Difficulties and potential of correlating local recurrences in prostate cancer with the delivered local dose

In the previous decades the distinction between a local relapse and distant metastases was difficult to accomplish in an early stage. As a consequence, a failure could only be coarsely related to the original radiotherapy treatment. Currently, due to better imaging and position verification techniques, the actual dose within the prostate can be estimated, taking position uncertainties into account. Furthermore, advanced functional MRI techniques, such as MR spectroscopy (MRS) and dynamic contrast-enhanced MRI (DCE-MRI), increase the chance of localizing a local recurrence within the prostate. With this information the correlation between the actual previously delivered dose and a local relapse can be established, using non-rigid registration of the planning CT and the post-recurrence MRI. The current study describes the possibilities and problems in obtaining this correlation. This serves as a framework for investigating a reliable dose effect relationship in the future.