A patient is being given a chest X-ray. The X-ray beam is turned on for 0.20 s, and its intensity is 0.40 W/m2. The area of the chest being exposed is 0.072 m2, and the radiation is absorbed by 3.6 kg of tissue. The relative biological effectiveness (RBE) of the X-ray for this tissue is 1.1.
Concepts:
(i) How is the power of the beam related to the beam intensity? (ii) How is the energy absorbed by the tissue related to the power of the beam?
(iii) What is the absorbed dose?
(iv) How is the biologically equivalent dose related to the absorbed dose?
Calculation:
Calculate the biologically equivalent dose received by the patient.
When considering the biological effects of ionizing radiation, the concept of biologically equivalent dose is especially important. Its importance lies in the fact that the biologically equivalent dose incorporates both the amount of energy per unit mass that is absorbed and the effectiveness of a particular type of radiation in producing a certain biological effect. Problem 55 examines this concept and also reviews the notions of power (Section 6.7) and intensity (Section 16.7) of a wave. Problem 56 illustrates the decay of a particle into two photons, and provides a review of the principles of conservation of energy and conservation of momentum.