Radiation Therapy, Guided Therapy and Related Topics

Although a large number of men above age 50 will develop prostate cancer, only in a small proportion of patients will their tumor become aggressive. For the majority of men with non-aggressive tumors, one can delay invasive treatment until the tumor becomes aggressive (watchful waiting). It is essential to precisely characterize the tumor. This can be achieved with multimodality MRI. With nomograms based on the serum PSA-value, the tumor’s aggression (expressed in Gleason-grade), and the outcome of a digital rectal examination, an attempt is made to predict the aggression and local extension of the tumor, and detect the presence of lymph node metastasis. Based on these nomograms, the further treatment strategy is determined. Unfortunately, these nomograms are only moderately reliable, so that it is not always possible to make the right treatment decision. By means of functional (multi-modality) MR imaging, information can be acquired regarding the aggression of the tumor. Furthermore, an MR-examination, performed at high field strength (3 Tesla) with use of an endorectal coil (ERC), allows a very accurate determination of minimal (sub-millimeter) extra-prostatic spread. The sensitivity and specificity of 3T ERC MR imaging for determination of extra prostatic disease are respectively 87% and 96%3. If it is decided to surgically remove the prostate, it is important to know where the tumor is located and whether it shows extra-prostatic growth. If the tumor is distant from the neurovascular bundle, these bundles can be spared. This decreases the chance of postoperative impotence. If the MRI shows obvious extra-prostatic extension, it can be concluded that surgery is less useful so the best choice is hormonal therapy with or without radiotherapy. Nowadays, prostate cancer is increasingly treated with directed, local radiotherapy. If the precise location of the tumor is known, it is possible to give a local boost to this location in the prostate. This has the advantage that less radiation is given to the surrounding tissue, with fewer side effects. An MRI can supply this information . As MRI more accurately visualized the tumor in the prostate compared to Trans Rectal Ultra Sound (TRUS), these techniques potentially also can be used for improved local non-invasive therapy. An additional advantage of MR is the fact, that with this technique temperature changes cab be monitored in real-time.