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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.

The chief aim in developing radiation treatment plans is to maximise tumour cell kill while minimising the killing of normal cells. The acceptance by a radiation oncologist of a radiation therapy treatment plan devised by the radiation therapist, at present is largely based on the oncologists' previous clinical experience with reference to established patterns of treatment and their clinical interpretation of the dose volume histogram. Some versions of radiotherapy planning computer software now incorporate a function that permits biologically based predictions about the probability of tumour control (TCP) and/or normal tissue complications (NTCP). The biological models used for these probabilities are founded upon statistical and mathematical principles as well as radiobiology concepts. TCP and NTCP potentially offer the capability of being able to better optimise treatments for an individual patient's tumour and normal anatomy. There have been few attempts in the past to correlate NTCPs to actual treatment complications, and the reported complications have generally not shown any significant correlation. Thus determining whether either or both NTCPs and TCPs could be correlated with the observed clinical outcomes of prostate radiotherapy is the central topic of this thesis. In this research, TCPs and NTCPs were prospectively calculated for prostate cancer patients receiving radiation therapy, and subsequently assessed against the clinical results of the delivered treatments. This research was conducted using two different types of NTCP models, which were correlated against observed treatment-induced complications in the rectum and bladder. The two NTCP models were also compared to determine their relative efficacy in predicting the recorded toxicities. As part of this research the refinement of some of the published bladder parameters required for NTCP calculations was undertaken to provide a better fit between predicted and observed complication rates for the bladder wall which was used in this research. TCPs were also calculated for each patient using the best available estimate of the radiosensitivity of the prostate gland from recent research. The TCP/NTCP data was analysed to determine if any correlations existed between the calculated probabilities and the observed clinical data. The results of the analyses showed that a correlation between the NTCP and a limited number of toxicities did occur. Additionally the NTCP predictions were compared to existing parameters and methods for radiotherapy plan evaluation - most notably DVHs. It is shown that NTCPs can provide superior discriminatory power when utilised for prospective plan evaluation. While the TCP could not be correlated with clinical outcomes due to insufficient follow-up data, it is shown that there was a correlation between the TCP and the treatment technique used.