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Optimisation of treatment planning and delivery in 3D brachytherapy

Kari Tanderup  


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Accepted by: Faculty of Health Sciences Aarhus University
Defended on: January 11, 2008
Official opponents: Jack Venselaar , Erik Van Limbergen
Tutors: Cai Grau , Jacob Christian Lindegaard , Dag Rune Olsen

Published in the PhD Database: February 21, 2008


English abstract
Brachytherapy has been used for more than 100 years in the treatment of cancer and is still widely based on 2D imaging and classical dose planning systems. 3D image based brachytherapy integrates modern imaging and advanced computer technology. This approach makes it possible to individually shape the dose according to the tumour while avoiding normal tissue as much as possible. The technique has potential to lead to increased tumour control and less unwanted side effects.
3D image based brachytherapy has raised many questions concerning both the benefit and the reliability of the whole procedure. This thesis focuses on the technical and physics aspects of the procedure: reconstruction of applicator (Paper I), 3D dose optimisation (Paper II and III) and dose delivery (Paper IV).
In Paper I we analysed dose plans from 20 patients in order to assess uncertainties related to systematic and random reconstruction errors. We could conclude that 3D reconstruction of applicators can be done without introducing large uncertainties into the 3D dose planning procedure. Quality assurance of the reconstruction procedure is an essential tool to keep geometric errors under control.
In Paper II we evaluated the benefit of dose optimisation in single plane interstitial brachytherapy. We analysed CT based dose plans from 14 patients and 12 theoretical implant configurations. Two dose optimisation strategies were compared to non-optimised dose plans and we could conclude that dose optimisation significantly improved the dose distribution in terms of target dose, dose to surrounding tissue, high dose volumes and homogeneity. Optimisation was fast and reproducible.
In Paper III the benefit of MRI based dose optimisation in intracavitary brachytherapy was evaluated in 21 patients. DVH parameters were significantly improved, and DVH constraints could be met in 16/21 patients in optimised dose plans compared to 3/21 in 2D standard dose plans.
In Paper IV we analysed in vivo dose measurements from 14 patients. A mathematical model was developed that used the dose measurements to assess the geometric stability of rectum and applicator during treatment delivery. We could conclude that movement of rectum and applicator was limited, and that on line dose monitoring is a promising step forward in quality assurance of brachytherapy.
The findings in this thesis, strengthen the evidence that 3D based brachytherapy is a reliable procedure that leads to improvement of dose distribution.



Danish abstract
PhD projektet er udført på Onkologisk Afdeling, Aarhus Universitetshospital og har omhandlet optimering af 3D billedbaseret behandling med radioaktive kilder (brachyterapi) i cervix cancer. Ved kombination af ekstern strålebehandling (45-50 Gy), intracavitær brachyterapi (30-40 Gy) og kemoterapi kan man for nuværende opnå lokal kontrol på 60-85 % afhængig af stadium, tumorstørrelse og topografi. Sværere morbiditet (grad 3-4) ses hos ca. 10-15 %. Medens ekstern strålebehandling for flere år siden overgik til 3D planlægning baseret på CT scanning, er planlægningen af brachyterapi imidlertid ofte baseret på ortogonale røntgen billeder (2D), som giver begrænset information om tumorudbredningen og de omgivende normale vævs lokalisation. Anvendelse af MR scanning giver helt nye muligheder for at skræddersy stråledosis til tumoren i 3D. Formålet med PhD arbejdet har været at undersøge om 3D billedbaseret behandlingsplanlægning af brachyterapi kan forbedre fordelingen af stråledosis i patienten samt at validere, at det er muligt at planlægge og aflevere behandlingen med tilfredsstillende nøjagtighed.
Analyser af dosisplaner for 21 konsekutive cervix patienter har vist at tumor dosis kunne forbedres væsentligt ved anvendelse af 3D MR billedvejledt strålebehandling ¿ især i forbindelse med store tumorer. Samtidig kunne dosis til normalvæv mindskes. Præcisionen af dosisberegningen blev evalueret, og det kunne konkluderes, at beregningen er robust overfor de nye processer der indgår i 3D dosisplanlægning. Endelig blev en ny metode - baseret på dosismålinger - udviklet til monitorering af afleveringen af stråler. Analyser af 14 patienter kunne demonstrere en god geometrisk stabilitet under strålebehandlingen, hvilket indikerer at det er muligt at aflevere en moduleret og individuelt tilpasset strålebehandling med tilfredsstillende nøjagtighed.
PhD arbejdet styrker evidensen for at 3D billedbaseret brachyterapi er en pålidelig procedure, som leder til væsentlig forbedring af stråledosis i både tumor og normalvæv. Det forventes at anvendelse af den nye teknik indenfor lokal avanceret cervix cancer vil medføre en reduktion af antallet af patienter med lokalrecidiv eller alvorlige strålebivirkninger. Videre klinisk evaluering af 3D MR baseret brachyterapi i lokal avanceret cervix cancer vil finde sted i et internationalt prospektivt studie, som koordineres fra Aarhus Universitetshospital og General Hospital of Vienna. Studiet åbner for patienttilgang i 2008, og forventes at rekruttere 600 patienter over en periode på 3 år.