Abstract:
Treatment couch is an equipment used in the treatment of cancer patients. It is used to give comfort and support during treatment. This ensures good treatment outcome as the patient will be intact thereby maximizing the dose to the target while minimizing the dose to surrounding organs. In order to improve tumour dose coverage, more radiation beams are placed to come from different angles, others penetrating the couch before reaching the target. The treatment couch is made of carbon fibre thus making it radiotranslucence especially for the radiation beams penetrating through it before reaching the target. Research previously done, shows that the treatment couch causes poor dose distribution resulting to underdose. To solve this problem, the treatment Couch Transmission Factor (CTF) needs to be included in the Treatment Planning System (TPS) in order to compensate for the dose absorbed by the couch. This study investigated the CTF of the iBEAM evo treatment couch and virtual TPS couch model, and its incorporation in the Oncentra TPS. The study was carried out in three phases using a cylindrical CTDI phantom, ion chamber and a TPS generated virtual square phantom. Phases 1 and 2 gave an equal mean CTF of 1.00 for 6MV and 15MV while phase 3 gave a mean CTF of 0.97 for 6MV and 0.98 for 15MV. The highest deviations recorded between CTF values in phase 1 and phase 3 were at GAP 11 (-9.03%) for 6MV photon energy and GAP 4 (-4.96%) and GAP 11(-6.65%) for 15MV photon energy. The highest deviations recorded between CTF values in phase 2 and phase 3 were at 11 (-9.53%) for 6MV photon energies and 11 (-6.85%) for 15MV photon energy. The implication of these results was seen on the dose deviations between phases 1, 2 and phase 3 if the plans in the TPS could have been delivered. The highest recorded underdose was 12.71 monitor units in phase 2 at GAP 11(213.8°) and 10.63 monitor units in phase 1 at GAP 11 (213.8°) for 6MV, 7.02 monitor units in phase 1 and 7.97 monitor units in phase 2 for 15MV at GAP 11(213.8°). In conclusion, from this research done, the CTF is not incorporated in the TPS. However, further studies are recommended of the same when the CT couch attached on the CTDI scanned image is included in the external or body contour
