Emerging Technologies in Prostate Cancer Radiation Therapy: Improving the Therapeutic Window

Matthew C. Biagioli, MD, MS; Sarah E. Hoffe, MD

Disclosures

Cancer Control. 2010;17(4):223-32. 

In This Article

Low-dose Rate Permanent Radioactive Seed IPB

In patients with low-risk features (Gleason score < 6, PSA < 10 ng/mL, T1c/T2b), LDR IPB has resulted in high rates of biochemical control. Stock and Stone[60] found disease-specific survival to be 98% in patients with Gleason 6 score. In a prospective study, Khaksar et al[61] found a 96% bFS rate at 5 years for those patients with low-risk disease. Furthermore, Potters et al[62] evaluated 1,449 patients who underwent IPB and found a 12-year bFS rate of 89% among low-risk patients. The RTOG 98-05 prospective study performed at 27 institutions demonstrated that favorable results can be achieved among a multitude of users.[63] The 5-year bFS rate was 94%. However, physician skill with IPB is likely a more important factor than with other radiation modalities. In a review of 2,693 patients, Zelefsky et al[64] published an 8-year bFS rate of 93% in patients with quality implants. Yet, in the same population with lesser-quality implants, the 8-year bFS rate was 76% (P = .001), underscoring the importance of physician technical skill. Additionally, Grimm et al[65] reported on the issue of learning curve, demonstrating a significant difference in progression-free survival among patients implanted between 1986 to 1987 vs 1988 to 1990.

IPB in patients with intermediate- and high-risk disease is typically performed in combination with EBRT to a dose of 45 to 50.4 Gy. The reasons for this combined approach are to enhance the coverage to periprostatic tissue, to escalate dose to intraprostatic tumor, and to supplement inadequate tumor coverage from the implant. Intermediate- and high-risk patients treated with this approach have had favorable results. Critz et al[66] published their retrospective results on 689 intermediate- and high-risk patients. With a 7-year follow-up, they found a dFS rate of 88%. Similarly, long-term outcome data from Sylvester et al[67] showed a 15-year bFS rate of 80.3% for intermediate-risk patients and 67.8% for high-risk patients. Additionally, in a separate multi-institutional study of 179 patients, a bFS rate at 3 years was 79% among these risk groups combined.[68] Another multiinstitutional study at six centers has been reported by Stone et al.[69] Among 5,889 patients, 1,078 had Gleason score 7 (n = 845) or Gleason score 8–10 (n = 233) prostate cancer. With a median follow-up of 46 months, the bFS rate was 83.7% for patients with Gleason score 7 and 68.7% for those with Gleason score 8–10. However, in those patients treated with a higher brachytherapy dose, the bFS rate was 89.5% for Gleason score 7 and 85.7% for Gleason score 8–10, paralleling dose escalation results found with EBRT. The beneficial role of escalating dose with IPB has been further validated with postimplant biopsies.[70]

Despite these excellent results with a combined approach, the usefulness of supplemental EBRT has come into question for intermediate-risk patients who have had favorable results with IPB alone. Pathological studies indicate that the radial extension of extraprostatic cancer is almost always 5 mm or less, which is within the coverage of a monotherapy IPB implant. Blasko et al[51] reported a 9-year bFS rate of 82% for patients treated with IPB as monotherapy. Additionally, Taira et al[71] demonstrated bFS, cause-specific survival (CSS), and overall survival (OS) rates of 96.4%, 100%, and 74%, respectively. Other reports have demonstrated bFS rates of 74% to 77% with IPB as monotherapy in intermediate-risk patients.[52,53]

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