A simple technique for determining accurate urethral dosimetry after seed brachytherapy for prostate cancer

Is prostate-specific antigen percentage decrease predictive of clinical outcome after permanent iodine-125 interstitial brachytherapy for prostate cancer?

OBJECTIVE

To determine the usefulness of prostate-specific antigen (PSA) percentage (vs. pretreatment value assumed as 100%) in prediction of biochemical relapse, after iodine-125 ((125)I) permanent brachytherapy for prostate cancer, to employ a parameter independent by the initial PSA amount and by the individual prostatic volume.

METHODS AND MATERIALS

Our study included 133 patients, 102 still disease free (Group A) and 31 who experienced proven biochemical recurrence (Group B). PSA levels before and after (125)I brachytherapy were recorded, and PSA percentage vs. pretreatment values were calculated. Cox regression model, receiver operating characteristic curves, and Kaplan-Meier regression model with log-rank test were calculated.

RESULTS

We observed that, in patients submitted to brachytherapy for prostate cancer, a PSA percentage >20% of pretreatment value is highly associated with relapse risk (p<0.0001) and that this association is strongly present since t=6 months of followup (p<0.0001), with a hazard ratio near to five times (4.965), a sensitivity of 72.4%, and specificity of 79.8% related to the chosen cutoff.

DISCUSSION

Despite the amount of PSA is the only parameter that the clinicians can deploy to monitor patient's followup after permanent interstitial brachytherapy for prostate cancer, its evolution in time seems unable to predict early biochemical relapse as it is influenced by prostatic volume and initial PSA amount.

CONCLUSIONS

Our data suggest that a PSA percentage >20% of pretreatment value at 6 months might represent an early, inexpensive, and useful predictive tool of bad outcome in patients after permanent brachytherapy.

Impact of urinary catheterization on dosimetry after prostate implant brachytherapy with palladium-103 or iodine-125

PURPOSE

Postoperative dosimetry is integral to quality assurance for prostate brachytherapy. Images on Day 0 are typically obtained with a contrast-filled urinary catheter in place for urethral dose calculations. However, expansion of the urethra and perhaps the prostate by the catheter may affect target coverage. We assessed the effect of urinary catheterization on target dosimetry after implantation with palladium-103 ((103)Pd) or iodine-125 ((125)I) seeds.

METHODS AND MATERIALS

Patients were 29 consecutive men with postimplant dosimetry calculated with and without a urinary catheter after brachytherapy seed implantation; 19 patients received (103)Pd seeds and 10 patients received (125)I seeds. In each case, 14-French caude tip urinary catheters were placed before implantation, and axial CT slices of the pelvis were obtained before and after catheter removal for postimplant dosimetry. Dosimetric parameters were measured and compared with paired Student's t tests. Trends were assessed by linear regression with the Pearson correlation coefficient.

RESULTS

Removal of the urinary catheter significantly improved V(100) and D(90) for (103)Pd implants (mean±standard deviation (SD), 2.7%±4.2%; range, -0.4% to 15%; p=0.011 and mean±SD, 4.0%±3.4%; range, -0.1% to 13.8%; p<0.01, respectively). For (125)I implants, catheter removal improved D(90) (mean±SD, 1.5%±1.8%; range, -1.3% to 4.2%; p=0.027). For the (103)Pd group, the magnitude of change in V(100) correlated with prostate size (R(2)=0.16) and source number (R(2)=0.15).

CONCLUSIONS

Urinary catheterization can artificially reduce target coverage after prostate implant brachytherapy. The patients undergoing (103)Pd implantation with smaller (<30cm(3)) prostates and fewer (<90) sources are particularly susceptible to reduced D(90) and V(100) when a urinary catheter is present.

Is the use of a surrogate urethra an option in prostate high-dose-rate brachytherapy?

PURPOSE

To investigate the accuracy and the dosimetric consequences of substituting a surrogate urethra assumed to be at the geometric center of the prostate, in place of the true urethra when using high-dose-rate (HDR) brachytherapy for the treatment of prostate cancer.

METHODS AND MATERIALS

One hundred prostate cancer patients treated with HDR brachytherapy constituted the study group. A pre-plan was made with the urethra visualized. The true urethra was defined, and a surrogate urethra was placed at the geometric center of the prostate. The distance between the two urethras was measured. The deviation was evaluated at the base, middle, and apex. To evaluate the dosimetric consequences for the true urethra when using a surrogate urethra, two different dose plans were made: one based on the true urethra and one based on the surrogate urethra. The dose-volume histograms for the true urethra were analyzed.

RESULTS

The deviation between the true urethra and the surrogate urethra was greatest at the base of the prostate. A statistically significant difference was seen between the dosimetric parameters for the true and the surrogate urethra when the dose plan was made using the surrogate urethra. In this situation the dose to the true urethra was increased above our defined maximum tolerance limit.

CONCLUSIONS

When using dose plans made according to a surrogate urethra the dose to the true urethra might be too high to be acceptable. If the true urethra is not visualized, severe damage could easily develop in a significant number of patients.