Interstitial Prostate Brachytherapy
Compared with external beam forms of radiation therapy, interstitial prostate brachytherapy (IPB), in skilled hands, represents the superior form of conformal radiation therapy permitting dose escalation beyond other current modalities. The major advantage of IPB over external beam approaches is that radiation is delivered internally, allowing for greater sparing of normal tissue and negating concerns of prostate motion. The growing popularity of prostate brachytherapy in the late 1980s and early 1990s was fueled by an evolution in transrectal ultrasonography, the development of a closed transperineal approach, and more sophisticated computer treatment planning software. Currently, there are two major approaches to prostate brachytherapy: the initial low-dose-rate (LDR) permanent radioactive seed implant and the temporary catheter-based highdose-rate (HDR) implant. Both of these forms have been utilized alone as monotherapy and in combination with external beam radiation therapy (EBRT).
Although not all patients are appropriate candidates for brachytherapy, clear criteria to predict implant-related morbidity are not available. The American Brachytherapy Society currently recommends IPB monotherapy for patients with clinically staged T1-T2b disease, PSA level of < 10 ng/mL, and Gleason score of ≤ 6. For patients with clinically staged T2c and higher disease or Gleason score ≥ 7 or PSA of > 10 ng/mL, supplemental EBRT is recommended. However, an increasing body of literature reports that EBRT can be omitted in certain patient populations with high-quality implants.[51–53] Additionally, other relative contraindications include International Prostate Symptom Score (IPSS) > 15, prostate volume < 20 mL or > 50 mL, seminal vesicle invasion, and a tight pubic arch that could interfere with seed or catheter placement.
Large prostate size is widely believed to be a relative contraindication for IPB due to technical concerns regarding pubic arch interference and concern regarding higher urinary morbidity. For these reasons, patients with prostate volumes greater than 50 mL are frequently counseled not to undergo IPB or be placed on cytoreductive hormonal therapy. However, contrary to this perception, there are data to support that large prostates can be implanted with acceptable morbidity.[54,55] Alternatively, reports have also demonstrated that prostates < 20 mL can also be implanted with no increased urinary morbidity.[54,56,57] Also related to size, pubic arch interference may represent a technical issue, particularly in patients with a larger-sized prostate. However, with the use of extended lithotomy positioning and guiding needles around the arch, almost all patients can undergo implantation successfully.
Patients with urinary obstructive symptoms prior to implant are at a higher risk of postimplant urinary retention. However, this relationship is somewhat controversial. Terk et al reported that preimplantation IPSS predicted postimplantation urinary retention. Conversely, with the use of prophylactic and prolonged alpha-blockers, Merrick et al found no correlation with preimplant IPSS and urinary retention. Additionally, in a prospective study, Landis and Landis et al found little correlation with preimplantation IPSS and either acute urinary retention or long-term urinary function.
Cancer Control. 2010;17(4):223-32. © 2010 H. Lee Moffitt Cancer Center and Research Institute, Inc.
Copyright by H. Lee Moffitt Cancer Center & Research Institute. All rights reserved.
Cite this: Emerging Technologies in Prostate Cancer Radiation Therapy: Improving the Therapeutic Window - Medscape - Oct 01, 2010.