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- 1. Types of Radiations X-rays -particles neutrons -rays -particles +-particles Protons Carry enough energy which if deposited in matter can produce ions
- 2. Radiation therapy ideaSelective cell destruction (cancer) How it can be done?By destroying the cell using EnergyHigh energy particles damage a cell by altering its atomCause the atoms electron to become excited and then ionizedEnzymes repair this damage But cancer cell slower than healthy cellSo, the end results (during radiation exposure )More cancer cell end up dying more than healthy cell
- 3. Reminder Absorbed dose D is the energy (joules) deposited per unit mass (kg) of target material, D = dE/dm. The special unit of absorbed dose D is the Gray (Gy) 1 Joule/kg In biological systems Radiation Biologic effects dependent on the spatial distribution of energy deposition (LET)Linear Energy Transfer is energy deposited per unit path length = dE/dx with units ev/cm
- 4. Overview of presentation Photon therapy (briefly) Proton therapy (in detailed) How it works ? The remarkable phenomenon of physics Bragg peak Delivery of the beam (how it can be useful ) How it can be produced ? (synchrotron) RBE of protons . Proton therapy Vs Photon therapy .(summary)
- 5. The desirable goalIn order to treat cancer :The main goal is to delivers a defined dose distribution within the target volume and none out side it. Now Lets see what type of radiation would be the Best??
- 6. Treatment options 1) Photon therapy. 2) Proton therapy.
- 7. Interactions of PhotonsThere are 3 modes: Photo-electric effect.Entire energy transfer from photon to an atomic electron . Compton effect.Fraction of energy transferred to Compton electrons. Pair production.
- 8. What happen when a beam of photon entering a tissue ?
- 9. Exponential behaviour It falls exponentially E E o exp( en x) Number of photon gets attenuated as depth increases . As their number decreases, the dose that they deposit decreases also (proportionately ).
- 10. Photons therapy failure Based on how radiation interacts with matterThe failure is : Most of the radiation is deposited on healthy tissue.Cause of failure !! They are not easy to control Why ?(low mass & high energy) Low LET
- 11. Treatment options 1) Photon therapy 2) Proton therapy.
- 12. Did Proton therapy has the solution ? What can Proton therapy provide ?
- 13. Short story A man with a vision In 1946 Harvard physicist ,Robert Wilson suggested: Protons can be used clinically . Maximum radiation dose can be placed into the tumor . Proton therapy provides sparing of healthy tissues .
- 14. Characteristics of protons Subatomic particle . Stable , positively charged . Heavy particle with mass 1800 that of electron. Very little scattered as they travel through tissue . Travel in straight lines. Which leads to veryMp=1.672621636(83)1027 kgMe= 9.10938215(45)1031 kg different modes of interactions with matter . Lets see!!!!!!
- 15. Interactions of Protons Coulomb interactions with atomic electrons .Electronic (ionization ,excitation) Coulomb interactions with atomic nuclei .multiple Coulomb scattering. Nuclear interactions with atomic nuclei . Elastic nuclear collision Non elastic nuclear collision
- 16. Key fact Different modes of interactions Means Different dose distributions
- 17. The shape of dose distributionIt means that : Low entrance dose (plateau) Maximum dose at depth (Bragg peak) Rapid distal dose fall-off But Why this shape of distribution ? Lets see
- 18. Remarkable phenomenaBragg peakProtons have the ability of loosing little energy when entering tissue . But depositing more and more as they slow down..Finally, depositing a heavy dose of radiation just before they stop ,giving rise to theso-called Bragg peak
- 19. Energy loss dE/dx profiles a protons linear rate of energy loss linear energy transfer (LET) is given by the Bethe- Block formula:
- 20. Bragg Peak like (skiing)
- 21. Bragg peak dependence onenergy The range is( the depth of penetrationfrom the front surface to the distal point on the Bragg peak) Bragg peakdepends on the initialenergy of the protons sothe greater the energy, the greater the range
- 22. There is a problemIs the current shape of Bragg peak could provide the tumor with uniform dose ? No, it cant. BecauseThe Bragg peak is too narrow to fit the shape & depth of the tumor
- 23. Is there a solution ? So, how to make the beam of proton useful for treatment? Is it possible to shape the beam to fit the shape of the tumor ? Lets see!!!!!
- 24. Smart Idea The spread-out Bragg peak (SOBP): Extending the dose in depth meansAn extension in depth can be Superposition of Bragg-peaks by achieved by proton beams energy variation of successivelydelivering not just one, but many Bragg peaks each with different range (energy) energy variation
- 25. Beam delivery system Nozzle There are two main approaches ( techniques) for shaping the beam : (both laterally and in depth) 1) passive scattering. 2)Scanned beam.
- 26. passive scattering.
- 27. Shaping the beam LaterallyThe beam is spread laterally to clinically useful size bydouble scattererand com
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