Computed Verification of Light and Radiation Field Size Superimposition on Cobalt 60 Machine

Abstract

Before starting conventional radiotherapy, a virtual field is usually made using light to determine the actual field of tumor under treatment. The Light and Radiation fields should be matched. This matching however, is verified by using different methods including the portal film. The decrease or increase in the two fields should not exceed 5%. If the ratio is greater than 5%, the alignment of the light and radiation beam diagram should be reviewed. The study was conducted at the Radiation and Isotopes Center of Khartoum (RICK) during the period April to August 2009. The aim of the study was to verify the superimposition of light and radiation field size using image processing technique automatically. As cobalt-60 machine, the portal films used in the test were scanned using digitizer scanner. The scanning analysis was made using IDL to show the superimposition in which more concentration was made on field center and borders, provided that the analysis included the four borders of the two fields. Both the standard deviation and the mean methods were used in the analysis process. The result was as follows (10.0 X 10.0cm), Medical physicist score was (10.3 ± 0.11608 X 10.3 ± 0.099861 cm) and the field size that calculates by computerized score using IDL program was (9.9 ± 0.036049 X 9.9 ± 0.01123cm). This indicates that the result was within the acceptable limits for the automatic reading, as compared with the manual reading in which the penumbra was (8mm) which was very high and risky for the treatment process. The result showed the precision of automatic reading in terms of problem’s solution of noise created in small regions that require additional processing as well as other problems. On the Contrary to the manual method that ignores those details and focuses only on the expected borders which were determined incorrect.