<prompt> Conventional daily dose regimen in external beam radiotherapy is?100-150 cGy150-170 cGy180-200 cGy225-250 cGy  <response>: Ans. c 180-200 cGy. Ref. Harrisons medicine, 18thCh. 85Most 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. 