Respiratory and Physiological Gastrointestinal Motion-Informed Dosimetric Interplay Modeling: A Step Towards Personalized Treatment Planning Parameter Selection
Abstract
Purpose
To quantify the dosimetric consequences of physiology-composed abdominal motion on pancreatic cancer SBRT.
Methods
Ten patients with high-quality 4DCT imaging who had previously received SBRT were selected and replanned using a standardized prescription and contouring protocol. Target volumes were delineated according to the TIGeR-PaC Trial guidelines. The GTV and CTV were prescribed 50Gy and 33Gy in 5 fractions, respectively. We generated a continuous, topology-aware GI tract motility model and superimposed 4DCT-derived respiratory motion to form a composite abdominal motion. 60 continuous motion frames for each patient were generated over a 3-minute duration. We developed an ESAPI-based framework to simulate the temporal interplay between GI/respiratory motion and VMAT delivery. The clinical VMAT plan was discretized into unit control points, and control-point groups were calculated on the corresponding motion frames identified by the simulations. The frame-specific discretized dose distributions were mapped back to the planning CT using via deformable image registration and accumulated for dosimetric analysis. We performed 20 simulations for each patient and calculated the D95 of the GTV and D2cc of duodenum, stomach and small bowel.
Results
Simulated data suggested the probability of target-organ overlap ranges from 10% to 50%. Across the 20 simulations, the dose variability of combined GI track was quantified. The interquartile range-to-mean ratio of the D2cc was in range of 1.39% to 5.8%. The likelihood of any GI OARs exceeding the critical 33Gy was also quantified the fraction of samples above the threshold. The probability that a single simulation exceeded 33Gy was 43%, whereas the probability that the simulation mean exceeded 33Gy was at 20%.
Conclusion
We demonstrated that physiological GI motion, coupled with respiratory motion, can introduce significant variability in near-maximum dose of OAR that is associated with GI toxicities