Radiation Dosimetry and Dose Quantities
Core concepts
Master the dosimetric chain: exposure (C/kg) → absorbed dose (Gy = J/kg) → equivalent dose (Sv = Gy × wR) → effective dose (Sv = Σ wT·HT). Know ICRP/ICRU tissue weighting factors and radiation weighting factors (photons/electrons = 1, alpha = 20, neutrons energy-dependent). Understand the difference between equivalent dose to an organ and effective dose to the whole body. Know dose-area product (DAP), CTDIvol, and DLP for diagnostic metrics, and how DLP × conversion factor gives effective dose. Understand internal dosimetry concepts (committed dose, MIRD, residence time).
Traps
Questions conflate Gy and Sv; Sv only applies after weighting. Don't apply wT to a single organ and call it effective dose-effective dose sums weighted organ doses. Watch for the difference between absorbed dose and dose equivalent in older units (rad vs rem; 1 Gy = 100 rad, 1 Sv = 100 rem). Alpha emitters internalized are far more hazardous than external due to wR = 20. CTDIvol is a normalized index, not patient dose; DLP = CTDIvol × scan length.
Worked example / rule of thumb
A chest CT with CTDIvol 10 mGy over 30 cm gives DLP = 300 mGy·cm. With a chest conversion factor ~0.014 mSv/(mGy·cm), effective dose ≈ 4.2 mSv. Rule of thumb: effective dose ≈ DLP × region-specific factor.