Аннотация:The role of the additional radiation dose caused by secondary particles is underestimated at the stage of radiation therapy planning. The additional radiation dose from secondary neutrons in the target volume and from electrons beyond the field is considered. An assessment of the error of determining doses, which are calculated using planning systems and measured beyond the radiation field, is presented. The dose from secondary electrons can reach 2%, which is 1.2–1.5 Sv. The spectrum of neutrons measured on a Varian Trilogy accelerator and that calculated using the GEANT4 program code are compared. Average energies of neutrons of 0.89 ± 0.02 Gy for the experiment and 0.77 ± 0.12 Gy for modeling are obtained by the spectra. The radiation dose from neutrons in an aqueous layer with a volume of 10 × 10 × 1 mm in a water phantom is calculated by the data of the model spectrum. The contribution from neutrons to the total dose is 0.22%. Taking into account the radiation quality factor, the additional radiation dose can reach a value of 1.6 Sv at a total dose of 70 Gy for the presented spectrum energies. The total additional radiation dose from photons, electrons, and neutrons is estimated to be 3.6 Sv.
