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Patient Selection for Prostate Brachytherapy

US Oncology Review, 2005;1(1):1-7 DOI: http://doi.org/10.17925/OHR.2005.00.00.1l

Abstract:

Introduction
Although the majority of permanent prostate brachytherapy studies have demonstrated biochemical control rates and morbidity profiles that compare favorably with radical prostatectomy (RP) and external beam radiation therapy (XRT),1,2 it has become increasingly apparent that efficacy and morbidity are highly dependent on implant quality.1-3 Sophisticated dosimetric analyses have demonstrated that cure rates and brachytherapy-related morbidity are related to specific source placement patterns and the subsequent dose gradients produced.1,2,4

In addition, the need for supplemental XRT or androgen deprivation therapy (ADT) to optimize biochemical outcome is increasingly in doubt.5,6 With high quality brachytherapy, the vast majority of patients can be successfully managed without such supplemental therapies.5

With the emergence of brachytherapy as a mainstream treatment for clinically localized prostate cancer, a rapidly expanding body of literature regarding patient selection and treatment approach has been reported.1,2,7-11 Although not all patients are acceptable candidates for brachytherapy, a reliable set of pre-treatment criteria for predicting outcome has not been formulated. Fortunately, evidence- based factors are rapidly accumulating. The elucidation and widespread adoption of evidence- supported planning philosophies, intra-operative techniques, and medical management should further improve outcomes.

Prostate Size
Although no clear relationship exists between prostate size and a greater incidence of urinary morbidity,12-15 large prostate size remains a relative contraindication to brachytherapy due to technical concerns and the perception that large prostate size increases the risk for acute and prolonged urinary morbidity.16,17 In fact, patients with large prostate glands can be implanted with acceptable morbidity.12-15 In a study using the patient- administered Expanded Prostate Cancer Index Composite (EPIC), long-term urinary function did not correlate with prostate size.14 In the other extreme, favorable dosimetry with minimal urinary morbidity has been reported for patients with small glands (<20cm3).6,14,18

Transition Zone
Unlike overall prostate size, transition zone volume has consistently correlated with brachytherapy- related urinary morbidity (see Figure 1).19-21 Investigators at Harvard University reported that transition zone volume was the most important predictor of acute urinary retention following brachytherapy.19 In patients receiving neoadjuvant ADT for cytoreduction, International Prostate Symptom Score (I-PSS) normalization, prolonged catheter dependency, and the need for post- brachytherapy transurethral resection (TURP) were best predicted by the per cent decrease in transition zone volume.21 In particular, prolonged urinary morbidity was unlikely in patients with greater than a 30% decrease in transition zone volume.21 The currently available data suggest that the transition zone may have a greater predictive power for prediction of significant urinary dysfunction than any other single parameter.

Pubic Arch Interference
Pubic arch interference (the obstruction of anterior needle placement insertion by a narrow pubic arch) has long been considered a relative contraindication to brachytherapy. Surprisingly, prostate volume has proven to be a poor predictor of pubic arch interference.22 With use of the extended lithotomy position and/or veering needles around the arch, almost all patients can be successfully implanted with favorable post-implant dosimetry regardless of the degree of pubic arch interference.22,23