ESTRO 2024 - Abstract Book

S4095

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

In CCB 72 patients underwent APT between 2020 and 2023, which means about 10% of all treated patients. Most of the patients with APT have tumors located in the H&N area (~93%). 50% of cases required an adaptive plan in the first half of the irradiation cycle, and 50% in the second half of the cycle, which leads to the conclusion that exact determination of which period of radiotherapy is the most critical in terms of changes in the patient's anatomy is not feasible. In most of the selected cases, the motivation for the adaptation plan preparation was to spare critical organs (55%). In 35% of cases, there was a change in PTV volume caused by tumor progression (71%) or regression (29%). In 95% of cases, APT preparation was motivated by improving the quality of dose distribution which has given patients the dosimetric benefit of dose limitation in critical organs or/and more appropriate PTV dose coverage. In one case, an adaptive plan was prepared even though the dose distribution met the treatment plan constraints, although APT improved PTV coverage.

Conclusion:

The APT was driven by dose distribution disorders in critical organs, as well as in the PTV area, and was not associated with the time-point in which the control CT scan was acquired. Dosimetric patient benefits justify the currently applied APT procedure, requiring engagement of clinical resources, i.e., additional imaging, contour definition, and plan evaluation activities.

Keywords: adaptive proton therapy,

References:

[1] Paganetti, H., Botas, P., Sharp, G. C., & Winey, B. (2021). Adaptive proton therapy. Physics in Medicine & Biology, 66(22), 22TR01.

2600

Digital Poster

Surface guided RT for breast cancer: robustness of dose volume parameters for breathing movement.

Lars HP Murrer, Lotte Van der Werf, Femke Vaassen, Karolien Verhoeven, Kirsten Kremer, Debby Tissen, Liesbeth J Boersma

Maastro, Radiation Oncology, Maastricht, Netherlands

Purpose/Objective:

In left-sided breast cancer radiotherapy (RT) it is common to use breath hold techniques to spare the heart. Several breath-hold techniques are available [1]. At our institute we use voluntary moderate Deep Inspiration Breath Hold (vmDIBH), where we only give vocal instructions to our patients without a direct feedback measure of the chest wall position. In a previous study we established that this was feasible. We showed that both set-up and 2D EPID dosimetry