Group Meeting – 14/6/12

Naomi Ratcliffe

Introduction -BNCTA two stage treatment for advanced stage brain

cancers.

First stage - The patient is injected with a boron compound designed to collect in the tumour tissue.

Second stage - The patient is irradiated with epithermal neutrons to produce damaging alpha radiation in the tumour cells.

10B(n,α)7Li

BNCT Neutron Production

Reactor based sources vs accelerator based sources.

Safety, logistics, flexibility, public perception etc.

Reactors are built away from populated areas for a reason.

A medical procedure that requires a medical treatment facility.

Accelerators allow for more flexibility in neutron production and delivery.

Medical Isotopes–Current ProductionMain isotope is Tc99m used in SPECT-Single

Photon Emission Computed Tomography.

Current medical isotope production is reactor based the majority of the world supply coming from NRU and HFR.

Medical Isotopes-New Approaches

These reactors are becoming old and unreliable. When both reactors were offline simultaneously there was an ~90% decrease in world wide supply of Tc99m.

There is much interest in developing new accelerator based production methods.

Biggest developer is Canada with a programme looking into both generator and direct isotope production using both proton(TRIUMF) and electron(CLS) accelerators.

Study into using low energy accelerator to produce Tc99m and possibly other replacement isotopes.

Targets - Lithium

Original target design from the Birmingham group for their BNCT work used as a starting point for learning GEANT geometries and for moderated target designs.

High neutron production cross sections at lower energies.

Poor mechanical and chemical properties e.g. low melting point, which can cause design issues.

Targets - Beryllium

A second popular option for target designs from the literature and part of the development and modifications being made to the original designs.

Data available which makes for good benchmarking.

Lower neutron production cross sections.

Better mechanical and chemical properties e.g. higher melting point and more efficient heat conduction.

GEANT4.9.4.p01 - Lithium

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.60

0.00005

0.0001

0.00015

0.0002

0.00025

Ep (MeV)

Neutr

on Y

ield

(1

012/m

C)

A comparison shows that the simulated data differs significantly in both shape and value from the experimental data. 1.5 2 2.5 3 3.5 4

0

0.5

1

1.5

2

2.5

Ep (MeV)

Neutr

on Y

ield

(1012/m

C)

Most agreeable GEANT4 simulation results using QGSP_BERT_HP

Experimental data for a pure lithium target taken from Allen & Beynon.

GEANT4.9.4.p01 - Beryllium

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.60

0.0005

0.001

0.0015

0.002

0.0025

0.003

Ep (MeV)

Neutr

on Y

ield

(1012/m

C)

2 2.5 3 3.5 4 4.50

0.2

0.4

0.6

0.8

1

1.2

1.4

Ep (MeV)

Neutr

on Y

ield

(1012/m

C)

In terms of shape the simulation results show a much better correlation to experimental data. However there is still much discrepancy in values.

Most agreeable GEANT4 simulation results using QGSP_BERT_HPExperimental data for a pure Beryllium target taken from Randers-Pehrson & Brenner.

GEANT4.9.5.p01

Beryllium - The data from the updated GEANT4 version shows much better correspondence in all aspects with the experimental data.

Results obtained using the model QGSP_BERT_HP

1.5 2 2.5 3 3.5 4 4.5 50

0.5

1

1.5

2

2.5

Ep (MeV)

Neutr

on Y

ield

(1012/m

C) Experimenta

l data Simulation data

Lithium -The data from the updated GEANT4 version still shows a significant difference in terms of both shape and value

1.5 2 2.5 3 3.5 4 4.50

0.000001

0.000002

0.000003

0.000004

0.000005

0.000006

0.000007

Ep (MeV)

Neutr

on Y

ield

Conclusions

Lithium results are still a problem and unreliable, maybe try a quick study into where in the energy scale QGSP_BERT_HP starts to breakdown for this target.

Beryllium results are starting to make some progress and can cautiously move on with study into this target design using the QGSP_BERT_HP model.

A low energy model is being worked on by developers which hopefully will lead to more success with both targets.

Some progress is being made towards having a working model for low energy protons.