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Radiotherapy Physics

Radiotherapy Physics. Chris Fox Department of Physical Sciences Peter MacCallum Cancer Centre. Cancer: the numbers. In 2004, Victoria lost 9,613 people to cancer Nearly 30% of all deaths in 2004. By site. By time. Generally steady decline in mortality. Incidence -- men.

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Radiotherapy Physics

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  1. Radiotherapy Physics Chris Fox Department of Physical Sciences Peter MacCallum Cancer Centre

  2. Cancer: the numbers • In 2004, Victoria lost 9,613 people to cancer • Nearly 30% of all deaths in 2004

  3. By site

  4. By time • Generally steady decline in mortality Incidence -- men Incidence -- women Mortality: men Mortality: women

  5. Treatment • The gap between incidence and mortality is treatment

  6. Survivable? • M/I = Mortality/Incidence ratio • Good guide to survivability • Low M/I • high likelihood of surviving • Treatment effective

  7. Treatment • Three main forms of treatment • Radiotherapy • Chemotherapy • Surgery • Radiotherapy used in 30% – 50% of cases

  8. Radiotherapy: quick history • 1895 Roentgen discovers x-rays • 1895 X-rays used to treat breast cancer • 1896 Becquerel discovers radiation • 1898 Radium separated by Curies • 1901 Radium first used for therapy – skin cancer • 1904 First text on use of radium for therapy • 1951 Co-60 used for therapy • 1952 Linear accelerator used for therapy

  9. Basis of Radiotherapy • Radiation disables cells • Disrupts DNA • Attack via • direct ionisation/excitation • Free radicals formed from water in cell • Some repair may follow • Cell may not be killed, but can’t reproduce. Disabled.

  10. Timeline Stage Process Duration Physical Energy absorption, ionization 10-15 s Physico-chemical Interaction of ions with molecules, 10-6 s formation of free radicals Chemical Interaction of free radicals with seconds molecules, cells and DNA Repair Enzymes in cells hours Biological Cell death, change in genetic data tens of minutes in cell, mutations to tens of years

  11. Discrimination • Cancer tissue is poorly organised. DNA repair less effective than normal tissue • Therefore more sensitive to radiation than normal tissue = therapeutic advantage • Advantage often slender. Accuracy needed with dose!

  12. Radiation dose delivery • Three approaches used: • Beaming high energy x-rays into patient from outside • External beam Radiotherapy (EBRT) • Linear accelerators (Linacs) generate the x-rays • Radioactive sources inside diseased tissue • Brachytherapy • Administering radioactive solutions that concentrate in diseased tissue • Often part of Nuclear Medicine (NM) • We’ll focus on EBRT • Most widely used.

  13. Linear accelerators • High energy x-ray generators • Photon energies between 6MV and 25MV • Microwave devices • Generate x-rays using bremsstrahlung • Accelerate electrons, collide with high-Z material • Convert kinetic energy to radiation

  14. Linac

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