Wound counting correction factor determination following accidental Pu-238 hand injections

Pu-238 is an alpha emitting, high LET radioisotope produced in multiple national laboratory settings, as well as in NASA missions. Pu-238 may be accidentally absorbed, inhaled, or injected by workers during machining or fabrication processes. A fraction of Pu-238 entering the body will deposit within the bones, yielding ongoing irradiation. Therefore, a committed effective dose (CED) is necessary in assessing the potential health risks and cancer implications over a 50 year period for Pu-238 uptake. CEDs can be reduced through rapid medical intervention immediately following an intake.

In-vitro bioassays are often used to approximate CED. However, accumulation of bioassay data can take many days. Bioassay data may take a significant time to ascertain a dose, whereas wound counting can be rapidly accomplished. Wound counts are frequently used as a proxy for bioassays to assess contamination specific to injection pathways resulting in radiation dose. Correction factors are often used during wound counts to correct for tissue attenuation, source-detector distance, and wound geometry. At Los Alamos National Laboratory (LANL), current correction factors overcorrect activity by 118% at wound depths below 5 mm; beyond wound depths of 5 mm, the correction factors undercorrect by 76%.

This study aimed at assessing the effects of depth and tissue attenuation on the currently implemented LANL correction factors specific to Pu-238 hand injections. Through the use of an acrylic phantom, a geometrical factor was identified that accounts for distance and tissue attenuation. The experimental phantom results- incorporating the newly developed geometric factor- were compared with correction factors currently in use. Final results are still undergoing the LA-UR process, and will be published soon.