Cone-beam computed tomography for organ motion evaluation in locally advanced rectal cancer patients

Purpose Due to a reported dose-response relationship in rectal cancer radiotherapy, a greater interest in dose intensification on small boost volume arises. Considering the need of an appropriate target movements evaluation, this retrospective study aimed to use cone-beam computed tomography (CBCT) for GTV and mesorectum organ motion (OM) evaluation, in locally advanced rectal cancer (LARC) patients treated with neoadjuvant chemo-radiotherapy, in prone and supine position. Methods Thirty-two LARC patients were analyzed. GTV and mesorectum were delineated on MRI co-registrated with CT simulation. GTV and mesorectum OM was estimated on all CBCTs, performed during treatment, co-registrated with CT simulation. OM evaluation was obtained, as mean shift in left and right (L-R), postero-anterior (P-A) and cranio-caudal (Cr-C) directions. Volumes variability was calculated by DICE index. Results A total of 296 CBCTs were analyzed. Mean shifts of the GTV and mesorectum in prone position were - 0.16 cm and 0.15 cm in L-R direction, 0.28 cm and - 0.40 cm in P-A direction, and 0.14 cm and - 0.21 cm, in Cr-C direction; for supine position the mean shifts of the GTV were - 0.10 cm and 0.17 cm in R-L direction, 0.26 cm and - 0.23 cm in A-P direction, 0.09 cm and - 0.11 cm in Cr-C direction. Mean DICE index for GTV and mesorectum was 0.74 and 0.86, in prone position, and 0.78 and 0.89 in supine position, respectively. Conclusion GTV and mesorectum OM was less than 4 mm in all directions in both positions, with a 1 mm less deviation in supine position. CBCTs resulted effective for OM assessment, and it could be an appropriate method for the implementation on an intensification treatment.

Automated summary

This study utilized CBCT to evaluate GTV and mesorectum organ motion in rectal cancer patients, showing that the mean shifts were less than 4 mm in all directions in both prone and supine positions, with smaller deviations in the supine position.