RADIATION DOSIMETRY A THEORY RADIATION DOSES non-SI units (relationship between units) Dose Formula SI units Absorbed Dose, ΔΕ J/kg = Gray (Gy) rad 1 Gy = 100 rad Δm AE is the energy lost from the radiation beam, and Am is the mass of the material into which the energy is absorbed. до C/kg Roentgen (R) 1R = 2,58 · 104 C/kg Exposure dose, Дт where AQ is the electric charge freed by such radiation in a specified volume of air divided by the mass Am of that air. Relationship between absorbed dose and exposure dose D = f · X D is adsorbed dose , f is a coefficient depending on the kind of tissue being irradiated. Equivalent Dose, Sievert H = Q ·D where H is dose equivalent, Q is relative biological effectiveness of a particular kind of radiation, D is adsorbed dose. rem Н (Sv) 1 Sv =100 rem HE ΣΗΤ where HT = Wr ·H, is the tissue-weighted dose equivalent to an organ or tissue, Hr is the dose equivalent to the organ or tissue and the WT applicable to that organ or Effective Sievert rem Equivalent Dose , Нef (Sv) 1 Sv =100 rem tissue. Table 1 – Quality factors for different kinds of radiation Table 2 – Dimensionless weighting factors (Wt) Tissue WT Type of Radiation Gonads 0.25 Breast 0.15 х-гаys Red bone marrow 0.12 Lungs Thyroid Bone surfaces Remainder 0.12 0.03 20 0.03 Neutrons (fast) 10 0.30 Protons 10 Total body 1.00 DOSE RATES 1. Adsorbed dose rate: Np == Table 3 – Exposure constants Radionuclides k, (µGy-m³/GBq-h at 1 m)* 137CS н 2. Dose equivalent rate: Nµ = 88.11 99mTc 15.95 3. Exposure rate: Nx | 201TI 12.16 Exposure rate at a distance r from the source of "Mo radiation can be found as 39.46 67GA 20.54 1231 where is ky is exposure constant for a given radioisotope, A is activity of the radioactive source, r is distance from the source of the radiation. ky'A 41.89 Nx r2 "In 55.41 37.03 $ICo 15.16 1311 18Fb 58.65 154.05

A person with lymphoma receives a dose of 35 Gy in the form of γ radiation during a course
of radiotherapy. Most of this dose is absorbed in 18 g of cancerous lymphatic tissue. (a) How much
energy is absorbed by the cancerous tissue? (b) If this treatment consists of five 15 minute sessions
per week over the course of 5 weeks and just 1% of the γ photons in the γ ray beam are absorbed,
what is the power of the γ ray beam? (c) If the γ ray beam consists of just 0.5% of the γ photons
emitted by the γ source, each of which has an energy of 0.03MeV, what is the activity (in Ci) of the
γ ray source?