title: Stereotactic body radiotherapy as monotherapy or post-external beam radiotherapy boost for prostate cancer: technique, early toxicity, and PSA response.
abstract: OBJECTIVE
  High dose rate (HDR) brachytherapy has been established as an excellent monotherapy or after external-beam radiotherapy (EBRT) boost treatment for prostate cancer (PCa). Recently, dosimetric studies have demonstrated the potential for achieving similar dosimetry with stereotactic body radiotherapy (SBRT) compared with HDR brachytherapy. Here, we report our technique, PSA nadir, and acute and late toxicity with SBRT as monotherapy and post-EBRT boost for PCa using HDR brachytherapy fractionation.
  
  
  METHODS
  To date, 38 patients have been treated with SBRT at the University of California-San Francisco with a minimum follow-up of 12 months. Twenty of 38 patients were treated with SBRT monotherapy (9.5 Gy × 4 fractions), and 18 were treated with SBRT boost (9.5 Gy × 2 fractions) post-EBRT and androgen deprivation therapy. PSA nadir to date for 44 HDR brachytherapy boost patients with disease characteristics similar to the SBRT boost cohort was also analyzed as a descriptive comparison.
  
  
  RESULTS
  SBRT was well tolerated. With a median follow-up of 18.3 months (range, 12.6-43.5), 42% and 11% of patients had acute Grade 2 gastrourinary and gastrointestinal toxicity, respectively, with no Grade 3 or higher acute toxicity to date. Two patients experienced late Grade 3 GU toxicity. All patients are without evidence of biochemical or clinical progression to date, and favorably low PSA nadirs have been observed with a current median PSA nadir of 0.35 ng/mL (range, <0.01-2.1) for all patients (0.47 ng/mL, range, 0.2-2.1 for the monotherapy cohort; 0.10 ng/mL, range, 0.01-0.5 for the boost cohort). With a median follow-up of 48.6 months (range, 16.4-87.8), the comparable HDR brachytherapy boost cohort has achieved a median PSA nadir of 0.09 ng/mL (range, 0.0-3.3).
  
  
  CONCLUSIONS
  Early results with SBRT monotherapy and post-EBRT boost for PCa demonstrate acceptable PSA response and minimal toxicity. PSA nadir with SBRT boost appears comparable to those achieved with HDR brachytherapy boost.
authors.affiliation: Department of Radiation Oncology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Siavash
authors.initials: S
authors.lastname: Jabbari
authors.forename: Vivian K
authors.initials: VK
authors.lastname: Weinberg
authors.forename: Tania
authors.initials: T
authors.lastname: Kaprealian
authors.forename: I-Chow
authors.initials: IC
authors.lastname: Hsu
authors.forename: Lijun
authors.initials: L
authors.lastname: Ma
authors.forename: Cynthia
authors.initials: C
authors.lastname: Chuang
authors.forename: Martina
authors.initials: M
authors.lastname: Descovich
authors.forename: Stephen
authors.initials: S
authors.lastname: Shiao
authors.forename: Katsuto
authors.initials: K
authors.lastname: Shinohara
authors.forename: Mack
authors.initials: M
authors.lastname: Roach
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Gottschalk
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000726:Androgen Antagonists / Q000627:therapeutic use; D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005500:Follow-Up Studies; D041981:Gastrointestinal Tract / Q000528:radiation effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects; D017430:Prostate-Specific Antigen / Q000097:blood*; D011471:Prostatic Neoplasms / Q000097:blood* / Q000628:therapy*; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*
chemical_list: D000726:Androgen Antagonists; D017430:Prostate-Specific Antigen