Neutron Radiation Dose Measurements in a Scanning Proton Therapy Room: Can Parents Remain Near Their Children During Treatment?

Abstract

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.

A Monte Carlo study on the secondary neutron generation by oxygen ion beams for radiotherapy and its comparison to lighter ions

“…Overall trends obtained for the secondary neutrons generated by primary oxygen beams, both for the pristine Bragg peaks and the SOBPs, are in agreement with the previous study using primary protons, helium and carbon ions (Vedelago et al 2022). The secondary neutrons spectra follow the typical shape of energy distributions of secondary neutrons encountered in ion beam therapy, with one peak in the TE region and another peak in the FR region, with a flat thermalization region in between (Mares et al 2022, Shrestha et al 2022. In the obtained spectra, the evaporation peak is usually eclipsed by the cascade peak, as no additional room elements or room walls were considered (Englbrecht et al 2021).…”

Challenges and opportunities for proton therapy during pregnancy

“…Neutrons created during proton‐RT have a wide range of energies, ranging from thermal energies (<0.4 eV) up to the maximum proton energy (up to 250 MeV) 9,10 . As neutrons are indirectly ionizing, they will deposit energy by creating ionizing secondary particles.…”

“…Neutrons created during proton‐RT have a wide range of energies, ranging from thermal energies (<0.4 eV) up to the maximum proton energy (up to 250 MeV). 9 , 10 As neutrons are indirectly ionizing, they will deposit energy by creating ionizing secondary particles. These nuclear reaction cross‐sections strongly depend on the neutron energy, causing the relative biological effectiveness (RBE) of neutrons to vary greatly for different neutron energies.…”

Dose Measurements at Provision Proton Therapy Center

“…In the absence of robust shielding, these radiation fields could potentially present significant risks, not only to the healthcare professionals but also to the general public. It is worth noting that the effect of the secondary neutron field has been studied in the following studies: Agosteo et al (1998), Hälg and Schneider (2020), and Mares et al 2022. Agosteo et al reported that the estimated secondary gamma-ray dose was approximately one-tenth of the combined total dose from neutrons and gamma rays.…”