Hypoxic Target Volume Determination in PET/CT Imaging : The Impact of Deformable Image Registration

Sammanfattning: Using a tailored dose distribution for personalized radiotherapy with the help of positron emission tomography (PET) might give an edge for successful tumour elimination. One of the main determinants for tumour radioresistance in several solid tumours has been investigated as hypoxia, including head and neck cancer (HNC). Using novel methods of converting radiotracer uptake into partial oxygen pressure distribution in the form of partial pressure maps, it is possible to delineate the hypoxic region of a target to further escalate the treatment dose there, aiming at an increase in tumour control. However, the registration between functional and structural images may have an impact on the effectiveness of dose escalation, and choosing the correct registration method could be imperative. In this master’s thesis, the impact of choosing rigid or deformable image registration between planning-CT and PET/CT images on the characterization of the hypoxic compartment, as well as on the treatment evaluation in terms of tumour control and normal tissue complication, was assessed. This was achieved by, using hypoxic patients of a cohort of 22 HNC patients, creating a separate plan for each registration method, for each patient, and comparing them quantitatively. The results showed that both methods would yield distinctly different dose distributions when planned using the same objectives and constraints in terms of dose level and shape. Furthermore, they both give a distribution of similar quality. However, using rigid registration together with the deformed PET did not render lower results overall in tumour control. Thus, no advantage could be seen in choosing deformable registration over rigid registration when aiming at tumour control.