ESTRO 2024 - Abstract Book

S4291

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

ESTRO 2024

intrafraction motion. Furthermore, the expected coverage of 3-mm and 5-mm PTV margins was assessed by evaluating the inclusiveness index for the pre- and post-fraction GTVs. The inclusiveness index was calculated as the percentage of the GTV covered by the PTV. The inclusiveness index per fraction was quantified as the mean value of the pre- and post-fraction inclusiveness indices, and the inclusiveness index per lesion as the mean value over the entire treatment course.

Results:

The mean treatment time was 8.7 (± 2.7) minutes, and there was no correlation between fraction duration and lesion motion. Lymph node interfraction motion was limited to 5.0 mm and 3.0 mm in 96 – 97% and 92 – 95% of fractions, respectively, [HL1] for all translational directions. Lesion intrafraction motion was limited to 3.0 mm in 97 – 100% of fractions for all translational directions and the mean lesion intrafraction motion was nearly negligible in all translational directions (mean 0.1 – 0.3 mm). Para-rectal lesion location was associated with significantly larger 3D vector interfraction (mean 5.5 vs. 2.1 mm) and intrafraction motion (mean 2.4 vs. 1.4mm) compared to other pelvic locations. (Figure 1) The mean inclusiveness index for the 5-mm PTV margin was 98.5% (± 8.0%) per fraction and 98.5% (± 5.3%) per lesion. The mean inclusiveness index for the 3-mm PTV margin was 96.4% (± 11.9%) per fraction and 96.4% (± 8.9%) per lesion. (Figure 2) In only 3 lesions, the 5-mm PTV margin resulted in a mean lesion inclusiveness index <95%. These 3 lesions were located presacral (one lesion with inclusiveness index of 81%), and para-rectal (two lesions with an inclusiveness index of 85% and 75%).

Figure 1. Inter- and intrafraction lesion motion per lesion location

Tukey boxplots (+ indicating mean). The Kruskal-Wallis H test indicated a significant difference in the mean inter- and intrafraction lesion motion among the lesion locations (p <0.001 and p0.007).

Figure 2. Frequencies of mean inclusiveness index values per lesion for a 3-mm and 5-mm PTV margin