TY - JOUR
T1 - Clinical dosimetry of an epithermal neutron beam for neutron capture therapy
T2 - Dose distributions under reference conditions
AU - Raaijmakers, Cornelis P.J.
AU - Konijnenberg, Mark W.
AU - Mijnheer, Ben J.
N1 - Funding Information:
experimental assistance,a nd W. Voorbraak and A. Paardekoper for the activation foil measurements. This work was financially supported by a grant of the Netherlands Cancer Foundation (NKB Grant NKI 94-778). Accepted for publication 4 November 1996.
PY - 1997/3/1
Y1 - 1997/3/1
N2 - Purpose: The aim of this study was to asses the dose distribution under reference conditions for the various dose components of the Petten clinical epithermal neutron beam for boron neutron capture therapy (BNCT). Methods and Materials: Activation foils and a silicon alpha-particle detector with a 6Li converter plate have been used for the determination of the thermal neutron fluence rate. The gamma-ray dose rate and the fast neutron dose rate have been determined using paired ionization chambers. Circular beam apertures of 8, 12 and 15 cm diameters have been investigated using a 15 x 15 x 15 cm3 solid polymethyl-methacrylate phantom, a water phantom of the same dimensions and a 30 x 30 x 30 cm3 water phantom at various phantom to beam-exit distances. Results: The effect of phantom to beam-exit distance could be modeled using an inverse square law with a virtual source to beam-exit distance of 3.0 m. At a reference phantom to beam-exit distance of 30 cm, three-dimensional dose and fluence distributions of the various dose components have been determined in the phantoms. The absolute thermal neutron fluence rate at a reference depth of 2 cm in the 15 cm water phantom increased by 43% when the field size was increased from 8 to 15 cm. Simultaneously the gamma-ray dose rate increased by 46% while the fast neutron dose rate increased by only 5%. Conclusion: A reference treatment position at 30 cm from the beam exit allows convenient patient positioning with a relatively small increase in irradiation time compared to positions very close to the beam-exit. A more homogeneous distribution of thermal neutrons over a target volume, a higher absolute thermal neutron fluence rate and a lower contribution of the fast neutron dose to the total dose will result in improved treatment plans when using a 12 cm or 15 cm field compared to a 8 cm field. The dose distributions will be used as benchmark data for treatment planning systems for BNCT.
AB - Purpose: The aim of this study was to asses the dose distribution under reference conditions for the various dose components of the Petten clinical epithermal neutron beam for boron neutron capture therapy (BNCT). Methods and Materials: Activation foils and a silicon alpha-particle detector with a 6Li converter plate have been used for the determination of the thermal neutron fluence rate. The gamma-ray dose rate and the fast neutron dose rate have been determined using paired ionization chambers. Circular beam apertures of 8, 12 and 15 cm diameters have been investigated using a 15 x 15 x 15 cm3 solid polymethyl-methacrylate phantom, a water phantom of the same dimensions and a 30 x 30 x 30 cm3 water phantom at various phantom to beam-exit distances. Results: The effect of phantom to beam-exit distance could be modeled using an inverse square law with a virtual source to beam-exit distance of 3.0 m. At a reference phantom to beam-exit distance of 30 cm, three-dimensional dose and fluence distributions of the various dose components have been determined in the phantoms. The absolute thermal neutron fluence rate at a reference depth of 2 cm in the 15 cm water phantom increased by 43% when the field size was increased from 8 to 15 cm. Simultaneously the gamma-ray dose rate increased by 46% while the fast neutron dose rate increased by only 5%. Conclusion: A reference treatment position at 30 cm from the beam exit allows convenient patient positioning with a relatively small increase in irradiation time compared to positions very close to the beam-exit. A more homogeneous distribution of thermal neutrons over a target volume, a higher absolute thermal neutron fluence rate and a lower contribution of the fast neutron dose to the total dose will result in improved treatment plans when using a 12 cm or 15 cm field compared to a 8 cm field. The dose distributions will be used as benchmark data for treatment planning systems for BNCT.
KW - Boron neutron capture therapy (BNCT)
KW - Clinical dosimetry
KW - Epithermal neutron beam
KW - Field size
KW - Phantom size
KW - Treatment planning
UR - http://www.scopus.com/inward/record.url?scp=0030933386&partnerID=8YFLogxK
U2 - 10.1016/S0360-3016(96)00623-2
DO - 10.1016/S0360-3016(96)00623-2
M3 - Article
C2 - 9128973
AN - SCOPUS:0030933386
SN - 0360-3016
VL - 37
SP - 941
EP - 951
JO - International Journal of Radiation Oncology Biology Physics
JF - International Journal of Radiation Oncology Biology Physics
IS - 4
ER -