Dissertation committee:
Ευστάθιος Π. Ευσταθόπουλος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Παντελής Καραΐσκος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Βασίλειος Κουλουλίας, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Μιχάλης Μαζωνάκης, Αναπληρωτής Καθηγητής, Ιατρική Σχολή, Πανεπιστήμιο Κρήτης
Καλλιόπη Πλατώνη, Αναπληρώτρια Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Ελευθέριος Παππάς, Επίκουρος Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Γεωργία Λυμπεροπούλου, Λέκτορας, Ιατρική Σχολή, ΕΚΠΑ
Summary:
Purpose
Patient-specific quality assurance (PSQA) is integral to contemporary radiation
therapy. Currently, the evaluation of the verification plans is being performed
mainly with statistical methods, which could underestimate the clinical importance of the spotted differences, as per the literature. This work aims to present
a novel method based on the difference of the isodose surfaces as a dose distribution comparison tool to connect acceptance tolerance to QA limitations (equipment capabilities) and transfer a more clinical approach in the analysis procedure.
Methods
The distance of dose points from the isocenter can be used as a function to
define the shape of an isodose surface. Isodose surface differences (ISD) are
defined as the normalised differences of reference and evaluated surface histograms plotted against their corresponding isodose. Acceptance tolerances
originate from actual QA tolerances, and they are presented in a clinically intuitive way. The ISD method was compared to the gamma index using intentionally
erroneous VMAT and IMRT plans.
Results
Results revealed that the ISD method is sensitive to all errors induced in the
plans. Discrepancies are presented per isodose, enabling the evaluation of the
plan in two regions, which represent PTV and Normal Tissue.
Conclusions
In conclusion, the ISD method is a meaningful, QA-related, registration-free, clinically oriented technique of dose evaluation during the verification process. This
method can be used as a standalone or an auxiliary tool to the well-established
evaluation procedures, overcoming significant limitations reported in the literature.
