Partial Quality Assessment of 60Co-Teletherapy Machine Performance

The aim of this study was to assess the performance of 60Co-teletherapy unit at Radiation and Isotopes Center in Khartoum, using the common tools used for quality control (Front pointer, Graphic paper, Pin, Non-screen film, meter and Check plate). The collected and analyzed data revealed that: there was a difference between the calculated theoretical field size (FS) and the measured one relative to the change of SSD; and the average FS shift was 0.9 cm relative to the standard one, while the machine isocenter was almost fixed at 0 ̊ with a shift of 0.003 cm, which was within the standard limit (0.2 cm). The diaphragm isocenter showed a shift of ±0.36 cm (i.e. in clock and anti clock wise) in average relative to standard limit (±0.3 cm) and the couch vertical isocenter (CVI) relative to the SSD changes was exceeded the standard limit (0.2 cm) by a factor of 0.9 cm. Also the SSD determined by the optical distance indicator was greater than the actual SSD (determined by Front pointer and measured by scale meter) by an average of 0.8 cm; which exceeded the limit (0.3 cm) by an average factor of 0.5 cm. The study also showed that the penumbra profile (1.5 cm) was less than the actual specified for 60Co-teletherapy machine, while the radiation beam was so homogeneous across the field size.