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内容記述 |
Background: Clinical carbon ion beams offer the potential to overcomehypoxia-induced radioresistance in pancreatic tumors, due to their high dose-averaged Linear Energy Transfer (LETd), as previous studies have linked aminimum LETd within the tumor to improved local control. Current clinical prac-tices at the Heidelberg Ion-Beam Therapy Center (HIT), which use two posteriorbeams, do not fully exploit the LETd advantage of carbon ions, as the highLETd is primarily focused on the beams’ distal edges. Different LETd-boostingstrategies, such as Spot-scanning Hadron Arc (SHArc), could enhance LETddistribution by concentrating high-LETd values in potential hypoxic tumor coreswhile sparing organs at risk.Purpose: This study aims to investigate and verify different LETd-boostingstrategies using an anthropomorphic pancreas phantom.Methods: Various LETd-boosting strategies were investigated for a cylindri-cal and a pancreas-shaped target in an anthropomorphic pancreas phantom.Treatment plans were optimized using single field optimization (SFO) or multifield optimization (MFO), with objective functions based on either physical dose(Phys), relative biological effectiveness (RBE)-weighted dose, or a combina-tion of RBE and LETd-based objectives (LETopt). The LETd-boosting planning strategies were optimized with the goal of increasing the minimum LETd in thetumor without compromising its homogeneous dose coverage. Beam configura-tions investigated included the two-beam in-house clinical standard (2-SFO Phys ,2-SFORBE and 2-MFORBE-LETopt ),a three-beam configuration (3-MFORBE and 3-MFORBE-LETopt ) and SHArc (SHArcPhys , SHArcRBE and SHArcRBE-LETopt ) usingstep-and-shoot delivery. The different plans were verified using an anthropo-morphic pancreas phantom at HIT and compared to treatment planning system(TPS) predictions.Results: All investigated LETd-boosting strategies altered the LETd distributionwhile meeting optimization goals and constraints,resulting in varying degrees ofLETd enhancement. For the cylindrical volume, the SHArc plan resulted in thehighest LETd concentration in the tumor core, with the minimum LETd in theGTV scaling up to 91 keV/µm. For the pancreas-shaped volume, however, the3-MFORBE-LETopt achieved a higher minimum LETd in the GTV than SHArc RBE(75.6 and 62.3 keV/µm, respectively). When combining SHArc with LETd opti-mization, a minimum LETd of 76.3 keV/µm was achieved, suggesting a potentialbenefit from this combined approach.Most dosimetric verifications showed dosedeviations to the TPS within a 5% range,for both beam-per-beam and total dose.LETd-optimized and SHArc plans exhibited slightly higher mean dose deviations(2.0%—4.6%) compared to the standard RBE-based plans (<1.5%).Conclusion: This study demonstrated the feasibility of enhancing LETd in pan-creatic tumors using carbon ion arc delivery coupled with LETd optimization.The possibility of delivering these plans was verified through irradiation of ananthropomorphic pancreas phantom, which showed agreement between dosemeasurements and predictions. |
