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Towards the clinical implementation of deformable image registration in gynecological radiotherapy
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Resumo(s)
Radiotherapy (RT) plays a central role in cancer treatment, requiring a balance between tumor control and the preservation of healthy tissues. However, anatomical changes may occur during the course of treatment, potentially compromising the dose distribution initially planned. Furthermore, tumor recurrence after a first irradiation course introduces additional challenges, making strategies such as replanning and re-irradiation necessary. The aim of this dissertation is to evaluate the dosimetric implications of these two approaches, with particular emphasis on the detailed and systematic analysis of cumulative dose delivered to organs at risk (OARs) and its relationship with tolerance limits established in widely recognized clinical reference protocols. A total of 17 patients who underwent replanning during their initial treatment course and 7 patients who underwent re-irradiation were included. In both contexts, deformable image registration (DIR) was applied to transfer the initial treatment plan dose to the anatomy represented in subsequent imaging, thereby allowing a robust and clinically meaningful comparison between the Dose Plan and the Dose Deformed. These deformations were performed in Velocity® software, which allowed me to apply DIR to both replanning and reirradiation cases. For re-irradiation cases, doses from both treatment courses were summed, with conversion to EQD2 applied to ensure comparability between different fractionation schemes, followed by reconversion into a clinical reference framework. The results highlighted distinct trends: in replanning, Dose Deformed was frequently higher than Dose Plan, underscoring the necessity of plan adjustment to safeguard OARs. In contrast, in re-irradiation, lower mean Dose Deformed values were observed relative to Dose Plan, a finding associated with substantial anatomical changes occurring between treatments. Cumulative analysis also found cases in which tolerance limits were reached or exceeded, highlighting the need of careful dosimetric evaluation. It can be therefore concluded that such combined methodological approaches, including DIR conversion and EQD2 conversion, form an essential strategy for clinical decision-making and strongly support the need for both replanning and re-irradiation to be implemented as fundamental strategies for effective therapeutic personalization.
Descrição
Tese de Mestrado, Engenharia Biomédica e Biofísica, 2025, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Replanning Re-irradiation Cumulative dose Deformable registration EQD2