PurposeThis study aims to characterize the neutron radiation field inside a scanning proton therapy treatment room including the impact of different pediatric patient sizes.Materials and MethodsWorking Group 9 of the European Radiation Dosimetry Group (EURADOS) has performed a comprehensive measurement campaign to measure neutron ambient dose equivalent, H*(10), at eight different positions around 1-, 5-, and 10-year-old pediatric anthropomorphic phantoms irradiated with a simulated brain tumor treatment. Several active detector systems were used.ResultsThe neutron dose mapping within the gantry room showed that H*(10) values significantly decreased with distance and angular deviation with respect to the beam axis. A maximum value of about 19.5 µSv/Gy was measured along the beam axis at 1 m from the isocenter for a 10-year-old pediatric phantom at 270° gantry angle. A minimum value of 0.1 µSv/Gy was measured at a distance of 2.25 m perpendicular to the beam axis for a 1-year-old pediatric phantom at 140° gantry angle.The H*(10) dependence on the size of the pediatric patient was observed. At 270° gantry position, the measured neutron H*(10) values for the 10-year-old pediatric phantom were up to 20% higher than those measured for the 5-year-old and up to 410% higher than for the 1-year-old phantom, respectively.ConclusionsUsing active neutron detectors, secondary neutron mapping was performed to characterize the neutron field generated during proton therapy of pediatric patients. It is shown that the neutron ambient dose equivalent H*(10) significantly decreases with distance and angle with respect to the beam axis. It is reported that the total neutron exposure of a person staying at a position perpendicular to the beam axis at a distance greater than 2 m from the isocenter remains well below the dose limit of 1 mSv per year for the general public (recommended by the International Commission on Radiological Protection) during the entire treatment course with a target dose of up to 60 Gy. This comprehensive analysis is key for general neutron shielding issues, for example, the safe operation of anesthetic equipment. However, it also enables the evaluation of whether it is safe for parents to remain near their children during treatment to bring them comfort. Currently, radiation protection protocols prohibit the occupancy of the treatment room during beam delivery.

National Centre for Nuclear Research, NCBJ is one of the biggest research institutes in Poland, in which scientists deal with basic research in the various fields of subatomic physics, development of nuclear technologies and practical applications of nuclear physics methods, including those for nuclear medicine and radiotherapy. NCBJ operates the only Polish nuclear research reactor MARIA, around which a Reactor Laboratory for Biomedical Research, RLBR has been built in the last 4 years. One of the main aims of the RLBR team is to adapt the H2 channel, one of the eight MARIA’s horizontal channels, to a specific irradiation facility delivering a high flux thermal/epithermal neutron beam. The beam derived from the channel will be a tool for biological, physical and material studies for Boron Neutron Capture Therapy, BNCT. While NCBJ is focused on building a neutron research facility, the Polish scientific community expressed its interest in BNCT development and implementation as an alternative therapy for cancer treatment. Through the working group meetings organized in the form of regular scientific workshops since 2015, it led to the establishment of a national scientific consortium dedicated to BNCT. Polish Consortium for Boron Neutron Capture Therapy agreement was initially signed by twelve institutions including scientific institutes, universities and oncological centres in October 2019. National Centre for Nuclear Research was appointed the leader of the consortium. A year later the consortium was enlarged by two more institutions.