What is the role of combined prostate implantation and external beam radiotherapy (EBRT) in the treatment of prostate cancer?

Updated: Aug 17, 2020
  • Author: Isamettin Andrew Aral, MD, MS; Chief Editor: Edward David Kim, MD, FACS  more...
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Current data suggest that the clinical outcomes of patients treated with external beam radiotherapy (EBRT) and those of patients treated with permanent prostate brachytherapy are comparable if properly selection criteria are used (typically, T1 or T2 disease, prostate-specific antigen [PSA] level lower than 10 ng/mL, and Gleason score of 6 or less).

An ongoing Radiation Therapy Oncology Group (RTOG) trial should clarify the difference between the 2 forms of therapy. Although permanent brachytherapy is widely accepted for patients with low risk of extracapsular disease, its role in other patients is less clear.

A well-performed prostate implant is perhaps the most conformal type of radiation treatment available. To this end, brachytherapy has been used more frequently for boost purposes in patients with more advanced disease (eg, T3a). Prospective data demonstrating an improved outcome in comparison with EBRT alone are scant; however, the logic of combined treatment is irrefutable.

Using brachytherapy alone is reasonable if one wishes to treat only the prostate and immediate periglandular tissue. However, if the patient is believed to be at increased risk for extracapsular disease, brachytherapy may not adequately address all sites of potential disease. In this instance, many clinicians consider supplementing the brachytherapy dose with a shortened course of EBRT.

The proper sequence of the 2 treatments is uncertain; however, the authors believe that the biologic effectiveness of the therapy is improved when brachytherapy is provided first. In this setting, EBRT is offered 5-6 weeks after permanent prostate implantation. Although by then, the implanted radioisotopes have begun to decay, they contribute to the daily radiation dose from EBRT. This increased daily dose may improve the effectiveness of the radiotherapy in controlling the cancer.

It should be kept in mind that when EBRT is offered in conjunction with brachytherapy, neither form of treatment employs maximal doses. Conventional iodine (I)-125 prostate implants offer doses in the range of 144 Gy. Likewise, palladium (Pd)-103 implants offer doses of 110 Gy. Trials predict similar biologic outcome with cesium (Cs)-131, which is given in a dose of 115 Gy.

When implantation is followed by EBRT, the brachytherapy doses with I-125, Pd-103, and Cs-131 are reduced to 108 Gy, 90 Gy, and 90 Gy, respectively. When EBRT follows permanent prostate implantation, the dose usually is limited to 45 Gy per 5 weeks.

Selection of the isotope has varied widely in different practice settings. One of the strongest potential advantages to Cs-131 for combination radiotherapy is its markedly short half-life. This should allow successful integration with EBRT when this modality is initiated several weeks after implantation.

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