title: Rectal dose to prostate cancer patients treated with proton therapy with or without rectal spacer.
abstract: The purpose of this study was to evaluate whether a spacer inserted in the prerectal space could reduce modeled rectal dose and toxicity rates for patients with prostate cancer treated in silico with pencil beam scanning (PBS) proton therapy. A total of 20 patients were included in this study who received photon therapy (12 with rectal spacer (DuraSeal™ gel) and 8 without). Two PBS treatment plans were retrospectively created for each patient using the following beam arrangements: (1) lateral-opposed (LAT) fields and (2) left and right anterior oblique (LAO/RAO) fields. Dose volume histograms (DVH) were generated for the prostate, rectum, bladder, and right and left femoral heads. The normal tissue complication probability (NTCP) for ≥grade 2 rectal toxicity was calculated using the Lyman-Kutcher-Burman model and compared between patients with and without the rectal spacer. A significantly lower mean rectal DVH was achieved in patients with rectal spacer compared to those without. For LAT plans, the mean rectal V70 with and without rectal spacer was 4.19 and 13.5%, respectively. For LAO/RAO plans, the mean rectal V70 with and without rectal spacer was 5.07 and 13.5%, respectively. No significant differences were found in any rectal dosimetric parameters between the LAT and the LAO/RAO plans generated with the rectal spacers. We found that ≥ 9 mm space resulted in a significant decrease in NTCP modeled for ≥grade 2 rectal toxicity. Rectal spacers can significantly decrease modeled rectal dose and predicted ≥grade 2 rectal toxicity in prostate cancer patients treated in silico with PBS. A minimum of 9 mm separation between the prostate and anterior rectal wall yields the largest benefit.
authors.affiliation: Department of Radiation Oncology, University of Maryland, Baltimore School of Medicine, Baltimore, MD, USA.
authors.forename: Heeteak
authors.initials: H
authors.lastname: Chung
authors.affiliation: Department of Radiation Oncology, University of Maryland, Baltimore School of Medicine, Baltimore, MD, USA.
authors.forename: Jerimy
authors.initials: J
authors.lastname: Polf
authors.affiliation: Department of Radiation Oncology, University of Maryland, Baltimore School of Medicine, Baltimore, MD, USA.
authors.forename: Shahed
authors.initials: S
authors.lastname: Badiyan
authors.affiliation: Department of Radiation Oncology, Florida Hospital Cancer Institute, Orlando, FL, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Biagioli
authors.affiliation: Department of Radiation Oncology, H. Lee Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Fernandez
authors.affiliation: Department of Radiation Oncology, H. Lee Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Kujtim
authors.initials: K
authors.lastname: Latifi
authors.affiliation: Department of Radiation Oncology, H. Lee Moffitt Cancer Center, Tampa, FL, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Wilder
authors.affiliation: Department of Radiation Oncology, University of Maryland, Baltimore School of Medicine, Baltimore, MD, USA.
authors.forename: Minesh
authors.initials: M
authors.lastname: Mehta
authors.affiliation: Department of Radiation Oncology, University of Maryland, Baltimore School of Medicine, Baltimore, MD, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Chuong
mesh_terms: D006801:Humans; D008297:Male; D017785:Photons; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012007:Rectum / Q000528:radiation effects*; D012189:Retrospective Studies; D001743:Urinary Bladder / Q000528:radiation effects*
keywords: prostate cancer; proton beam scanning; rectal spacers