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