Removal of Alcyon II, CGR, MeV ⁶⁰Co Teletherapy Head and Evaluation of Exposure Dose

Teletherapy units containing 60Co source are used in Egypt and worldwide for treatment of cancer diseases. One of the widely used in Egypt is Alcyon CGR MeV. Different radiotherapy facilities need to unload this 60Co unit after being disused. The head containing the source was removed and put into approved package for transportation, after the source kept in safe position. This study describes the planning and removing process of the disused sources and, transports it into its head. The personal doses measured during the process. This work pre-estimates the doses received to workers during the removing process. The workers received doses of approximately 55 μSv during the whole process. This study shows that the original lead head can be used as the source container of this 60Co unit but not as a long term storage option. The 60Co machine was smoothly dismantled and transported by trained workers and driver, using planned and controlled radiation protection, followed by ALARA (as low as reasonably achievable) rule.

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.

Male Breast Cancer-Dosimetry Evaluation in Teletherapy

The rate of male breast cancer has increased in recent years, due to the deficiency of preventive examinations (male mammography). Besides, since male breasts are generally smaller than female breasts, it is essential to monitor the doses received by male breasts, as well as those received by close, healthy and critical organs in order to assess the plan used in this kind of treatment. To do this, the distribution of doses in male breasts was simulated and assessed, based on the procedures adopted in the treatment of female breasts, when submitted to a radiation beam from a linear accelerator. The Alderson Rando phantom was used and the relevant absorbed doses were measured by TLD-100 thermoluminescent dosimeters distributed throughout the volume of interest. The results of the treatment planning were compared with the results obtained by TLDs. A difference of up to 8.5%, in comparison with the planned dose, as well as a 6% relative standard deviation was found.