Protons Flashcards
Describe the properties of protons.
Protons have a positive electrical charge of one (+1) and a mass of 1 atomic mass unit (amu), which is about 1.67×10−27 kilograms.
Describe and explain the depth dose characteristics of protons.
Has, an excellent dose distribution, high linear energy transfer results in high relative biological effectiveness.
effectiveness Is less dependent on oxygenation of tumour and is less dependent on cell cycle. Type of damage cause reduces the amount of cell repair.
Draw a PDD curve for a 250 MeV proton beam.
SD= roughly 40% DMAX = starts at 30cm ends roughly 35cm
Explain the term SOBP. Briefly describe and explain the basic principle of producing a SOBP
SOBP means spread out barges peak. This is used when the target is wider than the original bragg peak. to spread out the peak different photon energy beams are combined. Surface dose increases
Name two types of accelerators that can be used to accelerate the protons for proton therapy machines.
Cyclotron and Synchrotron
Describe the production and acceleration of protons, focussing on their use in radiation therapy.
Each proton begins its journey at an injector located within an electric field
In the field, hydrogen atoms are ionised and separated into negatively charged electrons and positively charged protons , then sent through a vacuum tube within a pre-accelerator, where their energy is boosted to 2 MeV.
The protons continue to a synchrotron, they travel around the synchrotron about
10 million times per second. Each rotation, a radio-frequency cavity
within the ring delivers
a boost of energy. After leaving the synchrotron, the protons move along
a vacuum tube through a series of steering and focussing magnets. The magnets guide
the protons to the
treatment rooms. use gantries to deliver the proton beam The beam delivery system, or nozzle, shapes and spreads out the proton beam in three dimensions.
Passive scattering
Simple.
Poor proton scatter and only suitable for smaller field sizes.
Has a fixed depth of penetration and fixed modulation
Active (magnetic) Scanning
Irradiation of the target using a narrow beams, like a pencil beam scans the patient.
Beam controlled in three dimensions. Is more complex and must be totally reliable and can treat large fields.
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