The ideal candidates for permanent interstitial implantation are those with favorable-risk prognostic features who have a high likelihood of organ-confined
disease. This group includes those with prostate-specific antigen (PSA) levels <10ng/ml and with Gleason scores <7. Although not essential for staging, pre-treatment magnetic resonance imaging (MRI) of the prostate with endorectal coil may be helpful in the assessment of the integrity of the prostatic capsule as well as the geometry of the gland. Such information may be invaluable in the planning aspects of transperineal implantation (TPI), as well as determining whether a patient is a candidate for the procedure. The prostate gland size should preferably be less than 60 cm3. With larger gland sizes, the pubic arch may interfere with needle placement to the anterolateral portions of the gland, resulting in inadequate coverage of the target volume. In addition, larger glands require more seeds and activity to achieve coverage of the gland with the prescription dose, resulting in a concomitant increase in the central urethral doses and potentially increasing the risk of urinary morbidity. One report indicated that patients with median lobe hyperplasia have a higher incidence of acute urinary symptoms after prostate brachytherapy . The size of the prostate can be effectively reduced with combined androgen blockade therapy. A reduction in volume of approximately 30% is often observed after three months of androgen deprivation.
A prior transurethral resection (TURP) may increase the risks of urinary morbidity after permanent seed implantation [9,10]. In these patients implantation should be performed with caution. Using a uniform loading seed pattern, Blasko et al.  reported an increased incidence of incontinence and superficial ure-thral necrosis after permanent interstitial implantation among patients with a prior history of TURP. Wallner et al.  observed a three-year actuarial incidence of incontinence of 6% among 11 patients who underwent TURP prior to TPI. Stone et al.  reported on 43 patients treated with prostate brachyther-
apy using a modified peripheral seed loading technique. Although these authors observed no cases of urinary incontinence, the four-year incidence of superficial urethral necrosis was 16%. As noted above, patients with preexisting urinary obstructive symptoms are more likely to experience acute urinary morbidity after seed implantation and need to be appropriately counseled regarding this possibility.
Patients with relative contraindications for external-beam radiotherapy may be more suitable for prostate brachytherapy. These include patients with bilateral hip replacements where CT-based treatment planning is technically difficult due to the substantial artifact created by the prostheses, which preclude adequate visualization of the target volume. Ultrasound-based seed implantation would be an appropriate alternative for such patients. In most cases, patients with hip prostheses are able to tolerate the extended dorsal lithotomy position for adequate perineal exposure during the procedure. Patients in whom the small bowel is in close proximity to the prostate volume are not ideal candidates for high-dose three-dimensional conformal radiotherapy (CRT) and are better suited for seed implantation due to the lower doses to the bowel expected with the latter treatment intervention. In addition, brachytherapy appears to be safe for patients with a history of inflammatory bowel disease (IBD), a condition that represents a relative contraindication for external-beam radiotherapy .
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