Rectal bleeding, fecal incontinence, and high stool frequency after
conformal radiotherapy for prostate cancer: Normal tissue complication
probability modeling.

Peeters ST, Hoogeman MS, Heemsbergen WD, Hart AA, Koper PC, Lebesque JV.

Department of Radiation Oncology, The Netherlands Cancer
Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.

PURPOSE: To analyze whether inclusion of predisposing clinical features
in the Lyman-Kutcher-Burman (LKB) normal tissue complication probability
(NTCP) model improves the estimation of late gastrointestinal toxicity.

METHODS AND MATERIALS: This study includes 468 prostate cancer patients
participating in a randomized trial comparing 68 with 78 Gy. We fitted
the probability of developing late toxicity within 3 years (rectal
bleeding, high stool frequency, and fecal incontinence) with the
original, and a modified LKB model, in which a clinical feature (e.g.,
history of abdominal surgery) was taken into account by fitting subset
specific TD50s. The ratio of these TD50s is the dose-modifying factor
for that clinical feature. Dose distributions of anorectal (bleeding and
frequency) and anal wall (fecal incontinence) were used.

RESULTS: The modified LKB model gave significantly better fits than the
original LKB model. Patients with a history of abdominal surgery had a
lower tolerance to radiation than did patients without previous surgery,
with a dose-modifying factor of 1.1 for bleeding and of 2.5 for fecal
incontinence. The dose-response curve for bleeding was approximately two
times steeper than that for frequency and three times steeper than that
for fecal incontinence.

CONCLUSIONS: Inclusion of predisposing clinical features significantly
improved the estimation of the NTCP. For patients with a history of
abdominal surgery, more severe dose constraints should therefore be used
during treatment plan optimization.

PMID: 16757129 [PubMed - as supplied by publisher]

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