ESTRO 2024 - Abstract Book

S4176

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

ESTRO 2024

centered at the patient’s breath-hold level and perform their scan in breath-hold. After initial experience with patient training, we adapted the patch calibration procedure for SimRT, to be at the deepest possible couch position, while the patient patch position of the system is usually not being placed so deep.

Results:

The results for static phantom measurements can be found in Table 1. Different surrogate systems measured similar couch sag signals while staying below 4 mm total sag relative to the weightless acquisition even for loads of 130 kg. We measured a total couch sag of -1.39 ± 0.02 mm for the non-weighted situation. For the evaluation of the longitudinal sag along the couch, results showed that higher weight loads were related to steeper couch sag fall off towards the deepest couch position (label “1”). For DIBH CT scans, the visual guidance is heavily affected by these artifacts and threshold limits could not be achieved by 48% (n=21) of the patients (example in Figure 1B). Due to the new calibration workflow, the baseline drift could be compensated better and 90% (n=20) of the patients treated since were able to stay reasonably within the breath-hold threshold.

Table 1.Couch sag for different optical surrogate systems in dependency of weight and longitudinal table sag profile in dependency of position and weight.

Couch sag (weight) Weight (kg)

Polaris (mm)

RGSC (mm)

SimRT (mm)