There is an abundance of data that can be used to define clinical target volumes based on prostate cancer spread.
Data on the rate of extraprostatic tumour extension and seminal vesicle involvement are available and can be used to define risk categories and individualised target volumes.
The definition of risk groups remains a critical issue, as it is notonly the clinical tumour stage, PSA level and Gleason score that define a patient as being in the low, inter-mediate or high risk group. Factors such as the number of positive biopsies or perineural tumour invasion provide important additional information on the patients’ individual risk and possibly affect target definition.
Organ at risk definitions and delineations are crucial to precisely evaluate dose–volume histograms and their potential impact on acute and late toxicity. A general recommendation cannot be given due to the variety of de- finitions.
Yet clinical quality assurance protocols with respect to rectal and bladder filling, OAR delineation and dose constraints are mandatory for every institution. Patient positioning and/or prostate immobilisation remain controversial issues. Current data favour supine treatment position including a knee support. Treatment verification using either ultrasound based positioning systems, implanted markers or portal imaging alone with patients positioned in an immobilisation device or the use of a rectal balloon are still under investigation.
Therefore, so far no clear recommen-dations can be given. There seems to be an obvious advantage in using imaging modalities (such as MRI) for more precise target definitions. Although CT based treatment planning can be regarded as a standard, its weaknesses have become apparent. Not all centres are equipped with a MRI scanner at their disposal, however. Its implementation should be considered carefully, however, in view of the possible change in margins as compared to CT based planning.
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