentru radiatie, wRPentru cea mai mare parte a radiatiilor folosite in medicina (X, , e-) wR este= 1, astfel incat doza absorbita si doza echivalenta sunt numeric egaleExceptiile sunt: particulele alfa (wR = 20) neutronii (wR = 5 - 20).


Doza efectiva, EE = T wT.HT

E : doza efectivawT : factor de ponderare pentru tesut sau organ, THT : doza echivalenta in tesut sau organ T

UNITATEA DE MASURA: Sievert ( Sv )


Factori de ponderare pentru tesut, wT


ORGAN / TESUT

WT

ORGAN / TESUT

WT

Maduva osoasa

0.12

Pulmon

0.12

Vezica urinara

0.05

Esofag

0.05

Suprafata osului

0.01

Piele

0.01

San

0.05

Stomac

0.12

Colon

0.12

Tiroida

0.05

Gonade

0.20

Restul

0.05

Ficat

0.05

Adapted from Zaider 2000Atentie:Depozitarea energiei in materie este un eveniment intamplator si definirea dozei coboara pana la nivele foarte mici (de exemplu o singura celula). Micro-dozimetria se adreseaza acestei probleme.


Sunt intrebari?


Part No 2, Lesson No 1Part II: Radiation PhysicsModule 1: Two lectures as explained in slide 4Lesson 1: Basic radiation physicsLearning objectives: To become familiar with different types of ionizing radiationTo understand the most important interaction processes between radiation and matterTo be able to use and understand all basic radiation quantitiesTo have a basic understanding of the means of radiation detectionActivity: lecture - practical exercisesDuration: lecture 1: 2; lecture 2: 2Materials and equipment needed: Medical Physics textbookReferences: Johns H E; Cunningham J R. The physics of radiology. Springfield: CC Thomas; 1983. Khan F. The physics of radiation therapy. 2nd edition. Baltimore: Williams & Wilkins; 1994.Metcalfe P.; Kron T.; Hoban P. The physics of radiotherapy X-rays from linear accelerators. Madison: Medical Physics Publishing; 1997.VanDyk, J. Modern Technology of Radiation Oncology (Ed.: J Van Dyk) Medical Physics Publishing, Wisconsin 1999, ISBN 0-944838-38-3 Williams J; Thwaites D. Radiotherapy Physics. Oxford: Oxford University Press; 1993.

IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Point out the importance of physics as background to understanding radiationIAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Explanation or/and additional informationThe aim of this module is to have the foundation to understand the most important factors in radiotherapy1. Successful patient treatment2. Safe application including radiation safety

IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Point out that radiation is a general term for many physical (and non-physical) phenomena. The course here is only concerned with ionising radiation.References to non-ionising radiation (ICNIRP) could be given.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Explanation or/and additional information

Instructions for the lecturer/trainer

IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecture assumes familiarity with basic physics concepts - the present slide allows the lecturer to review the basic atomic model and the nomenclature for isotope labeling.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Depending on the background of the participants, the equation on the following slide could be left out.However, in general one would expect that all participants are familiar with the basic shape of an exponential curve. The lecturer should point out:similarity with photon attenuationactivity NEVER gets down to 0

IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1This plot can be used by the lecturer to re-introduce the participants to the logarithmic scale.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The isotopes involved here are transuranium - they are Segborium and RutherfordiumIAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecturer can point out that the neutrino which is also part of the decay equation is needed for conservation of energy and momentum. In the context of the present course it is of no consequence since its probability of interaction with matter is very small.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The isotope shown here is DysprosiumThe lecturer can point out that not decay is mentioned but transition - this is due to the fact that the isotope remains from the same element. Just some internal energy is lost and emitted in the form of electromagnetic radiation.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Explanation or/and additional informationThe next slide states the important fact that electrons and photons are the most important radiation types for radiotherapy.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Explanation or/and additional informationThe lecturer can state that in the following we will learn more about the two types of radiation of interest.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecturer could point out that the difference between the two types of radiation does NOT reflect on energy (it is sometimes stated that gamma rays are of higher energy than X-rays - this is not correct)IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The intention of this slide is not to cover X-ray production extensively. The important issues for the lecturer to point out are mentioned on the next slide.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1In both this and the next slide it is not important to go through all the details of the X-ray production - the important features to note are the target design and the angle of incidence.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecturer can mention that at high energies the efficiency of X-ray production can exceed 50% - however, target cooling is still a major issue because of the high beam currents.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The contents of this slide should follow from the previous discussions. The important points which should be mentioned by the lecturer are given in boxes. An alternative teaching approach would be to delete one or more of the boxes and ask the participants what is displayed.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Unlike in diagnostic radiology, this slide is used here just to illustrate the fact that low energy X-rays are preferentially absorbed by additional filtration.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Explanation or/and additional information

IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecturer should only describe the different processes:Photon - attenuation exponentially in matter - interaction with electrons resulting in a secondary electron depositing energy in matterElectron - interaction with other electrons with usually small transfer of energy. Therefore continuous slowing down. After all energy has been transferred to matter the electron is locally absorbed. This leads to a finite range of electrons in matter.Protons - similar to electrons, however more densely ionizing. More interactions per unit length. Higher energy required for same range in matter as electrons. As a heavier particle also less deviations from original path. Therefore, less angular struggling, less lateral spread of the beam (better penumbra) and better defined range.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The question is aimed at stimulating the students and providing feed back to the lecturer. The photon is the indirectly ionizing particle - it transfers parts of its energy onto the secondary electron which then distributes the energy in matter. If time and background of the students permits, the lecturer can point out that also neutrons are indirectly ionizing particles transferring energy to eg. Protons.

IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1This slide can be used to illustrate two things:1. Indirectly ionizing radiation is attenuated exponentially - the same would be true in eg. Shielding material. Therefore a photon beam will never be completely absorbed. Directly ionizing radiation has a finite range depending on the energy of the incident particle.2. The slide allows a deviation into the radiotherapy context - typical patient dimensions are of the order of 20cm (head) and 30-40cm (torso). One can see what percentage of dose is deposited by different radiation types at this depth.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecturer can point out that the wide spread use of photons is not necessarily linked to their favourable depth dose characteristics - protons would be more desirable. However, photons are the easiest and cheapest penetrating radiation type available.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1This slide rounds up the discussion of ionising vs non-ionising radiationIAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Lecture notes: ( about 100 words)

Instructions for the lecturer/trainerThe lecturer can point out that all of these interactions result in energy transfer onto an electron which then in turn deposits the energy in matter (indirectly ionizing radiation)IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1More details on the interaction types - this slide could be used as a handout.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1Attenuation is the most important property for medical imaging. Differences in the number of photons behind an inhomogeneous absorber create contrast.

In the second step illustrated in the slide we consider only the interactions which actually transfer energy to the matter. This means we exclude all elastic scattering processes such as Thompson scattering. This yields the Total Energy Released in Matter or TERMA. However one is also not interested in the scattered photons, which leave the object after some energy loss (eg. after Compton interaction). If we exclude also this component we obtain the energy which is actually transferred from the photon to electrons or - less importantly - the nuclei. This is also termed Kinetic Energy Released in Matter or KERMA and the coefficient describing this is called mass transfer coefficient m tr/r .IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1This slide introduces the notion of how radiation can be quantified - there are different steps where this can occur. This is discussed in the following in more detail.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1This is an insertion to help make sure all participants are at the same level.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1The lecturer should point out that the x-axis shows d for dimension or size. Similar figures have been drawn for mass as ordinate. In any case it is evident that the specific energy deposited in increasingly smaller volumes becomes less well defined. At small dimensions the line which defines absorbed dose macroscopically becomes blurred and a particular volume may have received a number of different energy quantities. At very small dimensions and low doses the question comes to either having received an event (or more than one) or not.IAEA Training Material: Radiation Protection in RadiotherapyPart No 2, Lesson No 1IAEA Training Material: Radiation Protection in Radiotherapy

01.Fizica Radiatiilor

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