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THE IMPACT OF TARGET VOLUMES OF EHRLICH ASCITES CARCINOMA IRRADIATED WITH A PENCIL SCANNING BEAM OF PROTONS AT A TOTAL DOSE OF 60 Gy ON THE TUMOR GROWTH AND REMOTE EFFECTS IN MICE

The purpose of the work was to study the growth of solid Ehrlich ascites carcinoma (EAC) and the remote effects (duration of remission, relapse rate, and average lifespan) in tumor-bearing mice exposed to oligofractionated irradiation with the pencil beam scanning of protons (PBSP) at a total dose of 60 Gy depending on the volume of the tissue being irradiated. Experiments were carried out on eight-to nine-week-old SHK male mice. Mice were irradiated with two fractions, 30 Gy each. In order to determine the volume of irradiated tissue, a tomogram of a mouse in a water phantom was obtained, and a gross tumor volume (GTV) that is equal to the average size of 470 mm3 from all mice was specified using a specially developed 3D planning system. In another group of animals, the irradiated tissue region was increased to the planning target volume (PTV), which was equal to 1500 mm3. An analysis of EAC growth dynamics during the first month showed higher irradiation efficiency in mice with a smaller irradiated volume (the GTV group) compared with the PTV group. In the group with GTV irradiation, survival was higher: the maximum life expectancy in mice without relapse was 5 months longer, and in mice with relapse it was 3 months longer than in the PTV group. The average lifespan (AL) of mice with EAC relapses in the group with GTV irradiation was higher compared to the group with PTV irradiation (96 and 77 days after irradiation or 58 and 31 days after the occurrence of a relapse, respectively; p ≤ 0.01). The AL of mice without tumors was also notably longer in the GTV group: 283 days compared to 228 days after PTV irradiation (p ≤ 0.01).