Simulation design and characteristics of multileaf collimators at rotational radiotherapy

• Κύριος συγγραφέας: Τσολάκη, Ευαγγελία
• Άλλοι συγγραφείς: Παλληκαράκης, Νικόλαος
• Μορφή: Thesis
• Γλώσσα: Greek
• Έκδοση: 2009
• Θέματα: Rotational radiotherapy; Linear accelerator; Multileaf collimator; Segmentation algorithm; Περιστρεφόμενη ακτινοθεραπεία; Γραμμικός επιταχυντής; Κατευθυντήρας πολλαπλών φύλλων; Αλγόριθμος τμηματοποίησης; 616.994 064 2

In treatment of cancer using high energetic radiation the problem arises how to irradiate the tumor without damaging the healthy tissue in the immediate vicinity. In order to do this, intensity modulated radiation therapy (IMRT) is used. In this thesis, the general goal is to modulate the homogeneous radiation field delivered by an external accelerator using a multileaf collimator in comparison with beam modifying devices. In order to generate intensity modulated fields in a static mode with multileaf collimators, the heuristic algorithm of Galvin, Chen and Smith is used. This method aims at finding a segmentation with a small number of segments, taking account of mechanical constraints such as leaves can move only in one direction, on one row, the right and left leaves cannot overlap (Interleaf Collision) and also every element between the leaf and the side of the collimator to which the leaf is connected is also covered (no holes in leaves). During the implementation of the algorithm, the initial intensity matrix with the desired radiation rates is inserted and using essential transformations, a positive combination of special matrices, segments, corresponding to fixed positions of multileaf collimator are obtained. All calculations end with the superposition of segments which leads to the creation of the 3-D matrix that will be used to irradiate the tumor. The algorithm is implemented in C++. The calculations are fast and the procedure is user friendly. The model is implemented for the case of protection the spinal cord while treating a tumor in the neck area. Furthermore, dose distributions obtained with this model and beam modifying devices in the neck area were compared.