Local protocol variations for Image-Guided Radiotherapy in the multicenter Dutch hypofractionation (HYPRO) trial: impact of rectal balloon and MRI delineation on anorectal dose and gastrointestinal toxicity levels

Publication date: Available online 3 August 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): R.C. Wortel, W.D. Heemsbergen, R.J. Smeenk, M.G. Witte, A.D.G. Krol, F.J. Pos, L. Incrocci
PurposeThe phase 3 XXX trial randomized intermediate to high-risk localized prostate cancer patients to conventionally fractionated (78Gy/39fr) or hypofractionated radiotherapy (64.6Gy/19fr). Differences in techniques and treatment protocols were present between participating centers. This study aimed to compare dose parameters and patient-reported gastrointestinal symptoms between these centers.Methods and MaterialsFrom the trial population we selected patients (n=572) from four treatment centers who received image-guided-IMRT (IG-IMRT). Center A (n=242) applied planning target volume (PTV) margins of 5-6mm and was considered the reference center. In center B (n=170, 7mm margins), magnetic resonance imaging (MRI) was integrated in treatment planning. An endorectal balloon (ERB) was applied in center C (n=85, 7mm margins). Center D (n=75) applied the largest PTV-margins of 8mm. The study protocol provided identical anorectal dose constraints and local protocols were applied for further treatment optimization. Anorectal dose-surface histograms were compared applying t-tests. Rectal complaints during follow-up (6 months-4 years) were compared in a generalized linear model, adjusting for age, follow-up, treatment arm, and hormone therapy.ResultsFavorable anorectal dose distributions were found for center B (MRI delineation) and C (ERB application) as compared to center A and D. This was associated with significantly lower incidences of patient-reported complaints of rectal incontinence, use of incontinence pads, and rectal discomfort in these centers. Furthermore, lower incidences of increased stool frequency (≥4/day) and mucous loss were observed for center C.ConclusionsDespite comparable IG-IMRT techniques and predefined dose constraints, pronounced differences in dose distributions and toxicity rates were observed. MRI delineation and ERB application were associated with favorable rectal dose parameters and toxicity profiles, whereas a 2-3mm difference in PTV-margins did not translate into observed differences. We conclude that choices for treatment optimization of IG-IMRT are important and clinically relevant for patients since these affect symptoms experienced in daily life.

Teaser

The effects of differences in techniques and treatment protocols on patient-reported rectal toxicity were compared between treatment centers participating in the prospective prostate XXX trial. All included centers applied image-guided-IMRT using identical anorectal dose constraints. As compared to reference center A (5-6mm PTV margins), favorable anorectal dose distributions were found for center B (MRI delineation, 7mm margins) and center C (endorectal balloon application, 7mm margins). This translated into significantly lower incidences of rectal complaints within both centers.


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