Update on brachytherapy in localized prostate cancer: the importance of dosimetry

Prostate brachytherapy has become a common treatment modality for clinical localized adenocarcinoma of the prostate. This is the result of prostate screening and improved technology that currently allows for an outpatient procedure that generally can be accomplished in 1-2 h. The modern technique of prostate brachytherapy includes three components, (1) treatment planning, (2) placement of the sources and (3) an evaluation of the implant quality. In this review, we will focus on the importance of dosimetric quantifiers in predicting freedom from biochemical recurrence.

A number of dosimetric quantifiers have been described. These include D90 (dose that covers 90% of the prostate volume) and V100 (fractional volume of the prostate that receives 100% of the prescription dose). The data from four recently reported series are reviewed. Each series looks at various dosimetric cutpoints that predict for freedom from biochemical recurrence making a definitive statement difficult. All series observe a relationship between freedom from biochemical recurrence and one or both of these dosimetric quantifiers.

It is clear that a dose-response relationship exists following treatment with prostate brachytherapy; in other words, dosimetry matters and poor dosimetry will result in fewer men being cured. The lack of consistency in the reports to date precludes any definitive statements about what constitutes a "good" compared with a "bad" implant. Further prospective data from multi-center trials are required.