Nuclear Medicine Physics Radiation Dose Jerry Allison Ph

Nuclear Medicine Physics • Radiation Dose Jerry Allison, Ph. D. Department of Radiology Medical College of Georgia

A note of thanks to Z. J. Cao, Ph. D. Medical College of Georgia And Sameer Tipnis, Ph. D. G. Donald Frey, Ph. D. Medical University of South Carolina for Sharing nuclear medicine presentation content

Definitions n Absorbed dose D (Gy): energy deposited in a unit mass of absorber n 1 Gy = 1 joule/kg (SI unit) n 1 rad = 100 erg/g (traditional unit) n 1 Gy = 100 rad 3

Definitions n Equivalent dose HT (Sv): quantity that expresses absorbed dose across an organ or tissue with a weighting factor for type and energy of radiation n H T = D T. w. R n DT: absorbed dose in a tissue n w. R : weighting factor that denotes relative biologic damage for type of radiation n For x, , e- , e+ : w. R = 1 n For n: depends on energy n For p (> 2 Me. V): w. R = 2, n For a, fission fragments, heavy ions: w. R = 20 4

Definitions n In diagnostic radiology, equivalent dose (Sv) is equal to absorbed dose (Gy) since: § w. R = 1 for x, , e- , e+ 5

Definitions n Effective dose E (Sv): measure of absorbed dose to whole body, the product of equivalent dose and organ specific weighting factors n Whole body dose equivalent to the nonuniform dose delivered 6

Definitions n From: International Commission on Radiological Protection: Recommendations of the International Commission on Radiological Protection. ICRP Publication 103; Ann ICRP. 37 (2 -4)2007 7 © Physics in Nuclear Medicine: Cherry, Sorenson and Phelps

Definitions n Dose equivalent H (Sv) n An obsolete unit that expressed absorbed dose at a point in an organ with a quality factor that depends on type of radiation n Rem (traditional unit) n 1 Sv = 100 Rem 8

Example n The mean glandular dose to the ACR mammographic accreditation phantom must not exceed 3 m. Gy (300 m. Rad) per view at the recommended techniques for imaging an average breast. 9

Example n What is effective dose to the patient if breasts receive an absorbed dose of 3 m. Gy? n w. R = 1 n w. T = 0. 12 n E = D * w. R * w. T n E = 3 m. Gy * 1 * 0. 12 n E = 0. 36 m. Sv n So, absorbed dose to the breasts of 3 m. Gy results in effective dose to the patient of 0. 36 m. Sv (to the whole body) 10

Definitions n Effective dose equivalent HE (Sv) n An obsolete unit that expressed absorbed dose to whole body, the product of dose equivalent and organ specific weighting factors n Rem (traditional unit) n 1 Sv = 100 Rem 11

Definitions n Exposure X (C/kg): charge liberated per kg of air by x- or -rays n C/kg (SI unit) n 1 R = 2. 58× 10 -4 C/kg (traditional unit) n Measures number of ionizations 12

Definitions n Air kerma K (Gy): kinetic energy liberated per kg of air by uncharged radiations ( rays, neutrons) n Kinetic energy of particles liberated through n Photoelectric absorption n Compton scattering n Pair production n Gy (SI unit) n In nuclear medicine n K (Gy) = X (C/kg) * 33. 7 n K (Gy) = X (R) * 0. 00869 13

Unfortunate Caveat: n In radiology: n Gy and Sv are often used loosely n Rad and Rem are often used loosely n 1 Gy = ~100 Rad n 1 Sv = ~100 Rem n 1 Air Kerma Gy = 33. 7 C/kg = 0. 00869 R 14

Effective dose of NM procedures 15

Dose limits Occupational: ALARA 1 & ALARA 2 Embryo/fetus: 5 m. Sv total 16 © Physics in Nuclear Medicine: Cherry, Sorenson and Phelps