FLUKA Monte Carlo Simulation for the Leksell Gamma Knife ... · FLUKA Monte Carlo Simulation for...

FLUKA Monte Carlo Simulation for the Leksell Gamma Knife© PerfexionTM

radiosurgery system

Collaboration Project:

radiosurgery system

Collaboration Project:

Θ INFN, Milan;

Θ Medical Physics Department, Niguarda Ca'Granda Hospital, Milan;

Θ l k d ( d )Θ Elekta AB Instruments Sweden (producer company).

Fabrizio CappucciINFN Milan

Leksell Gamma Knife Perfexion (LGK-PFX)

The Leksell Gamma Knife Perfexion is a 60Comedical device based, manufactured by Elekta Sweden, able to apply sophisticated radiation surgery technique. It is used to treat small brain and spinal cord tumors (both benign and malignant), blood vessel abnormalities in the brain, as well as neurologic problems.

The gamma rays are delivered by 192 sources (average activity 1TB h) d 8 id ti l t hi h lid~1TBq each), arranged on 8 identical sectors which can slide on a

cone configuration. In this way the source can be placed on correspondence of three different collimation set able to focus the

t ll d th i t f th fi ldgamma rays on a common spot, called the isocenter of the field, having a radial dimension of about 4, 8 and 16 mm respectively.

FLUKA Monte Carlo Simulation for the Leksell Gamma Knife© PerfexionTM radiosurgery system


Implementation of the simulation

The collimation system geometry, the sources positioning and all the involvedmaterial, have been properly simulated.

The starting point of the beams has been uniformly sampled inside the source volume.

The simulations have been performed splitting the runs in a Macintosh cluster made up of twelve quadri-processor nodes.

Each simulation has been performed in the homogeneous condition of the target.

FLUKA Monte Carlo simulation has been validate by means of a comparison with the TPS data provided by Elekta in the same condition.



Gamma Knife Perfexion geometry

TUNGSTEN



FLUKA implemented geometry and materials

flair geoviewerflair geoviewerSimpleGeo 4.2



ResultsBy means of FLUKA code the relative dose distribution along the three coordinated axes for each kind of collimator size and the output factors for various size of scoring volumes have been investigated.

1 O t t f t (OF)1- Output factor (OF).

By definition, the output factors (OF) are the ratio between the dose given by a set of collimators and the dose given by the largest collimators i e the 16 mm which iscollimators and the dose given by the largest collimators, i.e. the 16 mm, which is taken as reference size and its OF is set equal to 1.000. For the 8mm and the 4mm collimator size the Elekta OF values are 0.924 and 0.805 respectively.

Collimator size

ELEKTA OF FLUKA OF Δ

8 mm 0 924 0 915 ± 0 2% 1 0

Δ is the percentage difference between the results from Monte Carlo calculation and the Elekta values:

8 mm 0.924 0.915 ± 0.2% 1.0

4 mm 0.805 0.792 ± 0.2% 1.6 100% · 1-FLUKA

ELEKTA OF

OF⎟⎟⎠

⎞⎜⎜⎝

⎛=Δ



2- Relative dose profile 4mm Collimators X-Axis



2- Relative dose profile 8mm Collimators Y-Axis



2- Relative dose profile 16mm Collimators X-Axis



2- Relative dose profile 16mm Collimators Z-Axis



In the figure obtained from a FLUKA

Relative dose distribution inside the dosimetry phantom

In the figure, obtained from a FLUKAsimulation for the 16mm collimatorsize with 109 of primary hisories, canbe fully apreciated the superpositiony p p peffect, due to different sectorcontribution, in the final relative dosedistribution. It can be noticed how thiseffect causes a fast drop in the relativedose value, which pass from the 100%value in the isocentre spot, to 30%

ithi f b t 2 5

2.5 cm

within a range of about 2.5 cm.This technique allows to provide ahigh dose rate in a small target,lowering the dose value delivered tolowering the dose value delivered tothe surrounding healthy tissues.



Conclusions

The data comparison prove that FLUKA is capable to simulate succesfully the Leksell Gamma Knife Perfexion Treatment

l i f k ll l ( ) i hPlanning Software Leksell GammaPlan (LGP) in homogeneous conditions.

If 8mm OK SIMULATION CONSIDERED VALIDATED

The next step of this work should include the inhomogeneousp gcondition of the target and the importing in FLUKA of CT scans relative to real clinical cases in order to understand how the heterogeneity presence can affect the dose distribution The TPS doheterogeneity presence can affect the dose distribution. The TPS do not considers at all the heterogeneities presence.



THANKS FORTHANKS FOR YOUR ATTENTIONYOUR ATTENTION.



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