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Radiotherapy dose fractionation and treatment regimens


Radiotherapy doses have evolved empirically over a long period of time and there is a wide range in use. As a rule, the greater the fractionation employed, that is the more the total dose is broken down into smaller fractions, the better the cosmetic effect. This is obviously very important to some patients, but others are content to accept a poorer cosmetic effect if it allows fewer visits to hospital ( Table 79.1 ). Table 79.1 Commonly used superficial radiotherapy dosage regimens for skin BCC and SCC. Total dose No. of fractions Fractionation interval 18 Gy 1 — 28 Gy 2 7 weeks apart 35 Gy 5 Daily (for tumours less than 4 cm in diameter) 45 Gy 10 Daily (for tumours more than 4 cm in diameter) These fractionation regimens are only examples. Many centres will have other similar but locally derived dose fraction regimens. The SI unit of absorbed dose is called the Gray (Gy), and is 1 Joule/kilogram. This unit has replaced the rad. Note that 100 rad = 1 J/kg = 1 Gy; 1 rad = 1 cGy (centiGray). The dose prescription is defined by the total dose given, the energy of the beam, the number of fractions given, the total number of days over which treatment is given and the volume or area treated. For example, a typical prescription for the treatment of a small basal cell carcinoma might be ‘35 Gy using 90 kV superficial X-ray beam given in five fractions over 5 days to a 3-cm ... log in or subscribe to read full text

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