Neutron peripheral contamination in patients undergoing high-energy photon radiotherapy is considered as a risk factor for secondary cancer induction. Organ-specific neutron-equivalent dose estimation is therefore essential for a reasonable assessment of these associated risks. This work aimed to develop a method to estimate neutron-equivalent doses in multiple organs of radiotherapy patients. The method involved the convolution, at 16 reference points in an anthropomorphic phantom, of the normalized Monte Carlo neutron fluence energy spectra with the kerma and energy-dependent radiation weighting factor. This was then scaled with the total neutron fluence measured with passive detectors, at the same reference points, in order to obtain the equivalent doses in organs. The latter were correlated with the readings of a neutron digital detector located inside the treatment room during phantom irradiation. This digital detector, designed and developed by our group, integrates the thermal neutron fluence. The correlation model, applied to the digital detector readings during patient irradiation, enables the online estimation of neutron-equivalent doses in organs. The model takes into account the specific irradiation site, the field parameters (energy, field size, angle incidence, etc) and the installation (linac and bunker geometry). This method, which is suitable for routine clinical use, will help to systematically generate the dosimetric data essential for the improvement of current risk-estimation models.

A simple and straightforward method is presented for the direct proton beam activation of 18O‐enriched titanium dioxide nanoparticles (TiO2 NPs) via the 18O(p,n)18F nuclear reaction in order to assess the biological fate of the NPs using positron emission tomography (PET). The radiolabeling of the NPs does not alter their morphological properties as demonstrated by transmission electron microscopy and dynamic light scattering measurements. The simultaneous formation of other radioisotopes by activation of the titanium atom, i.e., 48V, 47V, 44gSc, has been investigated using high‐resolution gamma spectrometry and PET. The labeling of TiO2 NPs with radioactive 18F atoms makes it possible to perform short‐term in vivo biodistribution studies of the metal oxide NPs in rats after intravenous and oral administration using PET. The accumulation of NPs in different organs could be quantified during almost 8 h after administration.

The results obtained indicate that direct evaluation of equivalent dose estimation in organs, both in phantom and patients, is perfectly feasible with this new detector. This will open the door to an easy implementation of specific peripheral neutron dose models for any type of treatment and facility.

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