ESTRO 2024 - Abstract Book

S4166

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

ESTRO 2024

Results:

One patient could not complete the MR-linac treatment and received palliative radiotherapy (data not included). The median GTV volume was 6.5 cc with a minimum of 0.3 cc and maximum of 20.3 cc. Despite the proximity to dose limiting OARs for these patients, a mean dose to the GTV of more than 55 Gy was achieved in all plans delivered (Delivered in Figure 1). The PTV coverage in all delivered plans exceeded the palliative scheme (D 99% >26 Gy) with a minimum of 29.2 Gy, except for one patient (Number 4) who received a lower dose due to prior radiotherapy (Delivered in Figure 2). The adapted plan was chosen in 45 out of the 48 treatment fractions. As seen in Figure 1 and 2, the adaptive plan did not always lead to improvement in target coverage but was rather chosen, because the predicted plan violated OAR constraints (most often connective tissue). For patient 5, small constraint violations for the connective tissue were accepted, which could explain the increase in mean GTV dose in delivered vs predicted plans; normalizing the adapted plan to the OAR constraint would lead to a reduction in GTV mean dose by 2 Gy for fraction 6 (data not shown).

Figure 1 : The mean dose to the GTV in the predicted (blue) and the delivered (gray) plan for each fraction. The red circles mark the three fractions where the baseline plan (punctured line) was delivered.