Impact evaluation of intra-fractional variation on online adaptive radiotherapy for postoperative cervical and endometrial cancer
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Updated: May 10, 2026
Stereotactic Radiosurgery for Gynecologic Cancer
Published on: April 17, 2012
Guang-Yu Wang1, Yi-Ning Chen1, Yu-Liang Sun1
1Department of Radiation Oncology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China.
Background:
Online adaptive radiotherapy (oART) has demonstrated improved target volume coverage and enhanced sparing of surrounding pelvic organs through daily re-optimization based on pretreatment imaging. Recently, iterative cone-beam computed tomography (iCBCT) has been integrated into oART workflows, facilitating precise daily adaptation. However, the dosimetric consequences of intra-fractional variations for clinical target volume (CTV) and organs at risk (OARs) remain insufficiently characterized.
Aim:
To investigate intra-fractional CTV and OARs variation and their impact on iCBCT guided daily oART for postoperative cervical and endometrial cancer.
Methods:
Seventeen patients treated with daily postoperative iCBCT guided oART with rigorous bladder and rectal preparation protocols were enrolled. CTV and OARs were contoured on pre- and post-treatment iCBCT scans. The average surface distance (ASD), dice similarity coefficient (DSC), and 95% Hausdorff distance (HD) were utilized to evaluate the difference between pre- and post-treatment structures. Dosimetric outcomes for the pretreatment target volumes and OARs were recalculated using posttreatment contours to assess the impact of intra-fractional variation.
Results:
A total of 434 treatment fractions were analyzed, with an average interval time of 22 minutes between two iCBCT scans. Minimal variations were observed in the bladder, rectum, and CTV both pre- and post-treatment, with DSC exceeding 0.8. The vaginal CTV exhibited centroid deviations of 0.46 mm anteriorly, 0.11 mm laterally, and 0.58 mm superiorly, along with ASD of 1.69 mm and 95% HD of 6.42 mm. Weak correlations were observed between vaginal CTV posterior-anterior centroid deviations and rectal superior-inferior deviations (P = 0.017). Minimal dosimetric differences were observed pre- and post-treatment, with V100% for the adapted plan of nodal CTV being 99.94% vs 99.08% and vaginal CTV being 99.97% vs 98.66%.
Conclusion:
Daily iCBCT-guided oART with strict bladder and rectal preparation effectively compensates for intra-fractional variations, maintaining CTV coverage and OAR sparing across all treatment fractions.
