Compressed.

Ablative radiation approaches for unresectable pancreatic cancer can improve survival outcomes. Breath hold with tracking is the ideal form of motion management, but not all treatment systems have that capability. Here is a feasibility study of abdominal compression rather than DIBH during an 50Gy/5 MR-adaptive approach. Each patient had 3 MRIs per treatment: before, during, and after— note the during and after are after daily adaptive replanning. The objective of minimizing tumor motion to <5mm was achieved in 75% of fractions: median tumor motion across all fractions for all patients (150 MRIs) was 1.7 (0.7–7) mm in anterior-posterior direction, 2.1 (0.6–6.3) mm left-right, and 4.1 (1.4–10.0) mm superior-inferior. Nonetheless, key constraints to nearby GI structures were not invincible. These included D0.035cc ≤33 Gy to stomach (exceeded on 48/100 during/after MRIs) and small bowel (exceeded on 52/100) and D5cc ≤25 Gy to stomach (exceeded on 28/100) and small bowel (exceed on 34/100). A final note is that these calculations are likely overestimates because there is clearly a feathering effect of these organs at risk during beam on. | Tyagi, Phys Imaging Radiat Oncol 2021