This study discusses a computer simulation for the equivalent ambient dose due to photons, H*(10)p, and neutrons, H*(10)n, in the patient's plane undergoing radiation therapy. A standard radiotherapy room with an additional shielding made by one lead or steel tenth-value layer was considered. A Varian 2100/2300 C/D linear accelerator head operating at 18 MV was modeled. Jaw openings of 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, and 30 cm × 30 cm, as well as the multileaf collimator under eight different angles of gantry inclination, were also modeled. The use of steel in the shield generates a slightly raised average value of H*(10)p (0.527%) compared to when using lead. This finding can be interpreted as that the use of lead or steel coating makes no difference to the additional shield calculations when only photons are considered. When considering the contribution to H*(10)n, there is a significant difference (11.7% increase) for using lead compared to steel shielding.
Keywords: MCNPX; Neutrons; Radiotherapy; X-ray.
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