ESTRO 2025 - Abstract Book

S3152

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

We can see that, even though each patient is specially prepared (constant bladder volume) for the treatment, the average value of the change in OARs is approximately 10% for the urinary bladder and 5% for the rectum. The next stage was to designate the so-called cumulative dose using deformation image registration based on the first 5 treatment fractions. The graph below shows the volumes of the rectum that receive doses of 20Gy, 30Gy, 40Gy, 50Gy and 60Gy, respectively.

Conclusion: It turns out that despite efforts to ensure that each patient has a constant (comfortable) bladder volume, fluctuations in this volume in relation to CTplan are not negligible - 10%. The value of constant rectal volume during the treatment process is extremely difficult to implement. After analyzing the cumulative dose value, it turns out that despite fluctuations in rectal volume, almost all (95%) treatment plans simulated using deformation image registration meet the accepted clinical treatment conditions. In particular, the doses (V50Gy and V60Gy) that may potentially be responsible for complications after this type of treatment. The presented method, using AI and DIR tools, is very effective and useful. Moreover, the adopted protocol significantly reduces the number of CBCT images taken during treatment, which directly translates into a reduction in the dose of ionizing radiation.