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Authors
Advisor(s)
Abstract(s)
Charged particle beam therapy has been used for its twofold advantageous behavior: offering high precision to the target volume and minimum doses to organs at risk and normal function tissue. Treatment outcome of pancreatic patients is compromised by dose limits of the gastrointestinal tract and dose escalation is critical due to inter-fractional uncertainties. The aim of this work (at University Clinic of Heidelberg) was to assess tissue variations by water equivalent path-length (WEPL) changes and find the dosimetric criteria where corrective actions should be taken i.e. re-optimization of the treatment plan. Two types of analysis were performed by comparing planning-CT and rigidly co-registered weekly-CTs for 11 patients: A) Dose Forward calculation performed using a research TPS TRiP98, from the treatment plan clinically applied to the patients. The dose evaluation parameters were V95%PTV, V95%CTV and Gamma-index criteria. B) WEPL maps were generated using the MeVisLab framework to quantify densities variation as a percentage of voxels for the defined range of tissue variation (±3mm H2O). Both Gamma-index and V95%PTV showed tendency to increase or decrease with WEPL variations by strong correlation of 0.73 and 0.6, respectively. A criterion of WEPL as 56% interprets more than 3% variations in V95%PTV and Gamma passing rate lower than 96.5% (with distance to agreement as 3mm and dose difference of 3%). The studied method proved to be a prediction tool for physicians in decision making for treatment plan re-optimization need due to inter-fractional density variation, with less computational time and without contouring structures.
Description
Mestrado em Radiações Aplicadas às Tecnologias da Saúde - Área de especialização: Terapia com Radiações
Keywords
Pancreatic tumour Water equivalent path-length WEPL Charged particle therapy Plan adaptation Pancreas
Citation
Asim Z. Dosimetric criteria for plan adaptation in charged particle therapy for pancreatic tumour patient [Dissertation]. Lisbon: Escola Superior de Tecnologia da Saúde de Lisboa/Instituto Politécnico de Lisboa; 2016.
Publisher
Instituto Politécnico de Lisboa, Escola Superior de Tecnologia da Saúde de Lisboa