Post on 13-Jul-2015
History
– Three aspects that paved the way to discovery of xrays:electricity, vacuums, image recording materials
– Discovery of x-rays by Wilhelm Roentgen 1895, received Nobel Prize in 1901
– Edison experimented with x-rays in 1896 (specifically fluoro), stopped experiments due to damage to colleague Clarence Daly (died in 1904 from radiation side effects)
– Becquerel discovered radioactivity in 1896– Marie Curie discovered radioactive elements (polonium and radium) in
1898– Radium was then used for the first documented cancer treatment in 1898– Soon replaced by Cobalt and Cesium in mid 1900’s– Linacs were developed in 1940
Isodose Curves
• Isodose lines- lines connecting points of equivalent relative radiation dose
• Isodose curve- plotted % depth dose at various points in the beam along the CAX and elsewhere
kV Treatment
• Kilovoltage characteristics– Superficial treatment– CAX dose and physical penumbra are based on beam
quality• Ex. the 50% line of a 200kv beam reaches deeper than the
50% line of a 100kv beam
• Low energy equipment– Grenz– Contact– Superficial– Orthovoltage
MV Treatment
• MV characteristics– Energy above 1MV– Skin sparing– Ability to treat deep tumors– γ-ray beams produces by Radionuclides are included if energy is above
1 MeV
• High energy equipment– Cyclotron– Van de Graaff generator– Betatron– Cobalt 60 unit– Linear accelerator
SSD v SAD
SSD
• The distance from the source of radiation the patients skin
SAD
• The distance from the source of radiation to the axis of rotation of the treatment unit
Linac Components
• Drive stand– Klystron, Waveguide, Circulator, Cooling
System
• Gantry– Electron gun, accelerator structure, treatment
head
• Couch
Linac accessories
• Block- usually made of cerrobend (50% bismuth, 26.7% lead, 13.3% tin, 10% cadmium)
• Wedge• MLC• Electron Cone• Compensator
HDR/LDR Units
• LDR- 40-200cGy/hour• HDR- 1200cGy/hour or 20cGy per min• Both utilize a source
– Iridium, Cesium, Cobalt, and Radium
• Require an Afterloader• Brain, esophagus, rectum, GYN, breast etc.
HDR advantages
• can be given on outpatient basis• Treatment time is short• Implant reproducibility is more
precise• Complete radiation protection
exists• no general anesthesia or bed
rest• Ability to treat large volume• Increased comfort level
Simulator Equipment
• YouTube - CT vs Traditional Sim - Simple Sim• What is simulation?• Conventional• CT • Additions to CT SIM
– MRI– PET
What is simulation?
• Assists in the treatment planning process • Original set-up technique is produced
– Supine– Prone– FF vs. HF
• Process: who would be involved in each?
Diagnosis Consultation Simulation Treatment Planning
Treatment
Conventional SimulationFig. 19-7
• Mimics treatment machine• Enables field delineation• Information is obtained using:
– Fluoroscopy– Radiographs– Physical measurements
CT Simulation
• Patient data is obtained using CT “slices”
• Cost effective for departments: multi-function
• May have a “virtual simulation” component
Conventional & CT sim order of events
• Conventional Sim:1. Field location2. Target defined3. Fields are shaped
• CT Sim:1. Target defined2. Fields are shaped
Additions to CT sim
• MRI• PET• Both of the above are able to be merged
with the CT to help delineate the tumor site as well as other “critical” structures