Journal of Medical Physics
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Year : 2001  |  Volume : 26  |  Issue : 1  |  Page : 23-28

Dosimetric Characteristics Of Aluminium Tissue Compensator For 60Co And 6 MV X-Rays

Correspondence Address:
S Dayananda

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Dosimetric analysis of aluminium (Al) tissue compensator used for 60Co and 6 MV x-ray beams is presented. A method to determine the thickness of aluminium required to compensate various tissue deficit conditions at different depths of compensation and field sizes is described for both the energies. The thickness of Al required to compensate for a particular missing tissue thickness increases in a slight non-linear manner with the depth of compensation and decreases with field size. When the tissue compensator data generated at 5 cm depth and for 10 x 10 cm2 field is used to compensate at different depths and field sizes, the maximum error in dose delivery limits to 3.4% for both the beam energies. Another source of error in making tissue compensator is the thickness denomination of Al blocks and was found to be < 4% for extreme minimal depth of dose compensation (1.5 cm), when the thickness variation of Al blocks is 0.25 cm. This is the maximum error, which could arise from all possible sources of limitations encountered in clinical situations. Otherwise, the maximum error at the same depth of compensation (5 cm) when Al thickness is approximated to an integral multiple of 0.25 cm was estimated to be 2.1 %. Film dosimetry on a representative neck phantom with and without Al tissue compensator prepared from the generated data shows a significant improvement in beam flatness from 12.4% to 4.4%for 60Co and 7.7% to 2.4% for 6 MV x-rays. The beam flatness in the presence of tissue compensator was found to be comparable with the values observed for a normal open beam in a standard polystyrene phantom (2.5% for 60Co and 1.9% for 6 MV x-rays).

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