ESTRO 2024 - Abstract Book

S4381

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

ESTRO 2024

The shifts in the EUD distributions for CTV 5mm with oART towards lower than prescribed doses (PrescD) increased with increasing adaption times from 0 min (ADPt 0 ) in CBCT1, over 10 min (ADPt 10 ), to the clinical adaption time (ADPt cl ), pairwise comparison with p<0.006 in each case (Kruskal test). Thus, percentages of fractions with an EUD < 93% increased over the mentioned times and reached 32% by ADPt cl . The respective percentage with IGRT was 39%. In the intrapatient analysis and for dose fractions with an EUD < 93%, the increase in EUD with oART vs IGRT at ADPt 10 was in median 47.9% higher than for ADPt cl .

The accumulated EUD for CTV 5mm with oART was above 95% after 0 and 10 min for all patients, but after the clinical adaption time in only 5 out of 6 patients.

Conclusion:

The benefit of oART degrades over longer adaption times in bladder cancer. PTV margins of 5 mm appear to be adequate for oART of bladder cancer with adaption times up to 10 minutes, but are not sufficient for all patients given the adaption times currently required clinically.

Keywords: intrafractional changes, online adaption, bladder

2873

Digital Poster

Daily intra-fraction corrections in MRI-guided SABR

Miguel A. Palacios, Omar Bohoudi, Famke L. Schneiders, Cornelis J.A. Haasbeek, Suresh Senan, Anna M.E. Bruynzeel

Amsterdam UMC, location VUmc, Radiation Oncology, Amsterdam, Netherlands

Purpose/Objective:

Purpose/Objective

Magnetic resonance imaging guided SABR (MRIg-SABR) offers excellent soft-tissue contrast and the ability to reduce target volume margins. Furthermore, gated delivery with online visualization of the anatomy of the patient allows additional margin reduction and provides information about actual dose delivery and position of target volume. We report on the daily corrections applied in MRIg-SABR across all indications as a result of intra-fractional changes at our institution.

Material/Methods:

MRIg-SABR was applied with breath-hold gating for mobile tumors in the upper abdomen and thoracic regions. MRIg SABR treatments without breath-hold were administered for tumors in the pelvic region. PTV margins applied were 3mm for all patients, except for lung and liver patients (5mm). A gating Boundary structure of 3mm around the GTV