ESTRO 2024 - Abstract Book

S536

Clinical - Breast

ESTRO 2024

In the conventional whole breast radiation treatment, the current practice for treatment setup is to position patient using in-room laser alignment with patient skin marks. However, proper positioning is challenging as several factors, including arm position and breast-shape changes, may influence its reproducibility. In order to aid in setup and treatment accuracy, different procedures have been developed such as cone beam computed tomography (CBCT) or surface-based monitoring system (AlignRT). In this study, we intented to precisely analyze patient displacement during treatment while using AlignRT, thus questioning the need of daily CBCT.

Material/Methods:

Fourty breast cancer patients who underwent left-sided radiotherapy using either intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) were selected for this study. Patient positioning was acquired and ajusted based on surface AlignRT (VisionRT, London, UK), along with daily CBCT. Precision of AlignRT system was evaluated by measuring shifts done by medical electroradiology technicians in a daily manner, among the three plans. Measurements were acquired during three-periods of treatment : one-third, two-third and end of treatment.

Results:

We performed an initial analysis on a small cohort of 10 patients, that revealed minimal shifts during the first period of treatment and an average displacement value that increased along treatment (Table 1). Mean amplitude of shifts was lower than 0.25 cm with a standard-deviation (SD) of 0.9. This primary observation would suggest to reduce the frequency of CBCT to weekly imaging during the two-third of treatment, to in fine mimize patient exposition to ionizing radiations. Nevertheless, AlignRT might not be sufficiently ans solely accurate at the end of treatment, probably due to tissue modifications. To confirm this result, we extended our analysis with 30 additionnal patients and we did not report any major shift during treatment. Indeed, shifts were stable and varied between 0.20 and 0.25 cm (SD, 1.9 cm) (Table 2).