Medknow Publications on behalf of the Association of Radiation Oncologists of India (AROI)
Abstract
Purpose: To estimate the transit dose from motorized wedge (MW)
treatment in Equinox-80 telecobalt machine. Materials and Methods: Two
plans were generated in Eclipse treatment planning system with
universal wedge (UW) and MW each for 10x10 cm 2 . The transit dose was
measured with 0.6 cc cylindrical ion chamber and thermoluminescent
dosimeters (TLD) chips at a depth of 5 cm with source to axis distance
(SAD) 80 cm. Results: The measured dose with ion chamber was in well
agreement with the calculated dose from Eclipse within \ub1 2%. The
planned dose was 100 cGy while the measured absorbed dose with ion
chamber for 15\ub0, 30\ub0, 45\ub0 and 60\ub0 MW treatment was
found to be 100.94, 101.04, 100.72 and 99.33 cGy respectively. For
15\ub0, 30\ub0, 45\ub0 and 60\ub0 UW treatment, the measured
absorbed dose was 99.33, 97.67, 97.77 and 99.57 cGy respectively.
Similarly the measured absorbed dose with TLD was within \ub1 3% with
the planned dose for universal wedge (UW) and MW. From the experimental
measurements, it was found that there was no significant contribution
of transit dose during MW treatment. Conclusion: The actual
measurements carried out with ion chamber in Equinox-80 machine for UW
and MW revealed no variation between the doses delivered. The doses
were comparable for both UW and MW treatments. The results from TLD
measurements additionally confirmed no variation between the doses
delivered with UW and MW. It was also demonstrated that the observed
excess or less transit dose with MW does not have any significant
clinical impact. This assured the safe dose delivery with MW