Abstract
Image Guided Intensity Modulated Radiotherapy (IG-IMRT) has the potential to improve accuracy of treatment delivery, which in turn may improve the therapeutic ratio. This is particularly relevant for prostate cancer because the prostate moves independently to pelvic bony anatomy due to variations in rectal and bladder filling. Radiotherapy is associated with a rare risk of late second malignancy and biological and physical parameters can be measured to estimate this risk. The purpose of this thesis was to evaluate the dosimetric and radiobiological effects of IG-IMRT for patients receiving radiotherapy to prostate +/- nodes, and to evaluate second cancer risk in this group using a biological marker of DNA damage, gammaH2AX (yH2AX), in addition to physical measurements. A clinical study compared IGRT with online and offline matching with 2-dimensional (2D) kilovoltage (kV) matching to fiducial markers and 3-dimensional (3D) cone beam computed tomography (CBCT) matching to bone. There was variation in bladder and rectal volumes between planning CT and treatment which resulted in higher doses calculated on CBCT compared to plan and this also impacted on rectal normal tissue complication probability (NTCP). There was a significantly lower prostate tumour control probability (TCP) calculated from CBCT in patients with a larger initial rectal volume. There was satisfactory planning target volume (PTV) coverage and TCP for prostate and nodes when matching to bone and markers. There was no evidence of increased gammaH2AX levels with higher photon energy or larger treatment volume. There was a higher effective dose with prostate and node treatment compared to prostate only treatment, but this did not translate into a higher age specific risk of second cancer.