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Title: Rotational intensity modulated radiation therapy : dosimetric, treatment planning, and radiobiological aspects
Author: Iori, Mauro
ISNI:       0000 0004 2737 2971
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2011
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The introduction in Radiation Oncology of x-ray beams fluence modulation, the treatment technique known as Intensity Modulated Radiation Therapy (IMRT), is leading to the flourishing of new and increasingly sophisticated treatments. It is within this context that delivery systems have been evolving from static to rotational IMRT techniques through which significant advantages have occurred in terms of treatment plan quality, delivery efficiency and accuracy, although paying the price of longer calculation times for the plan optimization. The point has been reached where the perceived advantages of rotational IMRT techniques, for which some companies have marketed therapy systems with different architecture from that of conventional linear accelerators, have led users to question whether the established and more conventional systems are becoming obsolete. However, the newly available methods of delivering Intensity Modulated Arc Therapies (IMAT) using conventional accelerators, an advanced form of rotational IMRT that combines multiple arcs with variable fluence and gantry speed, seem to have provided a preliminary answer to this concern. Although it is difficult to know which of these treatment modalities will be discontinued in the near future, it is clear that the rotational IMR T is expected to become increasingly important. Therefore, the problem of understanding which are the strengths of these techniques, or the most effective methods (forward or inverse-planning based) of their treatment planning procedures, as well as the most robust and effective systems for verifying dosimetrically such rotational deliveries can be considered current research topics. As a results, different aspects of rotational IMRT techniques have been investigated in this work, starting with the pre-clinical dosimetry of IMAT therapies, passing through the planning procedures also in comparison with static IMR T, and advancing to a special application of 'rotational IMRT': the simulation of radiobiologically optimised, voxel-based dose-painting, guided by the metabolic tumour imaging. In particular we have worked on: two methods for the pre-clinical dosimetry of IMA T treatments using a matrix detector of ionization-chambers and an electronic portal imaging device, a forward and an inverse-planning approach for simulating IMAT treatments, a ranking of plans simulated with static and rotational IMRT modalities on prostate tumour. The high conformality achievable by rotational IMRT, as well as its potential to deliver selectively different doses inside a heterogeneous target volume, together with the image guidance capabilities of the newest therapy units, makes arc modulation the most appropriate and suitable instrument for assessing future "dose painting" treatments. In this regard, two radiobiological objective functions for guiding the dose redistribution inside a group of prostate tumours according to their estimated clonogenic density distribution (based on Position Emission Tomography imaging) were developed, compared and analysed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral