title: Dose-distance metric that predicts late rectal bleeding in patients receiving radical prostate external-beam radiotherapy.
abstract: The relationship between rectal dose distribution and the incidence of late rectal complications following external-beam radiotherapy has been previously studied using dose-volume histograms or dose-surface histograms. However, they do not account for the spatial dose distribution. This study proposes a metric based on both surface dose and distance that can predict the incidence of rectal bleeding in prostate cancer patients treated with radical radiotherapy. One hundred and forty-four patients treated with radical radiotherapy for prostate cancer were prospectively followed to record the incidence of grade ≥2 rectal bleeding. Radiotherapy plans were used to evaluate a dose-distance metric that accounts for the dose and its spatial distribution on the rectal surface, characterized by a logistic weighting function with slope a and inflection point d₀. This was compared to the effective dose obtained from dose-surface histograms, characterized by the parameter n which describes sensitivity to hot spots. The log-rank test was used to determine statistically significant (p < 0.05) cut-off values for the dose-distance metric and effective dose that predict for the occurrence of rectal bleeding. For the dose-distance metric, only d₀ = 25 and 30 mm combined with a > 5 led to statistical significant cut-offs. For the effective dose metric, only values of n in the range 0.07-0.35 led to statistically significant cut-offs. The proposed dose-distance metric is a predictor of rectal bleeding in prostate cancer patients treated with radiotherapy. Both the dose-distance metric and the effective dose metric indicate that the incidence of grade ≥2 rectal bleeding is sensitive to localized damage to the rectal surface.
authors.affiliation: Department of Radiation Oncology, British Columbia Cancer Agency, Vancouver Centre, 600 West 10th Ave, Vancouver, BC V5Z 4E6, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Lee
authors.forename: Elisa K
authors.initials: EK
authors.lastname: Chan
authors.forename: Robert
authors.initials: R
authors.lastname: Kosztyla
authors.forename: Mitchell
authors.initials: M
authors.lastname: Liu
authors.forename: Vitali
authors.initials: V
authors.lastname: Moiseenko
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006470:Hemorrhage / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000528:radiation effects*; D013223:Statistics as Topic; D013997:Time Factors