AUR after prostate brachytherapy linked to treatment trauma, not dose
MedWire News: The radiation dose of iodine-125 (125I) prostate brachytherapy (BT) received to the prostate tissue does not significantly influence a man's risk for developing acute urinary retention (AUR), report Dutch researchers.
By contrast, a large prostate volume, a high degree of pre-existing obstruction, and additional trauma to the prostate experienced during implantation of 125I needles may predict AUR after brachytherapy, says the team.
Ellen Roeloffzen and colleagues from University Medical Center Utrecht concluded that dose was unlikely to be a risk factor for AUR since the 125I half-life is 60 days and patients who developed the condition did so within the first month after implantation.
The team assessed the influence of dosimetric parameters including prostate volume before and after implantation, the number of needles and seeds used, and the percentage of the prostate to receive 100%, 150%, and 200% of the prescribed 144-Gy dose on the development of AUR - defined as any need for urinary catheterization within 3 months of implantation.
As well as undergoing magnetic resonance imaging and intra-operative three-dimensional transrectal ultrasonography before and after implantation, the 714 125I prostate BT-treated patients were assessed for their International Prostate Symptom Score (IPSS) during a minimum of 6 months' follow-up.
In all, 57 (8.0%) patients developed AUR, a median of 30 days after implantation. These patients had significantly higher pretreatment IPSS scores compared with patients without AUR, at 13.8 versus 7.2.
Univariate analysis revealed that AUR was significantly associated with pre- and posttreatment prostate volume, as well as the number of needles and seeds used.
However, after multivariate analysis, adjusted for dosimetric parameters and factors such as postimplant prostate edema and IPSS, the only independent predictive factors for AUR were IPSS (OR=1.76 per 10-point increase) and pretreatment prostate volume (OR=1.05 >35 cm3).
Specifically, patients with a pretreatment prostate volume greater than 35 cm3 had a 10.4% risk for developing AUR, compared with a 5.4% risk among those with a volume of 35 cm3 or below. et al.
They remark in the International Journal of Radiation Oncology Biology Physics that the additional trauma of implantation may be enough to result in AUR in these patients.
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By Sarah Guy