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})

$PIV \in \left[0.5, 250\right]$

where

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

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

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

$PIV \in \left[0.5, 250\right]$

$PIV = 0.5$ $CI = 52.27$

Along the curve

②

Domain of the variable — blue

PIV_{\min} = 0.5,\quad PIV_{\max} = 250

$PIV \in \left[0.5, 250\right]$

$PIV = 0.5$ $PIV = 0.5$

Along the curve

③

Response curve — green

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

$PIV \in \left[0.5, 250\right]$

$PIV = 0.5$ $CI = 52.27$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}CI}{\mathrm{d}PIV}

$PIV \in \left[0.5, 250\right]$

$PIV = 2.069$ $CI^{\prime} = -14.37$

Along the curve

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

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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