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Abstract
PRE-TREATMENT AND IN VIVO DOSIMETRY FOR VMAT RADIOTHERAPY TREATMENTS: CHARACTERIZATION AND CLINICAL IMPLEMENTATION OF TWO EPID-BASED SOFTWARE SOLUTIONS
Matteo Poli
Università degli Studi di Torino
Scuola di Specializzazione in Fisica Medica (A.A. 2014-2015) Direttore: Roberto Cirio
Fisica Sanitaria, Candiolo Cancer Institute – FPO, IRCCS (Candiolo, Italy) Relatore: Michele Stasi
Introduction
New procedures in radiotherapy, such as Volumetric Arc Radiation Therapy (VMAT), allows a higher dose deposition within the treatment volumes while sparing the surrounding organs at risks (OARs). Due to the high complexity of such treatments and the black-box nature of inverse planning optimization, Quality Assurance (QA) is crucial to avoid accidents like missing target or overdose to the OARs. Electronic Portal Imaging Devices (EPIDs) are clinically used for patient setup verification but they can also provide dosimetric information of the delivered treatment. However, theirs implementation as dosimetric tools is not obvious and models have to be developed to convert the raw EPID signal into dose in water distributions. Recently, the use of EPID for dosimetric verification, both in pre-treatment than in in vivo, was supported by several algorithms [1,2]. The aim of this thesis was to implement two different algorithms for VMAT plan verification on the new TrueBeam STx Linac (Varian Oncology, Palo Alto, California) with the final goal to include portal dosimetry verification in the clinical workflow. The two systems provide different approaches for commissioning and calculation, and these differences were analyzed and characterized on phantom measurements. In particular, both systems were tested for their ability to catch the main critical delivery dose errors. Moreover, the sensitivity and the specificity of the two software solutions to identify dosimetric and geometric discrepancies in VMAT pre-treatment QA were evaluated to define their error-detection thresholds. Implications on the DVHs of the patient treatments were also considered for establishing a QA protocol with reasonable tolerance levels. Finally, the first results on pre-treatment and in vivo patients’ QA are presented.
Materials and Methods
Tesi di Specialità
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