Question: Doctors can treat certain tumors with metal “seeds” that contain short-lived radioactive isotopes…

Doctors can treat certain tumors with metal “seeds” that contain
short-lived radioactive isotopes that emit short-range decay
products. Prostate cancer is often treated with seeds containing
103Pd, which decays by electron capture followed by the emission of
a 21 keV gamma ray, which has a short enough range that it will
only affect a 4.0 g mass of tissue immediately around the seed. The
seeds are placed in the tumor; the 103Pd quickly decays (the
half-life is 17 days), irradiating the tumor as it does, eventually
leaving the seeds inert and safe to stay in place. A typical seed
has an initial activity of 5.5 MBq. What dose (in Gy) will the
tissue surrounding the seed receive?