ESTRO 2024 - Abstract Book

S4248

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

1322

Digital Poster

Impact of time, tumour presence, and distance from the anorectal junction on rectum motion

Julien Pierrard 1,2 , Sofie Heylen 2 , Ad Vandermeulen 2 , Geneviève Van Ooteghem 1,2

1 UCLouvain, Center of Molecular Imaging, Radiotherapy and Oncology (MIRO), Brussels, Belgium. 2 Cliniques Universitaires Saint-Luc, Department of Radiation Oncology, Brussels, Belgium

Purpose/Objective:

The rectum motion is important to consider for pelvic radiotherapy (RT) planning. It can be impacted by multiple factors, which should be quantified and integrated to offer personalised treatments, including cone-beam computed tomography (CBC) adaptive RT or safe dose escalation with boost [1-3]. In this study, we evaluate the impact of three of these factors on interfraction and intrafraction rectal motion: (1) the RT session duration, (2) the presence of a tumour, and (3) the distance from the anorectal junction (ARJ).

Material/Methods:

We retrospectively included 9 patients treated by prostate stereotactic body RT (SBRT) and, prospectively, 10 patients treated by rectal RT. Three CBCTs per RT session were acquired during the five first treatment days, and, then, at the first session of each following week. Three groups of structure were delineated on CBCT: the whole rectum without tumour in prostate SBRT patients (rectumprostate), the whole rectum with tumour in rectum RT patients (rectumrectum), and the segment of the (same) rectum invaded by the tumour in rectum RT patient (tumour wall). We used two metrics to quantify the motion: the Hausdorff distance 95% (HD95) and the mean-distance-to-agreement (MDTA) between the volumes. For the interfraction motion evaluation, planning-CT volumes were compared to those of the first CBCT (CBCT1) of each included session. For the intrafraction motion, CBCT1 volumes were compared to those of the second (CBCT2) and the third CBCT (CBCT3) of a same session. The motion metrics as a function of time elapsed between CBCT1 and CBCT2/3 were reported using a Pearson correlation test to assess the impact of the RT session duration. The impact of the tumour presence was quantified by comparing the intrafraction and interfraction motion between the three groups of structure (rectumprostate, rectumrectum and tumour wall) using the Kruskal-Wallis test. Finally, we reported the rectal motion as a function of the distance from the AJR for the three groups of structure (Pearson correlation test) to evaluate if the motion of the inferior parts of the rectum is lower or higher than in the superior parts.

Results:

A significant positive correlation exists between the amplitude of the rectal motion (for both HD95 and MDTA, p<0.05) and the RT session duration for all the groups of structure. However, this correlation is weak; including all the