ABSTRACT
Background and
Purpose:
Interfractional geometrical and anatomical variations impact the accuracy of
proton therapy for
pancreatic cancer. This study investigated field-in-field (FIF) and simultaneous integrated boost (SIB) concepts for scanned
proton therapy treatment with different beam configurations. Materials and
Methods:
Robustly optimized
treatment plans for fifteen
patients were generated using FIF and SIB
techniques with two, three, and four beams. The prescribed
dose in 20 fractions was 60 Gy(RBE) for the internal gross
tumor volume (IGTV) and 46 Gy(RBE) for the internal clinical target volume. Verification computed
tomography (vCT) scans was performed on
treatment days 1, 7, and 16. Initial
treatment plans were recalculated on the rigidly registered vCTs. V100% and D95% for targets and D2cm3 for the
stomach and
duodenum were evaluated. Robustness evaluations (range
uncertainty of 3.5 %) were performed to evaluate the
stomach and
duodenum dose-volume
parameters.
Results:
For all
techniques, IGTV V100% and D95% decreased significantly when recalculating the
dose on vCTs (p < 0.001). The median IGTV V100% and D95% over all vCTs ranged from 74.2 % to 90.2 % and 58.8 Gy(RBE) to 59.4 Gy(RBE), respectively. The FIF with two and three beams, and SIB with two beams maintained the highest IGTV V100% and D95%. In robustness evaluations, the ΔD2cm3 of
stomach was highest in two beams plans, while the ΔD2cm3 of
duodenum was highest in four beams plans, for both concepts.
Conclusion:
Target coverage decreased when recalculating on CTs at different
time for both concepts. The FIF with three beams maintained the highest IGTV coverage while sparing normal organs the most.