HSC 34010-14-10
• Photon Dose Distributions– Single and multi-field distributions– Corrections– Tx plan essentials
• Electron Dose Distributions– Physics– Characteristics– Treatment Planning
Photon Dose Distribution
• What are dose distributions?– Pg. 528 PDD – Beam Profile– Flattening Filter
• What are isodose distributions?
Isodose distributions
• Open fields
• Wedged fields
• Multiple fields– POP– Wedged pair
Corrections
• Contour/ObliquityP’=P x {SSD+dm/SSD+dm+h}2
• HeterogeneityDactual= d1+d2+d3
deff= ped1+ped2+ped3
• Table 25-2 and table 25-3
Treatment Planning Essentials
• Rationale for 3-D conformal – Overall goal to deliver 100% dose to tumor and
deliver 0% to critical structures.– Figure 25-12
• 3-D treatment planning & delivery methods– Need CT– IMRT & 3D CRT
Algorithms
• Dose calc process
• Data driven– Bentley-Milan (rarely used)
• Model driven– ADAC Pinnacle
• 2-D vs 3-D – Pg. 25-4
Algorithms cont.
• What should an algorithm be evaluated on?
• Calculation Algorithms– Scatter Integration– Convolution Algorithm
Treatment Planning Concepts
• Planning volumes
• Read Box 25-2 on your own.
• Prescriptions are often based on iso lines
• DVH
Treatment Planning Process
• Image
• Contour
• Delineate Treatment Fields
• Evaluate and Implement
Electron dose distributions
• Interactions are different from photon beam
• Collisional and Radiation Interactions
• Energy Dependence
• Dependence of depth
• Production of Clinically useful e-
• Scattering foils vs. scanning beams
Characteristics of e- beams
• Dose gradients of clinically useful e- beams
• Shapes
Treatment Planning
• Rules of thumb
• Surface characteristics
• Build-up region characteristics
• Energy dependence
• Distance correction factors
• Effective point source
• Virtual source
Irregular fields and e- beams
• Shielding
• Internal shielding
• Effects on dose
• Tissue heterogeneity and dose
• Gaps
• Read Clinical Cases pg.559
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