AbstractID: 9258 Title: Couch Transmission Study on Clinical Photon Beams for Radiotherapy
A treatment couch has a big bar in the center. For the treatment planning, we usually tried to avoid the big bar to treat patients.
A question is arisen that if the radiation goes through the bar for some special cases, for example the head and neck, how large
effect does the couch have on the target dose distribution? In this work, we studied Siemens treatment couch transmission for
6MV, 10MV and 18MV clinical photon beams. First we measured the couch bar transmission and verified it using Monte Carlo
simulation. The calculated results are in good agreement with the measured data(less than 2%). Then we used the modeled
couch bar as a compensator to calculate the dose distribution for 4 fields and 6 fields both in with couch situation and in without
couch situation. Our results show that, the couch bar attenuation causes a big ‘cold spot’ in the target region. In with couch and
in without couch situations, for 6 fields at 18MV beam, the mean dose difference is 12.9%, the difference of dose that 98%
target volume received(D98) is about 18.1%, for 6MV, the mean dose difference is about 10% and the D98 difference is 12%.
According to the results, we should avoid the couch bar for treatment because of the large dose attenuation. The investigation of
different dose weight on fields for couch bar transmission will be discussed.