ESTRO 2024 - Abstract Book

S4379

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

ESTRO 2024

Table 1. Dosimetric characteristics of adaptive and scheduled treatment plans calculated on daily HyperSight CBCT. Data is represented as median (interquartile range). P-values are reported for the Wilcoxon signed-rank test, where a star sign (*) points at significant differences between the adaptive and scheduled plans. Till now, 3 patients were included. All are being treated with a chemoradiotherapy course of 25 fractions. The mean time to treatment was 7 days. So far, 57 treatment fractions were delivered. The median on-couch treatment time was 25 minutes (interquartile range 6.5 minutes). In 26 out 57 fractions (45.6%) the AI generated CTV had to be adapted. For those fractions, on-couch treatment time was significantly longer, 29.5 minutes, as compared to 23 minutes in fraction where the CTV did not have to be adapted (p-value < 0.001). In all fractions, the adapted plan was chosen for treatment. All adapted plans showed adequate PTV and CTV coverage and acceptable doses to organs at risk. Compared to the initial reference treatment plans recalculated on daily anatomy, all relevant dosimetric criteria for the targets and organs at risk were significantly improved (Table 1). In contrast, in 38 fractions (66.7%), the target coverage constraints for PTV were not met for the initial reference treatment plans applied to the daily anatomy. Patients’ quality of life assessments are ongoing.

Conclusion:

Treatment of patients with stage II and III rectal cancer based on an initial plan on a diagnostic CT scan and a daily online adaptive workflow is feasible. It results in a reduced time to treatment. Compared to the initial plan projected on the daily HyperSight CBCT, the adapted treatment plan better matches the changing daily anatomy of the patient, resulting in a significantly better coverage of the target volumes and an improved sparing of organs at risk.

Keywords: rectal cancer, planning on diagnostic CT scan