Conventional daily dose regimen in external beam radiotherapy is?
Ans. c (180-200 cGy). (Ref. Harrison's medicine, 18th/Ch. 85)*Most curative radiation Rx programs are delivered once a day, 5 days a week in 150- to 200-cGy fractions.BEAMS USED FOR EXTERNAL RADIOTHERAPY AREX-ray beams# Superficial: 40 to 120 kv# Orthovoltage: 250 to 400 kv# Supervoltage: 400 to 800 kv# Megavoltage: > 1MeV (Skin sparing effect and deep penetration - advantages).Gamma ray beams# Cobalt -60 beam# Cesium -137 beam (Primarily used for brachytherapy).Particle beams# Electrons, Protons, Neutrons.Radiation is quantitated on the basis of the amount of radiation absorbed in the patient; it is not based on the amount of radiation generated by the machine. The rad (radiation absorbed dose) is defined as 100 ergs of energy per gram of tissue. The International System (SI) unit for rad is the Gray (Gy); 1 Gy = 100 rad. Radiation dose is measured by placing detectors at the body surface or calculating the dose based on radiating phantoms that resemble human form and substance. Radiation dose has 3 determinants: total absorbed dose, number of fractions, and time. Thus, a typical course of radiation therapy should be described as 4500 cGy delivered to a particular target (e.g., mediastinum) over 5 weeks in 180-cGy fractions. Most curative radiation treatment programs are delivered once a day, 5 days a week in 150- to 200-cGy fractions.
100-150 cGy
150-170 cGy
180-200 cGy
225-250 cGy
Radiotherapy