Author: Nebi Demez, Michael Kasper, Noufal Manthala Padannayil, Haley Park, Shyam Pokharel, Suresh Rana, Lauren A. Rigsby, Tino Romaguera, Hina Saeed, Nishan Shrestha, Somol Sunny 👨🔬
Affiliation: Florida Atlantic University, Lynn Cancer Institute, Boca Raton Regional Hospital, Baptist Health South Florida 🌍
Purpose:
Pancreatic cancer poses therapeutic challenges due to the proximity of critical organs, requiring precise radiotherapy. Magnetic resonance (MR)-guided linear accelerators provide daily imaging and adaptive replanning, enabling adjustments to target volumes and critical structures for enhanced treatment accuracy. This study investigates daily variations in target volumes and dose distribution during MR-guided radiotherapy for a pancreatic cancer patient.
Methods:
Baseline target volumes were defined on the planning image obtained prior to the initiation of treatment. Reference high-risk (HR) and low-risk (HR) planning target volumes (PTVs) were contoured, with dose prescriptions of 60 Gy (PTV_HR_60) and 37.5 Gy (PTV_LR_37.5), respectively. Fractional dose distributions were initially calculated based on nominal plans derived from the planning image. Daily volumetric and dosimetric variations associated with these target volumes were analyzed over 15 treatment fractions.
Results:
Volumetric analysis revealed substantial daily changes in target volumes. PTV_HR_60 averaged 31.9±3.90 cm³, a 32.0±16.1% increase from baseline (24.2 cm³). Low-risk targets showed similar trends, with PTV_LR_37.5 averaging 327.9±23.73 cm³, 13.2±8.2% increase from baseline (289.6 cm³). Daily dose differences from baseline remained consistent. On average, PTV_HR_60 delivered 4.40±0.06 Gy/fx, differing by 1.1±1.4% from baseline of 4.35 Gy/fx. PTV_LR_37.5 delivered 3.48±0.06 Gy/fx, differing by -0.1±1.7% from baseline of 3.48 Gy/fx.
Conclusion:
Daily volumetric variations during MR-guided radiotherapy for pancreatic cancer highlight the dynamic nature of target volume changes and the importance of adaptive replanning. High-risk and low-risk target volumes exhibited substantial increases from baseline, underscoring the necessity of daily imaging to maintain accurate dose delivery. Despite these volumetric changes, fractional dose variations remained minimal. Further research is needed to optimize protocols and address inter-user variability in delineating the target volumes.