MEDICAL PHYSICS

The main elements in the course are basic interaction mechanisms between ionizing radiation and matter and the theoretical basis for dosimetry for the use in radiotherapy and risk assessment of radiation exposure of humans. Important topics are Interaction cross-sections (classical), mechanisms for the interaction of photons, neutrons and charged particles, fundamental entities in dosimetry, cavity theories, radiation equilibrium, applied dosimetry in radiation-based medical diagnostics and therapy, neutron dosimetry, detectors for dosimetry.

Teaching will consist of a combination of classroom lectures, electronic lectures/tasks, calculations and group tasks with a set of experimental activities that will be organised in laboratory.

The experimental activity will deal with:

• The measure of dose from a natural source with an absolute ionisation chamber
• The measure of microdosimetric spectra with a solid-state detector
• Measure of a gamma spectra emitted by a natural source with a Gernanium detector
• The analysis of a plastic detector irradiated with ion beams
• [Other experimental activities could be added depending on time disposal]

Moreover, we can discuss additional activities on medical physics experiments may be of interest

Basis on particle interaction with matter; basis on detector for ionization radiations

4/6 hours per week

1. Basic concepts
   • Quantities and units
   • The ionizing radiations
   • Mass, energy, velocity
   • Gamma, X and charged particles interaction with matter
   • Exponential law applications

1. The production, properties and measures of gamma radiation and its application in medical physics
   • The X-Rays tube and its circuits
   • Rating of diagnostic tubes
   • X-Ray spectra
   • Interaction of the electrons with a target and the bremsstrahlung radiation
   • Gamma radiation from linear accelerator and their therapeutic applications
   • Measurements of the characteristics and qualities of gamma radiation
2. Radiation dosimetry
   • Quantities for describing the interaction of ionizing radiation with matter
     1. KERMA
     2. KERMA to energy fluence, dose and exposure relation for photon and neutron beams
     3. Absorbed dose for direct and direct ionization radiation
     4. Compared examples of energy imparted, energy transferred and net energy transferred
     5. Exposure
   • Charged-particle and radiation equilibria
     1. Radiation equilibrium
     2. Charged particle equilibrium
     3. Use of the charged particle equilibrium in the measure of exposition
     4. Relation between absorbed dose and exposure
     5. Cases of the charged particle equilibrium failure
     6. Transient charged particle equilibrium
3. The cavity theory
   • Bragg-Gray theory
   • Spencer’s derivation of the Bragg-Gray theory
   • Averaging stopping powers
   • Spencer and Burlin cavity theory
   • The Fano theorem
   • Calculation of the absorbed dose for charged particle beams
     1. Dose in thin foils
     2. Mean dose in thicker foils
     3. Contribute of the electron backscattering
     4. Dose versus depth relation
4. Dosimetry fundamentals
   • Concepts of radiation dosimetry and dosimeter
   • Interpretation of a dosimetric measure
   • General characteristics of a dosimeter
5. The ionization chambers in radiological dosimetry
   • Cavity ionization chamber
   • Charge and current measurements
   • Ionisation and excitation
   • Ion-chamber saturation and ionic recombination effects
6. Dosimetry and calibration for photon, electron and ion beams with cavity ion chamber
   • Ion-camber calibration in phantom
   • The TRS398 IAEA international protocol
   • Practical procedures to determine the absolute dose with ion chamber
     1. Case of gamma beams
     2. Case of electron beams
     3. Case of charged particles
7. Microdosimetry
   • What is microdosimetry
   • Examples of the need of microdosimetry
   • Stochastic and non-stochastic quantities and connection between microdosimetry and dosimetry
   • Main approaches to microdosimetry
     1. LET distributions and their limitations
     2. Connection of LET with the biological damage
     3. Radial profile approach
     4. Track structure simulation approach
   • Proportional counters microdosimetry
   • Track structure simulations

1. F.H. Attix - Introduction to radiological physics and radiation dosimetry, Wiley-VCH Verlag edition
2. H. Johns and J. R. Cunninghan - The physics of radiology - Charles Thomas publisher
3. G.F.Knoll - Radiation detection and measurements - John Wiley & Sons, Inc.

The final exam will be organised in:

1. The discussion on one specific experimental activity performed during the class and discussed with the students
2. General questions on what is discussed during the classes

1. Calculate the absorbed dose of a gamma beam of given energy and flux in a given material
2. Calculate the absorbed dose of a proton beam of given energy and flux in a given material
3. Definition of LET and Stopping power
4. Definition of the most important dosimetric quantities
5. Explanations and discussion of the experiment performed during the course