ESTRO 2024 - Abstract Book

S4068

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Comparison of IGRT with oa-MRgRT using deformable dose accumulation showed significant differences between the two approaches on a DVH-level. Analysis of selected relevant DVPs demonstrated the capability of oa-MRgRT to ensure high target coverage while reducing critical OAR dose levels compared to classical IGRT. The potential clinical benefits of these DVPs need to be studied in prospective clinical trials.

Keywords: IGRT, MRgRT, Dose accumulation,

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Digital Poster

Cone beamCT correction for preoperative short course radiotherapy for locally advanced rectal cancer

Wisawa Phongprapun, Sawanya Suwandee, Jiraporn Setakornnukul, Janjira Petsuksiri

Division of Radiation Oncology, Faculty of Medicine Siriraj Hospital, Mahidol University, Department of Radiology, Bangkok, Thailand

Purpose/Objective:

To evaluate the differences in actual radiation doses delivered to the clinical target volumes (CTVs) and normal organs, comparing the outcomes of daily CBCT matches using bone correction versus bone and soft tissue correction.

Material/Methods:

Twenty patients with locally advanced rectal cancer underwent a short course of pelvic radiation therapy (25 Gy in 5 daily fractions). All patients were treated in a supine position, following the drinking and bowel preparation protocols established during the CT simulation day. The clinical target volumes (iCTV) were delineated on CT simulation images to encounter the target motion from sequential bladder volumes and adjacent bowel. Pelvic MRI was employed for mesorectal delineation. PTVs were established by adding a 5 mm anterior margin and 7 mm margins on other sides to the iCTVs. CTV and normal structures achieved the predetermined dose constraint criteria 1-3. Planning was performed with volumetric arc therapy, Eclipse TM v.16.1. A dose calculation was performed with the analytical anisotropic algorithm (AAA).Bowel and bladder preparation protocols were used on treatment days. Daily cone beam CTs were delivered on all patients, with the CBCT images extended by 5 cm at both the upper and lower end, resulting in a total CBCT length of 26 cm. The CBCT images were registered with the planning CT scans, employing three correction methodologies; bone (translation) correction, bone (translation and rotation correction), or bone/soft tissue correction. On each CBCT image, the CTVs, bladders, and bowel bags were recontoured on each CBCT image based on daily anatomy. The actual doses delivered to these structures were recalculated. Accumulative doses were compared among the different matching procedures. A pair-t test was used for volume comparison between CBCT and planning CT. A comparison of 3 procedure corrections was performed with repeated measure ANOVA.