Rectum Protection by Rectal Gel Injection in Cervical Cancer Brachytherapy: A Dosimetric Study Deformable Surface Dose Accumulation and Machine-Learning-Based Discriminative Modeling.

Purpose: This retrospective study aimed to evaluate the dosimetric effects of a rectal insertion of on rectal protection using deformable dose accumulation and machine learning-based discriminative modelling.

Materials And Methods: Sixty-two patients with cervical cancer enrolled in a clinical trial, who received a injection of 20 g into their rectum for rectal protection high-dose rate brachytherapy (HDR-BT, 6 Gy/f), were studied. The cumulative equivalent 2-Gy fractional rectal surface dose was deformably summed using an in-house-developed topography-preserved point-matching deformable image registration method. The cumulative three-dimensional (3D) dose was flattened and mapped to a two-dimensional (2D) plane to obtain the rectal surface dose map (RSDM). For analysis, the rectal dose (RD) was further subdivided as follows: whole, anterior, and posterior 3D-RD and 2D-RSDM. The dose-volume parameters (DVPs) were extracted from the 3D-RD, while the dose geometric parameters (DGPs) and textures were extracted from the 2D-RSDM. These features were fed into 192 classification models (built with 8 classifiers and 24 feature selection methods) for discriminating the dose distributions between pre- and pro-.

Results: The rectal insertion of dialated the rectum in the ambilateral direction, with the rectal column increased from pre- 15 cm to post- 18 cm ( < 0.001). The characteristics of DGPs accounted for the largest portions of the top-ranked features. The top-ranked dosimetric features extracted from the posterior rectum were more reliable indicators of the dosimetric effects/changes introduced by the rectal insertion of . A significant dosimetric impact was found on the dose-volume parameters D-D extracted on the posterior rectal wall.

Conclusions: The rectal insertion of incurs significant dosimetric changes on the posterior rectal wall. Whether this effect is eventually translated into clinical gains requires further long-term follow-up and more clinical data for confirmation.