Moser, K. (2019). Impact of organ motion and tumor regression on intensity modulated radiotherapy techniques for cervical cancer [Diploma Thesis, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2019.66364
The potential organ movement within the pelvic region in patients suffering from cervical cancer presents a substantial challenge in their treatment with modern precise radiation techniques. The aim of this research was to enhance the understanding of the consequences of using a single initial CT image as base for the patients entire treatment. A pool of 7 patients with cervical cancer whose actual treatment consisted of a prescribed dose of 45Gy delivered in 25 fractions was examined. During their image guided treatment 41 fan beam computed tomography (FBCT, out of room) and additionally 150 cone beam computed tomography (CBCT, in-room) images were taken. Based on these data, the impact of organ motion was compared for two radiation methods: intensity modulated radiation therapy (IMRT) and volumetric intensity modulated arc therapy (VMAT). By means of weekly FBCTs, the representative value of the initial CT and the advantage of weekly replanning was evaluated and the CBCTs were set in consequential relation to them. Additionally, a programme to optimise the evaluation for data for the EMBRACE II study was developed. In nearly all of the examined cases VMAT provided better outcomes regarding the treatment planning objectives: tumor coverage and sparing of the organs at risk (OAR). Comparing the FBCTs and the CBCTs with the initial plan showed that the organ movement during the treatment led to discrepancies between the predicted and the actually received dose. The results for the weekly replanning demonstrated that the effectivelydeliveredtumorcoverageexceededthecoveragereceivedbyatreatment based solely on one initial plan. For some patients the OARs were subjected to higher amount of dose with the weekly replanning while for other patients the weekly replanning method produced a more effective sparing of the OARs. All the values of the CBCT scompared to the valuesof the weekly FBCTs were within a close range except for the first week. Using a single initial plan as the sole base for the radiation treatment of patients suffering from cervical cancer does not deliver the desired results regarding tumor coverage or sparing of the OARs. Thus the weekly replanning procedure is to be preferred, even if in some cases it can lead to a slightly higher organ exposure to radiation, which, however can be accepted if it is unavoidable in order to ensure that the tumor coverage stays within the prescribed limitations.
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