Choice of Radioisotopes
Radiobiologic data from the 1980’s suggested that isotope dose-rate may be an important factor for treating prostate cancer as different grades of disease with different cell doubling times may have specific sensitivities to either I-125 or Pd-103 26. Nonetheless, clinical data has been reported for both I-125 and Pd-103 regardless of tumor grade that does not indicate any difference in biochemical control 27, 28. Cha et. al. reported on the results of a matched pair analysis comparing I-125 and Pd-103 was unable to identify any difference in PSA-RFS at 5 years (Table 2) 29. Furthermore, there was no subset of patients by Gleason score or pre-treatment PSA value for which a difference between I-125 and Pd-103 was identified. As the ABS does not currently recommend the use of one isotope over the other, selection should be based on experience and individual institutional and physician preference with each available isotope.
Two approaches for permanent prostate brachytherapy have developed over the last 10 years. One utilizes a pre-plan of the prostate in the treatment position 30. The other technique utilizes an intra-operative treatment planning approach 31. Generally, each center will develop a program based on either of these two approaches so that proficiency assures excellent dosimetry in all treated patients.
When utilizing the pre-planned approach, it is important to obtain a pre-implant transrectal ultrasound of the prostate using planimetric, cross-section images at 5 mm intervals. It is important to position the patient in the lithotomy position for this test in order to mimic the required positioning in the operating room. Unfortunately, at the time of the pre-planning TRUS, it is very difficult to obtain such a high degree of lithotomy in a patient without anesthesia, therefore, limiting the pre-planned technique to a lower angle of lithotomy. Once the dimensions of the prostate are outlined, the computer program automatically calculates the volume. The physician will need to assess the pubic arch both during the TRUS study and by palpating the perineum, and if there is a question of bony interference, a