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Treatment Planning I:

Isodose Distribution

Chung-Chi Lee, PhD

Reference:

1.Faiz M. Khan, The Physics of Radiation Therapy, 3rd ed.2003

Introduction

 Isodose curves

 lines passing through points of equal dose

 expressed as a percentage of the dose at a

reference point

 Isodose chart

 Consists of a family of isodose curves usually

drawn at equal increments of percent depth dose,

representing the variation in dose as a function of

depth and transverse distance from the central

axis

Introduction

 Isodose chart

Normalize to isocenter

for isocentric technique

Normalize to d max

for fixed SSD technique

Introduction

 Beam profile

 Field size defined by 50% isodose curves

Field size

Parameters of Isodose Curves

 Beam Quality

 Depth of an isodose curve increases with beam

quality

 The absorbed dose in the medium outside the

primary beam is greater for low-energy beams