Radiation Therapy Measurements

Introduction to Radiation Units

The American College of Cardiology states that Air Kerma is the standard unit for measuring x-ray beam exposure, measured in Gy (1 Gy = 1 J/kg), which is used to quantify the actual energy delivered during treatment 1, 2
The American College of Cardiology recommends using Kerma-Area Product (KAP), measured in Gy·cm², to account for both radiation intensity and area exposed, and Kerma-Length Product (KLP) for CT imaging to account for volume of tissue exposed 1, 2

The American Heart Association specifies that kilovolt (kV) is used to specify the peak tube voltage and maximum photon energy in diagnostic x-rays, typically in the 10-150 keV range 3, 1
The actual absorbed dose in tissue is measured in Gray (Gy), with Kerma-Area Product (KAP) used to measure radiation intensity and area exposed 1, 2
External beam radiation decreases exponentially through tissue, approximately by a factor of 2 for each 5 cm, with higher energy beams (MV range) providing better dose homogeneity for deep-seated tumors 2

The American College of Cardiology recommends using administered activity measured in Becquerel (Bq) or millicuries (mCi) for internal absorbed doses, calculating internal absorbed doses in mGy per unit administered activity, with different radionuclides emitting radiation at different energies (e.g., Tc-99m at 140 keV) 2, 4
X-ray fluoroscopy and interventional procedures are measured using Air kerma (Gy) and Kerma-area product (Gy·cm²), with energy typically specified in kV range (10-150 keV) 2
The standard unit of energy in radiation treatment is the gray (Gy), representing 1 joule of energy deposited per kilogram of tissue, used to quantify the actual energy delivered to tissues during radiation treatment 1
The sievert (Sv) is used for equivalent dose and effective dose, accounting for the biological impact of different radiation types, with 1 Gy equaling 1 Sv for medical imaging radiation (x-rays, gamma rays) 2

Air kerma measures the kinetic energy released in air by radiation, expressed in Gy, and is the standard unit for measuring x-ray beam exposure 1
Kerma-area product (KAP) is measured in Gy·cm² and accounts for both radiation intensity and the area exposed, particularly important in fluoroscopy 2
Kerma-length product (KLP) is used in CT imaging to account for the volume of tissue exposed along the scan length 1
Volume computed tomographic dose index (CTDIvol) in mGy and dose-length product (DLP) in mGy·cm are used in CT imaging to account for scan length 1
Administered activity is measured in Becquerel (Bq) or millicuries (mCi), where 1 mCi = 37 MBq, for nuclear medicine 4

External beam radiation therapy primarily uses absorbed dose (Gy) and involves calculating precise dose distributions to target volumes while minimizing exposure to healthy tissues 1
The absorbed dose (Gy) varies with depth and tissue composition, and external beam radiation decreases exponentially as it passes through tissue, approximately by a factor of 2 for each 5 cm 2
Radiation weighting factors account for different biological effects of various radiation types, though most medical imaging radiation has a weighting factor of 1 2
Patient-specific factors significantly affect actual dose absorption, making standardized measurements critical for treatment planning and safety 4