WORKLOAD AND USE FACTOR OF MEDICAL LINEAR ACCELERATORS IN RADIOTHERAPY

An important factor in the design of primary protective barriers is th e use factor, The present study was aimed at obtaining historical data on the use factor of two dual modality linear accelerators in a radio therapy department, Gantry angle, field size, and beam modifiers were recorded for all radiation qualities in use at two medical linear acce lerators with 6 MV and 18 MV x-rays and multiple electron energies ran ging from 4 MeV to 20 MeV, The data for one year of clinical use was e xtracted from a record and verifying system and an estimate of the phy sics workload on the machines was obtained by going through the qualit y assurance records and machine log books, Of the total dose of approx imately 37,000 Gy delivered in one year at isocenter on each unit 80% was given as 6 MV x-rays, As can be expected, most x-ray beams were di rected at the four cardinal gantry angles with the angular distributio n for 6 MV and 18 MV x-rays being very similar, Electron fields were b roadly distributed around the gantry pointing down position, Less than 25% of all clinical x-rag treatment fields extended beyond a field si ze of 200 cm(2).