Topic 18: radiotherapy uses Flashcards
(21 cards)
Give the 2 conditions for particle acceleration
- Particle being accelerated = must be charged
- Electric field must be in direction of particle acceleration
What causes variations between accelerators?
- Way of producing accelerated electric field
- How field act on particle accelerated
Give the 2 main classes of accelerator
1) Electrostatic
- Superficial +orthovoltage X-ray tubes
- Neutron generators
2) Cyclic
- LINAC
- Microtron/betatron/cyclotron
Describe LINACS
- Cyclic accelerators
- Accelerate e- to KE 4→25 MeV
- e- accelerated following straight trajectories
- In special evacuated structures = accelerating waveguides
What energies does a typical high-energy LINAC provide?
- 2 photon energies = 6 + 18 MV
- e- energies = 6/9/12/16/22 MeV
Give the 3 categories of saftey addressed by IEC
1) Electrical
2) Mechanical
3) Radiation
- Establishes specific requirements in design/construction/installation of LINACS
Give 5 sections of LINACS
1) Gantry
2) Gantry stand
3) Modulator cabinet
4) Patient treatment table
5) Control console
What does the length of the accelerating waveguide depend on?
- Final e- KE
- Range = 30 cm at 4 MeV →150 cm at 25 MeV
Give the 6 main beam forming components
1) Injection system = e- gun
2) RF power generation system
3) Accelerating waveguide
4) Auxiliary system = shielding/vacuum
pump/cooling system
5) Beam transport system
6) Beam collimation + monitoring system
Describe conformal radiotherapy
- Conforms + shapes prescribed dose volume to target volume = tumor
- Keeps dose to specified organ at risk below tolerance
- Tumor control can be improved = technique allows delivery of higher dose + acceptable normal tissue effects
What is conformal radiotherapy chain based on?
- 3D target localization
- 3D treatment planning
- 3D dose delivery techniques
How is target localization achieved?
- Anatomical + functional imaging
How is treatment planning achieved?
- Standard forward planning techniques
- Design uniform intensity beams shaped = geometric projections of target
- Advanced conformal radiotherapy techniques
- Inverse planning used as addition to beam shaping = use intensity modulated beams to improve target dose evenness + organ at risk
What are dose delivery techniques?
- Use standard regular + uniform coplanar beams
- Intensity modulated non-coplanar beams produced with multi-leaf collimators
Describe brachytherapy
- Short-distance treatment of cancer via radiation from small + encapsulated radionuclide sources
- Treatment = source placed directly/near volume being treated
- Dose delivered continuously + over short period / over lifetime of source to complete decay
- Common brachytherapy sources = emit photons
Give 2 types of brachytherapy treatment
1) Intracavitary = sources placed in cavity close to tumor
- Temporary + short duration
2) Interstitial = source implanted within tumor
- Temporary/permanent
How are temporary implants inserted?
- Using manual/remote after loading procedures
What is the advantage/disadvantage of brachytherapy?
ADVANTAGE:
- Improved localized delovery of dose to target
DISADVANTAGE:
- Only be used in cases which tumor is well localized + small
- Only 10-20% radiotherapy patients treated via
Describe geometrical misses
- Treatment doesn’t reach its goal if source misses aimed position by large margin
- Can be detrimental
- Therefore need for quality control
- Dose delivery can result in complex dose rate effect = influence therapeutic outcome
Give the factors influenced by continuous delivery of dose
- Repair of sublethal + potentially lethal damage
- Cell proliferation = growth
- Cell kinetics = cell behavior + cycle
> All can modify radiation response of tumor + normal tissue
Give factors that depend on the choice of appropriate photon for brachytherapy
- Photon energy
- Photon beam penetration
- Half-life
- Half-value layer in sheilding material
- Specific activity
- Source strength
- Inverse square fall off of dose with distance from source
