BETA ENHANCERS: TOWARDS A NEW

IMPLEMENTATION FOR BNCT ON SUPERFICIAL TUMORSEsteban Fabián Boggio1

Lucas Provenzano2

Sara Gonzalez2,3

Juan Manuel Longhino1

1Bariloche Atomic Center, Atomic Energy National Commission (CNEA)2Constituyentes Atomic Center, Atomic Energy National Commission

(CNEA)3National Council of Scientific and Technical Research (CONICET)

INTRODUCTION

RA-6 Reactor The RA-6 Reactor is located in

San Carlos de Bariloche, Patagonia, Argentina

It is a MTR, open pool type, with low-enrichment uranium fuels

1MW thermal power Used for Training, Research and

Education, being used on regularly basis within Nuclear Engineering at Balseiro Institute (IB) Operating facilities : neutrography, activation analysis and… BNCT

Facilities under construction: neutrons diffractometry and PGNAA

BNCT neutron beam Hyperthermal beam: developed through epithermal

neutrons spectra moderation, including a partial thermalization stage

Maximum thermal neutron flux at 1cm depth, suitable for treating skin melanoma

0 1 2 3 4 5 6 7 8 9 100.0E+00

2.0E+08

4.0E+08

6.0E+08

8.0E+08

1.0E+09

1.2E+09

Axial thermal flux

Axial epithermal flux

Depth in phantom [cm]

Neutr

on f

lux [

n/c

m2.s

]

Clinical trials As from October 2003 until June 2007: 10 irradiations

in 7 patients (Phase I-II protocol: toxicity and efficacy) Medical prescription: maximum dose on skin (Organ

At Risk, OAR)

9 skin areas 6/9 epithelitis G1 3/9 epithelitis G3

88 tumors (in field) 63% (CR) 72% (OR)

The new BNCT treatment facility

Argentine BNCT Project is at the moment ready to restart the melanoma clinical trials

BETA ENHANCERS

Beta Enhancers Due to beam penetration, total absorbed dose in the

first few millimeters of tissue is lower than in the maximum flux

Introduction of a suitable device over the irradiated volume has been considered in order to allow a local dose increase without substantially perturbing the primary in-depth dose profile

For the proposal, some materials have interesting properties: high neutron capture cross section very short-lived activation products high energy beta particles emission decay

This Beta Enhancers can be used to compensate or increase the absorbed dose in the first millimeters depth of BNCT treatment

MCNP calculations Three Beta

Enhancers foils were modelled on the surface of a polystyrene solid phantom, exposed to the BNCT calculation source: Indium (0,127mm thick) Rhodium (0,025mm thick) Silver (0,127mm thick)

0 2 4 6 8 10 12 140

10

20

30

40

50

60

Indium Rhodium Silver

Depth in phantom [mm]

Dose r

ate

by B

eta

Enhance

r [c

Gy/m

in]

MCNP calculations Thermal neutrons

flux perturbation as a depth function

0 2 4 6 8 10 12 14 160%

20%

40%

60%

80%

100%Indium (electrons + photons)

Rhodium (electrons + pho-tons)

Silver (electrons + photons)

Indium (only photons)

Rhodium (only photons)

Silver (only photons)

Depth in phantom [mm]

Depth [mm] Indium Rhodium Silver0,5 5,4% 1,7% 2,2%1,5 4,1% 1,3% 1,7%2,5 3,4% 1,1% 1,3%3,5 2,9% 0,9% 1,1%4,5 2,4% 0,8% 0,9%7,5 1,7% 0,6% 0,6%15 0,8% 0,3% 0,3%

Relative dose depth distribution by Beta Enhancers

Experimental validation Thermoluminescence detectors TLD700 (Harshaw) Four TLDs at 1, 2, 3 and 4mm depth at a polystyrene solid

phantom Irradiated at hyperthermal beam with and without Beta

Enhancer on surface in order to measure the enhanced local dose Results are compared with MCNP experiment modelling

0 0.5 1 1.5 2 2.5 3 3.5 40

10

20

30

40

50Indium (experience)

Rhodium (experience)

Indium (MCNP)

Rhodium (MCNP)

Depth [mm]

Dose r

ate

by B

eta

Enhance

r [c

Gy/m

in]

Experimental validation Gafchromic EBT3 films (Ashland) Film stack from 0 to 4.8mm depth at a polystyrene solid phantom Irradiated at hyperthermal beam with and without Beta

Enhancer on surface in order to measure the enhanced local doses

Results are compared with MCNP experiment modelling

-0.5 0.5 1.5 2.5 3.5 4.50

20

40

60

80

100Rhodium (experience)

Rhodium (MCNP)

Silver (experience)

Silver (MCNP)

Depth [mm]

Dose r

ate

by B

eta

Enhance

r [c

Gy/m

in]

TREATMENT PLANNING

Real case presentation Patient treated on 2005: four nodules in the foot base

Nodule I

Nodule II y III

Nodule IV

Multicell reconstruction Digital reconstruction of

the target volume geometry is performed by the Multicell software

In contrast to other reconstruction methods, which discretized the volume using cubic units (voxels) of constant size, this software is capable to perform an adaptive variation of these dimensions in order to optimize the geometric accuracy

Indium foils

Irradiation time criterion Conventionally, OAR (skin) is defined as

5mm thick tissue from surface of the treatment volume

BNCT irradiation time is obtained by maximum dose at skin

Therefore, total doses at nodules are assessed

When Beta Enhancers are applied, maximum dose at OAR is reached earlier, which impose a time limitation to the BNCT treatment

One approach is not to consider the nodules from the skin as OAR in order to not perturb the original treatment time

Results: Nodule IDose rate (MODE NP) [Gyw/min] Dose rate (MODE E) [Gyw/min] Dose rate (MODE NPE)

[Gyw/min]

+27%

Results: Nodules II and IIIDose rate (MODE NP) [Gyw/min] Dose rate (MODE E) [Gyw/min] Dose rate (MODE NPE)

[Gyw/min]

+14%+12%

Dose rate [Gyw/min]

Results: Nodule IVDose rate (MODE NP) [Gyw/min] Dose rate (MODE E) [Gyw/min] Dose rate (MODE NPE)

[Gyw/min]

+27%

Results: Skin (OAR)

This hot area represents less than 0.02% of the

total skin volumen

CONCLUSIONS

Three Beta Enhancers alternatives have been studied using adequate materials

MCNP calculations and its experimental correlations demonstrates a good agreement

A considerable improvement in local absorbed dose of cancerous tissue is shown in DVH, specially in the most superficial nodules

The original neutron flux used for the BNCT treatment is not significantly perturbed at depth

Therefore, Beta Enhancers are a useful complementary tool for superficial dose enhancement on very superficial tumors in patients treatment planning

Conclusions

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