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!