Abstract
In addition to the conventional radiotherapy techniques used in standard radiotherapy departments, several specialised techniques are known and used today based on accurate dose delivery and target localization. The basic advantage of these techniques is that tumour control can be improved since compared to conventional ones allow the delivery of a higher tumour dose while maintaining an acceptable level of normal tissue complications. These new techniques are based on 3-D target localization, 3-D treatment planning and 3-D dose delivery.Target localization is achieved through anatomical and functional imaging: CT, MRI, PET and ultrasound. Treatment planning is achieved either with standard forward planning techniques, which design uniform intensity beams shaped to the geometrical projection of the target, or, for more advanced conformal radiotherapy techniques such as IMRT (Intensive Modulated Radiotherapy) and stereotactic radiotherapy-radiosurgery, with inverse planning, which in ad ...
In addition to the conventional radiotherapy techniques used in standard radiotherapy departments, several specialised techniques are known and used today based on accurate dose delivery and target localization. The basic advantage of these techniques is that tumour control can be improved since compared to conventional ones allow the delivery of a higher tumour dose while maintaining an acceptable level of normal tissue complications. These new techniques are based on 3-D target localization, 3-D treatment planning and 3-D dose delivery.Target localization is achieved through anatomical and functional imaging: CT, MRI, PET and ultrasound. Treatment planning is achieved either with standard forward planning techniques, which design uniform intensity beams shaped to the geometrical projection of the target, or, for more advanced conformal radiotherapy techniques such as IMRT (Intensive Modulated Radiotherapy) and stereotactic radiotherapy-radiosurgery, with inverse planning, which in addition to beam shaping, intensity modulated beams are used to improve target dose homogeneity and spare organs at risk. Moreover, it has recently become possible imaging of patient anatomy just before delivery of a fraction of radiotherapy, thus gaining precise knowledge of the location of the target volume on a daily basis. This technique of dose delivery to the patient is known as IGRT (image guidance radiation therapy) and has the potential of ensuring that the relative positions of target volume and critical structures for each fraction are the same as is the treatment plan. This may allow reduced treatment margins, fewer complications, dose escalation and the avoidance of geographical misses. Accurate dosimetry in these advanced and innovative techniques is of great importance because of the requirement for tight conformance of the high-dose region to the target volume and the need of reducing doses to peripheral tissues and thus comprehensive quality assurance programme are needed.The main purpose of that PhD thesis is to compare these new techniques in terms of tumor control probabilities and normal tissue complication probabilities as well as their verification and optimisation for prostate and head and neck cancer. Firstly, in this study two different planning approaches were compared used in two different treatment planning systems (TPS) provided by Elekta for Volumetric Modulated Arc Therapy (VMAT) treatments. Ten prostate patients were studied retrospectively. Different plans were created for every patient using the anatomy-based approach used in ERGO++, as well as the fluence-based planning approach incorporated in Monaco TPS. Secondly, in this study two different optimization approaches used for IMRT and VMAT treatment were compared for two cancer types: prostate and head-and-neck cancer. Ten prostate and ten head-and-neck patients were studied respectively. Volumetric modulated arc therapy (VMAT) is a novel form of Intensity Modulated Radiation Therapy (IMRT) that allows more degrees of freedom such as variation of dose rate, gantry speed and collimator angle in addition to dynamically changing field shape. Different plans were created for every patient, using two different optimization approaches: a) biological cost functions and b) Dose-Volume-Histograms (DVH) functions using a commercially available treatment planning system (Monaco, Elekta), for IMRT and VMAT respectively. Plan comparison was performed in terms of delivery efficiency, target coverage and critical organ protection by utilizing physical (DVH values, conformity index-CI, target dose inhomogeneity- TDI, gradient index- GI) and radiobiological indices (tumor control probability- TCP, normal tissue complication probability- NTCP). Results of the different plans were compared using the two-sided Wilcoxon matched-pair signed rank test with a threshold of p =0.05 for statistical significance.Overall, high quality plans in terms of target coverage and critical organ protection were provided by the two approaches although differences between the compared plan approaches exist. The anatomy-based approach used in ERGO++ can provide plans with increased delivery efficiency (comparable to 3D conformal radiotherapy) in terms of number of MUs and delivery time due to the relatively relative large segments used. On the other hand advantages of the fluence-based approach used in Monaco TPS include increased conformity, better target dose homogeneity and higher dose gradient (lower dose to normal non-target-tissue) due to the higher degree of modulation of the fluence-based approach used. High quality plans in terms of target coverage and critical organ protection were also provided by the two different optimization approaches although differences between the compared plan approaches exist, respectively for each case. All plans had comparable target dose coverage, conformity and gradient indexes, with VMAT plans presenting increased delivery efficiency compared to the IMRT ones. Concerning organs at risk (OARs) the optimization approach based on the biological cost functions was found superior to the conventional one using DVH functions for both prostate and head and neck cases. In conclusion, biological optimization can generate superior plans in terms of OARS sparing using either IMRT or VMAT technique.
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