Feasibility of rectal spacer hydrogel in proton therapy for large prostate glands (>80 cc)

OncoLink Team
Last Reviewed: May 15, 2017

Reporter: Eric Ojerholm, MD

Study presenting author: Marcio Fagundes, MD

Presenting author affiliation: Miami Cancer Institute, Miamia, FL, USA

Session: Genitourinary, oral abstract #83

 

Background:

  • Prostate cancer is the most common cancer in men, and it is often treated with radiotherapy
  • This treatment carries a modest risk of acute and late rectal toxicity1,2
  • One way to reduce rectal toxicity is a hydrogel spacer that is injected into the patient’s pelvis and creates a physical space between the rectum and prostate. This reduces the radiation dose to the rectum.3
  • In a phase III trial, use of a hydrogel spacer decreased the 3-year incidence of grade 1 (9.2% versus 2%) and grade ≥ 2 (5.7% versus 0%) rectal toxicity3
  • That trial only included patients with prostate glands <80 cubic centimeters (cc). It is unclear whether the spacer can be safely used for patients with larger prostate glands

 

Purpose:

  • To analyze the feasibility of hydrogel spacer use in patients with prostate glands >80 cc treated with proton therapy

 

Materials/Methods:

  • The authors retrospectively analyzed 26 patients with prostate glands >80 cubic centimeters treated with proton therapy at the Provision Center for Proton Therapy in Knoxville, TN between 4/2015 and 9/2016
  • Important demographic factors included:
    • 14 patients with glands from 80-100 cc (mean 86.6 cc)
    • 12 patients with glands >100 cc (mean 130.9 cc)
    • Low/intermediate risk prostate cancer in 21 patients, and high risk prostate cancer in 5 patients
    • 30% of patients on pre-radiotherapy alpha blockers to reduce prostate size
    • Important treatment factors included:
      • Dose of 78 Gy in 39 fractions for 23 patients, and dose of 62 Gy in 20 fractions for 3 patients
      • Setup uncertainty margins of 6 mm around (except 4 mm posteriorly)
      • Majority of patients treated with opposed lateral beams

 

Results:

  • The average midgland prostate-rectum separation achieved by the hydrogel spacer was 1.29 cm in the 80-100 cc gland group and 1.09 cm in the >100 cc gland group
  • Amount of rectum getting at least 90% of the prescription dose was an average of 1.2% for the 80-100 cc gland group and an average of 1.1% for the >100 cc gland group
  • Amount of rectum getting at least 77% of the prescription dose was an average of 3.6% for the 80-100 cc gland group and an average of 3.8% for the >100 cc gland group
  • Amount of rectum getting at least 64% of the prescription dose was an average of 7.2% for the 80-100 cc gland group and an average of 7.6% for the >100 cc gland group
  • Acute toxicities included:
    • Grade 1 genitourinary (92%), grade 2 genitourinary (4%)
    • Grade 1 gastrointenstinal (38%), including diarrhea, mild rectal pain, and a bleed
    • Late toxicities included: grade 1 genitourinary (35%)
    • There were no late grade 2 genitourinary or gastrointestinal side effects

 

Study author’s conclusions:

  • Hydrogel was successfully placed in all patients attempted with prostate >80 cc
  • Hydrogel achieved good recto-prostate separation and very low doses to the rectum

 

Reporter’s take:

  • This study is important because the pivotal phase III trial3 of rectal spacers did not included men with prostate glands >80 cc
  • These results suggest that the conclusions of the phase III trial can be extended to this new population
  • These results will help doctors and patients when trying to decide whether to consider a hydrogel spacer
  • One caveat is that the authors of this study are experts in performing hydrogel spacer placement, and they teach a course on this topic. Therefore, results for large prostate glands may be more challenging for providers with less experience

References

  1. Chen RC, Basak R, Meyer AM, et al: Association Between Choice of Radical Prostatectomy, External Beam Radiotherapy, Brachytherapy, or Active Surveillance and Patient-Reported Quality of Life Among Men With Localized Prostate Cancer. JAMA 317:1141-1150, 2017
  2. Barocas DA, Alvarez J, Resnick MJ, et al: Association Between Radiation Therapy, Surgery, or Observation for Localized Prostate Cancer and Patient-Reported Outcomes After 3 Years. JAMA 317:1126-1140, 2017
  3. Hamstra DA, Mariados N, Sylvester J, et al. Continued Benefit to Rectal Separation for Prostate Radiation Therapy: Final Results of a Phase III Trial. Int J Radiat Oncol Biol Phys 97(5):976-985, 2017

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