School of Electrical and Electronic Engineering

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    A COMPARATIVE STUDY OF PENCIL BEAM AND COLLAPSED CONE CONVOLUTION DOSE CALCULATION ALGORITHMS IN PELVIC AND THORACIC TREATMENT PLANS
    (2023-11-01) Dina, Moraa
    Different algorithms used to calculate doses in radiotherapy planning adopt different techniques in simulating doses received by the target (tumor) volume. Such differences can come about in terms of dose distribution in the target volume and doses received by surrounding organs. Due to such differences, it is necessary to take into consideration the best algorithm suitable for a range of mediums i.e homogeneous and heterogeneous mediums. The differences in the way different algorithms simulate doses in different media may bring about dosimetric variations which can relatively affect treatment outcomes in 3D-conformal radiotherapy. The primary focus of this research was to compare dose variations for two dose calculations algorithms namely, Pencil Beam (PB) algorithm and the Collapsed Cone Convolution (CCC) in highly and less heterogeneous mediums. The study was an analytical retrospective study consisting of 8 pelvic and 7 thoracic treatment plans approved and scheduled to undergo 3D- CRT. The treatment plans were generated using PB and the same treatment plans recalculated using the CCC calculation algorithm. Dosimetric variations between the two dose calculation algorithms were observed and evaluated based on variations in plan parameters such as dose received by the tumor volume and the dose received by critical organs (OAR’s). Minimum and Maximum mean dose values were obtained from PTV and OAR’s from the two dose calculation algorithms. Differences in dose values between the two algorithms were analyzed using standard errors (SE) to determine if in fact the differences were significant. At a CI of 95% (P=0.05), it was found out that the two calculation algorithms demonstrated insignificant dose differences to a treatment plan. PB algorithm demonstrated high dose received to the tumor volume compared to the CCC algorithm. A visual analysis of the results using box plots demonstrated that the two algorithms showed no major differences in doses received by the PTV and OAR’s. It made no significant difference to a treatment plan if the planner (Medical Physicist) would adopt either of the algorithms in calculating doses for cervix or esophagus treatment plans using ONCENTRA Treatment Planning System
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    ETERMINATION OF THE COUCH TRANSMISSION FACTOR AND ITS INCORPORATION IN TREATMENT PLANNING SYSTEM
    (2023-11-01) Chanzu, Ian
    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