1 treatment planning systems for bnct the main role of the treatment planning (tp) the treatment...

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Treatment Planning Systems for BNCT

The main role of the Treatment Planning (TP)

The Treatment Planning System (TPS)

Requirements and Peculiarities of the TPS in BNCT

Some TPS examples:

NCTPlan

SERA

BDTPS (PET-based TPS)

Giuseppe G. DaquinoGiuseppe G. DaquinoCERN, 25CERN, 25thth April April 200 20055

SoFTware Development for Experiments GroupSoFTware Development for Experiments GroupExperimental Physics, CERNExperimental Physics, CERN

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The main role of TP

TP is the process which leads to the definition of the best irradiation modality, in terms of optimal dose distribution in tumour and healthy tissue

Parameters to take into account:

irradiation geometry (positioning)

number of irradiation fields

quality of the irradiation beams

duration of the irradiation



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Typical TP phases

a) CT and/or MRI scanning of the patient

b) Anatomical-computational model

c) Definition and positioning of the irradiation fields

d) Dose and fluence calculation based on Monte Carlo results

e) Evaluations of the related isodose curves

f) Simulation of the patient positioning in the irr. room, basedon the calculation results

g) Evaluation of the “monitor units”



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Apart from steps a) and g), the remaining ones are performed through a suitable software, called TPS

A TPS is basically composed by:

1) a module for the reconstruction of a 3D model (ROIs + OR): pre-processing phase

2) a module for the calculation of the radiation transport (MC or SD)

3) a module for the analysis and rep. of the calculation results(1D, 2D or 3D): post-processing phase

Treatment Planning System



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The 3D module

Clear identification of ROIs, OR and FM

Main OR: eyes, inner ears, optic chiasm, thalamus vessels, pituitary and salivary glands



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The fiducial markers Fiducial markers and patient positioning through the entry and

exit points of the beam centrelineHFR-Petten irradiation aperture



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Peculiarities of BNCT-oriented TPS

BNCT-oriented TPS is complicated by the presence of neutrons

Main nuclear reactions:

10B(n, )7Li; 14N(n,p)14C; 1H(n,n’)1H; 1H(n,)2H

Complexity of the problem can be faced using MC technique, but also SP3 approximation (in octree-grid) are in progress



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The calculation module

Main parameters required:

Materials and their nuclear properties associated to the 3D model

Boron identification plays an important role. It should beconsidered in case of transport affection. Fundamental in the post-processing

Neutron source characterization (basically, energy andspatial distribution)

Biasing techniques can increase the calculations speed (variance reduction techniques)



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The post-processing module The calculation results are represented in graphs



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In terms of isodose or isofluence curves, superimposed on the CT (or MRI) slices (2D rep)



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In terms of isodose or isofluence curves, superimposed on the 3D model (only SERA)



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TPS examples

Main TPSs used inside the BNCT Community: BNCT_rtpe (INEEL), SERA1 (INEEL), NCTPlan2 (MIT)

Generally, two models are prepared: 3D Model and Calculation Model (Monte Carlo technique) in the pre-processing phase

Japanese BNCT Community uses JCDS3 (JAERI Computational Dosimetry System)

BDTPS4 (boron model included)



1 Nigg D.W. et al., SERA, An advanced treatment planning system for neutron therapy and BNCT, Trans. Am. Nucl. Soc., 1999; 80:66-682 Zamenhof R. et al, Monte Carlo-based treatment planning for boron neutron capture therapy using custom-designed models automatically generated from CT data, Int.J. of Rad. Onc. Biol. Phys., 1996; 35(2): 383-3973 Kumada et al., Development of the JAERI Computational Dosimetry System (JCDS) for boron neutron capture therapy, JAERI-TECH 2003-0024 Daquino G.G., PET-based approach to treatment planning sytems: an improvement toward successful boron neutron capture therapy (BNCT), EUR 29678 EN, ISBN 9289455071

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Now, the question is:

Where is the boron ?

At the time when BNCT_rtpe was developed, no in vivo boron detection technique was available

Increasing interest towards the in vivo boron distribution detection: PGRA, MRI, PET

In vitro boron information used: ICP-AES, blood sampling, T/B and T/N ratios, SIMS (more recently)

No boron model present: only a rough 10B assignment to each region of interest (uniform distribution)



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PET for boron data acquisition Best actual spatial resolution (5 mm, physical)

Positron Emission Tomography needs:

+ +

cyclotron

suitable target

hot cells



high-speed electronics for data acquisition and high efficiency detector (BGO) at 511 keV

+

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PET for boron data acquisition (cont’d)

suitable tracer kinetic model



+

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PET for boron data acquisition (cont’d)

PET data can be coupled directly to the CT anatomical data

Need of co-registration between PET and CT scanning. The PET-CT combined machine could be an easy solution for a perfect coupling1



1 Klabbers B.M., Matching PET and CT scans of the head and neck area: development of method and validation, Med. Phys., 2002; 29(10), 2230-2238

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PET studies demonstrated that boron diffuses heterogeneously according to the patient metabolism1,2

1Imahori Y. et al., Positron Emission Tomography-based boron neutron capture therapy using boronophenylalanine for high-grade gliomas: Part I, Clinical Cancer Research 1998;4:1825-18322Kabalka G.W. et al., Evaluation of fluorine-18-BPA-fructose for boron neutron capture treatment planning, J. Nucl. Med. 1997; 38:1762-1767

A comparative study

PET images - Input for

heterogeneous B-distribution simulation

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BDTPS: Boron Distribution Treatment Planning System

Contains all the main characteristics of existing TPS (e.g. pre-processing based on CT images of the patient head, fiducial markers, organs at risk, Monte Carlo modelling, post-processing, etc.)

Combines the PET data on the boron concentration mapping with Monte Carlo modelling, to calculate the boron dose

BDTPS is a pixel-based TPS. 3D modelling similar to SERA

CARONTE1: feasibility study towards PET-based TPSs



1Cerullo N. et al., Use of Monte Carlo code in neutrons behaviour simulation in BNCT (Boron Neutron Capture Therapy), Technologies for the new century, ANS, 1998, vol.2, pp. 236-243

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Definition of the regions (skin, brain, target and air, at least), as depicted on the CT (or MRI) slices by the user

BDTPS: Main features

Pre-processing

Main concept: the colour uniquely identifies the region and assigns an ID, which is used in the MC model

In this phase, the boron conc. association to each region is facultative, especially if the regions are small (no transport affection)

Using this technique, the 3D model and the MC model are constructed. BDTPS is characterized by a third model: the B model



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+



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BDTPS: Main features The 3D model is the first to be prepared. Several 3D graphics tools

have been applied (Phong, Gouraud, Flat shadings and point, wireframe, solid 3D representation)



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The 3rd model (Boron model) is the main added value of BDTPS. The PET files are scanned and transformed according to their boron content (at pixel level) into binary files

The B model is used as a 3D linear multiplication factor, after the transport calculation. This means that the calculations can be re-normalized to the last 3D PET values matrix, which can be acquired just before the irradiation



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Post-processing

Representation of the isodose and isoflux surfaces on the CT planes with a 10-colours scale

10%

> 10% and 20%

> 50% and 60%

> 60% and 70%

> 70% and 80%> 20% and 30%

> 80% and 90%> 30% and 40%

> 90% and 100%> 40% and 50%




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The main features required to the heterogeneous phantom for the validation of a PET-based TPS should be the following:

It should contain a heterogeneous boron distribution

The distance between two boron zones should be at least enough to allow the PET machine to distinguish them separately

The maximum activity permitted during one PET scanning is 2 mCi

HEBOM: HEterogeneous BOron phantoM for BDTPS validation



The geometry distribution of the boron should not be extremely anisotropic in order to avoid possible scattering problems during the PET scanning

The phantom should be filled by the 18F-BPA in a very short time

The phantom should be also easy to transport

To this purpose, HEBOM has been designed and built at Petten, composed by 4 central slabs containing 64 vials with pre-defined heterogeneous boron patterns

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Modular structure




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PET-CT combinedPET-CT combinedPET scanningPET scanning

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Activation foilsActivation foils

Detectors used

p/n diodesp/n diodes

TE/TE andTE/TE andAr/Mg paired Ar/Mg paired ion chambersion chambers




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Validation studies

The experimental validation is based on the measurements related to: thermal neutron flux; proton recoil dose rate; total gamma dose rate.

The computational validation is based on the comparison to: MCNP-4C3 SERA

The computational validation evaluates also the boron dose rate



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SERA model of HEBOM MCNP-4C3 model of HEBOM

Validation studies



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The three models of HEBOM in BDTPS

3D model3D model MC modelMC model B modelB model

Validation studies



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Naming convention for the comparisons

Validation studies



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Thermal neutron flux

Good agreement of BDTPS and MCNP-4C3 on layer D. SERA slight overestimation at HEBOM surface

No evident affection of the boron heterogeneity in small volumes on the thermal flux

Validation studies (preliminary results)



Statistical error: 10%. Experim. error: 10%.

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Boron dose rate SERA slight overestimation (exp. in the 100 ppm vial) over MCNP-4C and BDTPS on layer D

SERA can calculate the dose in each single vial, provided that the boron conc. is inserted manually. This is impossible in complex structure (patient’s anatomy)

Boron dose rate (Layer D centreline)

0,00E+00

5,00E-04

1,00E-03

1,50E-03

2,00E-03

2,50E-03

0 5 10 15 20 25 30

Depth (cm)

Gy/

sMCNP4C

BDTPS

SERA




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A big discrepancy between SERA and BDTPS is evident in the boron isodose representation: SERA does not scale up the 1ppm-calculated isocontours on the grounds of the real macroscopic B distribution




SERASERA BDTPSBDTPS

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Conclusions Irradiation is only the last step of a toilsome process, where TPS

plays an important role for the optimisation of the parameters

This role is particularly stressed in BNCT by the presence of neutrons, which increase the complex level of the irradiation simulation

TPS constructs a 3D and a MC model. The first is made by a stack of CT slices, while the second is a calculated mesh superimposed on the first one.

Doses and fluences are represented via graph as well as via isocontours



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Conclusions (cont’d) A possible way to solve the requirement of the real boron macro-

distribution is to link the PET data to the TPS

This is the main added value offered by BDTPSBDTPS (v.1.0)

BDTPS is the only TPS, which completely integrates the 3D, MC and B models. Meanwhile, other studies in USA were directed towards PET-based TPS1, using SERA. However, SERA standard is not PET-based and the method used is not documented.

This shows that the idea of coupling PET and TPS was original and scientifically valuable.



1Kabalka G.W. et al., Improved treatment planning for boron neutron capture therapy for glioblastoma multiforme using fluorine-18 labeled boronphenylalanine and positron emission tomography, Med. Phys., 2002: 29(10), 2351-2358

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