rt.gamma.index: Gamma index 2D - 3D

In espadon: Easy Study of Patient DICOM Data in Oncology

Gamma index 2D - 3D

Description

The rt.gamma.index function computes the local or global Gamma index from a measurement and a reference. These latter are "volume" class objects containing one (2D) or several planes (3D).

Usage

rt.gamma.index(
  vol,
  vol.ref,
  over.sampling.factor = 1,
  vol.max = vol.ref$max.pixel,
  dose.th = 0.02,
  delta.r = 3,
  analysis.th = 0.05,
  local = FALSE,
  local.th = 0.3,
  project.to.isocenter = TRUE,
  alias = "",
  description = NULL
)

Arguments

vol	"volume" class object, which represents the measured volume.
vol.ref	"volume" class object, which represents the reference volume.
over.sampling.factor	Strictly positive integer, or a vector of 3 strictly positive integers, default to 1. Defined to oversample grids of vol and vol.ref. Oversampling can be very time consuming.
vol.max	Positive number, by default equal to the maximum value of the reference volume. See Details.
dose.th	Number between 0 and 1, used to determine the dose difference criterion. See Details.
delta.r	Positive number, in mm. Distance difference criterion.
analysis.th	Number between 0 and 1. Only the voxels whose value is greater than or equal analyse.th*vol.max are processed.
local	Boolean. If local = FALSE (default), a global Gamma index is computed, and a local Gamma index otherwise.
local.th	Number between 0 and 1. Local threshold, only used if local = TRUE. See Details.
project.to.isocenter	Boolean. If TRUE, and if vol and vol.ref are of modality "rtimage", the size of the pixels is corrected to correspond to that found if the sensor was at the isocenter.
alias	Character string, $object.alias of the created object.
description	Character string, describing the created object. If description = NULL (default value), it will be set to Gamma index setup. \loadmathjax

Details

The Gamma index of a voxel \mjeqnnascii was defined by Low and al [1]. It is computed from the formulae: \mjdeqn\gamma_n = min \left( \sqrt\frac(D_i-Dref_n)^2\Delta D^2 + \fracr_i^2\Delta r^2\right)ascii whith \mjeqnD_iascii the measured dose at voxel \mjeqniascii, \mjeqnDref_nascii the reference dose at voxel \mjeqnnascii, \mjeqnr_iascii the distance between voxels \mjeqniascii and \mjeqnnascii, \mjeqn\Delta rascii the distance difference criterion equal to delta.r, \mjeqn\Delta Dascii the distance difference criterion at voxel \mjeqnnascii defined as follows:

• If local = FALSE a global Gamma index is computed and \mjeqn\Delta D~=~dose.th~\cdot~vol.maxascii.

• If local = TRUE, then \mjeqn\Delta D~=~dose.th~\cdot~Dref_nascii when \mjeqnDref_n~\ge~local.th~\cdot~vol.maxascii, and \mjeqn\Delta D~=~dose.th~\cdot~local.th~\cdot~vol.maxascii otherwise.

Value

Returns a "volume" class object (see espadon.class for class definitions). The $vol3D.data field represents the Gamma index. Two fields are added: the $setup field recalls the calculation setup, and the $gamma.info field details the number of dose points, the number of evaluated dose points,the rate of evaluated dose points, the rate of Gamma indices below 1, above 1.2 and 1.5, the max and the mean Gamma index.

References

[1] \insertReflow1998espadon

See Also

rt.chi.index

Examples

# Creation of a reference volume  and measured volume
# loading of toy-patient objects (decrease dxyz for  better result)
patient <- toy.load.patient (modality = c ("rtdose", "rtstruct"), 
                             roi.name = "ptv", dxyz = c (5, 5, 5))
D.ref <- patient$rtdose[[1]]  
# We will assume that the measured dose is equal to the reference dose shifted
# by 3 pixels on the x axis
D.meas <- vol.copy (D.ref, alias = "measured_dose")
D.meas$vol3D.data[1:(D.meas$n.ijk[1] - 3) ,,] <- D.ref$vol3D.data[4:D.ref$n.ijk[1],,] 
D.max <- as.numeric(quantile(as.numeric(D.ref$vol3D.data), 
                             probs = 99.99/100, na.rm = TRUE))
gamma <- rt.gamma.index (D.meas, D.ref, delta.r = 6, vol.max = D.max)  
gamma$gamma.info  

# Display gamma index at isocenter
G.iso <- patient$rtstruct[[1]]$roi.info$Gz[
  patient$rtstruct[[1]]$roi.info$name == "ptv"]
display.plane(gamma, view.coord = G.iso, 
              bottom.col = c ("#00FF00", "#007F00", "#FF8000", "#FF0000", 
                              "#AF0000"),
              bottom.breaks = c (0, 0.8, 1, 1.2, 1.5, gamma$max.pixel), 
              bg = "blue", interpolate = FALSE)

espadon documentation built on April 11, 2025, 5:57 p.m.