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内容記述 |
Background and aims:Spatial fractionated (GRID) radiotherapy is expected to induce stronger immune responses by administering higher doses to a tumor while sparing the surrounding normal tissues. However, in vivo experimental data for GRID irradiation, especially for serial organs, are limited. Heavy ions exhibit small lateral scattering, potentially realizing GRID irradiation with small beam sizes without any physical collimator. This study evaluated the response of mouse intestinal tract to GRID irradiation using scanned carbon-ion beams.Methods:Monoenergetic 430-MeV/u scanned carbon-ion beams were irradiated to the abdominal region of 7–8 weeks old female C3H/He mice. The GRID irradiation field consisted of seven pencil beams, forming a hexagonal close-packed structure. The pencil beam size was 1.8 mm at 1σ (4.2 mm at FWHM), and the center-to-center distance was 10 mm. When “valley” was defined at the center position of the two and three peaks, the peak-to-valley ratios were 24 and 57, respectively. For the comparison, 20×20-mm2 conventional uniform (CONV) irradiation was performed. The primary endpoint was acute intestinal death within 15 days after irradiation; 3–9 mice were assigned for various dose levels (GRID peak: 13–141 Gy, CONV: 12–17 Gy). The body weights were measured at least three times per week for 30 days.Results:Acute intestinal death occurred between 6–10 days after irradiation. Median lethal doses within 15 days after irradiation were 51.8 Gy at GRID peak and 13.7 Gy for CONV irradiation, respectively; however, field-averaged dose was only 13% higher for the GRID irradiation. Recovery from weight loss was slower for survivors of lethal GRID irradiation (peak dose: 47 Gy) than those of lethal CONV irradiation (dose: 14 Gy). Mice receiving GRID peak dose of 14 Gy did not show weight loss. Between 24–30 days after irradiation, five mice died for GRID irradiation (peak dose: 39–94 Gy) and one mouse died for CONV irradiation (dose: 13 Gy).Conclusions:GRID irradiation using scanned carbon-ion beams allowed higher maximum dose to mouse intestinal tract. However, local radiation injury was indicated to be severe in lethal GRID irradiation. Results of long-term follow-up and pathological analysis will also be presented. |
