Patterns in ano-rectal dose maps and the risk of late toxicity after prostate IMRT

• Published in: Acta oncologica 2019-12, Vol.58 (12), p.1757-1764
• Main Authors: Onjukka, Eva, Fiorino, Claudio, Cicchetti, Alessandro, Palorini, Federica, Improta, Ilaria, Gagliardi, Giovanna, Cozzarini, Cesare, Degli Esposti, Claudio, Gabriele, Pietro, Valdagni, Riccardo, Rancati, Tiziana
• Format: Article
• Language: English
• Subjects: Anal Canal - radiation effects; Dose Fractionation, Radiation; Fecal Incontinence - etiology; Gastrointestinal Hemorrhage - etiology; Humans; Male; Medicin och hälsovetenskap; Prospective Studies; Prostatic Neoplasms - radiotherapy; Radiotherapy, Intensity-Modulated - adverse effects; Radiotherapy, Intensity-Modulated - methods; Rectal Diseases - etiology; Rectum - radiation effects; Risk
• ISSN: 0284-186X; 1651-226X; 1651-226X
• DOI: 10.1080/0284186X.2019.1635267

Purpose: The aim of this work was to determine how the spatial pattern of dose in the ano-rectal wall is related to late gastro-intestinal toxicity for prostate cancer patients treated with mainly IMRT. Patients and methods: Patients from the DUE-01 multicentre study with patient-reported (prospective) follow-up and available dosimetric data were included. Conventionally fractionated patients received 74-80 Gy and hypofractionated patients received 65-75.2 Gy. A large majority of the patients were treated with intensity-modulated radiotherapy (IMRT). Dose-surface maps (DSMs) for the anal canal and rectum as a single structure, and for the anal canal and the rectum separately, were co-registered rigidly in two dimensions and, for the patients with and without toxicity, respectively, the mean value of the dose in each pixel was calculated. A pixel-wise t-test was used to highlight the anatomical areas where there was a significant difference between the 'mean dose maps' of each group. Univariate models were also fitted to a range of spatial parameters. The endpoints considered were a mean grade ≥1 late fecal incontinence and a maximum grade ≥2 late rectal bleeding. Results: Twenty-six out of 213 patients had fecal incontinence, while 21/225 patients had rectal bleeding. Incontinence was associated with a higher dose in the caudal region of the anal canal; the most relevant spatial parameter was the lateral extent of the low and medium isodoses (5-49 Gy in EQD2). Bleeding was associated with high isodoses reaching the posterior rectal wall. The spatial dose parameters with the highest AUC value (.69) were the lateral extent of the 60-70 Gy isodoses. Conclusions: To avoid fecal incontinence it is important to limit the portion of the anal canal irradiated. Our analysis confirms that rectal bleeding is a function of similar spatial dose parameters for patients treated with IMRT, compared to previous studies on patients treated with three-dimensional conformal radiotherapy.