Esteban Fabián Boggio 1 Lucas Provenzano 2 Sara Gonzalez 2,3 Sara Gonzalez 2,3 Juan Manuel Longhino 1 1 Bariloche Atomic Center, Atomic Energy National Commission (CNEA) 2 Constituyentes Atomic Center, Atomic Energy National Commission (CNEA) 3 National Council of Scientific and Technical Research (CONICET)

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,  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

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 6/9 epithelitis G1 3/9 epithelitis G3 3/9 epithelitis G3 88 tumors (in field) 63% (CR) 63% (CR) 72% (OR) 72% (OR)

The new BNCT treatment facility  Argentine BNCT Project is at the moment ready to restart the melanoma clinical trials

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 high neutron capture cross section very short-lived activation products very short-lived activation products high energy beta particles emission decay 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 Indium (0,127mm thick) Rhodium Rhodium (0,025mm thick) Silver Silver (0,127mm thick)

MCNP calculations  Thermal neutrons flux perturbation as a depth function Depth [mm] IndiumRhodiumSilver 0,5 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% 15 0,8%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

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

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 I Dose rate (MODE NP) [Gy w /min] Dose rate (MODE E) [Gy w /min] Dose rate (MODE NPE) [Gy w /min] +27%

Results: Nodules II and III Dose rate (MODE NP) [Gy w /min] Dose rate (MODE E) [Gy w /min] Dose rate (MODE NPE) [Gy w /min] +14%+12% Dose rate [Gy w /min]

Results: Nodule IV Dose rate (MODE NP) [Gy w /min] Dose rate (MODE E) [Gy w /min] Dose rate (MODE NPE) [Gy w /min] +27%

Results: Skin (OAR) This hot area represents less than 0.02% of the total skin volumen

 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