Purpose: To expand the radiation dose rate measurement data set by measuring radiation under various prostate 125I brachytherapy situations. Methods and Materials: Measurements were obtained from 63 consecutive unselected patients at Tokyo Medical Center, Japan. Differences in factors during measurements, such as body postures, distances from the skin surface, and measurement directions were considered. Furthermore, shielding effects of lead-lined underwear, consisting mainly of 0.1-mm thickness of lead, were also assessed. Results: Radiation exposure varies according to the patient's body posture, with results differing as much as approximately 40.0% in measured radiation dose rates at 30. cm from the anterior skin surface. Weight, body mass index, and tissue thickness showed good correlations with measured radiation dose rates. The magnitude of radiation exposure attenuation by shielding was approximately 95.8%, similar to the attenuation ratio based on tissue measurements made in the lateral direction. The respective mean times required to reach 1. mSv were 1.2, 7.6, and 65.4 days in the standing position and 0.6, 4.6, and 40.4 days in the supine position at the site of contact, and at 30 and 100. cm from the anterior skin surface. Conclusions: This study obtained supplemental information pertaining to radiological protection and confirmed that shielding can be an effective tool for reducing exposures.
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