Outcomes following EBRT and an SBRT “boost” for localized prostate cancer

New data from the radiotherapy group at the University of Califronia, San Francisco suggests that stereotactic body radiation (SBRT) can be used to deliver a “boost” of focused radiation after external beam radiation therapy (EBRT). High dose rate (HDR) brachytherapy has also been used in this way in the past.

Jabbari et al. report data from a small group of 38 patients, all treated with SBRT at the University of California, San Francisco, with a minimum follow-up of 12 months:

  • 20/38 patients were treated with SBRT monotherapy (9.5 Gy × 4 fractions).
  • 18/38 patients were treated with an SBRT boost (9.5 Gy × 2 fractions) post-EBRT and androgen deprivation therapy.

The following results are reported to date:

  • Average (median) follow-up was 18.3 months (range, 12.6 to 43.5 months).
  • SBRT was generally well tolerated.
    • 42 percent of patients had acute Grade 2 genitourinary toxicity.
    • 11 percent of patients had  acute Grade 2 gastrointestinal toxicity.
    • No acute Grade 3 or higher toxicity has been observed to date.
  • No patient has shown evidence of biochemical or clinical progression.
  • Low nadir PSA levels have been observed so far.
    • For the entire patient cohort, the median PSA nadir is 0.35 ng/ml (range, < 0.01 to 2.1 ng/ml).
    • For the SBRT monotherapy cohort, the median PSA nadir is 0.47 ng/ml (range, 0.2 to 2.1 ng/ml)
    • For the SBRT boost cohort, the median PSA nadir is 0.10 ng/ml (range, 0.01 to 0.5 ng/ml).

For a comparable series of patients treated with EBRT and a “boost” of HBR brachytherapy, at an average (median) follow-up of 48.6 months (range, 16.4 to 87.8 months), the median PSA nadir is 0.09 ng/ml (range, 0.0 to 3.3 ng/ml).

Obviously this is a small series of patients followed for a relatively brief period of time, and the paper’s abstract offers no information about the patients’ PSA levels, Gleason scores, etc., prior to their treatment. However, the authors very reasonably conclude that, “Early results with SBRT monotherapy and post-EBRT boost for [prostate cancer] demonstrate acceptable PSA response and minimal toxicity. PSA nadir with SBRT boost appears comparable to those achieved with HDR brachytherapy boost.”

One Response

  1. Unfortunately, the UCSF abstract does not provide any info regarding the EBRT procedure, guidance, or total dosage.

    I was offered IMRT + HDR boost at UCSF, but rejected it as studies I found online indicated this combined therapy appears to result in increased acute GU/GI side effects over the IMRT/IGRT monotherapy I eventually chose. As far as I know, long term GU/GI side effects for either of these combo radiation therapies are currently unknown.

    I could see many men opting for EBRT + SBRT boost over the far more invasive HDR boost because at least two quite uncomfortable overnight hospital stays are typical with HDR therapy.

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