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 1895Roentgen discovers x-rays 1895X-rays used to treat breast cancer 1896 Becquerel discovers radiation 1898Radium separated by Curies 1901Radium first used for therapy – skin cancer 1904First text on use of radium for therapy 1951Co-60 used for therapy 1952Linear 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 StageProcess Duration Physical Energy absorption, ionization10 -15 s Physico-chemicalInteraction of ions with molecules, 10 -6 s formation of free radicals ChemicalInteraction of free radicals with seconds molecules, cells and DNA RepairEnzymes in cellshours BiologicalCell death, change in genetic data tens of minutes in cell, mutationsto 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