Biomedical Engineering Reference
In-Depth Information
10.
P
ROTON
T
HERAPY IN
W
ATER
The Physical Properties of Protons....................................................213
Coulomb interactions of protons with atomic electrons .......................213
Coulomb interactions of protons with atomic nuclei............................213
Bremsstrahlung .....................................................................................214
Nuclear interactions of protons with atomic nuclei ..............................214
The Depth
Dose Distribution of a Broad Proton Beam ....................215
The Bragg peak .....................................................................................215
Bragg peak dependence on energy and energy spread of the beam .....218
The spread-out Bragg peak (SOBP) .....................................................220
The Electron's Bragg Peak.................................................................222
The Depth-Dose Distribution of a Small Diameter Beam .................223
The Lateral Dose Distribution of a Proton Beam...............................225
Pencil beams..........................................................................................225
Pencil beam broadening due to material upstream of the patient.........227
Broad beams..........................................................................................228
All Things Considered….....................................................................228
Proton Therapy: accelerator and beam delivery................................229
Accelerator ............................................................................................230
Beam-transport system..........................................................................231
Treatment delivery device: gantry ........................................................232
Beam Delivery System: scattered beams ............................................233
Lateral enlargement of the beam...........................................................233
Tailoring the beam in depth: the range modulator................................235
−
Tailoring of the depth of penetration: compensators ............................235
Achieving a sharp penumbra: apertures................................................236
Beam Delivery system: scanned beams ..............................................237
Interplay effects due to organ motion ...................................................240
Beam wobbling .....................................................................................241
Current status of beam scanning ...........................................................242
Beam Control......................................................................................242
Monitoring and dosimetry.....................................................................242
Control and safety systems ...................................................................242
Dosimetry ...........................................................................................242
Absolute dosimetry ...............................................................................243
Relative dosimetry ................................................................................244
In Conclusion......................................................................................245
The ideal radiation with which to treat cancer is one that
delivers a defined dose distribution within the target
volume (generally a uniform distribution, but possibly
a non-uniform one) and none outside it. This is
unachievable. The next best thing would be a radiation
Robert Wilson
Robert Wilson
211
