Upload
ginger-sabrina-wiggins
View
215
Download
0
Embed Size (px)
Citation preview
M.G. Pia et al.
Brachytherapy at ISTResults from an atypical Comparison Project
Stefano Agostinelli1,2, Franca Foppiano1, Stefania Garelli1, Matteo Tropeano1
1National Institute for Cancer Research and 2Physics Dept. Univ. of Genova
Petteri Nieminen & Maria Grazia Pia
M.G. Pia et al.
History
March 2000Comparison Projects were approved by the CB/TSB as a milestone 2000
The group decided to contribute to the milestone
June 2000Proposals were presented to the TSB First results shown to the TSB
The status of comparison projects is presented at the Geant4 Workshop
Further results presented at the Calor2000, MC2000, AIRO conferences and Geant4 workshop
October 2000
April 2000Letters of intent were presented to the TSB by the experiments
Work on the Comparison Project started
May 2000 First results presented at the ICCR conference
September 2000 Further results presented at the ESTRO conference
December 2000 Code to be released as an advanced example
Publications2001
M.G. Pia et al.
• a radioactive source, for example 192Ir, is used
• the source moves along catheters inserted in natural cavities of the body, e.g. vagina or bronchi; this allows the deposition of the therapeutic tumor dose right where it is needed
• the source track is programmed by an after-loading unit
What is brachytherapy?What is brachytherapy? Brachytherapy is a medical therapy used for cancer treatments Radioactive sources are used to deposit therapeutic doses near tumors
while preserving surrounding healthy tissues
In HDR endocavitary brachytherapy:
Catheter along which source moves
After-loading unit
M.G. Pia et al.
Brachytherapy treatment planningBrachytherapy treatment planning
A typical vaginal treatment plan: source moves along a single catheter
A typical intra-uterine treatment plan: the source moves along
3 catheters
M.G. Pia et al.
Monte Carlo for brachytherapyMonte Carlo for brachytherapy
Monte Carlo simulation topics for brachytherapy: Dose calculation
Computation of dose deposition kernels for treatment planning dose
calculation algorithms based on convolution/superposition methods
Separation of primary, first scatter and multiple scatter components for
complex dose deposition models
Computation of other model-dependent parameters, e.g. anisotropy
function
Accurate computation of dose deposition in high gradient regions (i. e.
near sources)
Verification of experimental calibration procedures
M.G. Pia et al.
Comparisons with dataComparisons with data
Simulated water (photon attentuation coefficient)
Comparison of NIST data with Geant4
Standard electromagnetic package
and Low Energy extensions results
Comparison with in-house experimental data
and
certifications of the supplying company
Tests of Low Energy/Standard e.m. Physics packages
ESA Radioactive Decay Module
Full simulation of the radioactive source
Simulation of a simple set-up
M.G. Pia et al.
Comparisons with full source simulation
Air kerma rate at various distancesAir kerma rate at various distances
Comparisons with measurements of the air kerma rate at IST, following the Protocol for the Basic Dosimetry in Radiotherapy with Brachytherapy Sources of the Italian Association of Biomedical Physics
AnisotropyAnisotropy
Comparisons with published reference treatment planning data
IsodosesIsodoses
Comparisons with tabulated isodoses for superficial brachytherapy applicators
M.G. Pia et al.
Photon attenuation coefficient, Water
0.01 0.1 1 10
0.1
1
10
Geant4 LowEn NIST
/
(cm
2 /
g)
in w
ater
Photon Energy (MeV)
0.01 0.1 1 10-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
16
Delta = (NIST-G4EMStand) / NIST Delta = (NIST-G4LowEn) / NIST
Del
ta (
%)
Photon Energy (MeV)
(Statistical errors are smaller than dot size)
Comparison of Geant4 LowE/standard e.m. processes and NIST data
M.G. Pia et al.
Photon attenuation coefficient, Fe
(Statistical errors are smaller than dot size)
0.01 0.1 1 100.01
0.1
1
10
100
1000
Geant4 LowEn NIST
/ (
cm 2
/g)
in ir
on
Photon Energy (MeV)
0.01 0.1 1 10-18-16-14-12-10-8-6-4-202468
1012141618
E = (NIST-G4EMStandard)/NIST E = (NIST-G4LowEn)/NIST
E (
%)
Photon Energy (MeV)
Comparison of Geant4 LowE/standard e.m. processes and NIST data
M.G. Pia et al.
Photon attenuation coefficient, Pb
(Statistical errors are smaller than dot size)
0.01 0.1 1
0.01
0.1
1
10
100
Geant4 LowEn NIST
/ (
cm 2
/ g
in le
ad
Photon energy (MeV)0.01 0.1 1
-10
-8
-6
-4
-2
0
2
4
6
8
10 E = (NIST - G4EM Standard)/NIST E = (NIST- G4LowEn)/NIST
E (
%)
Photon Energy (MeV)
Photons are all absorbed with Standard below 100 keV
Comparison of Geant4 LowE/standard e.m. processes and NIST data
M.G. Pia et al.
Description of Description of -Selectron -Selectron 192192Ir sourceIr source
Geant4 allows complete flexible description of the real geometry
3 m m ste e l c a b le
5.0 m m
0.6 m m
3.5 m m
1.1 m m
Ac tive Ir-192 C o re
192Ir energy spectrum currently described as monochromatic at 356 keV will soon be described by the ESA Geant4 RadioactiveDecay class
M.G. Pia et al.
Simulation of dose deposition in waterSimulation of dose deposition in water
The simulated source is placed in a 30 cm water box The dose deposition is investigated in the longitudinal plane The plane is partitioned in 1 million 1mm3 voxels A minimum of 10 millions photons are generated on the 4 solid angle
Longitudinal plane partitioned in cells
-Selectron 192Ir source
M.G. Pia et al.
Investigated quantities: anisotropyInvestigated quantities: anisotropy
The dose deposition is not isotropic due to source geometry and auto-absorption, encapsulation and shielding effects
Anisotropy can be described by a simple angular function which can be computed by re-sampling our simulated voxels grid calculations
0
30
60
90
120
150
180
M.G. Pia et al.
Investigated quantities: isodosesInvestigated quantities: isodoses
The simulated dose deposition data can also be used to derive isodoses
M.G. Pia et al.
Products of this Comparison Project
Tests of Geant4 LowE/standard e.m. processes
Tests of the Geant4 Radioactive Decay Module A physics test () to become part of regular LowE testing
An Advanced Example to be released to the user communities
The porting of Geant4 2.0 to Windows/Cygnus 4 common presentations at conferences so far
2 common publications in preparation (+ IST group’s ones)
A wide promotion of Geant4 in the medical environment
A contribution to technology transfer
M.G. Pia et al.
Conclusions and future goalsConclusions and future goals
This Comparison Project has already generated valuable products
The activity of the experimental group and of the Geant4 collaborators are fully integrated, with mutual benefit
Further developments and comparisons are planned in the next weeks
More realistic description of 192Ir source energy spectrum with the new Geant4 RadioactiveDecay class
Comparison with in-house data Simulation of shielded brachytherapy applicators
Many thanks to Gabriele Cosmo and Alessandro Brunengo for their invaluable help!