RTH-26

Paddick conformity index

CI = (TV_PIV)² / (TV × PIV). Unity is a perfectly conformal cloud.

Reading speed

Plan qualityPaddickRTOG

Governing equation

\mathrm{CI}=(\mathrm{TV}_{PIV})^{2}/(\mathrm{TV}\cdot\mathrm{PIV})

where

TV_{PIV}: Target in PIV (cm³)
TV: Target volume (cm³)
PIV: Prescription isodose volume (cm³)
CI: Paddick CI (—)

Lecture brief

Historical brief

The linear-quadratic model, BED, tissue-maximum ratio and Clarkson scatter turned radiotherapy into fraction arithmetic. MU calculation on these sheets is that clinical closed form. This sheet (RTH-26 — Paddick conformity index) is the form associated with Paddick · RTOG. Working symbols: $TV_{PIV}$ , $TV$ , $PIV$ $\rightarrow$ $CI$ . RTOG CI = PIV/TV over-rewards covering a huge isodose. Paddick multiplies coverage by selectivity.

Purpose

Purpose: compute

CI

from

TV_{PIV}

TV

PIV

in Radiotherapy via

\mathrm{CI}=(\mathrm{TV}_{PIV})^{2}/(\mathrm{TV}\cdot\mathrm{PIV})

CI = (TV_PIV)² / (TV × PIV). Unity is a perfectly conformal cloud. Use it when a real radiotherapy question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

TV_{PIV} = 28.000\,\mathrm{cm^{3}}

TV = 30.000\,\mathrm{cm^{3}}

PIV = 36.000\,\mathrm{cm^{3}}

, the governing relation

\mathrm{CI}=(\mathrm{TV}_{PIV})^{2}/(\mathrm{TV}\cdot\mathrm{PIV})

yields

CI = 0.726\,\mathrm{—}

. A PTV blob and a prescription isodose cloud. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Target in PIV TV_{PIV}28 cm³Target volume TV30 cm³Prescription isodose volume PIV36 cm³

Outputs

Paddick CI CI0.726 —

Reading speed

Watch on YouTube

Free library

Full library

Free PDF / open book

YouTube channels

00:0 / 00:08

Narration of this film

A PTV blob and a prescription isodose cloud.

RTOG CI = PIV/TV over-rewards covering a huge isodose. Paddick multiplies coverage by selectivity.

Reading speed

Watch on YouTube