ESTRO 2024 - Abstract Book

S4354

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

ESTRO 2024

Material/Methods:

A prospective evaluation was conducted on 15 patients who had completed adaptive treatment at our clinic, encompassing a total of 272 fractions. Initial CBCT scans were utilized to generate adaptive treatment plans. To monitor potential set-up variations, a second CBCT scan was acquired immediately prior to treatment. Changes in anterior-posterior (AP), medial-lateral (ML), and superior-inferior (SI) directions were analyzed, yielding median, minimum, and maximum values. The correlation between time and set-up changes was assessed.

Results:

The median time interval between the two CBCT scans was 16±5.1 minutes, ranging from 9 to 37 minutes. Set-up changes were found to be 1mm±0.9mm (range: 0-8.7mm) in the AP direction, 0.3±1.2mm (range: 0-14.6mm) in the SI direction, and 0.3±0.9mm (range: 0-8.9mm) in the ML direction. Graphical representations of these changes are presented in Figure 1. However, no significant correlation was observed between the time interval and set-up shifts in any direction ( p =0.381, p =0.981, p =0.307).

Conclusion:

Our findings suggest that acquiring a second CBCT scan immediately before adaptive treatment is crucial, particularly when small treatment margins are employed. Clinics opting not to use a second CBCT scan should take into account these set-up variations when determining the planning target volume (PTV) margin. This study underscores the importance of considering real-time patient positioning during online adaptive therapy to ensure treatment accuracy and patient safety

Keywords: online adaptive, second CBCT, intra-fraction

2522

Digital Poster

Optimal pressure of CPAP for reduction mean heart dose in left-sided breast cancer radiotherapy