Purpose: Pancreatic cancer is a leading cause of cancer death in the US. Limiting ITV(Internal Target Volume) margin in order to escalate the treatment dose for better local tumor control is investigated to in this work. One way to reduce ITV is treating the patient using the breath-hold technique. With breath-hold treatment, conventional treatment planning is assumed to be performed on the breath-hold simulation scans. However, the different extents of breath-hold magnitudes between simulation and treatments could introduce uncertainties for the target and PRV(planning organ at risk volume) determination. One may choose to perform dose calculation on free breathing scans to lessen the discrepancies. This study is to investigate the dosimetric differences between free-breathing and breath-hold scan planning for pancreatic breath-hold treatment.
Methods: Six pancreas cancer patients underwent dose escalated regime; three of them were originally planned on breath-hold scans and the others on free-breathing scans. All six plans were recalculated on alternative scans with the same leaf sequences and MUs, e.g. if originally used breath-hold scans, the alternative scans are free-breathing scans and vice versa. The organ contours are also delineated with corresponding planning scans. DVHs(dose volume histograms) are compared with GTV, PTV coverages and PRV dose sparing.
Results: We found that the calculated DVH average differences between free-breathing and breath-hold scans are smaller(0.0% PTV/GTV coverage difference) when original planning was performed on free-breathing scans, while original plans calculated on breath-hold cases, the PTV/GTV is 2.8%/3.7% differences on maximum doses respectively. PRVs also shows larger discrepancies between calculations for this scenario. We noted these discrepancies could come from the breath-hold scans being far out of the regular breathing phases.
Conclusion: Dose calculations on free-breathing scans show less sensitive to the treatment respiratory phases. Breath-hold scan planning could introduce larger dosimetric differences due to the extents of the respiratory magnitudes.
Dose Volume Histograms, Motion Artifacts
TH- External Beam- Photons: Motion management - interfraction