ESTRO 2023 - Abstract Book

S1569

Digital Posters

ESTRO 2023

Results The HU-threshold target volume and length measurements for the fast (6s) and slow (60s) scans were similar for small amplitudes ( ≤ 10mm) and short periods (<6s). When varying breathing period, 9s periods produced the largest difference in target length and volume between the serial fast scans; while for varying amplitudes, 15mm amplitudes produced the largest difference in target volume and 10mm in length. For fast breathing (3s) and intermediate motion (5mm), up to 5% deviation in target volume/length were observed compared to 4DCT data. For slow breathing and/or large motion scenarios, slow scans showed better agreement with 4DCT for target volume, length, and width, with most differences <1% and the largest differences (6.5%) seen for the 20mm/9s combination (see Table 1).

Volume Width Breathing Amplitude & Period Fast CBCT Slow CBCT Fast CBCT Slow CBCT Fast CBCT Slow CBCT 0 mm/0 sec 0.6% 0.6% 4.9% 4.9% 1.6% 1.3% 5 mm/3 sec 4.5% 0.6% 5.3% 4.1% 4.6% 1.0% 20 mm/9 sec 9.7% 6.5% 13.0% 2.4% 5.0% 4.9% Length

Table 1 - Percent Deviation of Target Measurements from 4DCT: Comparison of HU threshold-defined target volume, length, and width between the average values calculated for the 2-serial fast CBCTs (6s) and slow CBCT (60s) compared to the 4DCT image acquisitions.