1. Bremsstrahlung Example of conservation of energy Radiative energy loss by fast electron when slowed near nucleus Results in spectrum of energies from many interactions

2. Diagnostic x-ray production Electrons accelerated by E field Energies < 120kV Can still generate therapy beams this way, but lack penetration Need MV, not kV! 0V + 120kV

3. MV x-ray production Carefully tuned microwave source ~ 3 GHz = 10cm wavelength Intense electric field Phase problem!

4. Microwave resonance cont. Sideline every second cavity Solves phase problem

5. Operation Inject bunches of electrons into cavity Time to coincide with pulses of microwaves Makes compact system

6. Waveguide for 4MV

7. Waveguide cont

8. Target and flattening filter Electrons bent through 270 degrees Collide with tungsten target Beam shaped for flatness

9. Linac

11. Vital statistics Output:6Gy/min at 1m. Lethal dose in ~ 10 min. Weight:~ 8 tonnes Cost: $2.5m to $4m Lifespan:~10y Facility:1.2m to 2.4m concrete as shielding for staff Support:Maintenance contract >$100k per year.

12. The radiation beam 6MV 18MV

13. X-ray dose Vs Depth

14. Combining beams -- a pair

15. Combining beams – three beams

16. A patient plan